Cocatalysts for Selective Photoreduction of CO2 into Solar Fuels

Review Cite This: Chem. Rev. XXXX, XXX, XXX−XXX

pubs.acs.org/CR

Cocatalysts for Selective Photoreduction of CO2 into Solar Fuels Xin Li,† Jiaguo Yu,*,‡ Mietek Jaroniec,*,§ and Xiaobo Chen*,∥ †

Chem. Rev. Downloaded from pubs.acs.org by WEBSTER UNIV on 02/14/19. For personal use only.

College of Forestry and Landscape Architecture, Key Laboratory of Energy Plants Resource and Utilization, Ministry of Agriculture, South China Agricultural University, Guangzhou, 510642, P. R. China ‡ State Key Laboratory of Advanced Technology for Material Synthesis and Processing, Wuhan University of Technology, Wuhan, 430070, P. R. China § Department of Chemistry and Biochemistry, Kent State University, Kent, Ohio 44242, United States ∥ Department of Chemistry, University of MissouriKansas City, Kansas City, Missouri 64110, United States ABSTRACT: Photoreduction of CO2 into sustainable and green solar fuels is generally believed to be an appealing solution to simultaneously overcome both environmental problems and energy crisis. The low selectivity of challenging multi-electron CO2 photoreduction reactions makes it one of the holy grails in heterogeneous photocatalysis. This Review highlights the important roles of cocatalysts in selective photocatalytic CO2 reduction into solar fuels using semiconductor catalysts. A special emphasis in this review is placed on the key role, design considerations and modification strategies of cocatalysts for CO2 photoreduction. Various cocatalysts, such as the biomimetic, metal-based, metalfree, and multifunctional ones, and their selectivity for CO2 photoreduction are summarized and discussed, along with the recent advances in this area. This Review provides useful information for the design of highly selective cocatalysts for photo(electro)reduction and electroreduction of CO2 and complements the existing reviews on various semiconductor photocatalysts.

CONTENTS 1. Introduction 2. Fundamentals of Heterogeneous CO2 Photoreduction 2.1. Key Points in Heterogeneous Photocatalysis 2.1.1. Basic Principles of Heterogeneous Photocatalysis 2.1.2. Carrier Dynamics and Band Bending 2.1.3. Strategies for Improving Photoactivity 2.1.4. Stability of Photocatalysts 2.1.5. Selectivity of Photocatalysts 2.1.6. Fundamentals of Cocatalysts 2.2. Thermodynamics of CO2 Photoreduction 2.3. Kinetics of CO2 Photoreduction 2.4. Adsorption and Activation of CO2 2.5. Mechanisms of CO2 Photoreduction 2.6. Mechanisms of CO2 Electroreduction 2.7. Processes for Photoassisted CO2 Reduction 2.8. Interfacial Charge-Transfer Reactions 2.9. Cocatalyst−Semiconductor Interactions 3. Engineering Strategies for Selective Photoreduction of CO2 3.1. Modulating Morphological and Band-Gap Structures 3.1.1. Tuning the Band-Gap Structures 3.1.2. Exposing Highly Reactive Facets 3.1.3. Exfoliating Ultrathin 2D Nanosheets 3.1.4. Fabricating 3D Hierarchical Architectures © XXXX American Chemical Society

3.2. Tailoring Surface Chemical Compositions 3.2.1. Introducing Functional Groups 3.2.2. Utilizing Hydrophobic−Hydrophilic Properties 3.2.3. Creating Surface Overlayers 3.2.4. Constructing Surface Vacancies 3.3. Tuning Acidity−Basicity of Supports 3.4. Using Solvent Effects 3.5. Improving Interfacial Properties 3.6. Loading Suitable Cocatalysts 4. Key Role of Cocatalysts in CO2 Photoreduction 4.1. Improving Selectivity of CO2 Photoreduction 4.2. Minimizing Overpotentials of CO2 Photoreduction 4.3. Promoting Charge Separation in Photocatalysts 4.4. Enhancing Adsorption and Activation of CO2 4.5. Suppressing Photocorrosion and Undesirable Reactions 5. Design Considerations for CO2 Photoreduction Cocatalysts 5.1. Fermi Level of Cocatalysts 5.2. Electrical Conductivity of Cocatalysts 5.3. Interfacial Coupling of Semiconductor/Cocatalyst

B D D D G K L M O Q S T X Y AB AC AC AC AC AD AE AG

AK AK AM AO AQ AY AZ BA BD BE BE BF BN BN BO BQ BQ BS BU

Received: June 29, 2018

AJ A

DOI: 10.1021/acs.chemrev.8b00400 Chem. Rev. XXXX, XXX, XXX−XXX

Chemical Reviews 5.4. Surface Reactive Sites and Location of Cocatalysts 5.5. Stability and Ad(De)sorption Ability of Cocatalysts 6. Modification Strategies of CO2-Photoreduction Cocatalysts 6.1. Fabricating Nanostructured Cocatalysts 6.1.1. Optimizing the Size of Nanoparticles/ Nanoclusters 6.1.2. Exploring 2D Ultrathin Nanosheets 6.2. Designing Single-Atom Cocatalysts 6.3. Controlling Composition of Cocatalysts 6.4. Exploring Edge Sites and Facets of Cocatalysts 6.5. Constructing 2D−2D Coupling Interfaces 6.6. Loading Dual Cocatalysts on Semiconductors 7. Selective CO2 Photoreduction over Different Cocatalysts 7.1. Biomimetic Cocatalysts 7.1.1. Biocatalysts (Enzymes) 7.1.2. Biomimetic Complexes 7.2. Noble Metal Cocatalysts 7.2.1. Monometallic Cocatalysts 7.2.2. Bimetallic Alloy Cocatalysts 7.2.3. RuO2 and Other Cocatalysts 7.3. Earth-Abundant Metal Cocatalysts 7.3.1. CuOx Cocatalysts 7.3.2. NiOx and CoOx Cocatalysts 7.3.3. Mixed Oxide Cocatalysts 7.3.4. Sulfide, Carbide, and Other Cocatalysts 7.4. Metal-Free Cocatalysts 7.4.1. Nanocarbon Cocatalysts 7.4.2. Molecular Cocatalysts 7.5. Multifunctional Cocatalysts 7.5.1. Hybrid Cocatalysts 7.5.2. Metal−Organic Frameworks 7.5.3. Plasmonic Cocatalysts 7.5.4. Photothermal Cocatalysts 7.5.5. Water Oxidation Cocatalysts 8. Conclusions and Perspectives Author Information Corresponding Authors Notes Biographies Acknowledgments References

Review

various useful low-carbon fuels.4,5 At the present time, as compared to the capture and geological sequestration of CO2 with high-energy demands, conversion or reutilization of CO2 seems to be more attractive, feasible and promising route to simultaneously solve energy and environmental issues in a long term. So far, many approaches for converting CO2 into hydrocarbon fuels have been explored, including catalytic, photocatalytic, electrocatalytic and photoelectrocatalytic processes.6−9 For each approach, efficient catalysts and sufficient energy input are indispensable to activate linear CO2 molecule, which is thermodynamically stable due to the highly oxidized state of carbon (Δf G298 ° = −394.36 kJ/mol).10 Among these potential approaches for CO2 reduction, an economical and sustainable photoconversion of CO2 with H2O using solar energy and heterogeneous photocatalysts, which is known as artificial photosynthesis, can admirably mimic the natural photosynthesis and perfectly achieve the production of solar fuels and high-value chemicals (such as CO, formic acid, methane, and methanol) (Figure 2) via more ecofriendly manner.11,12 The artificial photosynthesis, with many grand thermodynamical and kinetic challenges, has been considered as one of the best strategies to solve both the global climate change and potential shortage of energy supply without producing additional CO2 because of the abundance and free access of sunlight as a renewable energy source and the better durability of the heterogeneous semiconductors than that of homogeneous transition metal complexes.13 In 1978, Halmann et al. demonstrated that the photoelectrochemical reduction of CO2 could be achieved over p-GaAs under a highly cathodic applied bias.14 In the next year, the pioneering work on the selective photoreduction of CO2 over different semiconductor powders suspended in aqueous solutions was reported by Inoue et al.15 Since then, the photoreduction of CO2 with H2O over various nanostructured titanium oxides,13,16−19 non-titanium metal-based (such as CdS, ZnO, WO3, NaNbO3, ZnGa2O4, ZnGa 2 O 4 ), 20,21 Ag/AgX, layered double hydroxides (LDHs),22−28 inorganic perovskite halides (CsPbBr3),29,30 Ti2CO2 MXene,31 metal−organic frameworks (MOFs),32,33 and metal-free (SiC and g-C3N4)34 semiconductors has been investigated.13,21,25,35−47 Especially, as shown in Figure 3A, since 2011, the studies on the selective photoreduction of CO2 into solar fuels have been published at a rapid growth rate. More importantly, many different modification strategies, including energy band-gap engineering, surface vacancy engineering, crystal facet engineering, micro/nanoengineering, cocatalysts engineering, and interfacial engineering (heterojunction and Z-scheme system), have been developed to improve semiconductors’ activity and stability for selective CO2 photoreduction.41,45,48−53 It is known that artificial photosynthesis, the photoreduction of CO2 with H2O, is still challenging because of the grand thermodynamic barrier of CO2 and the sluggish reaction kinetics for producing solar fuels (e.g., CO, CH4), which has been considered to be more uncontrollable and sophisticated than solar hydrogen generation. Based on Figure 3, since 2011, the average annual number of academic papers on the photocatalytic hydrogen generation is about 4 times larger than the number of articles on the photocatalytic reduction of CO2. Clearly, the state-of-the-art advances in materials and reactors for photoreduction of CO2 have been lagged far behind those in solar water splitting for several tens of years because of the complicated multielectron reduction kinetics, low quantum efficiency (catalytic activity), photostability and selectivity of photocatalysts.54 For example, it was

BV BY BZ CA CA CB CE CH CK CN CR CS CT CT DE DI DI DL DM DN DN DR DT DW EA EB EK EM EM ES ET EW EX FC FG FG FG FG FG FG

1. INTRODUCTION Nowadays, there is a growing interest in addressing the issues related to the increasing concentration of the main greenhouse gas (CO2) in the atmosphere and other related detrimental environmental pollutions because of the depletion of the carbon-emitting fossil fuels. As shown in Figure 1, if strategies limiting CO2 emissions are not available, the steadily increasing annual CO2 emission will lead to the synchronized increase in the global-mean air surface temperature on the earth and sea level from 1990 to 2100.1−3 Therefore, it is urgent to develop advanced technologies that are capable of decreasing the CO2 concentration in the atmosphere and achieving the “loopclosing” carbon sequestration schemes through renewable and environmentally friendly conversion of CO2 into CO and B


Chemical Reviews

Review

Figure 1. (A) Atmospheric CO2 concentrations and (B) surface air global-mean temperature for the Special Report on Emissions Scenarios (SRES) fossil intensive (A1FI) and HALVED-BY-2050 (halving the 1990 global Kyoto-gas emissions by 2050) scenarios. Reprinted with permission from ref 1. Copyright 2009 Springer Nature.(C) Sea-level change from 1990 to 2100, based on the A1FI, A2 (regionally oriented economic development), and B1 (global environmental sustainability) emission scenarios. Reprinted with permission from ref 3. Copyright 2009 National Academy of Sciences.

A rate of above 2000 μmol g−1 h−1 for selective methane production over Au−Cu alloy nanoparticles deposited on P25 was achieved under sun simulated light.62 Clearly, although significant achievements have been made by combination of cocatalysts and semiconductors with nano or mesoporous structures, all these studies are still far from achieving the goals for the practical artificial photosynthesis. Some primary challenges in CO2 photoreduction have not been fully elucidated, such as the extremely complicated photocatalytic reaction mechanisms and pathways involving the multiple proton-coupled electron transfers with high energy barriers, complex activation and adsorption of CO2 molecules, low efficiency and selectivity of different products (i.e., CO, HCOOH, HCHO, CH3OH, and CH4), the richness of excited state dynamics and the semiconductor surface chemistry.63 Therefore, overcoming the aforementioned issues in solar CO2 photoreduction is inevitable, though it is challenging to understand in-depth the CO2 photoreduction mechanism at the atomic level, including the role of protons in aqueous CO2 hydrogenation conversion and the competitive H2 formation reaction, which could provide guidance for the design of highly selective photocatalysts for target reactions. Surprisingly, to the best of our knowledge, there is no a comprehensive review focused on cocatalysts and on the tailoring selectivity of heterogeneous photocatalytic reduction of CO2 over semiconductors. Most published reviews are focused on the

verified that the rate of solar water splitting over ZrO2 photocatalysts was more than 100 times higher than that of selective CO2 photoreduction.55 Consequently, there is an urgent need to accelerate artificial photosynthesis research and reveal the really crucial and challenging issues in selective photoconversion of CO2 and water into valuable hydrocarbons or liquid fuels. A significant progress has been made in the selective photoreduction of CO2 (considered as important model reaction of artificial photosynthesis) over semiconductor powders with/without metals during the past decades (Table 1). In the 1990s, Anpo and his co-workers developed a series of highly dispersed TiO2 photocatalysts (or films) containing isolated single Ti-sites in silica matrices.56−59 Those photocatalysts exhibited an excellent activity for selective photoreduction of CO2 to methane and methanol. The best activity for selective photocatalytic formation of methane from CO2 (12 μmol h−1 gcat−1) was achieved over Pt cocatalyst loaded Ti-MCM-48.56 The highest rate of 160μLg−1 h−1 for selective production of hydrocarbon (such as CH4, other alkanes, and olefin) was also demonstrated over the nitrogen-doped TiO2 nanotube arrays loaded with bimetal Cu/Pt cocatalysts under the outdoor global AM1.5 sunlight.60 More recently, the maximum yield of 1361 μmolg−1 h−1 for selective CH4 formation was obtained on the 1D TiO2 single-crystal films coated with the ultrafine Pt nanoparticles (NPs, 0.5−2 nm).61 C


Chemical Reviews

Review

ments of new cocatalysts for highly selective conversion of CO2 into target products, but also could be beneficial for a deeper understanding of the reaction mechanisms for CO2 photoreduction at molecular level. The Review is organized as follows: it starts with the fundamentals of photocatalytic CO2 reduction, including the fundamentals of heterogeneous photocatalysis, thermodynamic and kinetic considerations, and mechanisms of this process. The next chapters present the main engineering strategies for selective photoreduction of CO2 and discuss the design and modification of cocatalysts and their key role in the aforementioned photocatalytic process. Afterwards, the comparative review summarizes the emerging applications of various cocatalysts in tuning the CO2 photoreduction selectivity. At the end, we present the perspectives for possible future directions.

2. FUNDAMENTALS OF HETEROGENEOUS CO2 PHOTOREDUCTION 2.1. Key Points in Heterogeneous Photocatalysis

2.1.1. Basic Principles of Heterogeneous Photocatalysis. Basic principles of heterogeneous photocatalysis have been extensively discussed in the previous reports. Four basic photocatalytic mechanisms for inorganic and organic semiconductors, surface plasmon resonance (SPR) and interfacial charge transfer (IFCT) (see Figure 4) have been mostly considered. As shown in Figure 4A, traditional inorganic semiconductors, such as TiO2,38 ZnO, WO3,112 CdS,113−115 and BiVO4,116 can become active photocatalysts, when the electrons in the ground state valence bands (VB) are photoexcited into the vacant conduction bands (CB) by absorption of incident high-energy photons with energy larger than their corresponding band gap energies. The photoinduced electrons in CB can rapidly migrate to the surface and initiate the reduction reactions, while the holes in VB can quickly migrate to the surface and participate in the oxidation reactions. In this case, their band structures can be tuned by doping and co-doping with metals and nonmetals, and creating vacancies.117−120 Similarly, organic semiconductors (Figure 4B), including the dyes,121 complexes,122−125 polymers,126−130 graphene131, and g-C3N4,132−135 can be activated by absorption of the suitable incident photons. Then, the spatially separated photogenerated e−/h+ pairs in their lowest unoccupied molecular orbital (LUMO) and highest occupied molecular orbital (HOMO) can further drive the surface redox reactions. More importantly, besides atomic doping, the molecular doping can also be employed as a strategy to finely tune the energy band structures of organic semiconductors.132 The photocatalytic mechanisms for SPR are shown in Figure 4C. Nanostructures of noble metals (mainly Au and Ag) can generate hot plasmonic electrons by SPR-mediated charge injection.136−147 It should be noted that the near-field electromagnetic and scattering mechanisms can also be used to explain the plasmonic photocatalysis observed in the systems where semiconductors are separated with plasmonic metals by non-conductive spacers.137,148 Recently, to avoid the high cost and the low abundance of noble plasmonic metals, noble-metalfree plasmonic metals, such as Bi and Cu have attracted a lot of attention.149−157 It is expected that in the future the plasmonic photocatalysis can be further enhanced through tuning the composition, morphology and structure of the metals. In addition, the mechanism of IFCT (Figure 4D) is used to explain the photoexcitation by the incident photons with

Figure 2. Schematic illustration for natural (A) and artificial (B) photosynthesis. Reprinted with permission from ref 11. Copyright 2017 American Chemical Society.

development of various modified TiO2 and non-TiO2 semiconductor photocatalysts for enhancing adsorption, activation, and photoreduction rates of CO2.13,17,36,42 Furthermore, it is well known that many electrocatalysts play significant roles in enhancing the activity and selectivity for electrocatalytic CO2 reduction.6 Interestingly, these electrocatalysts can also function as cocatalysts for heterogeneous semiconductors used in photocatalytic reduction of CO2, leading to improved activity and selectivity for CO2 photoreduction. More importantly, it is critically important to improve the selectivity of the CO2-reduction products for their viable applications, avoiding the high costs of additional separation64 and reconversion65,66 processes. Additionally, it should be noted that methane (CH4) is the second most prevalent greenhouse gas after CO2, but its global warming potential is 25 times higher than that of CO2. Thus, the selective photoreduction of CO2 into CH4 is less desirable due to its lower importance in producing portable liquid fuels. By contrary, liquid products such as methanol and formic acid, are more desirable because of their potential use in alleviating the depletion of fossil fuels.67 Most importantly, our intention is to provide a critical appraisal of the significant advances and opportunities focusing on the remaining challenges and future directions in the field of cocatalysts for selective CO2 photoreduction. Therefore, it is timely to summarize the past efforts in the related research areas of the selective generation of solar fuels via CO2 photoreduction. Herein, we mainly focus on the recent experimental and theoretical advances in unraveling the selective photoconversion of H2O and CO2 to solar fuels through tailoring the different kinds of cocatalysts. The design principles, concepts and functional mechanisms of each cocatalyst in selective photoreduction of CO2 are discussed and summarized. We believe that a comprehensive and thoughtful review could not only promote further developD


Chemical Reviews

Review

Table 1. Some Famous Advances in Developing Efficient Heterogeneous Photocatalysts for Selective CO2 Reduction photocatalysts

highlights

team Halmann

p-type GaP photocathode

first report on the photoassisted electrolytic reduction of aqueous CO2

TiO2, CdS, and SiC powders Cu(1 wt %)−ZrO2

first report on the photocatalytic reduction of aqueous CO2 over semiconductor powders and Inoue the proposal of a positive dependence of the reactivity of CO2 reduction on the CB value photocatalytic overall water splitting and CO2 reduction to CO in NaHCO3 aqueous solution H. Arakawa

Pt-loaded ex-Ti-oxide/Y zeolite

high reactivity and high selectivity reported for the formation of CH4

M. Anpo

Pt (1.0 wt %)-loaded Ti−MCM-48

M. Anpo

2.0% Cu/TiO2

Pt cocatalyst could switch the selectivity of Ti-MCM-48 from CH3OH to CH4 (12 μmol h−1 gcat−1) selective formation of CH3OH in a CO2/NaOH aqueous solution

2% Cu/TiO2 (precursor: CuCl2)

an important role of highly dispersed Cu(I) sites in CO2 photoreduction to methanol

Wu, J. C. S.

TiO2 and ZrO2

selective formation of CH4 and CO over TiO2 and ZrO2, respectively

C. S. Yuan

TiO2/MWCNT

selective formation of C2H5OH and HCOOH over the sol−gel and hydrothermal samples, respectively selective conversion of CO2 to CH3OH with Faradaic efficiency of 100% in a pyridiniummediated process photocatalytic conversion of CO2 and water vapor into hydrocarbon fuels

X.-H. Xia

primary formation of CH4 (48 ppm g−1 h−1), with CH3OH, H2, and CO as byproducts

C. Wang

anatase TiO2 with different particle sizes

anatase TiO2 with the optimum size (14 nm) shows highest yields of CH4 and CH3OH

K. Koci ́

Ag/TiO2

improving the yield of CH4 and CH3OH by Ag doping and fabricating Schottky barrier

K. Koci ́

0.5%Cu/TiO2−SiO2 composite

Cu2O cocatalyst affords the selective conversion of CO2 into CH4

Y. Li

Zn2GeO4 nanoribbons

selective production of CH4 with gaseous H2O using RuO2 and Pt as dual cocatalysts

Z. G. Zou

N-doped Ta2O5 linked with Ru complexes enzyme-modified TiO2 nanoparticles

selective conversion of CO2 to HCOOH in a CO2-saturated MeCN/TEOA (5:1) solution using Ru complexes as cocatalysts photoreduction of CO2 to CO using enzyme as a cocatalyst

S. Sato

RuO2/meso-ZnGa2O4

selective conversion of CO2 into CH4 using RuO2 as a cocatalyst

F. A. Armstrong Z. G. Zou

Cu(I)/TiO2

first evidence on the formation of CO from carbon residues using 13C labeled CO2

G. Mul

surface-modified carbon QDs

formation of HCOOH via CO2 photoconversion

Au nanoparticle/TiO2

selective formation of CH4 using plasmonic Au as a cocatalyst

C. E. Bunker, Y. P. Sun S. B. Cronin

Ag/ALa4Ti4O15 (A = Ca, Sr, and Ba)

p-type InP/Ru complex

selective formation of CO, HCOOH and H2 accompanied with water oxidation using Ag as a A. Kudo cocatalyst first application of graphene as a cocatalyst for the selective photoreduction of CO2 to CH4 K. A. Gray, M. C. Hersam selective formation of HCOO− (>70%) using Ru complexes as cocatalysts S. Sato

highly crystalline UiO-67 frameworks

first application of MOFs for selective photoreduction of CO2 to CO

W. Lin

NH2-MIL-125(Ti) frameworks

Z. H. Li

deficient TiO2 with different phases

selective photoreduction of CO2 to HCOO− in a CO2-saturated MeCN/TEOA (5:1) solution selective photoreduction of CO2 to CO (main) and CH4 using oxygen defects

graphene-Ti0.91O2 hollow spheres

selective photoreduction of CO2 to CO using 2D−2D coupling heterojunctions

Z. G. Zou

ultrafine Pt-loaded TiO2 single crystals

Biswas

g-C3N4 synthesized by urea or melamine

selective photoreduction of CO2 to CH4 with a yield of 1361μmol/g-cat/h using ultrafine Pt as a cocatalyst selective photoreduction of diluted CO2 into light hydrocarbons using the CuPt bimetallic cocatalysts suppression of H2 generation for selective formation of CH4 (main) and CO using a Pt@Cu2O core−shell cocatalyst first application of g-C3N4 in selective formation of CH3OH and C2H5OH

Q. Zhang, Y. Wang T. Peng

Ag/TaON/Ru(II) complex Z-scheme

photoreduction of CO2 to HCOOH using methanol as a reducing agent

O. Ishitani

p-GaP photocathode Cu and Pt co-loaded TiO2 nanotube arrays CdSe quantum dots (QDs)/Pt/TiO2

defect-free graphene/TiO2

Cu0.33-Pt0.67/TiO2 nanotube arrays Pt@Cu2O core−shell cocatalyst on TiO2

E

Wu, J. C. S.

A. B. Bocarsly Grimes

Y. Li

K. Shankar

ref (year) 14 (1978) 15 (1979) 55 (1993) 68 (1997) 56 (1998) 69 (2002) 70 (2004) 71 (2007) 72 (2007) 73 (2008) 60 (2009) 74 (2009) 75 (2009) 76 (2010) 77 (2010) 78 (2010) 79 (2010) 80 (2010) 81 (2010) 82 (2010) 83 (2011) 84 (2011) 85 (2011) 86 (2011) 54 (2011) 87 (2011) 88 (2012) 89 (2012) 90 (2012) 61 (2012) 91 (2012) 92 (2013) 93 (2013) 94 (2013)


Chemical Reviews

Review

Table 1. continued photocatalysts

highlights

team

Pt-TiO2/MgO

first application of MgO as an additive for photoreduction of CO2 with H2O to CH4

group VIII nanocatalysts modified Al2O3

photothermal reduction of CO2 with H2.

amine-functionalized TiO2 AuCu/P25

amine functionalization to improve the chemisorption and activation of CO2 and charge transfer from excited TiO2 selective photoreduction of CO2 into CH4 using AuCu alloy nanoparticles as cocatalysts

H. Garcia

RGO-CdS nanorod composites

selective photoreduction of CO2 to CH4 over 1D−2D hybrid heterojunctions

J. Yu

g-C3N4/TiO2 heterojunction

selective generation of CO using the type-II heterojunction

TiO2 (001)/(101) surface heterojunction hierarchical CdS-WO3 Z-Scheme systems

construction of the surface heterojunction for selective photoreduction of CO2 to CH4 over TiO2 selective photoreduction of CO2 to CH4 using the hierarchical Z-Scheme systems

G. Jiang, Z. Zhao J. Yu

g-C3N4/Bi2WO6 Z-scheme composites

highly selective CO2 photoreduction to CO using the direct Z-Scheme systems

J. Shi

g-C3N4 modified with barbituric acid

enhancement of the selective photoconversion of CO2 to CO (15-fold) using the molecular copolymerization selective photoconversion of CO2 into CO and CH4 by the coordinatively unsaturated Co active centers simultaneous texture and surface modification of g-C3N4 for improving CO2 photoreduction

X. Wang

single Co atoms implanted MOF hierarchical amine-functionalized g-C3N4

Q. Zhang, Y. Wang J. Ye C. Xue

J. Yu, W. Ho

J. Ye J. Yu, S. Cao, M. Jaroniec J. Yu

Ag and MnOx modified TiO2 microsheets with coexposed (101) and (001) facets TiO2-protected GaAs/InGaP/TiO2/Ni photoanode Ti2CO2 MXene

application of MXene photocatalyst for selective reduction of CO2

Z. Zhou

Pd/TiO2 nanosheets

selective reduction of CO2 through improving the edge of Pd cocatalysts

S. Bai

PdH0.43/TiO2 nanosheets

first application of metal hydride (PdH0.43) cocatalyst for selective reduction of CO2

Y. Xiong

CsPbBr3 QD/graphene oxide

application of perovskite CsPbBr3 QD for selective reduction of CO2

D.-B. Kuang

one-unit-cell ZnIn2S4 layers

selective reduction of CO2 through introducing zinc vacancies

Y. Xie

spongy Ni-organic cocatalyst

nearly 100% selective CO production by using a Ni-MOF cocatalyst with high concentration of defects

R. Xu and H. Zheng,

selective photoreduction of CO2 to methanol through loading two cocatalysts, Ag and MnOx, on the different exposed facets of TiO2 microsheets highest 10% solar-to-fuels energy-conversion efficiency for photoassisted CO2 reduction

N. S. Lewis

ref (year) 95 (2013) 96 (2014) 97 (2014) 62 (2014) 98 (2014) 99 (2014) 100 (2014) 101 (2015) 102 (2015) 103 (2015) 104 (2016) 105 (2016) 106 (2016) 107 (2016) 31 (2017) 108 (2017) 109 (2017) 30 (2017) 110 (2017) 111 (2017)

systems. To substantially enhance the photocatalytic efficiency, the reaction rates of OER, HER, and ORR should be efficiently controlled and strengthened. Clearly, the high efficiency of ORR is beneficial for the photocatalytic degradation of pollutants and various organic transformations.180−185 Especially, the four-electron OER with the large over-potential and sluggish kinetics has been recognized as the most challenging step to achieve the solar fuel production (overall water splitting and CO2 reduction).50 Therefore, during the past decades numerous efforts have been undertaken to better understand the OER mechanism and to develop highly active and durable OER cocatalysts.186−194 In addition, it is noteworthy that the multi-electron reactions of ORR and CO2 reduction reaction (CRR) generally exhibit more favorable overpotentials than those of the corresponding single-electron reactions.178 Notably, to design better photocatalysts for various practical applications five features should be taken into account: lowcost, toxicity, stability, visible, and NIR-light absorption and efficiency (high activity and selectivity) (Figure 6). On the basis of these features, the well-known photocatalysts, such as TiO2, g-C3N4, graphene, tungsten oxide (WO3), and Bi-based semiconductors195 have been developed for a variety of applications.

energy smaller than their corresponding band gap energies. So far, various clusters, such as CuS,158,159 CrxOy,160 Ag,161 Cu(II),162−169 and Fe(III),170−175 and chemical bonds176 have been proven to be good cocatalysts to carry out the photocatalytic O2 reduction or H2 evolution based on the IFCT mechanism. Clearly, these four mechanisms and their combinations are operational in photocatalysis over various kinds of the commonly used heterogeneous semiconductors. Each complete photocatalytic reaction should include both reduction and oxidation half-reactions. From thermodynamic viewpoint, the photoexcited electrons and holes can only accomplish the surface reduction and oxidation half-reactions with the smaller potentials than the CB and VB levels, respectively. The detailed energy bands of typical photocatalysts and the standard redox potentials of several halfreactions have been summarized in our previous reviews.133,177,178 Of note, most of redox reactions exhibit the same linear pH dependence (VpH = VpH(0) − 0.059 pH), except for the pH-independent single-electron O2 reduction (E0(O2/ O2−) = constant).178,179 The reduction and oxidation halfreactions in different photocatalytic systems are highlighted in Figure 5. Oxygen/hydrogen evolution reactions (OER/HER) and oxygen reduction reaction (ORR) are the three basic halfreactions that normally occur in the different photocatalytic F


Chemical Reviews

Review

Various parameters such as surface, interface, size, and shape of semiconductor nanoparticles (NPs) have a significant impact on their charge carrier dynamics.197 Thus, understanding the charge carrier dynamics in semiconductors could be essential for designing highly efficient nanoarchitectures or nanocomposites for emerging energy and environmental applications. Interestingly, dynamics of charge carrier trapping followed by surface recombination could be deeply investigated using powerful time-resolved laser spectroscopic techniques including transient absorption, transient bleach, and timeresolved fluorescence.198 Figure 7A shows schematically the major pathways for charge carrier relaxation and the pump− probe scheme for monitoring the carrier dynamics.198 The first step of relaxation should be electronic and hole relaxation in band edge states (including the excitonic state) at the bottom of CB and the top of VB, respectively, owing to electronphonon interaction on the time scale of 100 fs or less. As a result, the relaxed electrons at the bottom of CB and the holes at the top of VB, could recombine radiatively in the semiconductors with few or no band gap states on the order of nanoseconds or longer, thus leading to the strong band edge luminescence. However, for the semiconductors with surface or internal defects, the states within the band gap could trap the charge carriers on time scale of a few picoseconds to tens of picoseconds. The trapped charge carriers could further produce red-shifted trap state emission in comparison with band edge emission, due to the nonradiative or radiative recombination. In general, the lifetimes of trap states could range from tens of picoseconds to nanoseconds or microsecond or even longer, depending on the nature, energy levels or trap depth of the trap states. For example, the carrier dynamics in BiVO4 thin films obtained by spray pyrolysis as well as in a photoelectrochemical (PEC) cell under water-splitting conditions, were investigated

Figure 3. (A) Number of publications found by using the following keywords “light* or photo*”, “CO2 or carbon dioxide”, and “*reduction* or *convers*”. The number of papers (B) found by using the following keywords “light* or photo*” and “H2 or hydrogen*”. (Web of Science Core Collection search on October 18, 2018)

2.1.2. Carrier Dynamics and Band Bending. Dynamic properties of charge carriers, including trapping, recombination, and transfer, in a number of semiconductor nanoparticles play an important role in determining their photocatalytic activities.

Figure 4. Photocatalytic mechanisms for inorganic (A) and organic (B) semiconductors, (C) surface plasmon resonance (SPR), and (D) interfacial charge transfer (IFCT). G


Chemical Reviews

Review

Figure 5. Reduction and oxidation half-reactions in different photocatalytic reactions. OER and HER, oxygen and hydrogen evolution reactions; ORR and CRR, oxygen and CO2 reduction reactions.

Figure 7. (A) Schematic illustration of charge carrier relaxation following above band gap photoexcitation in semiconductor NPs. The long and short solid line with upward arrow indicate excitation, the bottom of the conduction band, shallow and deep trap (ST and DT) states, and valence band, respectively. The curved lines with downward arrows indicate different relaxation processes: (1) electronic relaxation within CB, (2) trapping into ST and DT states and further trapping from ST to DP, (3) band edge electron-hole recombination, (4) trapped electron-hole recombination, and (5) exciton−exciton annihilation.198 (B) Model of carrier dynamics in BiVO4.199 Reprinted with permission from ref 198. Copyright 2000 American Chemical Society. Reprinted with permission from ref 199. Copyright 2014 American Chemical Society.

Figure 6. Design rules for heterogeneous photocatalysts.196 Reprinted with permission from ref 196. Copyright 2018 Springer Nature.

by broadband transient absorption spectroscopy (TAS), as illustrated in Figure 7B.199 Notably, the power-dependent recombination on a 0.5 ps time scale is not displayed in Figure 7B due to its negligence under 1 sun conditions. The results confirmed that the trapping process of photogenerated holes was accomplished in 5 ps, whereas the electron relaxation and trapping were found to be on a time scale of 40 ps and 2.5 ns, respectively. In particular, the trap-limited recombination was found on time scales longer than 10 ns. Accordingly, to rationally design photocatalysts, Table 2 summarizes the charge dynamics parameters of various semiconductors. Clearly, all semiconductors exhibit relatively short carrier lifetimes on the time scale of picoseconds to nanoseconds or microseconds, indicating that the fast charge-carrier recombination in semiconductors should be the key bottleneck affecting the photocatalytic efficiency. Several widely used semiconductors such as TiO2, CdS, WO3, BiVO4, and g-C3N4 have longer carrier lifetimes in comparison to other semiconductors confirming their better photoactivity. Additionally, their longer minority-carrier diffusion length and charge mobility (cm2 V−1 s−1 at 300 K) are also crucial photocatalytic parameters that are useful for the design of highly efficient photocatalysts. As verified by carrier dynamics in heterogeneous photocatalysis, photon absorption could induce the electronic

excitation and the subsequent complex photogenerated charge carrier separation and transfer process. Particularly, the charge carrier transfer process between semiconductor surface and contact components (e.g., adsorbed molecules, surface states, metals, and semiconductors), could lead to the band bending, which has been demonstrated to be a complex and fundamental step in light-driven chemical processes.252 Band bending at the surfaces and interfaces of semiconductors is of great importance for deep understanding the photoexcitation process and for the rational design of highly efficient photoactive materials and processes.252 Figure 8 illustrates the free charge carrier densities and energy levels for three kinds of the space charge regions for a n-type semiconductor with the majority carriers (electrons). Clearly, in the flat band region, there is no space charge. When the positive charges and electrons accumulate at the semiconductor surface and in the semiconductor near the surface, respectively, the accumulation layer with the downward band bending is created due to the accumulation of electrons in the semiconductor. In this case, an increase of the density of free electron carriers (ne) and a decrease of density of hole carriers (nh) is achieved. In contrast, when negative and positive charges exist at the surface and near the surface, the depletion layer with the upward band bending is formed due to the depletion of H


Chemical Reviews

Review

Table 2. Comparison of the Band Gap Structures and Carrier Dynamics for Typical Semiconductorsa band gap structure (pH = 7, vs NHE) catalyst (type)

CB

Si TiO2(anatase) TiO2(rutile) SrTiO3 ZnO Cu2O SnO2 CdS226 CdSe g-C3N4 Ta3N5 TaON GaN:ZnO WO3 a-Fe2O3 BiVO4244,245 CH3NH3PbI3 graphene

−0.81 −0.50 −0.32 −0.75 −0.61 −1.16 0.04 −0.9 −0.71 −1.3 −0.75 −0.75

0.29 2.7 2.7 2.75 2.58 0.85 3.54 1.5 0.99 1.4 1.35 1.75

−0.1 −0.03 −0.3

2.7 2.17 2.1

a

VB

Eg (eV) 1.1 3.20201 3.02201 3.5 3.2214 2.0 3.5 2.4 1.7 2.7 2.1 2.5 2.58−2.76 2.8 2.2 2.4

charge dynamics minority-carrier diffusion length

carrier lifetime 15 ns >1 μs202/80 μs203/500 ps204,205 1 ms203 50 ns210 400 ps215 >117 ps219 ∼500−2000 ps223,224 50 ns >500 ps231/10−100 ns232 1 ns−100 ms234/100−200 μs235 500 ps237 500 ns239/10 μs240 8 ps 40 ps−10μs199/40 ns246 100 μs 0.4−1.7 ps250

∼2-4 μm 104 nm206 10 nm

200

250 nm216 20−100 nm220−222 ∼1 μm227,228

charge mobility (cm2 V−1 s−1 at 300 K) 1350 4201/20207 0.1201,208/1209 6−8211−213 120−440214/100−200217/205218 260225 3−35229/100−300230 600−700230/∼100233 1.3−4.4236 ∼17238

150 nm241 2−4 nm243 100 nm247,248/70 nm246 >175 μm249

1242 0.2 cm2 V−1 s−1 4 × 10−2246 164 ± 25(h)/24.8 ± 4.1(e) 200000251

Detailed references to each parameter are given in the main text.

Figure 8. Schematic illustration of three kinds of space charge regions from the n-type semiconductor surface to the bulk (note logarithmic scale). The blue dotted lines indicate the corresponding space charge region of thickness, D. ne, nh, and ni respresent the free electron, hole, and intrinsic carrier density, respectively.252 Reprinted with permission from ref 252. Copyright 2012 American Chemical Society.

electrons. In this case, a decrease of ne and an increase of nh is observed. Particularly, for the upward band bending, if ne is significantly reduced below the intrinsic level (ni) (i.e., ne < ni < nh), a n-type semiconductor nature near the surface is switched to a p-type semiconductor surface, thus leading to the formation of the inversion layer. It should be pointed out that the amounts of charges with different polarity in the space charge region and the surface charge are almost the same due to the charge neutrality. Importantly, these band bendings could be used to reveal the formation mechanism of various heterojunctions used in photocatalysis. As shown in Figure 9,

the band alignment of two contact semiconductors could lead to the formation of five types of heterojunctions and the corresponding internal electric fields.253 Clearly, the internal electric fields in type I-1 (n/n junction) and type I-2 (p/n junction) could favor the separation of photogenerated holes and electrons, respectively. Instead, the internal electric fields in type II-1/direct Z-scheme (n/n junction) could favor the recombination and separation of photogenerated holes and electrons with weaker oxidation and reduction ability, whereas the internal electric fields in type II-2 (p−n junction) could favor the separation of both photogenerated holes and I


Chemical Reviews

Review

Figure 9. Photogenerated charge carrier transfer process for five types of heterojunctions induced by the existing internal electric field: (A) type I-1 (n/n junction), (B) type I-2 (p/n junction), (C) type II-1/direct Z-scheme (n/n junction), (D) type II-2 (p−n junction), and (E) type III-1.253 Reprinted with permission from ref 253. Copyright 2018 Elsevier.

Figure 10. Schematic illustration of direct Z-scheme with staggered band configurations (W1 < W2): (A) before contact, (B) in contact, photogenerated charge carrier transfer process in direct Z-scheme mode (C), and type-II mode (D, failure). Schematic illustration of p−n junction: (E) before contact, (F) in contact, transfer of photogenerated charge carriers in p−n junction mode (G) and direct Z-scheme mode (H, failure).254 Reprinted with permission from ref 254. Copyright 2018 Elsevier.

electrons. Unfortunately, the internal electric fields in type III-1 are unfavorable for the separation of both photogenerated holes and electrons. To accurately understand the formation mechanism of direct Z-scheme and p−n heterojunction, the band bending and photogenerated charge carrier transfer process after contact and band alignment are analyzed and

displayed in Figure 10.254 On the basis of the band bending, it is impossible to create the type II heterojunction and direct Zscheme heterojunction for the contact n−n and p−n interface, respectively. Accordingly, in the practical applications, the formation of different types of heterojunctions should be carefully evaluated by considering the exact CB/VB potentials, J


Chemical Reviews

Review

Figure 11. Different stages in various photocatalytic reactions and the corresponding enhancement strategies.

ent on the cumulative efficiency in four tandem steps, including light harvesting efficiency (ηabs), charge separation efficiency (ηcs), charge migration and transport efficiency (ηcmt), and charge utilization efficiency (ηcu) for photocatalysis. The relationship between them could be calculated according to eq 1119,177

the semiconductor type (p- or n-type) and corresponding Fermi levels.253,254 2.1.3. Strategies for Improving Photoactivity. The main processes in the different photocatalytic reactions are illustrated in Figure 11. The occurrence of photocatalytic reactions over a given semiconductor photocatalyst includes the following processes in unit cells, bulk, and surface phases: (i) the formation of photoexcited electron−hole pairs in the unit cells of semiconductors driven by absorption of incident highenergy photons; (ii) the separation/migration of photogenerated charge carriers to the surface without recombination; the bulk (iii) and surface (iv) recombination of the photoexcited charge carriers; surface reduction (v) and oxidation (vi) reactions driven by the trapped charge carriers on the surface of the corresponding cocatalysts; and (vii) the unexpected surface back reaction (SBR). Generally, these processes can be classified into three steps as shown in Figure 11. It is clear that the overall photocatalytic performance is closely related to the thermodynamic and kinetic balance of all involved processes in the three steps, which is strongly determined by the surface/bulk properties and the electronic structure of a given photocatalyst. Particularly, it is commonly accepted that the photocatalytic quantum efficiency (ηc) is strongly depend-

ηc = ηabs × ηcs × ηcmt × ηcu

(1)

Therefore, to develop highly active and stable photocatalysts, all these steps must be systematically designed and optimized. Since most visible-light semiconductors have been available, the processes in the bulk and surface phases seem to be crucial for boosting the overall photocatalytic efficiency, as compared to the light harvesting and charge excitation in the unit cell. So far, various kinds of surface and interface modification strategies have been extensively explored for improving charge carrier dynamics, accelerating the slow transport process and sluggish surface reaction kinetics of photogenerated electrons and holes involved in complex processes, which are very crucial for achieving the high activities and stabilities through effective solar-to-chemical energy conversion.255−258 In particular, the multifunctional integration and optimization of some popular engineering strategies is essential for enhancing the overall K


Chemical Reviews

Review

Figure 12. Schematic illustration of three kinds of photocorrosion: (A) oxidative photocorrosion, (B) reductive photocorrosion, (C) dual photocorrosion and (D) stable. Er(SC) and Eo(SC) are the thermodynamic oxidation/reduction potentials of semiconductors, respectively.

heterogeneous photocatalysis. Particularly, the coupling of nanocarbons and semiconductors can enhance light absorption, charge separation, photostability, adsorption, and reaction kinetics,113,177,349−352 and seems to be one of the most promising strategies for development of robust and efficient photocatalysts. 2.1.4. Stability of Photocatalysts. Besides the photocatalytic redox reactions, the photogenerated electrons (holes) with higher (lower) quasi Fermi energy than the thermodynamic reduction (oxidation) potential of the semiconductor can also drive the degradation or decomposition of semiconductor itself in aqueous solution under illumination, known as photocorrosion of semiconductors.177,353 In general, the thermodynamic oxidation/reduction potentials of a given semiconductor can be obtained by ab initio calculations and by using electrochemical experimental data available in literature.353,354 Thus, according to the thermodynamic oxidation/reduction potentials and the valence/conduction band edges of semiconductors, the thermodynamic instabilities can be divided into the oxidative, reductive and dual photocorrosion (Figure 12). Clearly, the reductive photocorrosion is caused by the photoexcited electrons (as shown in Figure 12A), whereas the oxidative photocorrosion is mainly induced by the photoexcited holes (Figure 12B). In some cases, dual photocorrosion can be simultaneously motivated by both photogenerated electrons and holes, respectively (Figure 12C).353 Additionally, it should be noted that some semiconductors with the proper CB and VB potentials are stable (Figure 12D). The commonly used semiconductor materials are summarized in Figure 13 in terms of the three types of photocorrosion. As shown in Figure 13, the reductive photocorrosion is generally observed for various Ag-based semiconductors (i.e., Ag3PO4,355AgBr,356 Ag2CO3357, and AgI358), whereas the oxidative photocorrosion occurs on the typical non-oxide semiconductors (i.e., CdS,113,359 GaAs, GaP, Ta3N5, and CdSe). In addition, Cu2O221 and SiC commonly

photocatalytic efficiency due to the possible synergistic effects. For example, loading plasmonic metals as cocatalysts can simultaneously lead to the enhanced visible-light harvesting, charge separation and accelerated surface reaction kinetics, thus significantly boost the overall photocatalytic efficiency. In other words, all the processes in each stage can be enhanced by loading suitable amounts of plasmonic metals on semiconductors, including the generation, trapping, dynamic vectorial transfer, and storing of photogenerated electrons across the Schottky junction.259 Thus, it is not surprising that the plasmonic metals cocatalysts have been widely applied in photocatalysis, including photocatalytic H2 evolution, degradation of organic pollutants, and CO 2 reduction. 260−266 Furthermore, fabrication of various kinds of hierarchical semiconductor structures at the micro/nanometer scale not only favors the light harvesting but also is beneficial for enhancing charge separation and adsorption of reactants, and consequently enhances the overall photocatalytic efficiency.105,178,267−273 In addition, the strategy of loading suitable cocatalysts (electrocatalysts) can simultaneously solve the large onset overpotential and sluggish kinetics, two key factors limiting the overall photocatalytic efficiency, thus significantly boost the surface electrocatalytic reduction and oxidation reactions (surface charge utilization).274,275 Of note, from the viewpoint of sustainable development, the earth-abundant noble-metal-free cocatalysts are essentially crucial and promising for practical photocatalytic applications.158,275−294 More importantly, cocatalysts (electrocatalysts) can also greatly improve the charge separation performance and photostability of semiconductors.275,295 Finally, it should be pointed out that the fabrication of heterojunctions has attracted a lot of attention during the past decades. So far, various kinds of heterojunctions,296−301 such as Schottky junctions (metal and nanocarbons), phase junctions (homojunctions),302−310 facet junctions,100,311−315 type II n−n/n−p heterojunctions316−326 and all-solid-state Z-scheme systems,310,327−348 have been successfully explored and utilized in the different fields of L


Chemical Reviews

Review

be pointed out that the in situ produced metallic Ag cocatalyst on the Ag-based semiconductors by partial self-corrosion can be used to further enhance their self-stability under light illumination.167,363−370 Additionally, nanocarbons, such as graphene, carbon nanotubes, and ultrathin amorphous carbon layers, can greatly inhibit the unfavorable reductive and oxidative photocorrosion.371−376 On the one hand, the reductive photocorrosion can be significantly inhibited by conductive nanocarbons, which can act as reservoirs to extract the photoexcited electrons in semiconductors needed for reduction reactions and, thus, greatly decrease the possibility of reductive corrosion.351,357,377−381 On the other hand, the oxidative photocorrosion can be also greatly inhibited by nanocarbons, which can be partly oxidized or mineralized by photogenerated holes and induced •OH radicals in an aqueous phase, thus avoiding self-oxidation of semiconductors.382−384 In addition, the nanocarbon layers wrapped on unstable photocatalysts can protect them against active species in solution, especially •OH radicals, to avoid the unexpected photocorrosion.349,384−386 The above discussion shows clearly that nanocarbons are excellent photostabilizers and have been extensively used to inhibit both the reductive and oxidative photocorrosion, thus improving significantly the overall photocatalytic efficiency of photocatalysts. In addition to the semiconductor-cocatalyst and semiconductor-carbon heterojunctions, heterojunctions consisting of two different semiconductors have been effectively used to improve the photostability of semiconductors and boost their overall photocatalytic activity. Typically, the type II heterojunctions, such as Cu2O/TiO2387−391 and CdS/TiO2,392−397 and all-solidstate Z-scheme systems398−400 have been extensively and rationally designed to decrease photocorrosion of unstable Cu2O and CdS. Finally, preparation of protective overlayers, such as TiO 2 , 401−405 SrTiO 3 , 406 g-C 3 N 4 , 407−409 Co− Pi, 295,410−412 CoO x , 413−415 Al 2 O 3 , 416 Ga 2 O 3 417 , and SiO2,418−423 on semiconductors can “passivate” or “catalyze” their surface to reduce charge recombination or enhance charge transfer, respectively, thus effectively boosting the overall photocatalytic activity.12 In future, it is expected that the photostability can be rationally regulated and significantly improved by fabricating multiple-heterojunction photocatalysts to take advantage of possible synergistic effects in these systems.424−430 2.1.5. Selectivity of Photocatalysts. Typically, during the different photocatalytic reactions, the photoinduced electrons and holes, and the highly reactive radical species (e.g., •OH and O2−) generally do not exhibit photocatalytic selectivity for transformation and decomposition of targeted organics.431 It remains a significant challenge to achieve the desirable photocatalytic selectivity for various reactions. In general, the selective photocatalysis can be achieved by taking advantage of electrostatic adsorption and structural432−435 interactions between photocatalysts and reactant molecules, as well as by loading different cocatalysts. It is known that the strong electrostatic interactions between reactant molecules and the photocatalyst surface play a crucial role in achieving selectivity towards photocatalytic degradation. It is also demonstrated that mesoporous titanium dioxide can selectively convert strongly adsorbed molecules into weakly adsorbed molecules in the presence of water being a source of oxidant.436 For example, it is demonstrated that the fluoridation and hydroxylation of hollow TiO2 microspheres with positive and negative charges can degrade the negatively charged methyl

Figure 13. Band structures and thermodynamic reduction (oxidation) potentials of typical semiconductors with oxidative, reductive, and dual photocorrosion.

suffer from the dual photocorrosion, which leads to their extremely poor photostability. To avoid the unexpected photocorrosion, the simple method is the development of stable semiconductors, such as pCuRhO2360 and p-AgRhO2.361 Besides this, many different strategies have been developed to effectively suppress undesired photocorrosion of unstable semiconductors. Figure 14

Figure 14. Strategies for inhibiting photocorrosion of unstable semiconductors: (1) use of sacrificial agents, (2) deposition of cocatalysts, (3) incorporation of nanocarbons, (4) formation of heterojunctions, and (5) preparation of protective overlayers.

illustrates five typical strategies used to suppress photocorrosion, namely: introduction of sacrificial agents, deposition of cocatalysts, incorporation of nanocarbons, formation of heterojunctions and preparation of protective overlayers. Firstly, it is clear that the introduction of suitable sacrificial electron donors (e.g., S2−/SO32−, lactic acid, triethanolamine, and methanol) and electron acceptors (e.g., Ag+), can fundamentally consume the superfluous photogenerated holes and electrons in the semiconductors, respectively, which results in more efficient utilization of counter charge carriers. Furthermore, the deposition of proper cocatalysts can greatly improve the surface redox reaction kinetics and charge separation, and consequently, reduce the reductive and oxidative photocorrosion. For example, the loading of cobalt oxide terminated with phosphate groups, cobalt phosphate (Co-Pi), or CoOx into semiconductors as oxidative cocatalysts can enhance their photostability and photocatalytic efficiency due to the inhibited self-oxidation.295,362 Also, incorporation of expensive noble metal or earth-abundant nanoparticles/clusters as reductive cocatalysts to semiconductors reduces the reductive photocorrosion, and consequently, enhances photocatalytic stability and activity.167,171,363 Interestingly, it should M


Chemical Reviews

Review

Figure 15. Schematic illustration for six configurations of the semiconductor/cocatalyst composites: (a) semiconductor supported single reduction or oxidation cocatalyst systems; (b) semiconductor−dual (reduction and oxidation) cocatalyst systems; (c) plasmonic metal−semiconductor− cocatalyst systems; (d) dye/quantum dots−semiconductor (irradiated or unirradiated)−cocatalyst systems; (e) dye/quantum dots−cocatalyst systems; and (f) semiconductor−carbon/metallic bridge-cocatalysts or semiconductor−cocatalysts with coated layers. CB, VB, RC, OC, Eg, and QDs represent the conduction band, valence band, reduction cocatalyst, oxidation cocatalyst, energy band, and quantum dots, respectively.

degree of crystallinity. It is believed that the strong adsorption of hydrophobic benzaldehyde on the surface of the poorly crystallized rutile TiO2 prevents its desorption and thus facilitates its further oxidation.441 Furthermore, the presence of suitable hydrophobic surface groups (−OCH3) in the reactants effectively increases the selectivity of rutile TiO2 catalysts toward photooxidation of 4-methoxybenzyl alcohol to 4-methoxybenzaldehyde, whereas the presence of −NO2 groups has a detrimental effect on the selectivity enhancement.442 Apart from the selectivity achieved due to the electrostatic interactions, the shape-selective photocatalysis is also possible because of the competitive diffusion of molecules into the cavities.432−434 In 2001, Calza et al. for the first time provided the evidence for selective photodegradation in aqueous solutions.433 They found that the degradation rate of large 2,3-dihydroxynaphthalene (2HPP) molecules on ETS-10 (Engelhard Titanosilicate Structure 10) is of the same order of magnitude as that on TiO2, about 56 times higher than that of small phenol (P) molecules. It is believed that TiO2 and ETS-10 have similar degradation rates toward 2HPP due to the similar external surface area, whereas the smaller P molecules could easily diffuse inside the zeolitic internal cavities with a shielding effect against photodegradation, thus leading to the

orange (MO) and positively charged methylene blue (MB), respectively.431,437 More interestingly, the exposure and reduction of etching of reactive (001) facets in films composed of flower-like TiO2 microspheres are favorable for selective photocatalytic degradation of positively charged methyl violet (MV).437 Similarly, the calcined TiO2 anatase nanoplates with increased (101)/(001) facet ratio can achieve the highest photoactivity toward oxidation of NO gas into NO2 and NO3−, while the washed anatase TiO2 nanoplates with NaOH show the largest photocatalytic efficiency toward degradation of acetaldehyde due to tuned adsorption selectivity of these air pollutants.438 Additionally, coupling negatively charged graphene and TiO2 facilitates the selective adsorption and photodegradation of positively charged MB.439 Modification of the TiO2 particle surface with chelating agents (arginine) enhances much more specific adsorption of nitrobenzene than that of phenol, thus accomplishing the adsorption-induced selectivity in photocatalysis.440 More interestingly, a significant effect of crystallinity on selectivity can be also observed due to the improved adsorption performance. The selective photooxidation of aromatic alcohols into aldehydes in water can be also achieved because of the very different adsorption affinities of benzaldehyde (hydrophobic compound) and 4-methoxybenzaldehyde toward nanostructured rutile TiO2 with a low N


Chemical Reviews

Review

Table 3. Fundamentals of Heterogeneous Cocatalysts category type role274,275,473,520

composition

design considerations

synthesis methods modification strategies

comments (1) reduction cocatalysts (H2O,120,279,359,502−506 CO2,507−509 N2,510−512 and O2 reduction184,502,513−515) (2) oxidation cocatalysts (O2 evolution516−519) (1) improve the photocatalytic activity, selectivity, stability (2) promote the interfacial charge separation and collection (3) enhance the adsorption/desorption/activation of reactants (4) suppress the reverse reaction (1) reduction cocatalysts: bioenzymes, molecular complex,473 metals/alloys,474−476 metal compounds (oxides,477 hydroxides,335,478,479 sulfides,480−484,521 selenides,485,486 phosphides,285,487−497 carbides,114,286,498 borides,478 nitrides499−501), and metal-free carbon-based materials (2) oxidation cocatalysts: metal compounds (hydroxides, oxides, oxyhydroxides, phosphates, borates) (1) high electrocatalytic activity and selectivity, large number of active sites (2) the structural and electronic properties, electrical conductivity, structural and Fermi-level matching with semiconductor (3) interfacial coupling, loading the lower Schottky barrier (4) amount, location, particle size, dispersion (5) adsorption and desorption of reactants, long-term stability, the environmental impact, low cost (1) in-situ procedures (ion exchange, photodeposition, hydro(solvo)thermal, coprecipitation, chemical bath deposition, epitaxy growth, atomic layer deposition (ALD), chemical vapor deposition (CVD), high-temperature solid-state reactions) (2) ex situ procedures (ultrasonic treatment, mechanical grinding, electrostatic self-assembly, and van der Waals coupling) optimization of cocatalysts’ composition (surface/interface), morphology, size, shape, structure, facets, grain boundary, strain, phases, oxidation states, defects, edges, crystallinity, dispersion, dimensionality, and loading location

vacancies similar in size and shape to the nitrogen atom in N2.435 More importantly, nitrogen vacancies could also improve the separation efficiency of photogenerated carriers and the electron transfer from g-C3N4 to adsorbed N2. The simplest method to tune the photocatalytic selectivity is to load suitable cocatalysts on the surface of semiconductors. Previously, the tunable selectivity of cocatalyst-modified semiconductors has been extensively investigated for different photocatalytic systems, such as photodegradation,455−460 CO2 reduction, disinfection461 and organic synthesis.156,462−469 Various aspects related to the use of cocatalysts for tuning the selectivity of CO2 photoreduction will be highlighted in this Review. 2.1.6. Fundamentals of Cocatalysts. Through the above analysis, it is clear that the reduction and oxidation cocatalysts over semiconductors play the key role in activating their surface reactive sites and reducing the activation energy for surface chemical reactions, thus fundamentally improving the overall photocatalytic efficiency of semiconductors. Since pioneering works by Bard and his group reporting the concept of an integrated micro-PEC cell for particulate photocatalysts and the method for photodepositing Pt islands on TiO2 powder and other semiconductor substrates for potential photocatalytic applications,470−472 various effective electrocatalysts have been widely employed as active cocatalysts over semiconductor particles for carrying out heterogeneous photocatalysis, and considered as the dominant active sites to accelerate the surface electrocatalytic reduction and oxidation reactions driven by photogenerated electrons and holes, respectively. Interestingly, six basic configurations of the semiconductor/cocatalyst composite photocatalysts have been designed and developed over the past decades (Figure 15); namely, (a) semiconductor supported single reduction or oxidation cocatalyst systems; (b) semiconductor−dual (reduction and oxidation) cocatalyst systems; (c) plasmonic metal−semiconductor−cocatalyst systems; (d) dye/quantum dots−semiconductor (irradiated or unirradiated)−cocatalyst systems; (e) dye/quantum dots− cocatalyst systems; and (f) semiconductor−carbon/metallic bridge-cocatalysts or semiconductor−cocatalysts with coated layers. Notably, the semiconductors in these six configurations could be replaced by the p−n and Z-scheme heterojunctions or

much lower degradation efficiency. Interestingly, they further found that a mild modification of ETS-10 with HF leads to about 2.5-3 times higher accessibility of titanium sites (titanol groups), thus leading to a remarkable increase in the shape selectivity and activity toward photodegradation of large aromatic molecules, which are not capable of penetrating into zeolitic pores.434 These results offer a new strategy for shapeselective photocatalysis. In contrast, a core−shell structured TiO2@hollow silica photocatalyst showed the size-selective photocatalytic decomposition activity toward the relatively small organic molecules because the hollow silica shell effectively prevented adsorption of large molecules on the surface of TiO2 core by blocking effect.443,444 Besides using SiO2 surface coating (silica shells), a ultrathin layer of molecularly imprinted polymer (MIP) has been coated on the surface of TiO2 to achieve the shape-selective photocatalysis, based on the unique molecular recognition capacity toward template molecules.445 The MIP-coated TiO2 photocatalysts exhibited greatly improved activity toward the selective photodegradation of the target 2-nitrophenol and 4-nitrophenol pollutants when using a bisphenol A as a non-target pollutant because of the special interaction between the target molecules and the coating polymer because of the presence of suitable functional groups (−OH and −NO2). More interestingly, the core−shell CdS@ZIF-8 structures could improve the photocatalytic selectivity toward H2 generation from formic acid, but hinder the CO evolution.446 This is because the smaller size of narrow windows (3.4 Å) in ZIF-8 shell prevents the diffusion of CO with a larger kinetic diameter (3.8 Å) into its micropores, thus achieving the shape-selective photocatalysis. The precisely controlled porous structures of anodized TiO2 films could also exhibit the size-selective photodecomposition of methylene blue (MB) in a mixture of MB direct red 80 (DR), suggesting the importance of the nanochannel diameter and uniformity in this process.447 More interestingly, a surface molecular imprinting technique has been employed to prepare molecularly imprinted semiconductors with specific recognition of target molecules for achieving the shape-selective photocatalysis.445,448−454 In particular, the concept of imprinted semiconductors in the shape-selective photocatalytic N2 fixation over g-C3N4 has been also verified through inducing nitrogen O


Chemical Reviews

Review

Figure 16. Active sites in various graphene structures and their heterostructures: (A) edges and defects, (B) doped heteroatoms or single atoms, (C) metal clusters and functional groups, (D) hot electron (e−) transfer from metal to graphene layer, (E) confinement environment nanoreactors in the space between a metal surface and 2D crystals, and (F) sandwich van der Waals heterojunction based on different 2D materials.522 Reprinted with permission from ref 522. Copyright 2016 Springer Nature.

Figure 17. (A) Calculated adsorption free energy of H atoms on different sites at a potential U = 0 relative to the standard hydrogen electrode at pH = 0. (B) Active sites in (left) nitrogenase and (middle) hydrogenase and (right) MoS2 slab with sulfur monomers present at the Mo edge.523 Reprinted with permission from ref 523. Copyright 2005 American Chemical Society.

presence of electrocatalysts on semiconductor photocatalysts as cocatalysts could play multi-function role in improving the photocatalytic activity, selectivity, stability, interfacial charge, and adsorption/activation of reactants and suppressing the

homojunctions. To understand the fundamentals of these cocatalysts in photocatalysis, their role, composition, design considerations, fabrication, and modification strategies have been systematically summarized in Table 3. Clearly, the P


Chemical Reviews

Review

reverse reaction.274,473 So far, according to the different chemical compositions of cocatalysts, it is clear that bioenzymes, molecular complex,473 metals/alloys,474−476 metal compounds (oxides,477 hydroxides,335,478,479 sulfides,480−484 selenides,485,486 phosphides,285,487−497 carbides,114,286,498 borides,478 nitrides499−501) and metal-free carbon-based materials have been extensively developed to boost the photocatalytic reduction reactions,119,275 whereas the metal compounds (hydroxides, oxides, oxyhydroxides, phosphates, borates) have been available for the photocatalytic oxidation reactions. More importantly, various factors (i.e., high electrocatalytic activity and selectivity, large number of active sites, the structural and electronic properties, electrical conductivity, structural and Fermi-level matching with semiconductor, interfacial coupling, loading amount and location, particle size, dispersion, the lower Schottky barrier, adsorption and desorption of reactants, longterm stability, the environmental impact and low cost) should be comprehensively considered for rational design and fabrication of the high-efficiency cocatalysts for different photocatalytic applications. Additionally, various kinds of insitu procedures (i.e., ion exchange, photodeposition, hydro(solvo)thermal treatment, coprecipitation, chemical bath deposition, epitaxy growth, atomic layer deposition (ALD), chemical vapor deposition (CVD), high-temperature solid-state reactions), and ex situ procedures (i.e., ultrasonic treatment, mechanical grinding, electrostatic self-assembly, and van der Waals coupling) have been exploited and applied for the fabrication of the composite photocatalysts. The in situ synthesis process could ensure sufficient and intimate interfacial contact between cocatalysts and semiconductors, thus facilitating the efficient interfacial charge separation, whereas the ex situ synthesis methods could accurately control and maintain the microscopic structure (i.e., the size, shape, and morphology) of cocatalysts and semiconductors in a uniform manner through preselection of desirable semiconductor components. Thus, the ex-situ synthesis methods are especially suitable for the fabrication of 2D layered cocatalysts and 2D semiconductor nanosheets to create the favorable 2D−2D layered heterojunction. However, the insufficient interfacial contact in the other composites fabricated by the ex situ synthesis methods should be carefully optimized and improved to achieve the maximum photocatalytic activity through the post annealing and high-temperature treatment. In this regard, the conductive binders are promising for enhancing the interfacial coupling in the composite photocatalysts prepared by ex situ synthesis methods. Finally, it should be pointed out that many modification strategies of cocatalysts have been developed through rational optimization of their surface/interface composition, structure, dimension, size, shape, facets, strain, phases, defects, edges, and crystallinity to enhance photocatalysis. Furthermore, it is of vital importance and challenging to precisely control and identify the amount, structural, and electronic properties of reactive sites in the cocatalysts. For example, active sites in various graphene and its heterostructured catalysts (Figure 16) could be originated from their (A) edges and defects, (B) doped heteroatoms or single-atom metal, (C) metal clusters and functional groups, (D) hot electron (e−) transfer from metal to graphene layer, (E) confinement environment nanoreactors in the space between a metal surface and 2D crystals, and (F) sandwich van der Waals heterojunction (stacks of several 2D crystals) based on different 2D materials.522 The tunable and unprecedented flexibility of

electronic states and active sites in various graphene-based catalysts have led to a variety of cocatalyst applications through a range of catalytic mechanisms, including the oxygen reduction reaction, water splitting, and CO2 activation. Similarly, in 2005, using quantum chemical methods, Nørskov and his coworkers first found that MoS2 nanoparticles supported on graphite are a promising hydrogen-evolution electrocatalyst with a moderate overpotential of 0.1−0.2 V because of the zero-approaching binding free energy of atomic hydrogen (Figure 17A).523 More importantly, it was pointed out that the edges of MoS2 are potential active sites, instead of its basal plane (Figure 17B). Subsequently, Chorkendorff and his coworkers further identified the edge sites of MoS2 nanocatalysts as active sites for electrocatalytic H2 evolution.524 More recently, it was found that the edge sites of 1T−MoS2 are more active than those of 2H−MoS2 and that suitable dopants and enlarged interlayer spacing could further boost electrocatalytic hydrogen evolution of MoS2 because of the triggered new basal plane active sites.525−528 Interestingly, these active sites on 2D graphene and transition metal dichalcogenide nanosheets could be characterized by density functional theory (DFT) calculations and high-resolution imaging tools, such as in situ scanning tunneling microscopy and transmission electron microscopy (TEM), during reaction process. Additionally, the surface interrogation scanning electrochemical microscopy (SI-SECM) mode was used to identify the active sites and reveal the electrocatalytic mechanism. For example, NiIV and FeIV were found to be the “fast” and “slow” sites in nickel−iron mixed metal oxyhydroxides for electrocatalytic oxygen evolution reaction (OER), respectively.529 The presence of the lowvalence-state oxide of Ni over metallic Ni could significantly improve the electrocatalytic HER activity because of the enhanced dissociative adsorption of water at the Ni/Ni oxide interface.530 More recently, the electrochemical in situ X-ray absorption spectroscopy (XAS) studies reveal that transformation of Ni-thiolate coordination polymer or two-dimensional nickel disulfide (NiS2) into metallic Ni is the dominant active species for alkaline HER.531,532 However, so far, there is a lack of effective characterization tools and theory for in situ identification of the exact active sites of electrocatalysts for guiding the rational design and fabrication of efficient cocatalysts for photocatalytic applications. Clearly, there is still a big gap between the quickly developed theoretical calculations and realistic reaction systems. Therefore, more in situ characterizations and calculations close to the real conditions are still highly desired. 2.2. Thermodynamics of CO2 Photoreduction

The standard redox potential ΔE° and free energy ΔG for many multielectron CO2 reduction reactions are listed in Table 4.533 It is obvious that the multielectron reactions for CO2 reduction, involving a positive change in enthalpy, ΔH, are thermodynamically unfavorable because they are typically endothermic processes. In this case, these thermodynamically uphill conversions of CO2 to organic products (with a positive Gibbs free energy, ΔG) are difficult to proceed at ambient temperature when there is not enough supply of energy to initiate them. However, it should be pointed out that the photo- and electrochemical CO2 reduction are inherently different from CO2 hydrogenation to formate and methanol. In fact, the latter reactions, including hydrogenation of CO2 to methanol, methane, ethylene, propene, and butylene are all exergonic because of their negative ΔH values (as shown in Q


Chemical Reviews

Review

Table 4. Standard Molar Enthalpy, ΔH°298, and the Gibbs Free Energy, ΔG°298, for the Reduction Reactions of CO2 reaction

ΔH°298 (kJ/mol)

reduction reactions of CO2 with H2O H2O(l) → H2(g) + 1/2O2(g) CO2(g) → CO(g)+ 1/2O2(g) CO2(g) + H2O(l) → HCOOH(l) + 1/ 541 2O2(g) 795.8 CO2(g) + H2O(l) → HCHO (l) + O2(g) CO2(g) + H2O(l) → CH3OH(l) + 3/ 727.1 2O2(g) 890.9 CO2(g)+ H2O(l) → CH4 (g) + 2O2(g) CO2 hydrogenation reactions535 CO2 + H2 → CO + H2O(g) 41.2 CO2 + H2 → HCOOH(l) −31.2 CO2 + 3H2 → CH3OH + H2O(l) −131.0 CO2 + 4H2 → CH4 + 2H2O(g) −164.9 2CO2 + 6H2 → C2H4 + 4H2O(g) −127.91 3CO2 + 9H2 → C3H6 + 6H2O(g) −249.84 4CO2 + 12H2 → C4H8 + 8H2O(g) −360.44

ΔG°298 (kJ/ mol) 237 257 275 520 703 818 28.6 33.0 −9.0 −113.5 −57.52 −125.69 −179.95

Figure 18. Schematic illustration of CO2 photoreduction on a semiconductor.

photogenerated electrons on the semiconductor surface could typically reduce CO2 to solar fuels,120,543,544 whereas, the photogenerated holes on the surface react with water to produce O2.543,544 Theoretically, to achieve the CO2 photoreduction by water, the CB level of a given semiconductor must be much higher than the proton-assisted multielectron reduction potentials of CO2, whereas, the VB edge must be much more positive than the four-electron water oxidation potentials. The standard reduction potentials of CO2 reduction reactions are also summarized in Figure 18 and Table 5 (at pH 0 in aqueous solutions versus NHE).122,354,545−549 Importantly, the reduction potentials of CO2 at different pH values can be obtained by using the linear pH dependence with a slope of -0.059 V (except for the reaction of CO2/HCOO−). The relationship between pH values and potentials for the formation of HCOOH from CO2 as well as other related

Table 4). Thermodynamically speaking, the “hydrogenation of CO2” reactions are favorable, which can even be easily achieved through the thermal reduction of CO2 by highenergy H2 in the absence of light at a moderately low level of energy to repel side and reverse reactions. In fact, the activities of photocatalytic CO2 hydrogenation reactions are significantly higher than those previously reported for CO2 photoreduction reaction with water.536−539 More interestingly, it is also demonstrated that the H2 reductant can facilitate the CH3OH production and inhibit the CH4 formation over Cu-loaded In2O3/TiO2 photocatalysts.540 However, the main problem of CO2 hydrogenation is the source of hydrogen supplied to the system. An ideal source of hydrogen, which is an important alternative fuel, should be electrolysis of water using solar energy as the power source (i.e., photovoltaic electricity) or direct solar water splitting (i.e., artificial photosynthesis). In this regard, water is considered as one of the most advantageous reducing agents for CO2 reduction. Among all reduction routes of CO2, the photo(electro)chemical reduction of CO2 by H2O into solar fuels and chemicals, regarded as artificial photosynthesis, has been demonstrated to be a straightforward and promising strategy to recycle CO2, from the viewpoint of the direct utilization of renewable and inexhaustible solar energy.541 Thus, over past three decades the major effort has been directed toward multielectron CO2 photoreduction utilizing solar energy and H2O, though the efficiency and selectivity of this process are currently still very low for production of solar fuels on a large scale. The mechanism of photocatalytic reactions has been widely investigated since Honda and Fujishima first discovered in 1972 water photoelectrolysis under illumination of TiO2 electrodes.542 Generally, it is well accepted that the photocatalytic redox reactions are driven by the photogenerated charge carriers on the surface of a semiconductor.472 For a given semiconductor photocatalyst, electrons in its VB are excited into its CB when the absorbed photon energy is equivalent to or higher than its band gap energy, leaving holes in its VB (as indicated in Figure 18).543,544 Then, the photogenerated holes and electrons migrate to the semiconductor surface and participate in reduction and oxidation processes, respectively. For CO2 photoreduction, as shown in Figure 18, the 534,535

Table 5. Standard Potentials for CO2 Reduction Reactions (at 1.0 atm and 25 °C)a electrochemical half-reactions 2H+ + 2e− → H2(g) 2H2O (l) + 4h+ → O2(g) + 4H+ CO2(g) + e− → CO2− 2CO2(g) + 2H + + 2 e− → H2C2O4(aq) CO2(g) + 2H+ + 2e− → HCO2H(l) CO2(g) + 2H+ + 2e−→ CO(g) + H2O(l) CO2(g) + 4H+ + 4e− → C(s) + 2H2O(l) CO2(g) + 4H+ + 4e−→ HCHO(l) + H2O(l) CO2(g) + 6H+ + 6e− → CH3OH(l) + H2O(l) CO2(g) + 8H+ + 8e− → CH4(g) + 2H2O(l) 2CO2(g) + 8H2O(l) + 12e−→ C2H4(g) + 12OH− 2CO2(g) + 9H2O(l) + 12e−→ C2H5OH(l) + 12OH− 3CO2(g) + 13H2O(l) + 18e−→ C3H7OH(l) + 18OH−

standard potential E0 (V, vs NHE at pH 0) 0 1.229 −1.9 −0. 475 −0.2 −0.12 0.21 0.07 0.03 0.17 0.07 0.08 0.09

a E(pH) = E0(pH = 0) − 0.059 pH. CO2(g) + H2O(l) +2e− → HCOO−(l) + OH− (−0.43 V vs SHE at pH 7.0).549

R


Chemical Reviews

Review

larger driving force for CRR. To verify this point, in 1979, Inoue et al. found that formic acid, formaldehyde, and methanol can be obtained through direct photoreduction of CO2 in aqueous semiconductor suspensions, including SiC, CdS, ZnO, GaP and TiO215. The above work demonstrates that the yield of methyl alcohol obtained by photocatalytic reduction of CO2 is a function of the CB levels of the semiconductor used. The yield of methanol increases with upshifting the CB levels with respect to the redox potential of H2CO3/CH3OH, whereas methanol cannot be produced over photocatalyst with a CB level much lower than the redox potential of H2CO3/CH3OH.15 However, for a given semiconductor, the overpotential for target CO2 reduction reaction does not change with the difference in pH value, since its CB level has a similar linear pH dependence as the reduction potentials of CO2 (showing a slope of -0.059 V). At this point, the semiconductors with more negative CB levels such as ZnS, SiC, GaP, C3N4, Cu2O, CdS, TaON, Ta3N5 and Bi2S3 seem to be good candidates for the photoreduction of CO2, owing to their strong reduction capacities (as shown in Figure 20) and potential selectivity when appropriate electron donors are used. In contrary, the CB levels of WO3, Bi2WO6 and BiVO4 are too low to reduce CO2 by the photogenerated electrons under illumination. However, those semiconductors with suitable nanosized structures have proven to be highly selective photocatalysts for photoreduction of CO2 because their CB potentials can be efficiently upshifted due to the quantum size effects.553−562 In addition, the semiconductors with more positive CB levels and smaller band gaps can be efficiently integrated into the typical Z-scheme “artificial photosynthesis” systems, in which they can serve as better water oxidation active sites owing to the strong oxidation abilities because of unrecombined holes.327 Thus, thermodynamically speaking, there are two ways to enhance the activity and selectivity of CRR. First, by increasing the overpotential for one desired CRR by utilizing semiconductors with more negative CB levels, and second, by lowering the thermodynamic barrier because of using cocatalysts and selecting multielectron reduction routes instead of the one-electron process. Besides those two methods, the improvement in the kinetics process of photocatalytic CRR plays also an important role in boosting both photoactivity and selectivity, which will be discussed in the following section.

substances at 298 K, based on the Pourbaix diagram by Hori, is displayed in Figure 19.549 As observed in Figure 19, it is clear

Figure 19. Pourbaix diagram for the formation of HCOOH from CO2 at 25 °C.549 Reprinted with permission from ref 549. Copyright 2011 Springer Nature.

that the formation of formate or formic acid, requires moderate potentials and an acidic environment to obtain a desirable current density, selectivity, and overpotential. Figure 19 also shows that the electrolyte and operating conditions have important effect on the selectivity and the potentials for electrochemical reduction of CO2. Figure 18 and Table 5 show that the one-electron reaction of forming CO2•− radical is highly unfavorable due to its large kinetic “overvoltage” (−1.9 V versus NHE) and the geometric rearrangement from linear to bent shape.122,545,546 As compared to the two-electron water reduction, the multielectron and multiproton reduction reactions of CO2 are more favorable because of the substantially lower thermodynamic barriers.550 Relatively speaking, the multielectron and multiproton reactions of CO2 photoreduction to methanol and methane are thermodynamically more favorable than the photocatalytic H2 evolution reaction because their reduction potentials are even lower than that of H2 generation from water splitting. In principle, all the photocatalysts used in photocatalytic H2 evolution are capable of performing the reactions of photocatalytic CO2 reduction into methanol and methane. However, it is especially challenging to get the target product(s) with high selectivity, due to very similar thermodynamic potentials for these reduction products of CO2 and H2O (i.e, HCOOH, HCOH, CH3OH, CH4, and H2). Thus, to achieve high activity in the selective photoconversion of CO2 with H2O, the two-electron H2 evolution via reduction of H+, as the dominant pathway and competing reaction, must be effectively suppressed by using suitable surface coating or multifunctional cocatalysts.92,551,552 In addition, as can be seen in Figure 18, the overpotential for driving the desired CRR increases as the energy levels of CB of one semiconductor become more negative, thus leading to a

2.3. Kinetics of CO2 Photoreduction

In general, the photosynthetic reactions are strongly dependent on three successive reaction processes: light harvesting, charge separation/transport, and surface reactions.563,564 For photoreduction of CO2 over powdered photocatalysts, there are eight processes during photocatalysis (as shown in Figure 21). They include the following: (1) the light harvesting and excitation of

Figure 20. Energy diagrams of some commonly used semiconductors and some redox levels for species related to the CO2 reduction at pH 7 in aqueous solutions. S


Chemical Reviews

Review

2.4. Adsorption and Activation of CO2

In principle, the interactions of the reactants and intermediates with the surface active sites are generally considered to be the determining factors in governing the catalytic activity and selectivity. In other words, due to the low solubility of CO2 in the electrolyte, increasing the local concentration of CO2 and electrolyte cations on the surface active sites of cocatalysts and semiconductors is significantly favorable for the subsequent catalytic reduction reaction with the enhanced reaction rate.565,566 Accordingly, in addition to thermodynamic limitations and kinetic challenges of photocatalytic CO2 reduction, adsorption and activation of CO2 also play crucial roles in boosting the photoactivity for selective CO2 photoreduction and suppressing the competing HER. In general, the formation of adsorbed CO2 surface species on the semiconductor surface is often viewed as the rate-limiting and selectivity-determining step during photocatalytic reduction owing to the significant reorganizational energy between bent anion radical CO2•− and linear CO2 molecule, which is governed by the chemical constituents, surface microstructure, electronic band structure, and crystal phase.567 To achieve a large CO2 uptake, various strategies, including exposure of either internal or external surface (or enlargement of the surface area), enhancement of the basic sites, and improvement of the mass transfer properties, have been successfully developed.35,50 The simplest strategy is to fabricate mesoporous single-metal/ multi-metal semiconductors by using hard, soft or reactive templates. So far, it has been demonstrated that the mesoporous TiO2,568−572 N-doped Ta2O5,573 ZnGaNO,574,575 ZnGa2O4,81 In(OH)3,576 CeO2,577,578 Ti-MCM-48/Ti-MCM48/Ti-containing nanoporous silica,56,579−581 CeO2−TiO2 composites582 and WO3,556 can achieve high selectivity for the photoconversion of CO2 into CH4, CO or CH3OH because of the large surface area, uniformly distributed pores and ordered channels enhancing CO2 adsorption, activation and charge separation. Furthermore, various mesoporous materials as supports, such as SBA-15,583−592 SiO2,77,593−598 zeolites, and mesoporous molecular sieves,57,599 have been widely coupled with semiconductors to avoid the unexpected agglomeration of semiconductor nanoparticles and increase their specific surface area for significantly boosted photocatalytic CO2-reduction performance. However, despite small micropores or mesopores that assure larger surface area and more active sites available for surface photocatalysis, they also have a negative effect on the gas diffusion.35 Thus, to effectively balance the larger surface area and better mass transfer properties, the hierarchically nanostructured semiconductor photocatalysts with large mesopores (10−50 nm) or macropores (>50 nm), have recently gained a considerable attention because the hierarchical structures possess many excellent characteristics and advantages, such as improved molecular diffusion/transport, enhanced light harvesting and increased surface area.101,178,559,600−603 For example, Cheng et al. fabricated hierarchical Bi2WO6 hollow microspheres from BiOBr solid microspheres through an anion exchange route (Figure 23A and B). The formation mechanism of Bi2WO6 hollow microspheres with the surface area of 23.8 m2 g−1 could be well explained by the Kirkendall effect because of the lower solubility of Bi2WO6 than that of BiOBr. The resulting Bi2WO6 hollow microspheres produced much more methanol (yield of 32.6 μmol g−1) without any cocatalyst, which is 25.5 times higher than that achieved on Bi2WO6 powder fabricated by solid state reaction (1.28 μmol g−1, SSR) under the same

Figure 21. Process of CO2 photoreduction with water.

semiconductor; (2) the formation of photogenerated e−/h+ pairs and their migration to the semiconductor surface; (3) and (4) the bulk and surface recombination of photogenerated e−/ h+ pairs; (5) and (6) the trapping of photogenerated electrons by CO2 reduction cocatalysts and the electrocatalytic H2 evolution and CO2 reduction reactions on them; (7) the trapping of photogenerated holes by water oxidation cocatalysts and the electrocatalytic O2 evolution reaction on them; and (8) the reoxidation of reduction products initiated by water oxidation cocatalysts. Clearly, the unfavorable processes 3−5 and 8 could significantly decrease the quantum efficiency of CO2 photoreduction. Thus, apart from enhanced light harvesting by narrowing the band gap of semiconductor and promoting the charge separation through fabrication of novel nanostructures and heterojunctions of semiconductor photocatalysts,37,51 continuous research efforts have been made toward design multifunctional cocatalysts with controlled nanostructures to enhance the photocatalytic activity for CO2 reduction. 49 More importantly, those unfavorable four processes (3−5 and 8) could be efficiently suppressed or avoided by loading suitable CRC or WOC cocatalysts, which play a key role in enhancing the surface photoactivity for selective CO2 photoreduction under light illumination because of the significantly enhanced CO2 adsorption and reduction reaction kinetics, as well as water oxidation kinetics. In a word, to improve the selective CO2 photoreduction, key kinetic factors, including surface adsorption/activation and reaction kinetics of CO2 and charge carrier dynamics, should be comprehensively considered and optimized (as shown in Figure 22).

Figure 22. Key kinetics factors for selective CO2 photoreduction to solar fuels. T


Chemical Reviews

Review

Figure 23. (A and B) SEM images of the as-prepared Bi2WO6 hollow microspheres (HMSs), (C) visible-light-driven methanol production yields, and (D) CO2 adsorption isotherms measured on the Bi2WO6 HMSs and SSR samples.557 Reprinted with permission from ref 557. Copyright 2012 Royal Society of Chemistry.

LaPO4 hierarchical hollow spheres,638 β-SiC hollow spheres,639 zinc germanium oxynitride hyperbranched nanostructures,640 graphene−g-C3N4 sandwich-like nanostructures,641 porous Odoped graphitic carbon nitride (g-C3N4) nanotubes,642 sandwich-like ZnIn2S4−In2O3 hierarchical tubular heterostructures,643 In2S3−CdIn2S4 heterostructured nanotubes,644 3D ZnIn2S4 nanosheets/TiO2 nanobelts,645 N-doped carbon@ NiCO2O4 double-shelled nanoboxes,646 flower-like Bi2MoO6 microspheres,647 alkaline tantalates MTaO3 (M = Li, Na, K),621 ATiO3(A=Sr, Ca, Pb),648 SrTiO3 leaf’s 3D architecture,648 ZnGa2O4,649 ZnO/ZnTe hierarchical superstructures,650 and ZnTe microspheres.650,651 To further enhance the acidic CO2 adsorption over those mesoporous or hierarchical semiconductors, alkaline organic or inorganic modifiers can be selectively loaded into their porous structures to introduce the basic adsorption sites. Inspired by the interesting polyethylenimine incorporated mesoporous materials known as “molecular basket” absorbents for highly selective CO2 capture,652 recently amine functional groups were introduced to significantly boost the selective photocatalytic reduction of CO2 over different semiconductors.97,105,653−656 In general, the terminal amine groups can be covalently attached to different photocatalysts, such as TiO2,97,655 g-C3N4,653 and ZnO nanosheets,654 by simple chemisorption of organic amines, such as monoethanolamine (MEA) and diethylenetriamine (DETA) and by NH3-mediated thermal exfoliation strategy.105,653,655 It is believed that the amine-containing groups present on the surface of semiconductors can greatly enhance CO2 sorption due to the strong interactions between

conditions (Figure 23C). They further demonstrated that the enhanced methanol production rate could be ascribed to the highly increased CO2 adsorption capacity (Figure 23D) and large surface area of Bi2WO6 hollow microspheres.557 This work highlights that the rational design and control of novel nano/micro structures could effectively increase their surface area and porosity, resulting in an enhanced CO2 photoreduction and adsorption. Besides Bi2WO6 hollow microspheres, various kinds of other hierarchical photocatalysts have been fabricated by different strategies and widely applied in the photocatalytic CO2 reduction, such as ordered macro/ mesoporous TiO2 sponges or microspheres,604−610 TiO2 photonic crystals (slow photon effect),611,612 TiO2 nanorod array@carbon cloth,613 Ti0.9O2−graphene hollow spheres,90 TiO2−graphene architectures,614,615 CdIn2S4 microspheres,616 Mn0.8Cd0.2S microspheres,617 Zn1.7GeN1.8O hyperbranched nanostructures,618 porous TaON microspheres,619 BiOBr microspheres,620 cadmium−aluminum LDH microspheres,28 NaTaO3 hierarchical porous structure,621 Bi-rich Bi4O5BrxI2−x microspheres,622 tree trunk derived tantalates MTaO3 (M = Li, Na, K),621 3D ordered mesoporous Fe-doped CeO2577 and TiO2/CeO2,582,623 CdS@CeO2 core/shell microspheres,624 CeO2/Bi2MoO6 heterostructures,625 Bi2S3/CeO2 superstructure, 626 foam-like Cu 2 O structure, 627 flower-like CdS/ CdV2O6,628 flower-like ZnxCa1−xIn2S4,629 TiO2 nanofibers,630 irregular CoTe nanoflakes,631 flower-like Bi2WO6,558,559,632 Bi2S3 urchin-like microspheres,633 CuO−TiO2 hollow microspheres,634 ZnV2O6 nanosheets,635 double-shelled ZnGa2O4 hollow spheres,636 ZnO/NiO porous hollow spheres,637 U


Chemical Reviews

Review

Figure 24. (A) TEM of the TN200 sample (200 °C, fabricated by the alcohothermal method), (B) comparison of CO2 adsorption isotherms for various samples.655 Reprinted with permission from ref 655. Copyright 2015 American Chemical Society.

CO2 and amine-functionalized photocatalysts. Subsequently, the surface-activated CO2 can be readily reduced by the photogenerated electrons on the semiconductor surface, thereby significantly promoting charge transfer and separation, resulting in remarkably boosted photoreduction rate of CO2 into different solar fuels and enhancing the activity for selective CO2 photoreduction. Recently, it is also reported that the amine-functionalized hierarchical TiO2 nanosheets-based yolk@shell microspheres (Figure 24A) show a highly selective production of dominant CH3OH by CO2 photoreduction under visible light.655 The enhanced activity is ascribed to the excellent visible-light absorbance and light-harvesting ability, and high CO2 adsorption capacity (as shown in Figure 24B). Clearly, this study implies a significant synergetic effect between abundant basic sites and hierarchical nanostructures resulting in the enhancement of both adsorption and photoreduction of CO2. It is well known that the reduction of extremely inert and stable CO2 molecules under ambient conditions is difficult due to their closed-shell electronic configuration and linear geometry.7 Although a few semiconductors could directly achieve the formation of anion radical CO2•− through the single-electron CO2 reduction reaction owing to their strongly negative electrochemical potential (-1.9 V vs NHE), the activation of the linear CO2 molecule to a bent form is desirable for initiating multistep reactions for CO2 reduction, since the destabilized nonlinear CO2•− molecules exhibit much higher reactivity for CO2 photoreduction.48,657,658 Accordingly, it is of practical importance and great interest to deeply investigate the adsorption capture and activation steps of CO2 on the surface active sites of cocatalysts and semiconductors for the photoreduction of CO2 molecules. Typically, there are three kinds of interactions between CO2 and surface atoms, namely, single coordination of O/surface Lewis acid centers (Figure 25A and B) and C/surface Lewis base centers (Figure 25C), and mixed coordination (Figure 25D and E), respectively.48,659 Taking TiO2 as an example, the adsorbed CO2 can be reduced to bent CO2•− species by Ti3+ defects on TiO2, which can be then rearranged to Ti4+ sites for further reduction as electron trap states (as shown in Figure 26).567,660 Meanwhile, the dominant oxygen defects on the surface of TiO2 are beneficial for the CO2 activation both under light illumination and in the dark due to the effective generation of CO2− intermediates.89 The density functional theory (DFT) calculations and experiments verify that the surface bridging

Figure 25. Photoactivation of CO2 to the CO2− radical on catalysts.

Figure 26. Schematic illustration of the CO2 activation and the formation of bent CO2•− species over surface Ti3+ and oxygen vacancy defects present on TiO2.

oxygen vacancy defects present on TiO2 can exhibit strong interactions with oxygen atoms of CO2, thus leading to the dissociation of CO2 to bind CO and a healed vacancy (as shown in Figure 27).657,661,662 Especially, to reveal the reaction mechanism of thermodynamically feasible formaldehyde pathway over the perfect and defective anatase TiO2(101) surface, Ji et al. carried out the first-principles calculations and found that a direct dissociation of CO2 to CO on the Ov sites can exhibit a barrier of 0.73 eV (Figure 27A), which is obviously much smaller than the total barrier of 1.19 V for the dissociation of CO2 via hydrogenation of CO2 to COOH (Figure 27B) and that on a perfect surface (1.49 and 1.41 eV for COOH and CO).663,664 The results imply that the direct dissociation to CO on the Ov sites is the most feasible pathway for the reduction of CO2. Subsequently, CO can be further hydrogenated to CH3OH or CH4. Full potential energy surfaces for hydrogenation of CO to CH3OH could be divided into four steps V


Chemical Reviews

Review

Figure 27. (A) Adsorption and direct dissociation of CO2 at the Ov sites. (B) Dissociation of CO2 via hydrogenation of CO2 to COOH. (C) Full potential energy surfaces for the hydrogenation of CO to CH3OH. Step H-I, hydrogenation of CO to HCO; step H-II, HCO to CH2O; step H-III, CH2O to CH3O; step H-IV, CH3O to CH3OH. (D) Formation of CH•3 and CH4. Step M-I, Formation of CH•3 via breaking the C−O bond leaving a cured Ov; step M-II, an electron transfer to CH•3 , and formation of CH3− anion; and step M-III, recombination of CH−3 anion with Hb to form CH4. Blue, red, gray, and black atoms are oxygen atoms of the molecule, oxygen atoms of TiO2, Ti, and C atoms.664 Reprinted with permission from ref 664. Copyright 2016 American Chemical Society.

Table 6. Different Multiple-Electron Reaction Mechanism for Photocatalytic Reduction of CO2 over Photocatalysts

W


Chemical Reviews

Review

The simplest reaction scheme (two-electron, two-proton formaldehyde pathway) was firstly proposed by Inoue et al. in 1979. This mechanism explains well the products (formic acid, formaldehyde, methanol, and methane) of the photocatalytic reduction of CO2 in aqueous suspensions of semiconductors or photoelectrocatalytic reduction of CO2 at the illuminated photoelectrodes.15 Fifteen years later, Anpo et al. demonstrated that CH3•, C•, H•, and Ti3+ as the key intermediate species can be directly detected by the ESR spectra.666,683,684 Thus, a carbene pathway was proposed in 1995.59,666,677,678 Furthermore, Subrahmanyam et al. also proposed a one-electron, oneproton formaldehyde pathway for the CO2 photoreduction in 1999.676 Recently, Yang et al. found that the increase in the concentration of formaldehyde could significantly lead to an enhanced formation rate of hydrocarbon (including C1, C2, and C3), indicating the important role of formaldehyde and CO in the photoreduction of CO2 to hydrocarbons over semiconductors.585 However, for the one-electron, one-proton formaldehyde pathway, the step from methanol to methane has proven to be impossible by the ESR spectra because the methanol is readily oxidized.585,680 In contrast, the carbene pathway involving the stepwise one-electron reaction has been verified by ESR spectra and kinetic equations,13 thus it has been widely used to explain the reaction of CO2 photoreduction.75,672,678,685,686 In addition, Asthagiri et al. pointed out that the reduction of CO is the key selectivity-determining step for CO2 electroreduction on Cu(111).687 The dominant formation of COH from CO reduction in an aqueous environment leads to a good selectivity of CHx species. Thus, it is suggested that the selectivity of CH4 and CH3OH in CO2 (photo)electroreduction can be tailored by controlling the relative formation energetics of COH versus CHO, which implies that the controlled formation of a specific intermediate in the key selectivity-determining step is the potential strategy to design heterogeneous catalysts with an optimized selectivity.687 Recently, after examining the redox reactions of formate, formaldehyde, and methanol on TiO2, it was found that oneelectron reduction of these adsorbates is not observed.679,688 Thus, a new glyoxal cycle pathway has also been proposed by Shkrob et al.679 Importantly, this reaction mechanism can be used to explain the formation of several known products, such as formate, methanol, acetaldehyde, formaldehyde, methylformate, HOC•HCHO radicals and some C2/C3 reduction products.679 Furthermore, the two-electron, two-proton enollike intermediates pathway has also been proposed, which can well explain the formation pathway of all C1−C3 products, especially for the ethylene pathway, during the electroreduction of carbon dioxide over metallic copper surfaces.681,682 However, the surface C1 and C2 intermediates in C−C coupling reactions have not been fully recognized. So far, only limited intermediates, such as CO* and HCOO*, have been identified by kinetic experiment data due to the absence of effective experimental techniques as well as ultra-short lifetimes of reaction transition states. In a word, a deep understanding is still needed on the CO2 reaction mechanisms (C−O bond breakage, the formation of C−H and C−C bonds, and important intermediates) and key pathways at molecular levels. Actually, all the reaction intermediates associated with CO2 reduction need to be carefully measured and evaluated. Accordingly, it is expected that this mechanism can be further examined and applied in the photocatalytic reduction of CO2 through both experimental and theoretical modeling approaches.

(Figure 27C). More interestingly, it was found that the Ov site is more active for the reduction of CO to HCO− anion in the first step, whereas the high adsorption energy of CH2O (2.41 eV) and CH3OH (1.33 eV) at the Ov sites and larger reduction barrier of CH2O to CH3O− anion (1.26 eV) make CH3O− an intermediate for formation of CH3•, instead of CH3OH. The details of formation of CH3• and CH4 from CH3O− anion displayed in Figure 27D can be divided into three steps. Thus, the excess electrons from Ov can promote the reduction of CH3O− anion to CH3• radical with a barrier of 0.63 eV, which may capture the OH group and H atom (excess electron plus proton) to yield CH3OH and CH4, respectively. Clearly, the hydrogenation of CH2O to CH3O at the Ov sites is the ratelimiting step (step H−III in Figure 27C), which shows a much lower barrier (1.26 eV) than that of the rate-limiting step on the perfect surface (1.41 eV), indicating the key role of Ov in promoting the formaldehyde pathway. The simultaneously detected H atoms and CH3• radicals on P25 with CO2/H2O (1:1 molar ratio) under illumination also suggest that the adsorbed/bound CO2•− radical can be further reduced to many different reduction products (CO and CH4 in gas phase, whereas methanol in solution) by using water as the source for both protons and electrons.665,666 Similarly, the selective conversion of CO2 into CO over defective ZnAl-layered double hydroxide nanosheets,24 BiOCl nanoplates667 and CeO2 nanorods,668 can be achieved by using water as the reductant showing a much higher activity as compared to those over defect-free bulk samples. The enhanced adsorption and activation of CO2 by defect sites are shown to be the dominant factors for improving CO2 photoreduction activity. Additionally, it is also reported that the ultrathin W18O49 nanowires669 and Cu(I) supported TiO2 nanosheets670 with a large number of oxygen vacancies exhibit much higher activity for selective CO2 photoreduction to methane than the corresponding defect-free or commercial samples. The greatly enhanced adsorption of carbon dioxide molecules attracted by oxygen vacancies is responsible for the improved photoactivity. Additionally, the promoted chemical adsorption of CO2 on Cu active sites was evidenced by higher CO2 adsorption and the asymmetric stretching vibration νas(OCO) of the “end-on” and “C-coordination” states on the FTIR (Fourier transform infrared spectroscopy) spectra of Cu-added MOF photocatalyst, thus leading to the significantly enhanced photocatalytic activity for CO2 reduction.671 Thus, doping of Cu(I)/ Cu(II) ions into TiO2,672 LDHs,673,674 and ZIF-67675 has been extensively employed to enhance the CO2 capture capability through the coordination between Cu active sites and the π orbital of CO2, to facilitate the dissociation of adsorbed CO2− or CO2 and subsequent CO2 photoreduction. In a word, more attention has been given to study the enhanced chemical adsorption and activation of CO2 on the active sites, such as Cu2+ and oxygen vacancies, aiming to provide a scientific basis and concept for design and synthesis of new, better photocatalyst materials for highly efficient and selective CO2 photoreduction. 2.5. Mechanisms of CO2 Photoreduction

In addition, the complicated multistep mechanisms and product distribution of CO2 photoreduction also make it extremely challenging because of the existence of multielectron kinetics. Thus, so far, many favorable pathways for protonassisted multielectron transfer have been proposed, as summarized in Table 6. X


Chemical Reviews

Review

Figure 28. Schemes of cells for electrochemical CO2 reduction: (A) two-compartment cell, (B) cell with electrodes separated by a protonconducting membrane, and (C) cell with a gas diffusion electrode.6 Reprinted with permission from ref 6. Copyright 2013 Royal Society of Chemistry.

2.6. Mechanisms of CO2 Electroreduction

pathways, and intermediates are of the vital importance and challenging for development of active, stable and selective electrocatalysts for CRR. Especially, elucidation of the true reaction mechanisms for electrochemical CRR is challenging because of multiple products and multielectron processes. Thus, the experimental investigations, DFT calculations and insitu/operando spectroscopy are required to reveal the true CRR mechanism. Typically, several basic parameters, such as the onset potential, current density, Faradaic efficiency, and the electrochemical surface area should be measured to evaluate the CRR performance of electrocatalysts.509 More importantly, various kinds of experimental and density functional theory (DFT) calculation investigations, should be also utilized to propose the rate-determining step (RDS) for electrocatalytic CRR and understand the true mechanism of CRR. In general, many important aspects such as binding energies of the key intermediates (thermodynamic barriers), electrokinetic studies, intermediates and the reaction pathway should be considered in the detailed investigations. The calculation and determination of the Gibbs free energy of each step could identify the RDS, which is the maximum change in the Gibbs free energy of two subsequent adsorbed intermediates. More precisely, accelerating the reaction rate in the elementary step could provide some directions for rational design and optimization of the structures and composition of CRR electrocatalysts to meet the performances required for specific industrial applications. Furthermore, electrokinetic studies such as analysis of the Tafel slope and reaction order can reveal the detailed reaction mechanism and the number of electrons involved in the reaction steps for multiple electron−proton transfer reactions, thus allowing the identification of RDS. Typically, as shown in Table 7, the Tafel slopes of 118, 59, and 39 mV dec−1 indicate

Since heterogeneous CRR cocatalysts are generally selected from the efficient CRR electrocatalysts, the studies of the complex and comprehensive mechanisms of the electrocatalytic CRR, electrocatalyst properties and operating conditions are essential for guiding the design and development of heterogeneous CRR cocatalysts for photocatalytic applications. A deep understanding of the CRR mechanisms is beneficial for achieving high efficiency conversion system with tuned product selectivity, enhanced conversion rate, and reduced overpotential for practical implementation. To achieve these challenging goals, many advances in the CRR mechanisms over metallic, non-metallic, and molecular electrocatalysts have been accomplished during the past decades.6,509,689−701 Three typical cells have been developed for electrochemical CO2 reduction (Figure 28),6 in which anode and cathode are separated in two chambers connected by a proton-conducting membrane. Water oxidation and CO2 reduction are performed at anode and cathode, respectively. As for a practical process, an overpotential (the difference between the onset potential and the standard reduction potential) is usually required and decided by the highest kinetic activation barrier of the individual reaction steps in the complex proton/electron-coupled procedures, thus achieving the enhanced overall current density and Faradaic efficiency of the electrolytic cell. Notably, the standard cells with undivided electrodes were employed to enable proper chemical analysis of the products formed at the electrodes. Because of the low solubility of CO2 in water and mass transport limitation, gas diffusion electrodes, organic solvents, or supercritical fluid are usually required for the practical applications. In comparison with the simple electrochemical cells, the understanding of the electrocatalytic CO2 reaction mechanisms (C−O, C−C, and C−H bonds formation), Y


Chemical Reviews

Review

Table 7. Tafel Slopes and Reaction Orders for the Generation of CO and HCOO− Based on the Assumption of the Well-known RDSsa

product CO

HCOO−

a

rate-determining step

∂(− E) ∂ log j

∂(− E) at T = 298 K ∂ log j

⎛ ⎞ ∂ log j ⎜ − ⎟CO2 , E ⎝ ∂ log[HCO3 ] ⎠

* + CO2(aq) + e− → CO2−* CO2−* + HCO3− → COOH*+ CO32− COOH* + e− + HCO−3 → CO* + H2O + CO32− CO* → CO + * * + CO2(aq) + e− → CO2−* CO2−* + HCO3− → OCHO*+ CO32− OCHO* + e− → HCOO−* CO2−* + e− + HCO3− → HCOO−* + CO32 HCOO−* → HCOO− + *

2.3RT/βF 2.3RT/F 2.3RT/(β +1)F 2.3RT/2F 2.3RT/βF 2.3RT/F 2.3RT/(β + 1)F 2.3RT/(β + 1)F 2.3RT/2F

118 59 39 30 118 59 39 39 30

0 1 0 −2 0 1 −1 1 −1

Reprinted with permission from ref 689. Copyright 2018 Royal Society of Chemistry.

Figure 29. Volcano plots for (A) CRR partial current density vs CO binding strength at −0.8 V (vs RHE),709 (B) CO partial current density vs *COOH binding energy, and (C) HCOO− partial current density vs *OCHO binding energy at −0.9 V (vs RHE). (D) Mechanism that includes pathways for CO and HCOO− production from CO2.708 Reprinted with permission from ref.709 Copyright 2014 American Chemical Society. Reprinted with permission from ref 708. Copyright 2017 American Chemical Society.

the formation of the CO2− anion, a proton transfer step from bicarbonate and a second concerted electron−proton transfer as the RDS, respectively. For example, an electrokinetic study was used to explain better performance of the oxide-derived Au electrodes than polycrystalline Au counterparts. It was shown that polycrystalline Au and oxide-derived Au achieved the Tafel slopes of 114 and 56 mV dec−1, indicating the electron transfer to form the CO2− anion and the proton transfer step from HCO3− (the first-order dependence with respect to the HCO3− concentration), respectively, as RDSs. Thus, faster stabilization

of the CO2− intermediate over oxide-derived Au electrodes could be achieved.702 It was theoretically revealed that the moderate binding energies of the key intermediate species are of great importance for achieving higher intrinsic CRR activity and selectivity,703−705 which should be carefully controlled and improved. For example, the Nørskov group suggested that CO is produced through adsorbed COOH* intermediates,706 whereas HCOOH production was proposed to proceed via the OCHO* intermediate,707 indicating the influence of intermediate binding energy on the catalyst properties. Jaramillo Z


Chemical Reviews

Review

Figure 30. Overview of CO2 reduction pathways over Cu(100) examined starting from CO*.711 Reprinted with permission from ref 711. Copyright 2016 American Chemical Society.

group performed electrochemical CRR and obtained the volcano-type relationships between intrinsic intermediate binding energies and CRR activities for various metals, as shown in Figure 29.708,709 Clearly, Au on the top of the volcano plots exhibits the highest partial current density for CO production, while Sn shows the highest reactivity towards HCOOH production. This shows that the moderate binding affinities of Au toward both COOH* and CO* key intermediates (Figure 29A and B) results in high efficiency and selectivity for CO production. In contrast, a moderate binding energy of Sn for OCHO* key intermediate (Figure 29C) results in the highly selective HCOOH production. As a result, two different pathways from a single adsorption intermediate, *COOH, and a bidentate *OCHO intermediate were proposed for CO and HCOO− production, respectively (Figure 29D). In another example, CO* dimerization steps over a Cu electrode have been identified as RDSs for hydrocarbon production via CO2 reduction.710,711 The density functional theory (DFT) confirmed the Cu(111) and Cu(100) favor the formation of hydroxymethylidyne (COH*) and formyl (CHO*), respectively.711 Ethylene formation on Cu(100) could be achieved through C−C coupling of two preferentially formed CHO* species and the corresponding reduction steps of the C2 intermediates under relatively low overpotential (−0.4 to −0.6 V vs RHE) (Figure 29). Interestingly, the overpotential for the C2 production on the Cu (100) electrode could be decreased through introduction of the (111) step sites on its flat surface via surface reconstruction. Additionally, increasing negative applied potential can lead to high CO* coverage, which can change the relative stability of

CHO* and COH*, thus switch reduction products from ethylene/ethanol to methane/ethylene (Figure 30).711 However, in-situ/operando spectroscopy remains necessary to reveal the true valence state of electrocatalysts at real examination conditions of CRR. For example, by means of the in-situ attenuated total reflectance infrared spectroscopy (ATRIR), Baruch et al. found the formation of a tin oxide layer on the thermodynamically stable metallic tin electrode under electrolysis conditions,712 indicating the important role of metastable SnOx oxides in enhancing the CRR activity and selectivity at the Sn/SnOx interface. The results confirmed that the surface-bound carbonate species, instead of the formation CO2− radical, are the important reaction intermediates for CRR to formate. In another example, Rosen et al. investigated their dendritic Zn electrodes by the in situ XAS.713 Based on the Xray absorption near-edge spectroscopy (XANES) results, it was shown that the Zn dendrite electrode was fully oxidized to Zn2+ because of the presence of continuous change of Zn oxidation state toward the binding energy for Zn2+ at operando conditions.713 In contrast, at potentials more negative than −0.7 V, Zn dendrite electrodes were confirmed to exhibit the ZnO states, which can be likely stable at this operating window for the Zn dendrite catalyst. Additionally, the in-situ/operando Raman spectroscopy, in situ FT-IR (information on adsorbed carbon species), in situ ambient pressure X-ray photoelectron spectroscopy (AP-XPS used to monitor the change in the surface coordination number) and the surface-enhanced infrared absorption spectroscopy in the attenuated total reflection mode (ATR-SEIRAS) have been demonstrated to be useful tools for unraveling the structural changes in the AA


Chemical Reviews

Review

Figure 31. Schematic illustration of the photoelectrocatalytic reduction of CO2 in the cells of (A) semiconductor-based photocathodes, (B) semiconductor-based photoanodes, and (C) semiconductor-based photocathodes and photoanodes. Photocatalytic reduction of CO2 in (D) solid− vapor and (E) solid−liquid systems.

voltage and the spatial isolation of the H2O oxidation and CO2 reduction half-reactions in the PEC cells will afford much higher overall efficiencies than those in the photocatalytic systems for the reduction of CO2 because of the combined advantages of both photocatalysis and electrocatalysis. Clearly, for the two different photocatalytic systems, the photocatalysts in the solid−liquid systems generally exhibit a much lower CO2 reduction efficiency owing to the restricted solubility of CO2 in H2O and the preferential adsorption of H2O on photocatalysts, whereas those in solid−gas or solid−vapor systems can show a relatively higher activity for selective photoreduction of CO2 by H2O, owing to the decreased rate of competitive H2 formation from the reduction of H2O and the preferential adsorption of CO2.49 Additionally, it should be noted that the CO2 reduction electrocatalysts can be applied in either PEC or photocatalytic systems for tuning their CO2 reduction selectivity. Other selectivity and activity tuning strategies for photocatalytic systems, such as the increase of light harvesting efficiency, rational design of semiconductor nanostructures and heterojunctions, and the enhancement of the separation of photogenerated electron−hole pairs, can be also extended to the PEC systems to realize the highly active and selective photoconversion of CO2 with H2O into the desirable products. However, undoubtedly, the fabrication of high-quality PEC systems is more expensive and complicated than the accomplishment of photocatalytic systems. As a result, these two photocatalytic CO2 reduction systems have received more extensive attention in the past 40 years. Herein, we will mainly focus on the tuning CO2 reduction selectivity in two photocatalytic systems through proper selection of cocatalysts.

catalysts, identifying the catalytically active sites, and elucidating the reaction mechanisms and the intermediates formed during CO2 electroreduction.714−717 It is highly desired that in future more and more in-situ and surface sensitive techniques can be developed and applied in probing the reaction interface at operando conditions, thus revealing the true active sites, associated intermediates and CRR pathways. Especially, it is still challenging to understand the real reaction pathways towards C2−C4 products for electrocatalytic CRR due to the insufficient investigations regarding the reaction intermediates. Consequently, the interplay and powerful combination of experimental studies, DFT calculations and in situ/operando spectroscopy, is highly desirable for future CRR investigations to obtain the groundbreaking discoveries in the next-level highly active and selective electrocatalysts. 2.7. Processes for Photoassisted CO2 Reduction

In general, the photoassisted heterogeneous reduction of CO2 can be achieved by the photocatalytic and photoelectrocatalytic processes.567 Typically, three kinds of photoelectrocatalytic cells are employed to convert CO2 and H2O into solar fuels and O2: namely, semiconductor-based photocathodes (Figure 31A), semiconductor-based photoanodes (Figure 31B), and semiconductor-based photocathodes and photoanodes (Figure 31C).49,567 Meanwhile, the systems for the photoreduction of CO2 can be classified into two different types: solid−vapor (Figure 31D) and solid−liquid (Figure 31E) systems. The most essential difference between them is the application of a bias voltage (a voltage other than zero) in the photoelectrocatalytic cells for reduction of CO2. This will not only tune the CO2reduction selectivity, but also favor the charge separation in semiconductors and avoid the direct contact of the reduction/ oxidation sites. Thus, in principle, the introduction of a bias AB


Chemical Reviews

Review

2.8. Interfacial Charge-Transfer Reactions

increased amount of active sites and tuned selectivity in the traditional catalysis.738−744 For example, a partial confinement of metal actives sites in the pores of supports can create strong interactions between them, thus tremendously improve the catalytic activity of metals and the metal-support interface.743,744 Especially, it should be noted that the strong interfacial electronic interactions between semiconductors and cocatalysts play a vital role in boosting the interfacial electron transfer from the semiconductor to cocatalysts and improving the overall photocatalytic efficiency.745−748 Thus, a deep understanding of the interactions between cocatalyst and semiconductor is of key significance for the rational design and fabrication of the next generation of highly efficient photocatalysts for production of solar fuels. In general, the cocatalyst/semiconductor electronic interactions could be efficiently enhanced by different strategies, such as varying the size of semiconductors,749 thermal treatment,750,751 creating chemical bonds,176,745,752−754 tuning the exposed crystal facets,755 assuring π−π interactions and so on.747,756 It is believed that the enhanced cocatalyst/semiconductor interactions, could (1) markedly promote the efficient separation and transfer of photogenerated electron-hole pairs,176,745,747,755 (2) change the flatband potential, Fermi level, band structures and charge carrier lifetimes,753,757,758 (3) enhance absorption of visible light,745,747,756,759 (4) increase the stability of small metal clusters and even single atoms.759 Notably, in some cases, the cocatalyst/semiconductor interactions have negative effects on the photocatalytic activity.760 In theory, the cocatalyst/semiconductor interactions could be used to effectively tune the selectivity, activity and stability of cocatalysts and adsorption/ activation of CO2, thus leading to the enhanced photocatalysis. However, so far, limited investigations have been reported for the enhanced CO2 photoreduction by strong cocatalyst/ semiconductor interactions. Thus, it is expected that extra efforts will be undertaken toward optimization of the cocatalyst/semiconductor interactions for tuning the activity and selectivity of CO2 photoreduction.

In most cases, the interfacial charge transfer is the ratedetermining step. This means that the rate of CO2 photoreduction is strongly dependent on the interfacial chargetransfer step between semiconductor and CRR cocatalyst. The CO2 photoreduction could be enhanced through improving the rate of interfacial conduction band electron transfer to CRR cocatalyst, and then to the adsorbed/active CO2 species in the electron-transfer event. The dynamics of charge-transfer reactions at the semiconductor/cocatalyst interface and semiconductor/solution interphase should be carefully investigated and controlled for achieving the maximum CO2-photoreduction efficiency. Previously, Kamat has pointed out that both electron and hole transfer across the interface with comparable rates are important in maintaining high photocatalytic efficiency and stability of the semiconductor assemblies.718 More importantly, using transient absorption spectroscopy (TAS), the Kamat group monitored and confirmed the interfacial electron transfer between coupled semiconductor NPs (e.g., from CdSe QDs to SnO2, TiO2, and ZnO)719 and semiconductor/metal NPs (e.g., from excited CdSe into Pt),720 and hole transfer between semiconductor/ oxidation cocatalysts (e.g., from TiO2 colloids to IrO2)721 and semiconductor/sacrificial electron donor (e.g., from CdS and CdSe to S2−/Sn2−), based on the rapid decay. Furthermore, single-particle fluorescence spectroscopy has been successfully applied in probing electron transfer in the size-dependent Au/ TiO2 nanocomposites722 and CdSe/ZnS (core/shell)/TiO2 nanoparticles.723 More recently, the surface photovoltage spectra (SPS)724−727 or transient photovoltage (TPV) techniques were shown to be useful tools for investigation of the interfacial charge transfer between semiconductors and cocatalysts. For the SPS, the positive and negative signs suggest that positive and negative charges accumulate at the surface of the sample, respectively. Importantly, the transient photovoltage (TPV) response can not only explain the electron transfer from the Zn0.8Cd0.2S to CuS cocatalysts,728 and from gC3N4 to Ni cocatalysts,729 but also verify the hole transfer from TiO2 nanotube arrays to CoOx cocatalysts.730 Additionally, it should be pointed out that the density functional theory (DFT) calculations could be used to analyze the interfacial charge transfer between semiconductor and graphene.731−733 Although the interfacial charge transfer between semiconductors and complexes has been detected in the CO2 photoreduction systems by using the transient absorption spectroscopy,734−737 there are limited reports about the evidence of electron transfer from semiconductor to CRR cocatalysts by using these techniques. In general, the photocurrent, EIS, steady and transient PL spectra were employed to identify the promoted charge separation in the interfacial region. Unfortunately, the exact transfer directions of photogenerated electrons between semiconductors and cocatalysts are speculative in nature. It is difficult to use the transient PL spectra to give the direct evidence on the exact direction of interfacial charge transfer. Consequently, the above mentioned techniques such as transient absorption spectroscopy, single-particle fluorescence spectroscopy, transient photovoltage as well as DFT, are highly desirable for detailed study of the interfacial charge transfer during photoreduction of CO2.

3. ENGINEERING STRATEGIES FOR SELECTIVE PHOTOREDUCTION OF CO2 Thus, it is clear that CO2 can be simultaneously converted to many reduction products (such as CO, HCOOH, CH4, CH3OH, and HCOH) and intermediates (such as formaldehyde, carbene, and glyoxal) using water as reductant and solar light as photon source at ambient temperature and pressure because of the complicated multistep reduction process and low selectivity of photocatalysts for photocatalytic CO2 reduction.13 Considering the practical application of these compounds, it is highly desirable to control the selectivity of photocatalysts for a specific product and produce it as pure as possible. However, the key factors affecting selectivity of the photocatalytic CO2 reduction are still not well understood. So far, six typical strategies, including modulating surface morphological structures, tailoring surface chemical compositions, tuning the acidity-basicity of supports, using the solvent effects, improving the interfacial properties, and loading the suitable cocatalysts, have been explored to improve the product selectivity of the CO2 photoreduction (as shown in Figure 32). 3.1. Modulating Morphological and Band-Gap Structures

2.9. Cocatalyst−Semiconductor Interactions

It is now widely accepted that semiconductors with different bandgaps and surface structures generally exhibit different adsorption/activation capacities and redox potentials toward

It is well known that the strong metal−support interactions could assure the enhanced activity, improved thermal stability, AC


Chemical Reviews

Review

CB position (as shown in Figure 34B), the better crystallization and coexposed (100) and (001) facets.762 Furthermore, reducing the particle size of NPs,75 diameters of 1D nanostructures669,763,764 and the thickness of 2D nanosheets765 could be also used to tune the selectivity for CO2 photoreduction, because of the favorable quantum-size confinement effects. However, the increased band gaps will reduce the visible-light absorption, which is unfavorable for the enhancement in the photocatalytic efficiency. Accordingly, when utilizing the quantum-size confinement effects to tune the CO2 photoreduction selectivity, the improved selectivity and decreased absorption ability of visible light should be carefully balanced for specific practical applications. Meanwhile, optimizing the composition of semiconductors is also a facile strategy to tune the band gaps, thus achieving the tunable selectivity for the CO2 photoreduction. On the one hand, doping of various anions or cations into wide-band gap semiconductors, such as ZnO and TiO2, has been extensively employed to change their CB/VB levels and increase their absorption abilities for visible light. In a typical example, Wang et al. elaborately prepared an ordered mesoporous Co-doped TiO 2 by a multicomponent self-assembly process. Its absorption edge exhibits a continuous red-shift with gradual increase in the molar ratio of Co/Ti, suggesting the obvious narrowing of their band gaps (Figure 35A and B). The theoretically calculated energy-band structures of Co-doped TiO2 and pure TiO2 show that the states at the CB minimum and VB maximum of Co-doped TiO2 are composed of Ti 3d/ Co 3d/O 2p and O 2p/Co 3d, respectively, suggesting that doping of Co species into TiO2 was effective to decrease the apparent band gap of TiO2 and increase visible-light absorption and the ability for water oxidation of TiO2 through changing both the VB and CB of TiO2 (Figure 35C and D). The resulting Co-doped TiO2 displays a controllable product selectivity for CO2 reduction by tuning the molar ratio of Co/Ti in Co-doped TiO2 (Figure 35E). Clearly, a maximum activity of 1.94 mmol g−1 h−1 (CO) was achieved at the Co/Ti molar ratio of 0.025, whereas the higher generation rate of 0.258 mmol g−1 h−1 (CH4) was obtained with increasing the Co/Ti molar ratio up to 0.2 because of the formed oxygen vacancies in Co-doped TiO2 nanocomposites. As compared to TiO2, the Co-doped TiO2 shows a higher CB minimum and the up-lifted Fermi energy due to the increased octahedral ligand field stress in TiO2 and the distortion of the lattice through introduction of larger ionic radius CO2+ (65 pm) than the ionic radius of Ti4+ (60.5 pm) (Figure 35F). On the other hand, the construction of homogeneous-phase and heterogeneous-phase solid solutions with continuously adjustable composition is another promising strategy to tune the light absorption and electronic structure. For instance, Zeng et al. prepared a series of flowerlike heterogeneous-phase solid solutions, ZnxCa1−xIn2S4 (x = 1, 0.8, 0.6, 0.4, 0.2, 0), by a facile one-pot hydrothermal method.629 Notably, all of the solid solutions showed enormously enhanced visible-light photocatalytic performance (λ > 420 nm) for CO2 reduction as compared to that of ZnIn2S4 and CaIn2S4 (Figure 36A and B). Furthermore, the ZnxCa1−xIn2S4 solid solutions exhibited the monotonically red-shifted absorption edge in the range of 546− 638 nm when decreasing the X value from 1 to 0 (Figure 36C), which is consistent with the color change of sample suspensions from yellow to brownish red (Figure 36D). Especially, Zn0.4Ca0.6In2S4 possesses the most negative CB position and the highest charge-separation efficiency (Figure 36E and F),

Figure 32. Typical strategies for selective CO2 photoreduction.

reactant molecules, thus leading to the significantly band- and surface-dependent selectivity of the photocatalytic CO2 reduction. Over time, scientists have established various kinds of strategies to tune their surface and bandgap structures, to improve the selectivity and activity of the photocatalytic reduction of CO2 over different solid photocatalysts. Among them, tuning band-gap structures, exposing highly reactive facets and controlling the 2D and 3D morphological structures have been considered to be the main strategies to improve the surface and bandgap effects of semiconductors for selective CO2 photoreduction. 3.1.1. Tuning the Band-Gap Structures. It is known that up-shifting the conduction band (CB) position of a semiconductor is the most straightforward strategy to tune the selectivity for CO2 photoreduction because of the enhanced reduction potentials. Commonly, two strategies, namely, the quantum-size confinement effects and composition engineering are used to increase the CB potentials of semiconductors. It is well known that the nanostructures with different geometries or dimensions can achieve an enlarged energy gap owing to the quantum-size confinement effects (Figure 33) and shape/

Figure 33. Illustration for tuning the selectivity of CO2 photoreduction through the quantum-size confinement effects.

dimension effects.761 Thus, exploring nanostructured semiconductors is a simple strategy to improve the selectivity for CO2 photoreduction. For instance, as compared to the small selective yield rate of methane over P25 and the shortened bipyramid anatase TiO2 with 94% (101) facets and 6% (001) facets exposed (denoted as TW), and the well-defined anatase TiO2 nanocubes with 75% (100) and 25% (001) facets (denoted as TC) display much higher activity for selective photoreduction of CO2 to CH4 and CH3OH (as shown in Figure 34A) owing to the excellent synergy of a more negative AD


Chemical Reviews

Review

Figure 34. (A) CH4 and CH3OH produced over TiO2 nanocubes (TC), shortened bipyramid TiO2 (TW), and P25 samples (inset, TEM images of TC). (B) Energy-band positions of TW and TC samples.762 Reprinted with permission from ref 762. Copyright 2015 Royal Society of Chemistry.

which is responsible for its highest activity for selective photoreduction of CO2 into CO and CH4. That work may offer a new insight into the development of novel visible-light driven photocatalysts with controllable CB levels for selective CO2 reduction and other photoreduction reactions. In another example, Tang et al. successfully developed a series of ZnxCd1−xS monodispersed nanospheres with tunable band structures for visible-light CO2 photoreduction in aqueous solutions.766 The resulting Zn0.8Cd0.2S and Zn0.5Cd0.5S solid solutions with larger and narrower band gaps showed the excellent selectivity toward production of methanol (CH3OH) and acetaldehyde (CH3CHO), respectively. Additionally, ethanol (CH3CH2OH) besides CH3OH and CH3CHO was generated over Zn0.8Cd0.2S solid-solution photocatalyst. The results clearly suggest that the band structure-directing redox capacity and light absorption of ZnxCd1−xS solid solutions should be well balanced to simultaneously achieve the optimum product yield and selectivity of CO2 photoreduction. In a word, all these above promising strategies could be used to change the band gaps and upshift the CB levels of various semiconductors, thus achieving the tunable selectivity for CO2 photoreduction. 3.1.2. Exposing Highly Reactive Facets. Constructing 0D, 1D, 2D, or 3D nanosized crystal structures with the exposed reactive facets is a powerful and often used strategy to tune the selectivity for CO2 photoreduction through modulating the surface performance and energy-band structures of photocatalysts. Owing to their unique physicochemical properties, various kinds of nanoconfigurations can provide many unique features, such as high specific surface area, welldeveloped porous structures, good crystallinity, better charge carrier separation, large amount of host−guest species, improved electrical conductivity, increased Lewis base sites and abundant surface active sites for chemical adsorption and activation of CO2.765,767,768 In addition, different crystal facets of semiconductors with different atomic arrangements and electronic structures commonly exhibit different intrinsic reactivity, adsorption properties and selectivity for CO2 photoreduction.649,670,769−775 In particular, for TiO2, it is known that the (100) and (101) are reductive facets, whereas (001) is an oxidative facet,.776−778 The DFT calculations revealed that the activity of different facets for CO2 photoreduction reaction generally decreases in the following order: (100) > (101) > (001) because of the differences in the coordination number and electronic structure of Ti cations.779

On the contrary, the CO2 adsorption energy on different facets increases in the following order: (101) < (100) < (001). Clearly, taking into account both pre-adsorption and the subsequent photoreduction reaction of CO2, it seems that the coexposed two different facets of TiO2 may offer potential opportunities for achieving highly selective CO2 photoreduction. In fact, Yu et al. fabricated a series of anatase TiO2 with tunable ratios of coexposed (001) and (101) facets using different amounts of HF (Figure 37A). It was demonstrated that the HF4.5 sample with 58% of (001) facets can achieve the highest photocatalytic CH4-production rate of 1.35 μmol g−1 h−1(Figure 37B). Moreover, the DFT calculations revealed that the difference in the photocatalytic activity of TiO2 with coexposed (001) and (101) facets. As a result, the density of states (DOS) plots show that the coexposed (001) and (101) facets of anatase TiO2 possess different band structures and band edge positions (Figure 37C), which results in the formation of a surface heterojunction in single TiO2 particle (Figure 37D).100 Consequently, considering the electron overflow effect on (101) facets and unexpected recombination on (001) facets (as shown in Figure 37A), it is obvious that the formation of surface heterojunction leads to the improved charge separation, which results in an interesting shapedependent photoactivity for selective CH4 production during CO2 photoreduction over anatase TiO2.100 There are many reports related to this study concerning the enhanced photoreduction of CO2 over TiO2 with coexposed facets.312,314,780−787 Similarly, the CO2 photoreduction activity and selectivity of the brookite TiO2 quasi nanocubes (mean size of ∼50 nm) with coexposed four (210) and two (001) facets can be further improved by loading suitable amount of Ag NPs.780 It was found that the brookite nanocubes loaded with 0.5% of Ag NPs showed the highest photoactivity for selective CO production, 5.41 times larger than that of the pristine brookite, whereas the maximum activity for selective CH4 generation was achieved over the 1.0% Ag−TiO2 (28.8 ppm h−1), 3.80 times higher than that (7.56 ppm h−1) of the pristine one (Figure 38A and B). It was revealed that the high dispersion of small Ag nanoparticles on the brookite TiO2 (210) facets with loading below 0.5% of Ag is highly beneficial for enhancing the selective production of CO, while the aggregated Ag nanoparticles on the brookite TiO2 (210) and (001) facets with loading of Ag exceeding 0.5% is favorable for the selective CH4 generation (Figure 38C). This study offers a AE


Chemical Reviews

Review

Figure 35. (A and B) Absorption spectra of the samples. The density of states (DOS) of (C) anatase TiO2 and (D) CoxTi1−xO2 (x = 0.0625). (E) Average CO2-photoredcution activity of different samples under visible light in 6 h. (F) Schematic illustration of the energy-band structures of the samples.572 Reprinted with permission from ref 572. Copyright 2015 Royal Society of Chemistry.

(111) facets through solution-based crystallographic-oriented epitaxial growth.311 As expected, enhanced photoreduction activities of CO2 to CH4 were achieved by optimizing the density, length, and thickness of arms and by adjusting the amount of cocatalysts (Figure 39A and B). Clearly, a maximum CH4 generation rate of 1.12 μmol h−1 g−1 was obtained by coloading of 0.5% wt of Pt and 0.5% wt of MnOx as dual cocatalysts. Moreover, the different surface electronic structures of CeO2 (111) and (001) facets were revealed by the density of states (DOS) calculations (Figure 39C), indicating the formation of a homojunction between hexahedron prism and octahedron (Figure 39D). As a result, this unique hierarchical nanostructure exhibits an enhanced charge separation and high charge carrier mobility, which boost the photocatalytic reduction of CO2 into methane. These works clearly show that the fabrication of surface heterojunctions (or homo-

novel strategy to tune simultaneously the CO2 photoreduction activity and selectivity through tailoring the morphology and surface structure of Ag nanoparticles and brookite TiO2. Furthermore, to replace the noble metal Ag, metallic Cu nanoclusters were used to decorate brookite TiO2 quasinanocubes with coexposed (210) and two (111) facets and explored as an inexpensive cocatalyst to promote the activity and selectivity of CO2 photoreduction to CH4 in comparison to CO because of changing the amount of surface oxygen vacancies and CO2/H2O adsorption behavior.788 Furthermore, nitrogen self-doping has also been used as a successful strategy to significantly enhance the visible-light driven photoreduction of CO2 to methanol over TiO2 with coexposed (100) and (001) facets.783 Inspired by the above works, Li et al. fabricated crystalline CeO2 homojunctions composed of nanorod arms with exposed (001) facets and octahedron cores with exposed AF


Chemical Reviews

Review

Figure 36. Time dependence of the CH4 or CO yields (A and B) for visible-light photoreduction of CO2 over ZnxCa1−xIn2S4 solid solutions (λ > 420 nm). DRS spectra (C), digital photos of suspensions (D), schematic band structures (E), and transient photocurrent responses (F) for the ZnxCa1−xIn2S4 solid solutions.629Reprinted with permission from ref 629. Copyright 2017 American Chemical Society.

improved by using the atomically-thin 2D semiconductor photocatalysts because of their unique features such as large specific surface area, ultrahigh ratio of coordinated-unsaturated surface atoms, enormous amount of surface defects, shorter bulk phase transport distance, small moving resistance along the surface, and strong quantum confinement of electrons in two dimensions.804−806 So far, ultrathin semiconductor nanosheets or nanoplates, such as TiO2,670,770−772,807,808 ZnO,654 ZnSe,809 SnS2,810 g-C3N4,105,641,811−814 WO3,553 Bi2WO6,815 ZnGa2O4,649 BiOCl,667,816,817 BiOI,769 BiOBr,818 Bi4TaO8Cl,819 Nb3O8,820 GaN:ZnO,821 ZnAl-layered double hydroxide,24 KTaO3822, and SnNb2O6765 have been fabricated and shown to exhibit better photocatalytic activities toward selective conversion of CO2 to various valuable solar fuels, as compared to the corresponding bulk counterparts. For 2D photocatalysts, their surface chemical composition and thickness are two

junctions) between two coexposed different facets presents an advanced and effective strategy to enhance the photoactivity for CO2 reduction over various kinds of nanostructured photocatalysts. 3.1.3. Exfoliating Ultrathin 2D Nanosheets. Tunable selectivity for CO2 photoreduction can also be achieved over other semiconductors through controlling their morphological structures. As compared to the size-dependent and confinement effects of 0D789−791 and 1D792−801 nanostructured semiconductors, the atomically-thin 2D photocatalysts, such as nanoplates or nanosheets, have been proven to exhibit much better activity and selectivity for CO2 photoreduction because of their favorable surface, microstructural, optical, and electrical properties.802−804 Three key factors determining CO2 photoreduction efficiency, namely, light harvesting, charge separation, and interfacial CO2 reduction reactions, can be simultaneously AG


Chemical Reviews

Review

Figure 37. (A) TiO2 samples with coexposed (101) and (001) facets fabricated by varying HF amount and an overflow effect between anatase TiO2 (101) and (001) facets. (B) Selective photoreduction of CO2 to CH4 over P25 and TiO2 samples with coexposed (101) and (001) facets. (C) Density of states (DOS) plots for anatase TiO2 (101) and (001) facets. (D) (101) and (001) surface heterojunction.100Reprinted with permission from ref 100. Copyright 2014 American Chemical Society.

Figure 38. Dependence of the rate of CO2 photoreduction over the brookite TiO2 nanocubes (A) and the product selectivity (B) on the Ag loading. (C) Possible mechanism of the selective CO2 photoreduction to CO and CH4 over brookite with different Ag loading.780Reprinted with permission from ref 780. Copyright 2016 Elsevier. AH


Chemical Reviews

Review

Figure 39. (A) Time-dependent CH4 evolution over CP0 (CeO2 with regular octahedron morphology), CP1 (the octahedron surface with nanorodlike arm of ∼200 nm in length), CP2, and CP3 (with much denser, longer, and thicker nanorodlike arms) with 0.5 wt % of Pt and 0.5 wt % of MnOx loadings; (B) Production rates of CH4 and O2 over CP0, CP1, CP2, and CP3 with 0.5% wt of Pt loading. (C) Density of states (DOS) plots for cubic CeO2 (100) and (111) facets and bulk CeO2. (D) Illustration of charge transfer across (001) and (111) surface homojunction.311 Reprinted with permission from ref 311. Copyright 2015 American Chemical Society.

Figure 40. Selective photoreduction of CO2 to CH4 and CH3CHO over bulk and nanosheet-based g-C3N4 under UV-vis (A, B) and visible illuminations (C, D; λ ≥ 400 nm). Schematic illustration of the selective photoreduction of CO2 to CH4 and CH3CHO over bulk and nanosheetbased g-C3N4 in the presence of H2O molecules (E), and the band structures of bulk (right) and nanosheet-based (left) g-C3N4, as well as the redox potentials of different reactions (F).812Reprinted with permission from ref 812. Copyright 2014 Royal Society of Chemistry.

and gaseous H2O under UV and visible light.812 The major reasons for the switched selectivity can be largely ascribed to the significantly different surfaces and band structures (Figure 40E and F).812 It is believed that the mechanism of CO2 photoreduction over bulk g-C3N4 and g-C3N4 nanosheets with the same surface atomic structure follows the pathway for a single glyoxal reaction involving dimerization process and then stops at different elementary steps.812 Thus, the selectivity of CO2 photoreduction is strongly dependent on both the adsorption capability of intermediate products and chargecarrier kinetics. Clearly, the g-C3N4 nanosheets can not only offer much stronger redox catalytic capability because of long-

crucial factors determining the overall photocatalytic performance. Normally, decreasing the thickness of 2D nanosheets can lead to the significant improvement in their surface composition, atomic arrangement, and energy band structures, thus resulting in different selectivity for CO2 photoreduction.765,823 Thus, the thickness-dependent selective CO2 photoreduction attracts more and more attention.816 Impressively, Niu et al. demonstrated that the C3N4 nanosheets of ∼2 nm thickness with a bandgap of 2.97 eV exhibit higher activity for selective generation of CH4 (Figure 40A and C), whereas the bulk g-C3N4 with a bandgap of 2.77 eV shows better activity toward production of CH3CHO (Figure 40B and D) from CO2 AI


Chemical Reviews

Review

loading single atoms or surface atom tensile strains. More importantly, the exact type, quantity, and location of surface active sites and the in situ CO2 photoreduction reaction mechanism need to be carefully identified at the atomic or molecular level to better understand the structure-activity relationship and design highly efficient 2D CO2 photoreduction photocatalysts.805 3.1.4. Fabricating 3D Hierarchical Architectures. The avoidance of unexpected aggregation and improvement of light harvesting and adsorption/diffusion kinetics of individual nanoparticles, nanowires, nanotubes, nanosheets,178 that leads to the improved selectivity and activity, can be achieved by the self-assembly of 3D microsized uniform hierarchical architectures from 0D (nanoparticles), 1D (nanorods/nanoribbons), or 2D (nanosheets) used as primary building blocks. So far, various hierarchical semiconductors, including hollow, 101,557,559,634 mesoporous,608,651 flower-like,647,650,828 core−shell829, and yolk@shell655 microspheres, nanotubes642 and macro-/mesoporous systems,105,610,621 have attracted a considerable attention due to the excellent synergistic effects because of higher surface-to-volume ratio, special structural merits, and unique methodologies. For instance, Xia et al. constructed hierarchical assemblies of amine-functionalized gC3N4 nanosheets through a stepwise NH3-mediated thermal exfoliation.105 The as-obtained hierarchical g-C3N4 structures were composed of ultrathin nanosheets of 3 nm thickness (Figure 43A and B) into about 9-10 stacked layers (Figure 43D and E), which are totally different from the bulk g-C3N4 consisting of irregular aggregated particles (Figure 43C). The formation mechanism of ultrathin nanosheets through NH3treatment of the bulk g-C3N4 is displayed in Figure 43F. The exfoliated ultrathin g-C3N4 nanosheets exhibit a larger number of exposed internal C3N groups containing the N lone-pair electrons, able to form adsorption sites for proton and CO2 molecules (with larger CO2 adsorption). In addition, better CB and VB potentials can be also obtained after exfoliation, thus assuring stronger redox capability of photogenerated charge carriers (Figure 43G). As a result, the synergistic effects of both textural and surface modification of g-C3N4 lead to the enhanced activities toward both CH4 and CH3OH products (Figure 43H).105 Particularly, the adsorption capability of intermediate products and promoted charge transfer kinetics are believed to be the main factors for achieving the excellent selectivity toward CH4 production. Contrary, the same group also fabricated the hierarchical porous O-doped g-C3N4 nanotubes via successive thermal exfoliation and curlingcondensation of bulk g-C3N4 (Figure 44A).642 The resulting O-doped g-C3N4 nanotubes feature a methanol production rate of 0.88 μmol g−1 h−1 under visible light, five times larger than that of bulk g-C3N4 (0.17 μmol g−1 h−1) (Figure 44B). The increased activity for CO2 reduction can be attributed to the enhanced CO2 adsorption and charge separation, and the narrower bandgap (Figure 43C). The intermediates in the photocatalytic CO2 reduction reactions, such as HCHO, carbonate and bicarbonate species were detected by in situ FTIR (Figure 43D), whereas the gas-phase chromatograms show the formation of various C1 species (such as HCOOH, HCHO, CH3OH, and CH4) and the important C2 product, C2H5OH. Based on these results, the typical two-electron, twoproton reaction pathway (CO2 → HCOOH → HCHO → CH3OH → CH4) and the dimerization of C1 intermediate species are proposed for explaining the possible formation mechanism for hydrocarbon fuel. This work demonstrated that

living charge carriers and favor faster transfer of photoexcited electrons to all elementary intermediate species for producing CH4, but also increase the adsorption ability of intermediates and promote the subsequent elementary reactions.812 Previously, the studies have demonstrated that a decrease in the thickness and an increase in the surface bismuth content in 2D BiOX nanosheets could lead to the significant increase in their surface triple vacancy sites and conduction band minimum potential, respectively.824−826 Interestingly, Ye et al. recently revealed that the bismuth-rich surface and ultrathin-thickness of BiOBr play different roles in tuning the photocatalytic activity and selectivity for CO2 reduction, which could increase the CO and CH4 generation, respectively.812 As a result, Bi4O5Br2 nanosheet-assembled microspheres exhibit better selectivity for photoreduction of CO2 to both CO and CH4 in the presence of H2O molecules through integrating these two features into hierarchical structures (Figure 41).812 More

Figure 41. Schematic illustration of selective CO2 photoreduction over the surface bismuth-rich and ultrathin BiOX.827 Reprinted with permission from ref 827. Copyright 2016 Elsevier.

interestingly, Jiao et al., for the first time, successfully fabricated the atomic-thickness SnS2 layers with controllable oxidation degrees, through controlling the volumetric ratio of ethylene glycol to distilled water (EG:H2O) in a facile hydrothermal process.810 As a result, the mildly oxidized SnS2 atomic layers could show the significantly improved visible-light activity for selective CO production with a rate of 12.28 μmol g−1 h−1, roughly 2.6 and 2.3 times as high as those achieved over the SnS2 atomic layers and poorly oxidized SnS2 atomic layers, respectively (Figure 42A). In situ Fourier transform infrared spectroscopy spectra and density functional-theory calculations reveal that the formation of the main intermediate, COOH* radical, is the rate-limiting step (Figure 42B and C). The enhanced activity can be attributed to the improved charge− carrier separation kinetics because of the locally oxidized domains confined in SnS2 as the active sites (Figure 42D) and the lowered activation energy barrier for stabilizing the COOH* intermediates (Figure 42C). The atomic-level insight into correlation between oxidized sulfides and CO2 reduction properties provided in this study may pave a new way for designing 2D nanosheets with proper surface modification for high-efficiency CO2 photoreduction. However, there are few reports on the improvement of the CO2 photoreduction selectivity through rational tuning the surface composition and electronic structure of 2D nanosheets. In this regard, more efforts should be focused on the further modification of 2D nanosheets by using various strategies, such as heteroatom doping, defect and facet engineering, tuning surface states, and AJ


Chemical Reviews

Review

Figure 42. (A) Visible-light photoreduction of CO2 into CO over different samples. Inset in panel A: Full SVUV-PIMS spectrum at the photon energy of 14.5 eV. (B) In situ FTIR spectra for coadsorption of a mixture of CO2 and H2O vapor on the mildly oxidized SnS2 atomic layers. (C) Free energy diagrams of CO2 photoreduction to CO for different samples. (D) Schematic illustration of vectorial electron transfer mechanism over the SnS2/SnO2 composite semiconductors.810 Reprinted with permission from ref 810. Copyright 2017 American Chemical Society.

properties, creation of surface overlayers and construction of surface vacancies, will be highlighted. 3.2.1. Introducing Functional Groups. So far, the nonmetallic doping has paved an avenue toward efficient modulation of structural and textural properties, the adsorptive and mass transfer behavior, surface and active-site components, optical, electronic and electrochemical properties, as well as photocatalytic properties of various semiconductor photocatalysts.831−833 Indeed, the heteroatom doping has already attracted tremendous interest in the rational design and controllable fabrication of advanced photocatalysts.834−839 Typically, doping nitrogen into TiO 2 , 60,568,783,840−842 BiVO4,843 InTaO4844, and Ta2O579,845 has been found to improve their activity for selective photoreduction of CO2 to CH4 and CH3OH under visible light because of the favorable hybridization of a metal orbital and N 2p orbital to introduce basic sites for CO2 adsorption/activation.783,846−848 Clearly, visible-light oxynitrides have been extensively developed and applied in the selective CO2 photoreduction.575,640,793,849,850 It was also found that the selective CO2 photoreduction over visible-light-driven N-doped TiO2 could be exploited by using different nitrogen-sources.851 That is, CH4 and CO could be selectively produced over N-doped TiO2 by using N2H4 and NH3 as nitrogen sources, respectively. It is believed that the introduced N−N groups during N2H4-assisted preparation of N−TiO2 surfaces are responsible for the tunable CO2 reduction selectivity. Similarly as in the CO2 hydrogenation reaction, the N-TiO2 doped by using urea as nitrogen source exhibits good activity toward continuous selective formation of CH4.537 More

the O-doping of hierarchical porous g-C3N4 nanotubes is favorable for the selective generation of CH3OH, rather than CH4, implying the important role of surface composition in achieving the desired selectivity. On the contrary, the phosphorus doped g-C3N4 nanotubes obtained from g-C3N4 nanosheets exhibit a dramatically enhanced activity for selective production of CH4, which is likely attributed to the unique hierarchical mesoporous nanotubes structure, narrowed band gap, amino-rich surface, and down-shifted conduction and valence band positions.830 The observed selectivity of hierarchical porous g-C3N4 nanotubes implies the importance of surface composition in determining the final CO2-reduction products, which will be deeply discussed in section 3.2. Additionally, an interesting 3D printing approach is found to be an advantageous strategy in the potential scale-up of the hierarchical microleaves with 3D architectures for highly efficient artificial photosynthesis.604 3.2. Tailoring Surface Chemical Compositions

In addition to controlling surface and morphological structures, tailoring the surface chemical composition has also become an interesting strategy to achieve selective CO2 photoreduction. In general, the control of surface chemical composition could not only be used to effectively increase the visible and NIR light absorption and enhance the adsorption/activation of CO2, but also to promote the charge separation and surface reaction kinetics. Herein, four typical strategies, including introduction of functional groups, utilization of hydrophobic−hydrophilic AK


Chemical Reviews

Review

Figure 43. FESEM images of NS-CN (A and B) and the bulk CN (C). TEM (D) and AFM (E) images of NS-CN. (F) The formation mechanism of NS-CN photocatalysts. Band structure (G) and photocatalytic CO2 reduction performance (H) of the NS-CN and bulk-CN samples.105 Reprinted with permission from ref 105. Copyright 2016 Royal Society of Chemistry.

light-driven shell structures in metal oxide materials with wideband gaps, thus providing a very promising route to achieve an efficient charge transfer and high-performance CO2 photoreduction. More recently, it was demonstrated that the enriched intrinsic amino groups and K doping on the surface of g-C3N4 could lead to a 7.7-fold increase in CO2 adsorption, which results in 5.4- and 5.6-fold enhancement in the yields of CO and CH4 production as compared to those on urea-polymerized g-C3N4(UCN).853 Additionally, increasing the surface basic OH groups on the mesoporous TiO2 single crystal854 and cobaltbased metal-organic frameworks (MOFs)855 could enhance adsorption and activation, thus leading to the significantly improved CO2 reduction activity. On the contrary, it is also reported that the surface H2SO4 acidification treatment of TiO2 nanosheets enclosed with (001) and (101) facets can simultaneously enhance the surface protonation of oxygen atoms, and promote the formation of hydroxyl groups (Brønsted acidic sites for the oxidation of photogenerated holes) and oxygen vacancies/Ti3+ species (adsorption centers for CO2), which facilitate a rapid H2O oxidation and selective CO2 reduction to methane, as well as increase the visible-light absorption.856 Surprisingly, it is also reported that the oxygenrich TiO 2 exhibits the highly enhanced selective CO 2 photoreduction.846−848 Similarly, motivated by the important role of phosphate (PO43−) group in natural photosynthesis and a substantial boost of H2 evolution via Calvin cycle in the

interestingly, Dong et al. developed the core-shell titanium dioxide (HN−TiO2) nanocrystals of 25 nm diameter via different plasma etching treatments using N2, H2, and H2/N2 (Figure 45A).852 The H2/N2 plasma treatment was able to significantly narrow the wide-bandgap of TiO2 nanocrystals (3.27 eV) to two obvious bandgaps of 2.71 and 1.92 eV with strong visible light absorbance. In fact, the production rates of CO and CH3OH over cheap HN-TiO2 loaded Cu cocatalyst were approximately 2.67- and 8-fold larger, respectively, than those on the catalyst with Pt cocatalyst (Figure 45B and C). The DFT calculations demonstrate that the NH groups bonded to Ti cause some up shifting of the valence band maximum (VBM) because of the simultaneous introduction of Ns (substitutional nitrogen), VO (oxygen vacancy) states, and NiH (hydrogen bonded interatrial nitrogen). The markedly enhanced photocurrent (Figure 45D) and incident photon-tocurrent efficiency (IPCE) value under visible light and the donor density for HN−TiO2 are also observed (Figure 45E). Additionally, HN−TiO2 displays a fast fluorescence decay between 5 and 7 ns (Figure 45F), indicating the rapid charge separation induced by mid-gap states in the shell layers. The illustration of photoexcited charge-carrier separation and energy band levels in the core−shell HN−TiO2 further indicates the boosted photocatalytic CO2 reduction performance (Figure 45G and H). Consequently, these results show that the plasma treatments with N2, H2, and H2/N2 could create the visibleAL


Chemical Reviews

Review

Figure 44. (A) Typical FESEM of hierarchical porous O-doped g-C3N4 nanotubes, (B) photocatalytic conversion of CO2 to CH3OH, (C) band alignments of bulk g-C3N4 and O-doped g-C3N4 nanotubes, (D) in situ FTIR spectra of the adsorbed species on O-doped g-C3N4 nanotubes after irradiation of (i) 0, (ii) 10, (iii) 20, (iv) 30, (v) 40,(vi) 50, and (vii) 60 min under CO2 atmosphere.642 Reprinted with permission from ref 642. Copyright 2017 John Wiley & Sons, Inc.

solution system,857 Ye et al. fabricated mesoporous phosphorylated g-C3N4 (MPCN) through post-treatment of bulk g-C3N4 (BCN) with concentrated phosphoric acid.858 This study reveals that photocatalytic CO2 reduction activity of MPCN (mesoporous phosphorylated BCN via dialysis deacidifying and vacuum freeze drying processes) is much higher than those over BCN (obtained by using thiourea as a precursor), PCN (direct phosphorylation of BCN) and MCN (obtained by using urea as a precursor) (Figure 46A). In particular, the AQE of MPCN (0.86%) is about 8 times higher as that of BCN (Figure 46B). The synergism of mesoporous structure and phosphate group induced by phosphorylation could result in the significantly enhanced charge separation (Figure 46C), elevated CB position, and favorable Calvin cycle (Figure 46D−F). As a result, a strong synergy originating from surface PO43− groups enhances the activity and selectivity of CO2 photoreduction. Similarly, the thermal condensation of urea and barbituric acid was employed to improve the physicochemical properties of gC3N4 nanosheets, thus accomplishing a 15-fold enhancement in the catalytic activity toward effective photoconversion of CO2 to CO.103 In addition, it was demonstrated that the amount of hydroxyl groups on the g-C3N4 nanosheets increased with the ultrasonic exfoliation time in water, promoting the chargecarrier separation rate and up shifting the CB potentials, which led to the enhanced activity of g-C3N4 nanosheets toward visible-light photocatalytic reduction of CO2 to CH4.811 Additionally, it was found that the fluorination of Mg−Al LDH and Ni−Al LDH by incorporation of hexafluoroaluminate (AIF63−) species into the hydroxide sheets can enhance the selective photoconversion of CO2 to CO in an aqueous NaCl

solution.859 In addition, the treatment with other halogens such as I was used to improve the selective CO2 photoreduction with H2O vapor over various kinds of TiO2 photocatalysts.860,861 The DFT computations revealed that F atom with extremely high electronegativity is prone to be doped into the valence band and HOMO of monolayer g-C3N4, whereas the Cl, Br, and I atoms can affect the conduction band and LUMO.862 Clearly, the doping of all these halogen atoms can increase light absorption and reduce work function of monolayer g-C3N4 systems, thus resulting in the high photocatalytic activity. Recently, it was found that the effect of specific anions on the copper surface achieved through electrochemical treatment in I− and N3− ionic salts could significantly enhance the photoelectrochemical CO2 reduction activity due to the facilitated electron transfer between the possible cocatalyst (complex of these anions with Cu cations) and semiconductor.863 Further studies on the intercalation or doping of halogen atoms into different semiconductors to improve the selective CO2 photoreduction are highly desirable.276,864 3.2.2. Utilizing Hydrophobic−Hydrophilic Properties. The selectivity of the photoreduction of CO2 could be tuned by improving the hydrophobic−hydrophilic properties of photocatalysts, which could modify significantly the affinity characteristic feature of the H2O molecules on the surface reactive species through the adsorption interactions, thus resulting in the enhanced catalytic activity and selectivity.40,599,865,866 In particular, fluorine element with the strongest electronegativity has been extensively used for doping various semiconductors, such as TiO2, to enhance the separation rate of e−/h+ pairs, trap the photoexcited electrons, and accelerate the generation rate of AM


Chemical Reviews

Review

Figure 45. (A) HRTEM image of HN-TiO2 (scale bar: 5 nm). The production rates of (B) CO and (C) CH3OH via photoreduction of CO2 with water without any scavenger. (D) The time-dependent photocurrent curves. (E) The IPCE curves at 1.23 VRHE and MS plots (inset). (F) The timeresolved fluorescence decay spectra. (G) The illustration of photoexcited charge-carrier separation in a core-shell HN−TiO2 photocatalyst with Ns (substitutional nitrogen), VO (oxygen vacancy), and NiH (hydrogen bonded interatrial nitrogen). (H) The energy band levels versus RHE (pH 7) for photoreduction of CO2 to CO and CH3OH.852 Reprinted with permission from ref 852. Copyright 2016 John Wiley & Sons, Inc.

O2− and free (or bound) hydroxyl radicals.867−871 More importantly, it was also revealed by the theory and experiments that the surface fluorination can improve hydrophilic−hydrophobic properties, preferential selective adsorption of negatively charged reactants, enhance light absorption and thermodynamic stability.431,437,872−875 Therefore, the fluorinated or Fdoped photocatalysts with enhanced activities, selectivity and stabilities have been widely applied in the photodegradation of gaseous and aqueous pollutants.871,876−883 Naturally, it is expected that the surface fluorination can be widely applied in the selective photoreduction of CO2 over different semiconductors. In 2001, Ikeue et al. first investigated several factors such as hydrophilic/hydrophobic properties, the structure of active titanium oxide species on the zeolitic surface, and its affinity toward H2O.884 It was found that the Tiβ zeolites with large-pore structure fabricated using F− (Tiβ(F)) and OH− (Ti-β(OH)) ions showed hydrophobic and hydrophilic properties, respectively (Figure 47A). As a result, higher concentration of the charge-transfer excited complexes, (Ti3+−O−)* and adsorbed H2O on Ti-β(OH) lead to much lower reactivity of this catalyst toward selective formation of CH3OH (Figure 47B), in comparison to Ti-β(F), because of its hydrophilic properties. In situ XANES and FT-EXAFS investigations have revealed that the tetrahedrally coordinated

titanium oxide species are highly dispersed within the Ti-β zeolite framework.40,599,865 A significant photoluminescence quenching could be detected by introduction of CO2 or H2O onto these catalysts, further confirming the excellent affinity of CO2 and H2O to the Ti−oxide species.865 Similarly, the hydrophobic properties of Ti/FSM-16 catalysts could be obtained by the simple fluorination treatment (Figure 47C), resulting in much higher selectivity toward CH3OH generation, in comparison to the original catalysts without fluorination (Figure 47D). Recently, He et al. demonstrated that the surface fluorination of the low-energy (101) reductive facets of anatase TiO2 nanosheets facilitate the formation of Ti3+ species and charge-carrier separation, thus favoring the photoreduction of CO2 to CO2−.771 More recently, Dong et al. demonstrated that the fluorination treatment has no obvious effects on the adsorption of pure CO2 (Figure 48A), whereas the hydrophobic surface modification could indeed enhance the competitive adsorption of CO2 to H2O (Figure 48B).598 The resulting photostable hydrophobic modification led to 5.5- and 2.1-fold enhancement in the activity toward CH4 (Figure 48C and D) and CO formation rates, respectively. Interestingly, the metal-free hydrophobic modification can afford much higher yields of CH4 and CO than that achieved on the Pt-loaded sample. Importantly, unlike the Pt-loaded sample, during 4 h AN


Chemical Reviews

Review

Figure 46. (A) Selective photoreduction of CO2 to different products over BCN, MPCN, PCN, and MCN after 1 h of irradiation. (b) Apparent quantum efficiency for CO2 photoreduction over MCN, PCN, MPCN, and BCN at 420 and 365 nm. (C) Time-resolved photoluminescence spectra, (D) VB-XPS spectra, and (E) optical absorption spectra and plots of (ahν)1/2 versus hν (inside picture) for BCN and MPCN. (F) Mechanism for CO2 photoreduction over MPCN.858 Reprinted with permission from ref 858. Copyright 2016 Elsevier.

3.2.3. Creating Surface Overlayers. More interestingly, the suitable surface doping can create new overlayers on semiconductors to achieve the selective CO2 photoreduction. For instance, Wang et al. reported that increasing the amount of Zn doped species in the surface layer of Ga2O3 from 0.1 to 10.0 mol % can gradually decrease the competing HER, but retrain the evolution of CO. This suggests that the selectivity toward photoconversion of CO2 to CO is substantially enhanced with increasing amount of ZnGa2O4 layer as the H2-production inhibitor (Figure 49A).551 Surprisingly, 100% selectivity toward CO evolution could be achieved when the content of doped Zn was >3.0 mol %. The H2 evolution was found to be the dominant reaction over Ag-loaded Ga2O3 because of the existence of a considerable number of H2evolution active sites on Ga2O3 (Figure 49B), whereas the formation of the ZnGa2O4 layer on the surface of Ga2O3 could substantially decrease the number of H2-evolution active sites and suppress the evolution of H2, thus accomplishing the increased selectivity toward CO evolution (Figure 49C). This interesting result provides a new strategy to produce the

irradiation, hydrophobic modification (sample F-MASC (8:2)) assured the linearity of the CH4 formation rate (Figure 48E) with an obvious decreasing trend, avoiding the unexpected passivation of Pt surface active sites by adsorption of CO or other intermediates. Clearly, a controllable hydrophobic modification could decrease adsorption of H2O molecules and enhance the competitive adsorption of CO2 because of the partial replacement of the hydroxyl groups by hydrophobic Si− F bonds (Figure 48F). However, the selectivity in this study is obviously different from the previous report,884 suggesting that the underlying mechanism for selective CO2 reduction over surface fluorinated TiO2 with hydrophobic properties still needs to be revealed by various in-situ techniques and/or DFT calculations. In future, it is highly expected that the tuned surface hydrophobic−hydrophilic properties could be widely extended to selective CO2 photoreduction over various nonTiO2 photocatalysts. More importantly, other ecofriendly hydrophobic modification strategies without using fluorine should be developed. AO


Chemical Reviews

Review

Figure 47. (A) Adsorption isotherms of water vapor at 298 K and (B) photocatalytic yields of CH4 and CH3OH over the Ti-β(F), TS-1, Ti-β(OH), and P-25 photocatalysts. (C) IR spectra within OH stretching vibration region and (D) influence of fluorination on the CH3OH and CH4 yields in the photoreduction of CO2 with gaseous H2O over Ti/FSM-16 photocatalysts: (a) no treatment and (b) 12.5% and (c) 25.0% NH4F treatments.884 Reprinted with permission from ref 884. Copyright 2001 American Chemical Society.

photoreduction of CO2 into CO and CH4 due to an extended light absorption, efficient charge-carrier separation, and boosted surface adsorption towards reactants through decoration of the surface with Bi2O4 nanoparticles. More recently, the activity for selective CO2 photoreduction was enhanced by atomic layer deposition (ALD) of an ultrathin layer of amorphous Al2O3 on oxygen deficient TiO2 anatase nanorods with exposed (100) facets.887 It was shown that two cycles of ALD of Al2O3 overlayers results in the highest activity toward photoreduction of CO2 to CO and negligible production of CH4 due to the reduced charge carrier recombination rate through passivation of surface states. Whereas, more than five cycles of ALD create a layer that acts as an insulator to prohibit electron migration to the catalyst surface, thus leading to the decreased both CO and CH4 production. In another example, an optimal thickness of ultrathin ALD Al2O3 interfacial passivation layer between TiO2 and plasmonic Au NPs could promote electron−hole separation on the TiO2 surface, instead of suppressing the near-field enhancement effect and electron transfer, thus leading to a significant enhancement in the selective photoreduction of CO2 to CO.888 Similarly, it was demonstrated that the optimal ALD MgO overlayers (5 layers) over porous TiO2 with mixed anatase−rutile phases could enhance 4 and 21 times CO-production in comparison to that over pristine porousTiO2 and P25, respectively, because of the increased Mg bonded hydroxyl groups and surface Ti3+ species as active sites for CO2 adsorption and photoreduction and the promoted surface electron−hole separation through passivating the TiO2

synthesis gas with adjustable H2/CO ratio through varying the amount of Zn species present in the Zn-modified Ga2O3 photocatalyst. Besides surface-layer doping, loading suitable surface hetero-overlayers has been found to be a promising strategy to tune the selectivity towards CO2 photoreduction over various semiconductors. Yuan et al. constructed the core− shell structured TiO2@SiO2 composites through coating a SiO2 overlayer on P25 nanoparticles of ∼20 nm diameter by a facile sol−gel method at atmospheric pressure and room temperature (Figure 50A).885 The resulting TiO2@SiO2 composites exhibited a significantly enhanced activity and selectivity for photoreduction of gas-phase CO2 to CO using H2O as a reductant under simulated solar light irradiation (Figure 50B− C). It is believed that the improved CO2 photoreduction can be ascribed to the synergistic effects of the increased CO2 adsorption capacity and the lengthened lifetime of electron− hole pairs in TiO2@SiO2 (Figure 50D−F). Especially, the enriched CO2 at the interface between the active TiO2 surface and the SiO2 coating layer plays the crucial role in achieving high selectivity of CO formation (Figure 50G). This work could inspire the ongoing research in designing highly selective and active semiconductor-based materials for artificial photoreduction of CO2 to the value-added solar fuels. Similarly, a simple light-assisted alkali (NaOH) post-treatment was employed to in situ obtain BiOBr nanosheets decorated with Bi2O4 nanoparticles, whose content could be easily tuned by varying NaOH concentration.886 The resulting brown BiOBr0.01 nanosheets showed an exceptionally enhanced activity for AP


Chemical Reviews

Review

Figure 48. CO2 adsorption isotherms measured on MASC and F-MASC in the absence (A) and presence (B) of water vapor (0.1 g catalysts). (C) Selective photoconversion of CO2 to CH4 over MASC and F-MASC with Ti/Si=8:2. (D) CH4 yield comparison for different catalysts under solar light irradiation for 4 h. (E) Photocatalytic CO2 conversion to CH4 over different samples. (F) Mechanism for the competitive adsorption of CO2 and H2O molecules on the surface of MASC and F-MASC.598 Reprinted with permission from ref 598. Copyright 2016 American Chemical Society.

surface states.889 Additionally, an unique 1−2 nm disordered overlayer on the reduced TiO2 with high Ti3+ concentration and (001) facets significantly enhances its photocatalytic stability and activity for selective CO2 photoreduction to CH4 under solar light irradiation without any cocatalyst, by preventing the irreversible oxidation of the formed Ti3+ species in air.890 These results fully highlight that tuning the surface composition of semiconductors is a promising strategy that paves a new way to achieve highly selective and active photoreduction of CO2 to target products. 3.2.4. Constructing Surface Vacancies. Since the black TiO2 was first reported in 2011,891,892 more efforts have been aimed at the study of the promoting effects of defects/vacancies on the photocatalytic performance of semiconductors.893−896 Thus, apart from introducing new elements or groups on the surface of semiconductors, creation of surface oxygen, nitrogen,

or sulfur vacancies was shown to be a particularly appealing strategy to preferentially trap CO2 molecules and effectively achieve the improved activity and tunable selectivity for CO2 photoreduction.89,541,668,669,795,897−904 For example, Xi et al. fabricated the ultrathin monoclinic-phase W18O49 nanowires of 0.9 nm diameter with a large variety of oxygen vacancies by a relatively simple one-pot solution-phase method (Figure 51A− C).669 The cross section in the (010) plane and color change indicate the presence of defects in the W18O49 nanowires of 0.9 nm diameter (Figure 51D and E). Importantly, the rich oxygen vacancies on the surface of ultrathin W18O49 nanowires could significantly improve the visible and NIR light absorption and enhance the visible-light activity for photoreduction of CO2 to CH4 (Figure 51F and G). The results clearly highlight that the creation of surface oxygen vacancies offer a new design strategy to achieve the selective CO2 photoreduction. Recently, Zhang AQ


Chemical Reviews

Review

Figure 49. Evolution rates of O2 (white), CO (black), and H2(gray) and selectivity toward CO production in the photoconversion of CO2 with gaseous H2O over Ag-loaded Zn-modified Ga2O3 with various amounts of Zn species (A). Schematic illustration of the photoconversion of CO2 with gaseous H2O over Ag-loaded Ga2O3 (B) and controlled high selectivity toward preferential evolution of CO vs. H2 via a surface overlayer of Zndoped Ga2O3 (or the in situ formed surface ZnGa2O4 layer) (C).551 Reprinted with permission from ref 551. Copyright 2016 Royal Society of Chemistry.

Figure 50. (A) TEM images of TiO2@30%SiO2. Scale bar = 10 nm. (B) CO2-photoreduction product distribution and (C) the total conversion amount of CO2 and the selectivity of CO versus H2 and CH4 over TiO2 and TiO2@xSiO2 composites under simulated solar light. (D) CO2 adsorption isotherms (1 atm, 273 K) measured on TiO2 and TiO2@xSiO2 composites. (E) EIS Nyquist plots and (F) simulated solar light photocurrent−voltage curves obtained for TiO2 and TiO2@xSiO2 electrodes in different aqueous solution versus Ag/AgCl electrode. (G) Schematic mechanism for CO2 photoreduction with H2O over TiO2@SiO2 and TiO2 composites.885 Reprinted with permission from ref 885. Copyright 2016 American Chemical Society.

AR


Chemical Reviews

Review

Figure 51. (A) SEM, (B) TEM, and (C) HRTEM images of the W18O49 nanowires. (D) Schematic unit cell (0.9 nm) of W18O49 nanowire oriented along the (010) direction. (E) Defect-induced color conversion. (F) Optical absorption spectra and (F) time-dependent of CH4 formation over the tungsten oxide photocatalysts with different oxygen-vacancy concentrations. W18O49 (○), W−H2O20.5h (△), W−H2O2-1h (□), W−H2O2-3h, and commercial WO3 overlapping(▽,◁).669 Reprinted with permission from ref 669. Copyright 2012 John Wiley & Sons, Inc.

and a disordered shell layer with a thickness of 1.2−2.1 nm. The narrower Eg of 2.35 eV (Figure 53A) and a fingerprint signal on the ESR spectrum at about g = 2.0 (Figure 53B) are clearly observed, confirming the successful generation of OVs on the surface of Bi2WO6-OV. Surprisingly, Bi2WO6-OV exhibits significantly enhanced CO2 photoreduction activity toward selective formation of CH4 under UV, visible light and NIR irradiation (Figure 53C−E). Furthermore, the valence band XPS (VB XPS) analysis verifies the upshift of the VB maximum from 1.14 to 0.96 eV and downshift of the CB minimum from −1.56 to −1.39 eV because of the created defect states induced by OVs, thus accomplishing the NIR light harnessing via the in-gap bands excitation to CB of Bi2WO6. The NIR-light-driven CO2 photoreduction over Bi2WO6-OV can be illustrated by the sub-bands excitation of electrons (Figure 53F). This work provides a new approach for rational design of more efficient UV−vis−NIR broad spectrum photocatalysts for various applications. In addition, Ga2O3based photocatalysts are particularly attractive for formation of key CO2− species, due to their higher CB potential (−1.55 V). To explore the exact role of oxygen vacancies (VO) on Pt/ Ga2O3 for promoting photocatalytic CO2 reduction with water, Pan et al. loaded 1 wt % of Pt onto three Ga2O3 samples, namely, H-Ga2O3, A-Ga2O3, and O-Ga2O3, which were fabricated through annealing at 600 °C for 2 h in hydrogen, air, and oxygen, respectively.906 The as-obtained spindle-like HGa2O3 shows a 4.75 eV band gap, similar to A-Ga2O3 and OGa2O3. The EPR signals and O 1s XPS spectrum clearly confirm that the H-Ga2O3 possesses much higher Vo (oxygen vacancy) than both A-Ga2O3 and O-Ga2O3. Pt/H-Ga2O3 can also chemically adsorb much more CO2 molecules (1.11 mmol· g−1, Figure 54A) and activate them into the CO2− radicals (Figure 54B), in comparison to A-Ga2O3 and O-Ga2O3. All these factors lead to highly active and selective photoreduction of CO2 to CO (21.0 μmol·h−1, Figure 54C and D). The DFT calculations verify that the reduction of CO2 to CO is a more favorable path, both thermodynamically and kinetically, as compared to those leading to HCHO, HCOOH, and CH3OH production, which agrees well with experimental data (Figure

et al. confirmed the generation of light irradiation-induced oxygen vacancies in BiOCl nanoplates because of the low Bi−O bond energy and high oxygen atom density.667 The optical absorption spectra and several additional absorption bands on the PL spectra clearly show the formation of a large variety of oxygen deficiencies in BiOCl (BiOCl-LT) nanoplates after light treatment (Figure 52A and B). The intensities of IR bands at 1400−1700 (Figure 52C) and 3100−3600 cm−1 (Figure 52D) are significantly reduced, indicating the reduction of Bi3+ to Bi0 and the consumption of physically adsorbed H2O molecules, respectively. By contrast, the new bands at 2351 cm−1 (Figure 52E) are visible, confirming the formation of adsorbed CO species on the Bi0 surface. All these results verify that CO2 adsorbed on the BiOCl defect sites can be activated to CO by consuming surface oxygen vacancies and trapped photoexcited electrons (Figure 52F). However, these O atoms are readily released from the lattice after light irradiation, thus accomplishing the reversible surface oxygen vacancies. Accordingly, the defect-dependent photocatalytic CO2 reduction in water could be accomplished. This paves a new avenue for designing CO2 reduction photocatalysts by engineering the surface intrinsic defects of semiconductors. Besides the photoinduced fabrication in oxygen vacancies, large quantities of oxygen vacancies can be easily created on the (001) facets of BiOBr through simple combination of a one-pot ethylene glycol (EG)-assisted solvothermal synthesis with subsequent thermal treatment in a reducing atmosphere.901 The fabricated oxygen vacancies can act as the active and trap sites to improve the adsorption and activation of CO2 and promote the separation of the electron− hole pairs, thus accomplishing highly active and durable photoreduction of CO2 to CH4. More interestingly, the oxygen vacancies can be readily regenerated during CO2 photoreduction process without using any reducing agent or other post-treatment processes. In addition to exploration of efficient and cost-effective photocatalysts for UV-Vis-NIR full solar spectrum CO2 reduction, Kong et al. prepared the layered Bi2WO6 with oxygen defects (Bi2WO6-OV) through a facile one-pot solvothermal (ethylene glycol) method.905 The asprepared Bi2WO6-OV sample displayed a highly crystalline core AS


Chemical Reviews

Review

Figure 52. (A) Optical absorption spectra (inset, calculated bandgap value) and (B) PL spectra of of BiOCl-LT and BiOCl nanoplates. FTIR spectra of BiOCl nanoplates after adsorption of CO2 and H2O: (C) 1500−1800, (D) 3000−3800, and (E) 2250−2450 cm−1. (F) Mechanism for the generation of CH4, CO, and O2 via photoreduction of CO2 with gaseous H2O over BiOCl nanoplates.667 Reprinted with permission from ref 667. Copyright 2015 Springer Nature.

54E). The detailed mechanism for enhanced CO evolution can be attributed to the increased chemical adsorption of CO2 on the Vo (oxygen vacancy) sites, promoted electron−hole separation and transfer, and improved hydrogen production on Pt nanoparticles (Figure 54F). More interestingly, to verify the distinct activity of coordinatively unsaturated Znd+ for selective CO2 photoreduction, Zhao et al. synthesized ultrathin ZnAl−LDH nanosheets containing coordinatively unsaturated

Zn ions via either controlled hydrolysis or an inverse microemulsion technique (a bottom-up strategy).24 The resulting defect-rich ultrathin LDH nanosheets with exposed (110) basal plane were composed of two repeated stacking layers with lateral dimensions and platelet thicknesses 40 ± 20 and 2.70 nm, respectively. These defective ultrathin LDH nanosheets exhibited an excellent activity for selective photoreduction of CO2 to CO with gaseous H2O in comparison to an AT


Chemical Reviews

Review

Figure 53. (A) UV−vis absorption spectra, (B) ESR spectra, (C) UV−light CH4 production (λ < 400 nm), (D) visible-light CH4 production (λ > 400 nm), (E) NIR−light CH4 production (λ > 700 nm). (F) Mechanism of CO2 photoreduction to CH4 over Bi2WO6-OV.905 Reprinted with permission from ref 905. Copyright 2016 Royal Society of Chemistry.

of a new defect energy level hybridized by both occupied O 2p and Zn 4s orbitals in the defective ZnAl-LDH band gap. The defective LDH also possesses much larger adsorption energy for both of CO2 and H2O molecules as compared to those for defect-free LDH, which are more favorable for CO2 activation and photoreduction (Figure 55C). Clearly, the formation of the Zn+-VO complexes as trapping sites around the Zn atoms in the defective LDH (Figure 55D) mainly facilitates the extremely efficient association of electrons and their transfer to strongly adsorbed reactants, thus resulting in the promoted photo-

equivalent bulk LDH (Figure 55A). The defective ZnAl-1 sample exhibited a significantly lowered maximum peak on Zn K-edge X-ray absorption near-edge structure (XANES) spectrum by 1.1 eV, confirming the existence of a lower average oxidation state (Znd+, 1 < d < 2, Figure 55B). For fresh defective ZnAl-1 and corresponding samples under both UV− vis and visible illumination, the main peak at about g = 1.998 on the ESR spectra further demonstrates the existence of VO defects around the severely distorted octahedral Zn−O environment. The DFT calculations confirm the appearance AU


Chemical Reviews

Review

Figure 54. (A) CO2 adsorption isotherms, (B) FTIR spectra for adsorbed CO2 species, and (C) CO evolution rate over H-Ga2O3, A-Ga2O3, and OGa2O3. (D) Amount of products in the CO2 photoreduction with water on Pt/H-Ga2O3 after 8 h of photoirradiation. (E) DFT-calculated reaction pathways for production of HCHO (blue line), CO (black line), and HCOOH (red line) during CO2 photoreduction over Pt2/β-Ga2O3(100). (F) Mechanism of CO2 photoreduction over Pt/H-Ga2O3.906 Reprinted with permission from ref 906. Copyright 2016 Springer Nature.

Figure 55. (A) Production rate of CO via CO2 photoreduction with gaseous H2O under UV−vis light: (a) ZnAl-1, (b) ZnAl-2, and (c) ZnAl-3. (B) Zn K-edge XANES spectra. (C) DFT-calculated H2O and CO2 adsorption energies for (a) the VO-doped ZnAl-LDH and (b) bulk ZnAl-LDH. (D) Charge-density distribution for the VB maximum of the VO-doped ZnAl-LDH.24 Reprinted with permission from ref 24. Copyright 2015 John Wiley & Sons, Inc.

to CO. However, for the above oxygen-deficiency induced 2D multi-atomic-layer nanoplates/nanosheets, their complex microstructures, such as grain boundary, capping agents, as well as the lack of direct defect characterization techniques, are

induced charge separation and enhanced efficiency of CO2 photoreduction to CO. These works demonstrate that the rational design of VO (oxygen vacancy) is an promising strategy for developing active photocatalysts for selective CO2 reduction AV


Chemical Reviews

Review

Figure 56. (A) Photoreduction of CO2 to CO under 300 W Xe lamp irradiation, (B) photocatalytic O2 evolution, (C) O K-edge XANES spectra (before and after 24 h photocatalysis), (D) UV−vis diffuse reflectance spectra, (E) CO2 adsorption isotherms, and (F) electrochemical impedance spectra for the VZn-rich and VZn-poor one-unit-cell ZIS layers. (G) Scheme for the photoreduction CO2 into CO on the VZn-rich one-unit-cell ZIS layers.110 Reprinted with permission from ref 110. Copyright 2017 American Chemical Society.

showed remarkably higher photoabsorption ability (Figure 56D), CO2 adsorption amount (Figure 56E) and internal electron transfer (Figure 56F) in comparison to those on the VZn-poor one-unit-cell ZnIn2S4 layers, thus synergistically achieving the fully optimized primary CO2 photoreduction to CO (Figure 56G). Besides the effective activation of CO2, the defect engineering is also utilized for activation of H2O. More recently, both solid base and crystal defects on the LaTiO2N surface were designed to simultaneously achieve CO2 and H2O activation because of the lowered energy barrier of two half reactions in the CO2 reduction reaction.907 The optimized La2O3 modified LaTiO2N (La2O3/LaTiO2N) with OV defects shows a 2-fold higher CH4-production rate than that over pureLaTiO2N (Figure 57A and B).907 The DFT calculated energies for La2O3 (002) and LaTiO2N (002) with OVs for activation of CO2 and H2O are −12174.0 and −6792.6 eV, respectively (Figure 57C). As a result, strong basicity of O2− in La2O3 is favorable for CO2 chemisorption and bending of OCO

disadvantageous for gaining precise correlation between these defect structures and the CO2 photoreduction efficiency. Accordingly, to reveal the clear relationship between defect structures and electron−hole separation properties at atomic level, Jiao et al. successfully constructed an ideal model of oneunit-cell ZnIn2S4 atomic layers with tunable defect concentrations.110 The selective formation rates of CO and O2 (33.2 and 13.7 μmol g−1 h−1) over these one-unit-cell ZnIn2S4 layers with rich zinc vacancies are respectively about 3.6 and 1.5 times higher as those observed for one-unit-cell ZnIn2S4 layers with poor zinc vacancies (Figure 56A and B). The absence of O Kedge XANES signals for VZn-rich and VZn-poor one-unit-cell further verifies their superior stability after 24 h photocatalysis test (Figure 56C). The DFT calculations and ultrafast transient absorption spectroscopy confirmed the increased charge density at the nearby sulfur atoms and promoted carrier separation and transport rates, respectively, due to the presence of zinc vacancies. The VZn-rich one-unit-cell ZnIn2S4 layers AW


Chemical Reviews

Review

Figure 57. Time-dependent CH4 generation (A) and the average CH4 production rate (B) (for another 7 h irradiation except the first hour) over LaTiO2N with different amounts of La2O3. (C) The energies of CO2 and H2O on La2O3 (002) and LaTiO2N (002) with OVs. (D) Possible mechanism for activation and reduction of CO2 by H2O to CH4.907 Reprinted with permission from ref 907. Copyright 2017 John Wiley & Sons, Inc.

bond, facilitating formation of CO32− species, whereas OV on LaTiO2N surface can dominantly oxidize H2O to OH, and provide protons for CO2 reduction (Figure 57D). The study shows that simultaneous activation of CO2 and H2O on different spatial sites might offer a promising strategy to suppress the reverse reactions and achieve the rate-matching half reaction rates for CO2 photoreduction. At this regard, new design concepts for combining defect engineering and other modification strategies are greatly needed for highly efficient solar CO2 photoconversion.908 Notably, besides oxygen

vacancies, tunable nitrogen vacancies in g-C3N4 nanosheets have been recently shown to boost the visible-light-driven H2 evolution and CO2 reduction to CO, due to the induced midgap states under the CB edge.902 Clearly, the proper density of nitrogen vacancies could simultaneously increase the visible light absorption, maximize separation of photogenerated electron-hole pairs and uniformly deposit small Pt nanoparticles (1−2 nm) on g-C3N4, thus achieving the enhanced photoactivity.902 More importantly, the strategy of constructing surface vacancies can also be successfully extended to AX


Chemical Reviews

Review

Figure 58. (A) Support-dependent activity and selectivity of the reduction products.915 (B) The CO2-photoreduction product distribution over anatase TiO2 (a) and the Y-zeolite supported imp-Ti-oxide (10.0 wt %) (b), imp-Ti-oxide (1.0 wt %) (c), ex-Ti-oxide (1.1 wt %) (d), Pt-loaded exTi-oxide (e) photocatalysts.57 Panel A reprinted with permission from ref 915. Copyright 1995 Elsevier. Panel B reprinted with permission from ref 57. Copyright 1998 Elsevier.

Figure 59. (A) The CO2 photoreduction products over various basic and acid oxides supported photocatalysts in CO2 saturated solutions under irradiation. (B) Schematic illustration of the photoinduced CO2 reduction process over basic and acid oxides supported photocatalysts.676 Reprinted with permission from ref 676. Copyright 1999 Elsevier.

agent.912 This study provides a more convenient technique to remove CO2 through producing O2 and a storable solid carbon.912 Consequently, optimization of the surface chemical composition (such as hydroxyl and N−N groups), suitable modification (such as surface acidification, doping, defects or protonation) and controlling the 2D nanosheets’ thickness can be utilized to achieve the selective photoconversion of CO2 over various kinds of semiconductors (such as TiO2, g-C3N4, BiOX, In2O3‑x(OH)y, and solid solutions); all these issues deserve special attention.813,913,914

thermodynamically favorable hydrogenation reactions of CO2. For example, Hoch et al. demonstrated that the nonstoichiometric In2O3−x(OH)y nanoparticles prepared at 250 °C exhibit the suitable band gap/levels and the highest CO production rates at 150 °C.909 The synergetic effects of surface hydroxides and active oxygen vacancy sites lead to an optimum CO2 adsorption/activation capacity and band positions of In2O3−x(OH) y nanoparticles prepared at 250 °C, thus accomplishing the highest photocatalytic activity for CO2 reduction in the presence of H2 under simulated solar irradiation.910 The time dependent DFT calculations demonstrate that the coordinately unsaturated surface indium sites with low energy states can create surface frustrated Lewis pairs (FLPs), which enhance both Lewis acidic and Lewis basic character, thus decreasing the activation barrier and increasing the activity for the photocatalytic gas-phase reaction between H2 and CO2.911 More interestingly, the surface oxygen atoms over amorphous zinc germanate (α-Zn−Ge−O) semiconductor photocatalyst with weak lattice constraint could be continuously oxidized by the photogenerated holes under irradiation, thus fabricating the photoinduced oxygen vacancies, which have been demonstrated to achieve even direct splitting of CO2 into carbon and O2 without using H2O as a reducing

3.3. Tuning Acidity−Basicity of Supports

The acidity−basicity of supports has a significant impact on the selectivity of reduction products because of the changed adsorption/activation performance. Yamashita et al. found that the activity and selectivity of the reduction products over the anchored titanium oxide catalysts strongly depend on the types of substrate supporting the catalysts, which is shown in Figure 58A. A significant reactivity and selectivity differences among these photocatalysts can be observed. The titanium oxides anchored on ZSM-5 show a good selectivity for CO formation, while the titanium oxides anchored on Y-zeolite and PVG dominantly generate CH4 (main product) and CH3OH AY


Chemical Reviews

Review

Figure 60. (A) Product fraction vs dielectric constant over Q-TiO2/SiO2 for 3 h of irradiation in the 1 mol·L−1 2-propanol solution containing different solvents: (a) carbon tetrachloride, (b) dichloromethane, (c) 2-propanol (pure solvent), (d) ethylene glycol monoethyl ether, (e) acetonitrile, (f) sulfolane, (g) propylene carbonate, and (h) water. (B) Possible reaction pathways for CO2 reduction.916 Reprinted with permission from ref 916. Copyright 1997 Elsevier.

Figure 61. Schematic charge-transfer mechanism in (A) the type II heterojunction and three kinds of Z-scheme photocatalytic systems: (B) liquidphase, (C) all-solid-state, and (D) direct Z-scheme.

compounds (Figure 59A and B). More interestingly, the C1− C3 selectivity remains independent of the tested photoactive material.676

(accompanying product). The titanium oxides anchored on Yzeolite show the highest photoactivity and selectivity for the generation of CH3OH and CH4.915 Soon after, they also reported that the highly dispersed and excited titanium oxide species in zeolite cavities and zeolite framework are able to selectively photoreduce CO2 with gaseous H2O to CH3OH, while the aggregated octahedrally coordinated titanium oxide species loaded with Pt cocatalyst could selectively generate CH4 via CO2 photoreduction (Figure 58B).57 Subrahmanyam et al. tested catalysts of metal oxide systems: TiO2/Pd, CuO/ZnO, Li2O−TiO2 supported on MgO, Al2O3, and SiO2. They found that the basic oxide supported systems exhibit good selectivity for preferential photoconversion of CO2 to C1−C3 compounds, while the acidic oxide supported catalysts show good selectivity toward generation of C1

3.4. Using Solvent Effects

The selectivity of CO2 reduction products is also significantly related to the solvent polarity. For example, Liu et al. studied photoreduction of CO2 over SiO2 supported TiO2 nanocrystals in various kinds of solvents.916 They found that the HCOOH/ CO ratio increases with increasing solvent dielectric constant.916 CO2 is selectively photoreduced to CO in CC14 with a low dielectric constant (ε = 2.24), whereas HCOOH is exclusively produced in water with a high dielectric constant (ε = 78.5). As shown in Figure 60A, the fraction of formate increases and that of carbon monoxide decreases with increasing dielectric constant of the solvent used.916 As AZ


Chemical Reviews

Review

Figure 62. FESEM images of Fe2V4O13 (A and B), Fe2V4O13/RGO (C and D), Fe2V4O13/RGO/CdS (E). (F) Schematic illustration of Fe2V4O13/ RGO/CdS. (G) Average CH4 and O2 generation rate over four samples. (H) Proposed mechanism for photoconversion of CO2 to CH4 over Fe2V4O13/RGO/CdS photocatalyst.981Reprinted with permission from ref 981. Copyright 2015 Royal Society of Chemistry.

illustrated in Figure 60B, on the one hand, since the activated CO2•− radicals on Ti sites are not highly solvated in the low polar solvents such as CC14 and CH2C12, the CO generation occurs readily due to the fast oxygen atom removal from CO2•− radicals by a proton. In contrary, the CO2•− radicals are very stable in the high polar solvents, resulting in weak interaction with the photocatalyst surface. The C atom in the CO2•− radicals could easily react with a proton to generate HCOOH.916 Furthermore, Kaneco et al. demonstrated that HCOOH is dominantly generated through the protonation reaction of the intermediate CO2•− radicals over TiO2 powders in liquid mixed medium of CO2 and water.917,918 In addition, it is known that the CO2 solubility in water is extremely low (about 0.033 mol L−1).919 To increase the concentration of CO2 in solvents, methanol or cyclohexanol with high dielectric constant is also widely selected as better solvent and reductant for photocatalytic reduction of CO2 because the CO2 solubility in cyclohexanol and methanol is approximately 7.5 and 5 times larger than that in water, respectively.417,633,920−922 Additionally, it was demonstrated that the selective generation of

HCOOH is also achieved through photocatalytic reduction of CO2 over some photocatalysts (such as Bi2S3,633 CuO-TiO2,921 CdS/g-C3N4,923 Ni-doped ZnS920, and Ag-loaded SrTiO3922) in methanol solution. 3.5. Improving Interfacial Properties

It is known that the interfacial properties in the heterostructured composite photocatalytic systems are crucial for improving the separation and tuning migration path/direction of charge carriers, thus achieving the enhanced photocatalytic activity and selectivity for CO2 reduction.296,924 Typically, there are four important kinds of interfaces between two different semiconductors: type-II hetero(phase)junctions and three kinds of Z-scheme photocatalytic systems.925−927 Figure 61 illustrates the charge-transfer mechanism in (A) type II heterojunction and (B−D) three kinds of Z-scheme photocatalytic systems. As for the conventional type-II heterojunctions, the spatial separation of the photoinduced e−−h+ pairs could be readily achieved through the favorable band alignment between two semiconductors (see Figure 61A). Typically, a suitable combination of CdS and TiO2 produce the BA


Chemical Reviews

Review

potential for practical photocatalytic applications,263,327,979,980 especially for photocatalysis in the gas and solid phases. Interestingly, the all-solid-state Z-scheme photocatalysts based on CdS/TiO2 and proper solid interfacial mediators such as noble metals (i.e., Au and Pt) have been successfully constructed and applied for the selective CO2 photoreduction to methane in the gas phase.399,400 Besides the noble metal electron mediators, various indirect all-solid-state Z-scheme photocatalysts, including Fe2V4O13/RGO/CdS,981 CdS/RGO/ TiO2,982 Bi2WO6/Au/CdS,983 BiVO4/carbon-coated Cu2O,984 BiVO4(010)−Au−Cu2O,985AgBr/Ag/g-C3N4,986 g-C3N4/Al− O bridge/Fe2O3987, and CuGaS2-RGO-CoOx/BiVO4988 have been designed through earth-abundant RGO mediators for CO2 photoreduction. For example, Li et al. rationally designed an indirect all-solid-state Fe2V4O13/CdS Z-scheme system array using low-cost highly conductive RGO interlayer as a shuttle redox mediator through three-step process.981 As can be easily seen from Figure 62A−E that a lot of small CdS nanoparticles are uniformly deposited on the sheet-like RGO coating layers over Fe2V4O13 NRs of 10−20 mm length. The formation of an intimate interface between Fe2V4O13 nanoribbons, RGO nanosheets, and CdS nanoparticles is illustrated as shown in Figure 62 F. As a result, the selective CH4 generation rate via gas-phase CO2 photoreduction over the Fe2V4O13/RGO/CdS Z-scheme system is obviously higher than those observed on bare Fe2V4O13 nanoribbons, Fe2V4O13/RGO, and type-II Fe2V4O13/CdS heterostructure (Figure 62G). Notably, the production of O2 with the non-stoichiometric molar ratio to CH4 (less than 2:1) is also observed, demonstrating the simultaneous existence of water oxidation and photoabsorption of oxygen molecules on the photocatalyst surface. The obvious activity enhancement can be attributed to the Z-scheme chargeseparation mechanism, as graphically illustrated in Figure 62H, which are further supported by the photoluminescence decay profiles of various composite photocatalysts. This study clearly shows that the all-solid-state Z-scheme system has a great potential as an advanced photocatalyst-design tool for selective generation of renewable hydrocarbon fuels via gas-phase CO2 photoreduction. More interestingly, the Z-scheme charge separation mechanism could be also achieved through direct construction of an intimate interfacial contact without an electron mediator.927 In general, for these Z-scheme photocatalytic systems, the properties of the solid−solid interfaces are crucial factors determining the final performance, which is also significant for tuning the interfacial resistance levels for electron transfer and further improving the photocatalytic activity and selectivity.327 However, the use of noble metals and their strong light absorption greatly limits a wide application of the ASS Zscheme photocatalytic systems. More interestingly, on the basis of the experiments involving hydroxyl radicals, the concept of a direct Z-scheme photocatalyst was proposed by Yu et al. in 2013 for explaining the high photocatalytic formaldehyde (HCHO) degradation performance over the TiO2/g-C3N4 composite.974 In addition to the experimental investigations, the Z-scheme mechanism between TiO2 and g-C3N4 was also further revealed by the hybrid DFT method.989 It was shown that the negatively and positively charged surfaces of TiO2 and g-C3N4 are created by strong interfacial interactions, respectively, leading to the formation of a built-in interfacial electric field and the promoted recombination of photoexcited electrons and holes in TiO2 and g-C3N4 under illumination, respectively.989 The direct Zscheme photocatalyst exhibits several obvious advantages,

type-II heterostructured nanocomposite CdS/TiO2, which can selectively reduce CO2 with H2O to methanol and CO either in liquid or gas phases. 392,928,262,571,592 Besides CdS/TiO2 heterojunction, various other kinds of type-II heterojunctions, have been rationally designed and applied in the photoreduction of gaseous and aqueous CO2, such as mixed-phase TiO2 nanocomposites,929−933 Cu2ZnSnS4/TiO2,934 dyes/ TiO2,935−939 Cu2O/TiO2,940,941 TiO2/CeO2,582,942 TiO2/vanadate,943 TiO2/ZnO,944 NiS/TiO2,945 PbS/TiO2,789 NH2−UiO66/TiO2,946 Cu2O/S-TiO2/CuO,947 CdS/boron carbon nitride (BCN),948 SnO2/B−P codoped g-C3N4,949 Cd0.2Zn0.8S@UiO66-NH2,950P25@CoAl layered double hydroxide,26 CuO/ ZnO,764ZnO/CeO2,951 ZnO/Ag1−xCux/CdS,952ZnO@Cu− Zn−Al layered double hydroxides,829ZnO/ZnTe,650 N-doped graphene-supported copper complex,953 cobalt phthalocyanine/ graphene oxide, 9 5 4 g-C 3 N 4 /TiO 2 , 9 9 , 9 5 5 − 9 5 8 In 2 O 3 / WO3,959B4C/g-C3N4,960 CsPbBr3/g-C3N4,961 ZnO/g-C3N4,962 red phosphor/g-C3N4,963 CeO2/g-C3N4,964 MOFs/g-C3N4,965 noble-metal-free polyoxometalates/g-C3N4,966CdIn2S4/mpgC3N4,967Bi2WO6/g-C3N4,102 ZnGa2O4/Ga2O3,968 AgBr/gC3N4,969 In2O3/g-C3N4,970 g-C3N4/NaNbO3,971 Ta3N5/LaTiO2N972, and cubic-orthorhombic surface-phase junctions of NaNbO3.973 However, the photoreduction of CO2 mainly occurs on the semiconductor surface with much lower CB edge, suggesting the weaker CO2-reduction ability in this kind of systems. Clearly, the photogenerated electrons and holes in type-II heterojunction photocatalytic systems show the weakened reduction and oxidation ability for CO2 reduction and oxygen evolution, respectively. The electrostatic repulsion between electron−electron or hole−hole also restricts the effective separation of charge carriers.927 Thus, it is highly desired to prepare new heterostructured photocatalytic systems beyond conventional type-II heterojunctions to overcome these problems. In contrary, the Z-scheme photocatalytic systems, including the first generation (liquid-phase Z-scheme), second generation (all-solid-state Z-scheme) and the current third generation (direct Z-scheme), can not only boost the charge-carrier separation efficiency, but also optimize the redox potentials of semiconductor for photocatalysis (as shown in Figure 61B-D). In other words, for Z-scheme systems, the separated holes and electrons are retained in much higher VB and CB levels, thus achieving much stronger redox ability and tunable selectivity. Commonly, the heterogeneous artificial Z-scheme photocatalytic systems can overcome the shortcomings of singlecomponent or heterostructured photocatalysts, and simultaneously fulfill long-term photostability, high charge-separation efficiency, wide absorption range and strong redox ability.327,974,975 The concept of the liquid-phase Z-scheme photocatalytic system was first proposed by Bard in 1979.471 As shown in Figure 61B, with the aid of a shuttle redox mediator, the redox potentials can be easily optimized in the 1st generation of liquid phase Z-scheme photocatalytic systems. For example, the liquid phase Z-scheme BiOI/g-C3N4976 and gC3N4/Bi4O5I2977 have been fabricated for CO2 photoreduction through the intermediate I3−/I− pairs. However, the 1st generation of Z-scheme photocatalytic systems can only be achieved in the liquid phase and suffers from the obvious backward reactions.927 To overcome these problems, Tada et al. in 2006 proposed the 2nd generation of Z-scheme photocatalytic systems, namely, the all-solid-state (ASS) Zscheme photocatalysts.978 Commonly, the all-solid-state Zscheme photocatalysts with a variety of advantages exhibit great BB


Chemical Reviews

Review

Figure 63. FESEM (A, B) of the C0 sample. HRTEM images of the C0 (C) and C5 (D) samples. (E) Selective visible-light generation rate of CH4 via CO2 photoreduction over C0, C1, C2, C5, C10, C20, C100, and N5 samples. (F) Schematic charge-separation mechanism for the CdS−WO3 Zscheme photocatalyst under visible light irradiation.101 Reprinted with permission from ref 101. Copyright 2015 John Wiley & Sons, Inc.

Figure 64. Selective CH3OH generation rates over cm-ZnO, pure ZnO, G10, and pure g-C3N4. Schematic charge-separation mechanism for (b) conventional heterojunctions and (c) direct Z-scheme photocatalysts.1010 Reprinted with permission from ref 1010. Copyright 2015 Royal Society of Chemistry.

SEM images reveal that the as-prepared hierarchical monoclinic WO3 sample with 3 μm hollow sphere structures are composed of numerous small nanosheets of about 30 nm thickness (Figure 63A−C). The HRTEM image of CdS-WO3 heterostructure further confirms the formation of intimate interfacial contact between 4−8 nm CdS nanoparticles and WO3 nanosheets (Figure 63D). Furthermore, it was found that the CdS−WO3 heterostructures with optimal CdS content (the nominal molar ratios of CdS/(WO3 + CdS) = 5) could achieve the maximum CH4-generation rate of 1.02 μmol h−1 g−1, which is much higher than those obtained for other samples (Figure 63E). It is believed that the favorable Z-scheme chargeseparation mechanism could significantly facilitate the effective spatial separation of photoexcited charge carriers and enhance the redox ability of photocatalyst through retraining the photogenerated electrons and holes with much higher redox potentials, thus finally accomplishing the improved photocatalytic activity (Figure 63F). This study highlights the promising application of high-performance direct Z-scheme photocatalysts in the CO2 photoreduction. In another example, the intimate g-C3N4/ZnO Z-scheme contact interface without an electron mediator was rationally constructed via one-pot

such as easy preparation, low cost and the reduced lightshielding effect, thus leading to the wide applications in photocatalysis.253,304,328−331,975,990−994 To date, the direct Zscheme photocatalytic systems have been available for selective CO2 photoreduction to solar fuels, such as Si/TiO2,995 CuOTiO 2 , 921 Cu 2 O/TiO 2 , 996 Cu 2 O/ZnO, 997 polydopamine (PDA)/ZnO, 9 9 8 TiO 2 /CuInS 2 , 99 9 g-C 3 N 4 /Fe 2 O 3 , 1 00 0 Cu2V2O7/g-C3N4,1001 3D ZnIn2S4 nanosheets/TiO2 nanobelts, 645 InVO 4 /Fe 2 O 3 , 1002 Ag 2 CrO 4 /g-C 3 N 4 /graphene oxide,1003 Cu2ZnSnS4 (CZTS)-ZnO,1004 CdS-WO3,101 Fe2O3/ Cu2O,1005 SnO2−x/g-C3N4,1006 MnO2/g-C3N4,1007 g-C3N4/ SnS2,1008 Bi2WO6/g-C3N4,102 Ag3PO4/g-C3N4,1009 WO3/gC3N4555, and ZnO/g-C3N4.1010,1011 More importantly, the selectivity for CO2 photoreduction can also be manipulated by suitable design of advanced direct Z-scheme photocatalytic systems.976,981,1005,1010 These integrated direct Z-scheme systems show new horizons for exploration of more advanced composite photocatalysts for highly selective “artificial photosynthesis”. Interestingly, Jin et al. successfully synthesized a selfassembled hierarchical direct Z-scheme CdS−WO3 photocatalyst via a facile two-step strategy: chemically induced selftransformation and a subsequent precipitation method.101 The BC


Chemical Reviews

Review

Figure 65. (A) Photocatalytic production rates of reduction products and (B) IQE (internal quantum efficiency) and ethane selectivity of TiO2−Pt (1 wt %) photocatalyst. (C) Scanning tunneling spectroscopy (STS) data for TiO2−Pt (1 wt %) photocatalyst. (D) Photocatalytic production rates of reduction products and (B) IQE and selectivity evaluated for TiO2−Cu2−xO composite photocatalyst. (F) STS data for TiO2−Cu2−xO photocatalyst (demonstrating the overlapping energy levels of TiO2 and Cu2−xO). (G) Photocatalytic production rates and (H) IQE and selectivity obtained using the designed TiO2−CIS photocatalyst. (I) The formation of desired energy levels below the CB of TiO2 semiconductor.64 Reprinted with permission from ref 64. Copyright 2014 American Chemical Society.

facile calcination strategy.1010 It is demonstrated that the asfabricated direct g-C3N4/ZnO Z-scheme photocatalysts could achieve a 2.3-fold improvement in the photoactivity for selective CH3OH generation via CO2 reduction in comparison to that of pure g-C3N4, without changing the original selectivity of pure g-C3N4 (Figure 64A). The significantly enhanced photocatalytic performance of the g-C3N4/ZnO binary composites are attributed to the direct Z-scheme chargeseparation mechanism rather than the conventional heterojunction-type mechanism (as shown in Figure 64B and C), owing to the construction of intimate g-C3N4/ZnO contact interface through one-pot high-temperature calcination.1010 Hence, the design and formation of tight contact interface with the larger area and a small number of defects are essential to construct highly effective Z-scheme photocatalysts, which can be achieved through different physical (such as the electrostatic interactions and ball milling) and chemical (strong chemical bonds) formation strategies.102,327,974 In future, numerous efforts should be made toward development of more effective all-solid-state Z-scheme photocatalytic systems with optimal architectures (such as hierarchical and 2D−2D coupling structures) and their application for selective CO2 photoreduction.101,976 More interestingly, the verification and mechanism for the improved stability, light harvesting, redox ability, Z-scheme electron transfer, and tunable CO2 photoreduction selectivity need to be further investigated through detecting active oxidant species, reduction product distribution, and charge transfer kinetics, respectively.

3.6. Loading Suitable Cocatalysts

Finally, loading nanoparticulate electrocatalysts (as cocatalysts) onto semiconductors is an appealing strategy to achieve high selectivity and reasonable photocatalytic rates because these cocatalysts exhibit special selectivity for electroreduction of CO2. On the basis of the above analysis, the complicated mechanism and kinetic challenges of CO2 photoreduction on semiconductors lead to the very low efficiency and selectivity for CO2 photoreduction. Accordingly, for achieving highly selective CO2 photoreduction, the improvement of the slow reaction kinetics for target CO2 reduction reaction is required to enhance the overall efficiency and selectivity. There are numerous factors influencing the kinetics of the CO2 reduction, such as charge separation and transfer, water oxidation and catalytic reduction of CO2, all of which could be tuned by selecting proper cocatalysts. The electrocatalysts for CO2 electrochemical reduction can serve as the cocatalysts for modification of the semiconductor surface to achieve highly active and selective CO2 photoreduction. To date, different electrocatalysts with excellent selectivity for electrochemical reduction of CO2 have been widely developed and loaded on semiconductors to improve their selectivity and activities for CO2 photoreduction.48−50,659 In this regard, the studies devoted to the efficient and robust heterogeneous electrocatalysts (i.e., metals, carbon-based materials, transition metal oxides, and chalcogenides) for CO2 reduction are encouraged for future studies.694,1012 Especially, it should be pointed out that metal-free nanocarbons and composites have been widely BD


Chemical Reviews

Review

Figure 66. Periodic table depicting the selectivity of planar metal electrodes for electrochemical reduction of CO2.549 Reprinted with permission from ref 549. Copyright 2008 American Chemical Society.

cocatalysts, thus resulting in the improved dependence of catalytic yields and selectivity, which provides a new strategy to develop new inexpensive and selective photocatalysts through optimizing the energy levels. Besides the measurements of DOS using STS, density functional theory (DFT) calculations can successfully explain copper’s unique ability to selectively convert CO2 into hydrocarbons,706 and selective CO formation on Cu/g-C3N4(001) and cis-COOH production over Mo/gC3N4(001).1021 A considerable effort has been made to improve understanding of the molecular mechanism via the DFT calculations by explaining the fundamental role of cocatalysts on semiconductors in increasing the efficiency and product selectivity. More meaningfully, the DFT calculations can be used to help design new materials for making CO2 photocatalytic processes more efficient and selective.

employed as unique cocatalysts to achieve high selectivity for CO2 photoreduction because of their multifunctional role such as the ability to separate, transfer, enrich, and store photoexcited electrons, enhance CO2 adsorption/activation, improve absorption of visible light, increase the photostability of semiconductors and accelerate the CO2 reduction kinetics.1013−1020 Various advanced applications of carbon-based cocatalysts in photocatalytic CO2 reduction will be thoroughly discussed in section 7.4. Combining experimental and computational investigations is also highly expected. Recently, some interesting studies have been reported based on the experimental measurements and quantum chemical calculations. For example, Nagpal’s group investigated the DOS of cocatalyst-modified TiO2 responsible for photoreduction of CO2 with gaseous H2O during the typical artificial photosynthetic process using scanning tunneling spectroscopy (STS).64 For TiO2−Pt (1 wt %) photocatalyst, Pt dopant may not only enhance several times photocatalytic activity toward selective H2 or CH4 evolution owing to the increased oxygen atom adsorption on the Pt interface (Figure 65A), but also reduce the overall observed photogenerated hydrogen yields by increasing the light intensity (Figure 65B) because of the increased trapping and recombination of both photogenerated holes and electrons (Figure 65C). To prevent the unexpected charge recombination over metal dopants, the cheap Cu2O cocatalysts were incorporated on TiO2 to create the desired electronic DOS. Despite the lower overall conversion efficiency than that of TiO2−Pt (1 wt %) photocatalyst, the resulting TiO2−Cu2−xO composite photocatalyst showed a significant increase in the CO2 photoreduction activity as compared to that of bare TiO2 under AM1.5 light illumination (Figure 65D and E), owing to the combined energetic states of TiO2 and Cu2−xO (Figure 65F). The low overall activity might be attributed to variable oxidation state of copper-oxide nanoparticles, leading to the low stability of Cu2O. As expected, the designed stable TiO2− CIS photocatalyst exhibits good activity for selective gas-phase formation of ethane (>70%, Figure 65G and H). More importantly, the electronic DOS for the composite photocatalyst could be carefully tuned by hot electron states and quantum confinement effect (Figure 65I). Clearly, the electronic DOS of TiO2 can be tuned by loading suitable

4. KEY ROLE OF COCATALYSTS IN CO2 PHOTOREDUCTION Absolutely, the multifunctional role of cocatalysts in boosting the PEC and photocatalytic water splitting has been deeply investigated.274,275,925,1022,1023 So far only a few papers report systemic studies on the diversified function and role of cocatalysts during CO2 reduction at the molecular level. Typically, besides improved selectivity of CO2 reduction products, the cocatalysts could act as an electron trap to boost the charge separation and transport through extracting the photogenerated charges from semiconductor, increase stability of photocatalysts by improved water oxidation, lower the overpotentials related to the multielectron electrocatalytic water oxidation and reduction, and improve the catalytic kinetics by decreasing the activation energy for gas evolution.1023,1024 Importantly, a better understanding of the role and nature of cocatalysts can be used to guide the design and development of highly efficient composite photocatalysts. Consequently, these key functions of cocatalysts for CO2 photoreduction are worthy of further investigation, which will be thoroughly summarized and discussed in the sections below. 4.1. Improving Selectivity of CO2 Photoreduction

Generally, the metal-based electrocatalysts in electrochemical reduction of CO2 can be used to lower the impractically high overpotentials and intrinsic energy barriers for the selective BE


Chemical Reviews

Review

selectivities to advance practical applications and commercialization of these systems.

generation of target products. In the pioneering survey devoted to electrochemical CO2 reduction on planar metal electrodes, Hori and co-workers have deeply discussed the selective CO2 electroreduction over different metal electrodes in solution. Based on the primary products formed on the metal electrodes, the selectivity of reduced products in aqueous solution varied with electrode materials, which is displayed in Figure 66.549,1025 As shown in Figure 66, it is clear that Ag, Au, Pd, and Zn catalysts exhibit good selectivity for CO production, and Sn, Cd, Pb, In and Tl favor the formation of formic acid, whereas Pt, Ni, Co, Ti, and Fe exhibit good selectivity for H2 generation.549,1025 In particular, Cu, as the unique hydrocarbon-producing electrocatalyst, has been widely demonstrated to yield a wide range of hydrocarbons containing more than one carbon atoms.1026,1027 Interestingly, these metal electrocatalysts could also serve as cocatalysts to boost the chargecarrier separation and hence improve the photoactivity and selectivity for liquid or gas-phase CO2 reduction, which are summarized in Figure 67. However, a careful comparison of

4.2. Minimizing Overpotentials of CO2 Photoreduction

Commonly, when nonaqueous electrolytes are employed, both electrocatalytic and photocatalytic CO2 reduction reactions suffer from excessively high overpotentials, due to their kinetic limitations. Meanwhile, the competing hydrogen generation reaction could further lower the Faradaic efficiency of electrochemical carbon dioxide reduction, thus leading to the high overpotentials for the CO2 electroreduction process. In general, a variety of transition metal electrocatalysts, such as metal electrodes, are required to reduce the overpotentials for selective electrochemical reduction reactions of CO2 (Figure 68). Typically, Cu is commonly used as the most active for

Figure 68. Comparison of the activity of selected transition metal catalysts.266 Reprinted with permission from ref 266. Copyright 2017 American Chemical Society.

Figure 67. Selectivity for photocatalytic reduction of CO2 over different cocatalysts

selective hydrocarbon production via electrocatalytic reduction of CO2. As shown in Figure 68 the calculated electrocatalytic onset potential for CO2 and CO reduction is strongly dependent on the binding energy of CO on the metal surface, which could be used as a general principle to select the proper metal for selective CO2 electroreduction. Interestingly, these electrocatalysts can be loaded on the semiconductor nanoparticles as cocatalysts for photocatalytic CO2 reduction with H2O, facilitating the occurence of these photocatalytic processes at moderate overpotentials and high selectivity. For more detailed comparison, Table 8 lists various kinds of electrocatalysts and their overpotentials and Faradaic efficiency for selective electroreduction of CO2 to several useful lowcarbon fuels. As can be seen from Table 8 some electrocatalysts feature higher Faradaic efficiency at lower electrode potentials for selective electrochemical reduction of CO2. Since CH3OH is particularly useful and important liquid fuel that can be produced by CO2 electroreduction, we take the selective formation of CH3OH on different types of electrocatalysts as example for further analysis. As can be seen from Table 8 various nanostructured Cu-based oxide electrodes are attractive electrocatalysts according to both product selectivity and current efficiency.1032 To effectively improve the catalyst activity and reduce the overpotentials needed on Cu-based electrocatalysts, some research efforts have been directed toward precise engineering of the electrode surface area, morphology of catalysts (nanotubes/spheres/sheets, etc.), composition of multi-metal alloys, porosity of the supports, active sites, new complex Cu-based MOFs, and metal hybrid

Figures 66 and 67 shows that the selectivities for photocatalytic CO2 reduction over various cocatalysts are similar as those for electrochemical reduction of CO2 on the metal electrodes as electrocatalysts in the liquid-solid systems. In other words, the selectivity of metal electrodes for electrochemical reduction of CO2 could be used to design highly effective cocatalysts for selective CO2 photoreduction. For example, Cook and Adachi, respectively, demonstrated that the mixture of SiC and Cu nanoparticles or Cu-loaded TiO2 powder could achieve selective photoreduction of CO2 to CH4, C2H4, and C2H6 in a CO2 saturated aqueous electrolyte at ambient temperature.1028,1029 Also, Cu nanoparticles can act as cocatalysts to promote charge separation and selective CO2 photoreduction with similar product selectivity as on Cu electrodes in electrochemical or photoelectrochemical CO 2 reduction.1030,1031 However, it should be noted that the product selectivity of 1% Cu-loaded ZrO2 (CO evolution could be observed) for photocatalytic CO2 reduction in NaHCO3 solutions is slightly different than those in liquid phase or electrochemical reduction systems.55 It seems that the barrier height of the ZrO2-metal Schottky junction is relatively larger than those of TiO2-metal, which can make the migration of photogenerated electrons in the ZrO2 to metal impossible, thus leading to the unchanged selectivity for CO2 reduction after the addition of Cu cocatalyst.55 In future, the further developments of different electrocatalysts for CO2 reduction can be used to advance their applications as cocatalysts in CO2 photoreduction and one can take advantage of the relationship between both BF


faradaic efficiency (%)

BG

0.5 M KHCO3/CO2

>96 58 98 90

92 94 98 >60 60 90 92.8 80 91.2

60 90

−1.35 0.20 vs SCE −0.7 vs RHE −0.4 vs RHE −0.67 vs RHE −0.25 vs RHE −0.60 vs RHE −0.35 vs RHE −0.764 vs RHE −0.8 vs RHE −0.4 vs RHE −0.45 vs RHE −1.03 vs RHE −0.28 vs RHE −0.89 vs RHE 0.73 vs RHE −0.6 −0.5 vs RHE

Re film electrodeposited onto a polycrystalline gold support

silver cathode

Sn/SnOx

OD Au nanoparticles

Au (8 nm)

CNF

Ag

Au

MoS2

Ag/TiO2

highly dense Cu nanowires

Au

Ag (anodization treatment)

NCNT

Pd (3.7 nm)

Au3Cu bimetallic nanoparticles

An immobilized cobalt protoporphyrin

Cu−In alloy

∼60

EMIM-BF

87

1.8 vs Ag/AgCl

0.1 M KHCO3/CO2

0.1 M perchlorate solution saturated with CO2, pH = 3, 10 atm

0.1 M KHCO3/CO2 (pH 6.8)

0.1 M KHCO3/CO2

0.1 M KHCO3

0.1 M aqueous KHCO3

0.5 M KHCO3/CO2

0.1 M KHCO3

1 M KOH

H2O/EMIM-BF4

0.5 M KHCO3/CO2

0.5 M KHCO3/CO2

0.5 M NaHCO3

1-ethyl-3-methylimidazolium tetrafluoroborate, [emim][BF4] ionic liquid electrolyte 0.5 M NaHCO3

0.1 M LiClO4 CH3OH solution, 1 atm CO2, stirred conditions

0.1 M KHCO3 aqueous solution, 50 atm

0.1 M KHCO3 aqueous solution saturated with KCl, 25 °C

64.7 81.5 57.9

−1.6 vs Ag/AgCl

Ag (99.98%) electrode Au (99.95%) electrode Pd metal

CH3CN−Bu4NPF6 saturated with CO2

92.3

1045 (1991) 1046 (2001) 1047 (2011) 1048 (2012) 702 (2012) 1049 (2013) 1018 (2013) 1050 (2014) 1051 (2014) 1052 (2014) 1053 (2014) 1054 (2015) 1055 (2015) 1056 (2015) 1057 (2015) 1058 (2015) 1059 (2015) 1060 (2015) 1061 (2015)

1042 (1984) 1043 (1985) 1044 (1990)

0.1 M Et4NCl DMF−H2O (10%) solutions, 25 °C

ref (year) 1041 (1956)

conditions? 0.1 M KHCO3

−1.55 vs sodium SCE

two-electron reduction products (CO) −1.14 87.1 −1.37 81.5 −1.54 79.4 −1.25 vs NHE 98

potentials (V)

platinum gauze electrode (WE)/Re(CO)3(vbpy)Cl

Au Ag Zn glassy carbon electrode (WE)/Re(I)(bpy)(CO)3Cl

electrode (electrocatalysts)

Table 8. Summary of Electrocatalysts and Their Efficiency for Selective Reduction of CO2 to Several Useful Low-Carbon Fuels

Chemical Reviews Review




BH

64.6 99 70 98 >90 >80 11.3 80 86 39 90 96.1

80 84 98 94.2 96.8 >90 92 93 90

−1.6 vs SCE −1.9 vs SCE −0.55 vs RHE −1.46 vs Ag/AgCl −1.4 vs Ag/AgCl −0.8 vs RHE −0.99 vs RHE −0.6 vs RHE −0.89 vs RHE −0.45 vs RHE −0.6 vs RHE −2.0 vs Ag/AgCl −0.7 to −0.9 vs RHE −0.85 vs RHE −0.8 vs RHE −0.4 vs RHE −0.75 vs RHE −0.855 vs RHE −0.65 vs RHE −0.59 vs RHE −0.7 vs RHE −0.7 vs RHE

Ag−Cu

indium nanocrystals

CNT−Au nanohybrid

g-C3N4/MWCNT

nanostructured Au

Mesoporous Pd7Cu3 bimetal

S,N-doped carbon

oxide-derived Ag

Pd85Cu15 alloy

Cu oxides

Cu−Sn bimetals

36 nm Bi NPs

Ni−N-modified graphene

hierarchical hexagonal Zn catalyst

superfine Ag nanoparticle decorated ultrathin Zn nanoplates

nanosharp Au

amine functional group on Ag nanoparticles

triangular Ag nanoplates

AuNPs embedded in graphene nanoribbons

Co-Pc/carbon nanotubes

core/shell Cu/SnO2-0.8 nm

CuxIn1−x alloys, x = 0.5−0.8

>90

75

−0.6 V vs RHE

two-electron reduction products (CO) −0.67 vs RHE 91

potentials (V)

Cu2O with Sn and In

covalent organic frameworks (367-Co)

Table 8. continued

0.5 M KHCO3/CO2 (pH 7.2)

0.5 M KHCO3/CO2

0.1 M KHCO3 solution

0.5 M KHCO3/CO2 (pH 7.3)

0.1 M KHCO3

0.5 M KHCO3/CO2 (pH 7.3)

0.5 M KHCO3/CO2 (pH 7.2)

0.1 M KHCO3/CO2 (pH 6.8)

0.5 M KHCO3/CO2

0.1 M KHCO3/CO2

acetonitrile/1-butyl-3-methylimidazolium trifluoromethanesulfonate

0.1 M KHCO3/CO2 (pH 6.8)

0.1 M KHCO3/CO2

0.1 M KHCO3/CO2

0.1 M KHCO3/CO2 (pH 6.8)

0.1 M KHCO3/CO2

0.1 M KHCO3/CO2 (pH 6.8)

0.5 M KHCO3/CO2 (pH 7)

1.0 M KCl

0.5 M NaHCO3/CO2

acetonitrile−BMIMPF6 solution

0.5 M KHCO3/CO2 (pH 7.3)

0.1 M KHCO3/CO2 (pH 6.75)

pH 7.2 K3PO4 buffer (0.2 M), 0.5 M KHCO3/CO2, 0.5 M NaClO4

conditions?

1062 (2015) 1063 (2016) 1064 (2016) 1065 (2016) 1066 (2016) 1067 (2016) 1068 (2016) 1069 (2016) 1016 (2016) 1070 (2016) 1071 (2016) 1072 (2016) 1073 (2016) 1074 (2016) 1075 (2016) 1076 (2016) 1077 (2016) 1078 (2016) 1079 (2017) 1080 (2017) 1081 (2017) 1082 (2017) 1083 (2017) 1084 (2017)

ref (year)




80 93 95 93 85 90.2

−0.60 vs RHE −0.87 vs RHE −0.8 vs RHE −0.67 vs RHE −0.47 vs RHE −0.38 vs RHE

single-atom iron dispersed on nitrogen-doped graphene

Cu−Pd nanoalloys

single-atom Ni in N-doped rGO

Ni−N−C

Fe−N−C

dealloyed Au3Cu

BI

5.9 88.4 94.9

95 70 >93

−0.70 and −0.90 vs SCE −1.53 to −1.61 vs Ag/AgCl −1.3 −1.5 −1.6 1.8 vs SCE −0.8 vs SCE 1.7 vs SCE −1.6 vs NHE −1.8 vs SCE

formate dehydrogenase (FDH)

Fe wire (99.5%, 0.16−0.63 cm2) electropolished in HClO4−(CH3CO)O−H2O

Sn

In Pb granule electrodes

RuO2−TiO2 nanotube (NT) composite electrodes (WE); SCE (RE); Pt plate (CE)−RuO2

Sn foil (Alfa Aesar, 99.998%) with an active surface area of 1 cm2

Sn-powder-decorated gas diffusion layer electrode

Sn/graphene

Cu

3950

−1.4

CdPb

60.5

59.5−59.6

90

20

−1.4

Zn

two-electron reduction products (HCOOH/HCOO−) −1.63 97.4

99.4

−0.79 vs RHE

single-atom Co−N5 catalytic site

Pb

97

0.61 vs RHE

atomically dispersed Ni(I) on nitrogenated graphene

89.1

two-electron reduction products (CO) −1.6 vs SCE 95

potentials (V)

−0.89 vs. RHE


Au−CeOx interface

Ag

Table 8. continued

0.1 M KHCO3 aqueous solution

aqueous NaHCO3 solution, 27 mA cm2

0.1 M Na2SO4

0.5 M NaHCO3 solution saturated with CO2

0.2 M K2CO3 aqueous solution, 80 °C, 50 atm

0.1 M KHCO3

0.5 M K2SO4

phosphate buffer solutions (pH = 7), methyl viologen (MV2+) or pyrroloquinoline quinone (PQQ) as an electron mediator 0.1 M KClO4 25 1 C; 30 atm, 120 mA cm−2

0.1 M KHCO3

0.1 M KHCO3

0.1 M KHCO3

0.5 M KHCO3/CO2

0.5 M KHCO3/CO2 (pH 7.3)

0.5 M KHCO3/CO2 (pH 7.3)

0.5 M KHCO3/CO2

0.5 M KHCO3/CO2

0.1 M KHCO3/CO2

0.2 M NaHCO3/CO2

0.5 M KHCO3/CO2

0.1 M KHCO3/CO2

0.5 M NaHCO3 with 20 mM DTAB

conditions?

1099 (2004) 1100 (2005) 1101 (2012) 1102 (2013) 1103 (2014)

1041 (1956) 1044 (1990) 1094 (1990) 1095 (1994) 1096 (1995) 1097 (1995) 1098 (1995)

1085 (2017) 1086 (2017) 1087 (2018) 1088 (2018) 1089 (2018) 1090 (2018) 1091 (2018) 1092 (2018) 1092 (2018) 1093 (2018)

ref (year)




BJ

83 64.3 83.5 87.1 96.4 79.8 28 62

27 91 91.6 (92) 73 30 56 83 87

−0.8 vs SCE −0.88 vs SCE −1.8 vs Ag/AgCl −1.93 vs RHE −1.8 vs SCE −2.0 vs Ag/AgCl −0.5 vs RHE −1.7 vs RHE −1.4 vs Ag/AgCl −0.5 vs RHE −1.4 vs SCE −2.2 vs Ag/Ag+ −0.84 vs RHE −1.5 vs RHE −0.56 vs RHE −1.18 vs Ag/Ag+ −1.6 vs Ag/AgCl

Pd-polyaniline/CNT

1.72 nm thick Co3O4 layers

Sn-coated on Cu

Zn with a layer of nanoparticles

bismuth nanodendrites

Sn−Pb alloys

hierarchical Cu pillars

hierarchical SnO2 microspheres

ultrafine copper(II) oxide nanoparticles

carbon-supported Au−Pd core−shell nanoparticles

electro-deposited Sn catalysts

Pb (Sn)

N-doped graphene

Ni-modified Cu

crystalline SnO2 nanospheres

porous dendritic Cu

hierarchical mesoporous SnO2 nanosheets on carbon cloth

91.3 79

−1.5 vs Ag/AgCl −0.7 vs RHE

nanosized Bi on Cu foil

Cu−C Dots nanocorals

∼80%

−0.8 V vs RHE

AgSn/SnOx

Pd nanoparticles

95

−0.15 vs RHE

Pd

>60

85

two-electron reduction products (HCOOH/HCOO−) −1.16 vs RHE 85

potentials (V)

−1.8 vs Ag/AgCl


SnOx/Sn

PEI−NCNT

Table 8. continued

0.5 M NaHCO3/CO2

0.1 M KHCO3/CO2

0.5 M NaHCO3/CO2, pH 7.2

1 M KHCO3


[EMIM](BF4)/H2O (92/8 v/v)

0.5 M KHCO3/CO2

0.1 M KHCO3/CO2

0.5 M KHCO3/CO2

[Bmim]PF6 (30 wt %)/AcN-H2O(5 wt %)

0.1 M KHCO3/CO2

0.1 M Na2SO4/CO2, pH 4

0.5 M NaHCO3/CO2

0.5 M KHCO3/CO2

0.1 M KHCO3/CO2

0.5 M KHCO3/CO2


0.5 M KHCO3/CO2

0.1 M KHCO3/CO2

0.1 M KHCO3 aqueous solution

0.1 M KHCO3/CO2

2.8 M KHCO3

0.1 M KHCO3/CO2

0.1 M KHCO3

conditions?

1104 (2014) 1105 (2015) 1106 (2015) 1107 (2015) 1108 (2016) 1109 (2016) 1110 (2016) 1111 (2016) 1112 (2016) 1113 (2016) 1114 (2016) 1115 (2016) 1116 (2016) 1117 (2016) 1118 (2016) 1119 (2016) 1120 (2016) 1121 (2016) 1122 (2017) 1123 (2017) 1124 (2017) 1125 (2017) 1126 (2017) 1127 (2017)

ref (year)




BK

41.3 100 22 38 36.3

−1.9 vs SCE −0.8 vs SCE −0.52 vs SCE −0.58 vs SCE −1.1 vs SCE −0.70 vs SCE

anodized Cu-based electrode

Ru/Cu

p-GaP photoelectrode

pyridinium-based over Pt disk electrode

electrodeposited cuprous oxide film

Cu88Sn6Pb6 alloy cathode

38

−0.8

19.8 15.5

−1.39 −1.52

Cu (111)

eight-electron reduction products (CH4) −1.44 33.3

71.2

Cu (100)

Cu

30% Cu2O-MWCNTs

Mo−Bi bimetallic chalcogenide

15.9

75

42.7

45

−0.7 vs SHE

+0.16 vs SCE

Cu/Cu2O electrode

Cu63.9Au36.1 alloy supported on nanoporous Cu film

−1.77 vs SCE

Cu(core)/CuO(shell) catalyst

electrodeposited Cu2O/carbon paper cathode

100

−0.7 to 0.8 vs SCE

molybdenum metal ∼240

55

−1.3 vs SCE

six-electron reduction products (CH3OH) −1.4 vs SCE 60

p-GaP

p-GaAs

four-electron reduction products (HCHO) −0.9 vs RHE 65

75

−0.9 vs RHE

CuSx

BDD

80

two-electron reduction products (HCOOH/HCOO−) −0.4 vs RHE

potentials (V)

−0.8 vs. RHE


Sulfur-modified copper catalysts (Cu−S)

Pd nanoparticles

Table 8. continued

0.1 M KHCO3

0.1 M KHCO3

0.1 M KHCO3

0.5 M KHCO3/CO2

1-butyl-3-methylimidazolium tetrafluoroborate in MeCN

0.5 M KHCO3

0.1 M Na2CO3−NaHCO3

1 M KHCO3

2 M HCl solution

0.5 M KHCO3 solution saturated with CO2

0.1 M acetate buffer containing 10 mM pyridine maintained at pH 5.2 10 mM 4-hydroxypyridine in 50 mL of H2O + 0.5 M KCl

0.5 M NaHCO3 solution saturated with CO2

0.5 M KHCO3

0.2 M Na2SO4 solution saturated with CO2, 20 °C, pH 4.2

0.1 M MeOH (TBAP)

0.1 M KHCO3

0.1 M KHCO3/CO2

1 M KHCO3/CO2

conditions?

1041 (1956) 549 (2008)

14 (1978) 1131 (1984) 1132 (1986) 1032 (1991) 1133 (1997) 73 (2008) 1040 (2010) 1034 (2011) 1035 (2012) 1036 (2013) 1037 (2014) 1038 (2014) 1039 (2014) 1134 (2016) 1135 (2016)

1130 (2014)

1124 (2017) 1128 (2018) 1129 (2018)

ref (year)




55 19.5 58

−1.25 vs NHE −2 vs NHE −1.8 vs RHE

ultrathin 5-fold twinned copper nanowires

Ag−Co bimetals

Cu-doped, mesoporous CeO2 nanorods

46 43 19 20.3 41 36.3 38.1

−0.58 −0.5 vs Ag/AgCl −0.9 vs RHE −1.1 vs RHE −1.1 vs RHE −1.38 vs RHE −1.08 vs RHE

Cu2O-derived Cu (18 nm)

Cu NPs assembled on a pyridinic-N rich graphene

Cu nanowire arrays

cube-shaped copper nanocrystals 5 wt % Cu

Cu(OH)2 nanowires

111.58

−1.3 vs SCE

MoS2-rods/TiO2 nanotubes (photoelectrocatalysis)

Cu nanoparticles with large surface roughness

32.3

−3.5 vs Ag/AgCl

99.98% Cu electrode

>100

−1.9 vs SCE

Cu foil electrode

twelve-electron reduction products (C2H4) −1.40 vs NHE 48.1

93.5

−1.4 vs NHE

N-doped carbon (graphene-like)

99.999% Cu electrode

21

eight-electron reduction products (CH4) −1.25 vs NHE 80

potentials (V)

−1.6 vs SCE


Cu3Pt

Cu

Table 8. continued

BL

0.1 M KHCO3/CO2, pH 6.8

0.1 M KHCO3/CO2 0.1 M KHCO3/CO2

0.1 M KClO4/CO2 (pH 5.9)


0.1 M KHCO3/CO2

0.5 M KHCO3,

0.1 M KHCO3 (λ ≥ 420 nm, 100 mW cm−2)

CH3OH with 80 mM CsOH supporting salt, −30 °C

0.5 M KHCO3

0.1 M KClO4, aqueous solution saturated with CO2, 19 °C, pH 5.9

0.1 M KHCO3/CO2, pH 6.8

0.5 M NaHCO3


[Bmim]BF4


0.1 M NaHCO3

conditions?

1148 (2017) 1149 (2018)

1141 (1988) 1032 (1991) 1142 (1999) 1143 (2014) 1144 (2016) 1145 (2016) 1146 (2016) 1147 (2016)

1136 (2014) 1137 (2015) 1019 (2016) 1138 (2017) 1139 (2017) 1140 (2018)

ref (year)



Chemical Reviews

Review

Figure 69. Schematic illustration of charge transfer mechanism between metal and n-type or p-type semiconductor: (A) the Schottky junction and the plasmonic hot carrier effect and (B) the ohmic contact and the plasmonic hot carrier effect. Ec, Ev, W, and Ef represent the conduction band, valence band, work function, and Fermi level, respectively.256 Reprinted with permission from ref 256. Copyright 2015 Royal Society of Chemistry.

photocatalysts for photoreduction of CO2, which will be thoroughly discussed in section 6. Absolutely, the electrocatalysts with higher Faradaic efficiencies and minimized overpotentials for selective electrocatalytic CO2 reduction should have great potential as cocatalysts for fabrication of highly effective composite semiconductor photocatalyst systems for CO2 reduction. In particular, it should be pointed out that further efforts toward application of the different electrocatalysts for selective formation of other non-methanol

catalysts/assemblies, which may result in more efficient proton/ electron conduction, better accessibility of active sites and faster surface reaction kinetics for the CO2 electroreduction process due to the improved diffusion pathways.1033,1039 Additionally, more attention should be paid to the applications of nonaqueous media or pyridine solutions, such as ionic liquids, in the selective electroreduction of CO2 to CH3OH.1040 More interestingly, these oxidized Cu-based electrocatalysts have also been widely utilized as cocatalysts to fabricate composite BM


Chemical Reviews

Review

Figure 70. Photoactivation of CO2 (A) by H2 over Ga2O31168 and (B) by H2O as the electron donor over ZnGa2O4/Ga2O3.1177 Reprinted with permission from ref 1168. Copyright 2010 American Chemical Society. Reprinted with permission from ref 1177. Copyright 2017 American Chemical Society.

holes in semiconductor back to the metal, thus leading to the significantly boosted photocatalytic activity. In the absence of an effective barrier, the ohmic contact cannot promote the separation of hot carriers in the plasmonic effect and improve the photoactivity (Figure 69B) because of the presence of obvious back-flow of hot carriers in semiconductors. For example, the Schottky barriers of the Pt cocatalysts/ TiO213,17,48,567 and the earth-abundant semimetallic RGOCdS nanorod98 heterojunctions could be readily fabricated because of much higher work function of cocatalysts as compared with those of TiO2 or CdS, which has been widely applied in the photocatalytic CO2 reduction. The resulting Schottky barrier can not only significantly boost the charge separation in TiO2 or CdS but also accelerate the reaction kinetics on the surface of cocatalysts, due to the enriched electrons.

products (including CO, CH4, and HCOOH) as cocatalysts for photocatalytic CO2 reduction are required to advance this area of research. 4.3. Promoting Charge Separation in Photocatalysts

Apart from improving the selectivity and minimizing the overpotentials for CO2 photoreduction, the loaded cocatalysts can also act as effective electron traps, therefore achieving the significantly prolonged lifetime of separated charge carriers and improved reaction rates owing to the successful construction of Schottky barrier or ohmic contact between the semiconductor photocatalyst and metallic cocatalysts such as noble metalbased nanoparticles,544 semimetal nanocarbons925,1150−1153 and disulfide nanosheets.1154−1156 The formation mechanism of the metal−semiconductor Schottky barrier and ohmic contact has been extensively discussed in the previous reports.256,544,1157 As shown in Figure 69A, after contacting the metal and n-type semiconductor with work function Wm and Ws (if Wm< Ws), the photoexcited electrons in semiconductors are readily transferred to the metal with lower Fermi level, until the equilibrium of two Fermi energy levels is achieved. Accordingly, an upward band bending in the n-type semiconductor is created owing to the accumulation of excess positive charges in the semiconductor caused by the favorable electron migration. As a result, a small Schottky barrier is created due to the effective interface bending, which serves as an electron trap, thus leading to a high electron density on the cocatalysts for CO2 reduction and preventing the unexpected migration of electrons from cocatalysts back to the semiconductor. Similarly, if the work function of a p-type semiconductor is smaller than that of a metal (Ws < Wm), an accumulation layer is formed due to the gathered holes in the space charge region of p-type semiconductors. In the absence of a barrier, ohmic contact with low resistance is formed (Figure 69B), which results in the favorable transfer of photogenerated electrons and holes from an n-type or p-type semiconductor to the metal, respectively. Relatively speaking, the ohmic contact exhibits much smoother charge transfer and photocatalytic efficiency in comparison with the Schottky junction because of the absence of a barrier.1158 Unlike the Schottky junction, the plasmonic metal under light irradiation in a Schottky junction (Figure 69A) can inject the hot electrons or holes to the CB or VB of the neighboring ntype or p-type semiconductor, respectively. Herein, the Schottky barrier can obstruct the transfer of hot electrons or

4.4. Enhancing Adsorption and Activation of CO2

Besides the positive role of defects in CO2 adsorption/ activation described in section 2.4, the suitable addition of cocatalysts, such as CaO,581 Bi2O3,1159 MgO,95,1160−1163 NaOH, 1 1 6 4 1 1 6 5 Ga 2 O 3 , 1 1 6 6 , 1 1 6 8 SrO, 1 1 6 9 BaCO 3 , 1 1 7 0 MOFs, 946,965,1171,1173 LDH,1174,1175 nanocarbons,35,98,352 amine-functionalized groups, 655 polymers 559,1176 , and Na2CO31164 have been extensively employed to boost the CO2 activation/adsorption over semiconductors. On the one hand, these robust basic cocatalysts could greatly enhance the acid CO2 adsorption capacity.1163 On the other hand, either in gas phase or in aqueous solution, the adsorption of dissolved CO2 on the surface hydroxyl groups can be readily activated to the stable photoactivated species, such as monodentate bicarbonate and bidentate formate intermediates, which can further lead to the formation of CO through the decomposition of formate (as shown in Figure 70A and B).11681177 It should be noted that the hydrated CO2 molecule (CO2(aq)), is an important intermediate in the photoconversion of CO2 in liquid H2O as the electron donor, instead of HCO3−, H2CO3 and CO32− ions. Additionally, the hydroxide ion (OH−) not only serves as a hole acceptor but also keeps a dynamically stable amount of H2CO3 (the most likely form of reduced CO2 species) for further reduction.1165 In this regard, it was revealed that KOH was much better promoter than NaOH for enhancing the photocatalytic CO2 reduction over g-C3N4 because of much stronger binding of H2CO3 (1.13 eV) on BN


Chemical Reviews

Review

73A).1178 Although 2 h of treatment at 800 °C could provide some additional sites for CO2 adsorption due to the removal of more carbonate species than at 400 °C(Figure 73B), the lowcoordinated O2− and Mg2+ sites on the (111) surface, corresponding to the observed features at 1325 and 1645 cm−1 identified by adsorption of tridentate carbonate species, and the removal of hydroxyl functionality from the (111) facets could be important factors that increase CO2 adsorption (Figure 73B). Notably, this study is the first example showing the effect of different facets on the CO2 capture, which could provide a new idea for designing MgO-based cocatalysts with exposed facets for improving CO2 adsorption and its activation during photoreduction. In fact, the cocatalysts can also play the key role in accelerating the sluggish surface reaction kinetics by decreasing the CO2 reduction activation energy. For example, Gunlazuardi et al. found that the loading 3 wt % of CuO on the commercial P25 could lower its activation energy from ∼26 to 12 kJ·mol−1, suggesting that the introduced Cu species as cocatalysts are crucial for enhancing the methanol generation in CO2 photoreduction.1179 This study also demonstrates that desorption of reduction products is a rate limiting step in CO2 photoreduction.

KOH-decorated g-C3N4 than that (0.86 eV) on NaOHdecorated g-C3N4.1165 For example, it was shown that NaH2PO2 and BaCO3 as additives can significantly promote the photocatalytic CO2 reduction reaction on the CaFe2O4 powders in aqueous solutions.1170 As compared to free CO2 or CO32− ion dissolved in the solution, the adsorbed CO2 or CO32− ion on the surface of BaCO3 powder can be readily activated, thus leading to the enhanced CO2 photoreduction at the multicomponent interface of BaCO3 (solid), CaFe2O4 (solid), and liquid H2O.1170 In the gas−solid reaction systems, it was also observed that the rate of CH4 formation obeys a linear relationship with the amount of chemisorbed CO2 on the surface of a basic metal oxide/Pt/TiO2 composites (as shown in Figure 71).95 These results demonstrate that the strong

4.5. Suppressing Photocorrosion and Undesirable Reactions

In addition to the above mentioned issues, the loading a suitable cocatalyst as photostabilizer can be used to enhance the photostability of photocatalysts through suppressing the photoinduced corrosion (degradation or decomposition) in aqueous solution under illumination. Clearly, the reductive corrosion (i.e., Ag3PO4, AgX, and Cu2O) caused by photogenerated electrons could be decreased through loading metallic cocatalysts, whereas the oxidative corrosion (i.e., CdS, Cu2O, and ZnO) caused by the photogenerated holes could be suppressed via loading suitable hole-transferring cocatalysts, such as RuO2. For example, Tang’s group found that the coupling of Cu2O with graphene and RuOx could suppress the photocorrosion of Cu2O caused by photogenerated electrons and holes, respectively.1180,1181 The resulting composite photocatalysts, such as Cu2O/graphene and Cu2O/RuOx, exhibited significantly enhanced selective photoreduction of CO2 to CO due to the effectively suppressed photocorrosion. Similarly, other combinations including CdS/ RGO,98,1182 AgX/CNTs1183 and AgBr/g-C3N4/RGO (as shown in Figure 74)1184 also exhibited improved photostability and selective CO2 photoreduction due to promoted charge carrier separation. During CO2 photoreduction, the competitive two-electron hydrogen evolution reaction usually occurs in the systems. Therefore, to enhance the efficiency and selectivity of CO2 photoreduction, it is of significant importance to suppress the competitive water reduction to H2.50,1185 Interestingly, Wang and his coworkers found that Pt and Cu2O as cocatalysts could selectively promote the H2 generation and CH4 production over TiO2 nanoparticles, respectively (as shown in Figure 75A).92 Then, to effectively improve the CO2 reduction selectivity and suppress the undesirable competing H2evolution (side reaction), they prepared the ternary TiO2/Pt/ Cu2O multi-heterojunctions with a Pt@Cu2O core−shell cocatalyst by a stepwise photodeposition technique.92 The resulting cocatalysts exhibit excellent synergistic effects for the selective CO2 photoreduction with H2O vapor to CO and CH4. It is believed that the Cu2O shell has been proposed to offer

Figure 71. Promoting effects of basic metal oxides on the CO2 photoreduction activity over Pt−TiO2 photocatalysts in the presence of H2O vapor.95 Reprinted with permission from ref 95. Copyright 2013 Royal Society of Chemistry.

chemisorption ability and subsequent activation of CO2 on the basic metal oxides are crucial to enhance the photoreduction of gaseous CO2 with H2O vapor to CH4. Specifically, the excellent synergistic effect between Pt cocatalysts and the basic sites seems to be the decisive factor for improving CO2 reduction activity. More recently, to better understand the promoted effect of basic oxide overlayer on TiO2 in CO2 photoreduction, Kwon et al. thoroughly investigated via DFT calculations the CO2 adsorption and photoreduction on the (100) surfaces of TiO2 covered by a thin layer of basic, alkaline-earth metal oxides (MgO, SrO, CaO, BaO).1169 More favorable CO2 adsorption was verified in the following order MgO < CaO < SrO < BaO due to more suitable lattice parameter and adsorption energy of BaO than those of MgO (Figure 72A−C). Particularly, it was shown that the CO2 adsorption and activation on the SrO/TiO2 surface can be dramatically improved as compared to those observed on bare TiO2, whereas the dissociation of water into hydroxyl group and hydrogen is thermodynamically more favorable than intact water on the SrO/TiO2 surface, suggesting that the dissociation of water would be thermodynamically beneficial for the transformation of CO2 to CO. Additionally, the SrO half layer on the 0.5 ML SrO covered TiO2 was found to favor two important CO2 reduction steps on pure TiO2, activation of CO2 and desorption of CO (Figure 72D). Therefore, loading the MoSe2 > WSe2,1190 which is consistent with the trend of the experimental activities as measured by current densities, suggesting that WSe2 is the best transition metal dichalcogenide for CO2 electrochemical reduction in ionic liquids because of the lowest work function among these four materials.1190 However, for design of highly efficient semiconductorcocatalyst systems, both the work functions of cocatalysts and flat band potentials of semiconductors must be simultaneously considered and balanced. As compared to the semiconductorcocatalyst p−n junction mechanism,1191,1192 it is commonly accepted that electrocatalysts on semiconductors serve as superior cocatalysts to promote charge separation through collecting photogenerated electrons from semiconductors and increase the dominant reaction sites for photocatalysis.119 For noble metal cocatalysts, their Fermi levels should be much

5. DESIGN CONSIDERATIONS FOR CO2 PHOTOREDUCTION COCATALYSTS Although an effective electrocatalyst for specific reactions is generally employed as an active cocatalyst for the corresponding photocatalytic reactions, there are some essential differences between electrode electrocatalysts and cocatalysts on semiconductors for selective CO2 reduction reactions.274,275,359,1187 Obviously, the existence of external electric fields (or currents) over electrocatalysts could make the electrons readily accessible on the surface active sites for expected reactions, whereas the photoinduced internal electric fields, such as Schottky barriers, must be first constructed to achieve the transfer of photogenerated electrons from the semiconductor to cocatalysts for the desired reactions due to the formation of appropriate surface junctions.119,1188,1189 Thus, electrocatalysis and photoelectrocatalysis are much easier than the corresponding photocatalysis due to the presence of external electric fields. Specifically speaking, for semiconductor-cocatalyst composite BQ


Chemical Reviews

Review

Figure 76. Time-dependent generation of (A) H2 and (B) CH4, (C) UV-driven (λ < 400 nm) CH4 production rates (in the presence of H2) in photocatalytic CO2 reduction over bare TiO2−Pd NCs, and TiO2−PdH0.43 NCs. (D) Average carrier lifetimes (τn) obtained by transient OCVD measurements. (E) Schematic illustration for the CO2 photoreduction with gaseous H2O over TiO2−PdH0.43 NCs and TiO2−Pd NCs.109 Reprinted with permission from ref 109. Copyright 2017 Springer Nature.

recently showed that the Fermi level of earth-abundant phosphide electrocatalysts is a feasible descriptor for the photocatalytic H2-evolution activity.1193 The spectroscopic characterization and theoretical calculations confirm the transfer of photoexcited electrons from CdS to phosphide electrocatalysts, which act as active sites for driving H2 evolution reaction. More importantly, it was found that the Co2P/CdS NRs exhibited much larger H2 evolution photoactivity than CoP/CdS NRs and Ni2P/CdS NRs, owing to the higher Fermi level and the efficient Fermi-level upshifting of metallic Co2P. Clearly, for either noble metal or earth-abundant metallic cocatalysts, the Fermi level of cocatalysts should be higher than the flat band potentials of semiconductors, facilitating the electron injection from the semiconductors to cocatalysts and their necessary Fermi-level upshifting for the photocatalytic reactions. Thus, it is proposed that the higher Fermi level of cocatalysts should be necessary for improving the CO2 photoreduction activity over different semiconductors.

Figure 77. Typical processes in semiconductor-cocatalyst composite systems during the CO2 photoreduction: (1) the excitation of semiconductor, (2) the electron transfer from semiconductor to cocatalyst across the interface between them, (3) the electron transfer from Fermi level of cocatalyst to its active sites, and (4) the surface redox reactions on active sites.

larger than the flat band potentials of semiconductors, which are advantageous for the formation of Schottky junctions and preferential electron transfer from the semiconductor to metal cocatalysts. Similarly, for non-noble-metal cocatalysts, Bi et al. BR


Chemical Reviews

Review

leading to higher photoactivity for the selective photocatalytic production of CH4 and H2. Table 11 shows the work function for different cocatalysts,1194−1196 which might provide some important advice for design and fabrication of highly effective and selective composite semiconductor photocatalysts for CO2 photoreduction. As shown in Table 11, the expose of different facets of metal cocatalysts seems to be a promising approach to further enhance the photoactivity toward CO2 reduction.

Table 9. Comparison of Noble Metal and Earth-Abundant Cocatalysts cocatalysts advantages

disadvantages

design considerations

noble metal-based cocatalysts (e.g., Pt and plasmonic Au)

noble metal-free cocatalysts (e.g., Fe, Co, Ni, Mo, W)

high activity (low overpotentials) high stability high selectivity high conductivity (metallic properties) expensive

earth-abundant

interfacial coupling Fermi level location surface reactive sites selectivity ad(de)sorption properties

5.2. Electrical Conductivity of Cocatalysts

For photocatalytic applications, enhancing the conductivity of electron transport at the cocatalyst/semiconductor interface and on the surface of cocatalysts is of great importance to improve their catalytic performance. Namely, the enhancement of the intrinsic electronic conductivity of cocatalysts is an appealing approach toward design highly active and selective cocatalyst/semiconductor hybrid systems. It is well-known that metallic cocatalysts with high electronic conductivity are responsible for superior catalytic activity and selectivity due to the delocalized valence electrons. However, the earthabundant semiconducting cocatalysts are often p-type semiconductors with poor electrical conductivity and stability, restricting the efficient electron transfer from the semiconductor to p-type cocatalyst, owing to the creation of typical p−n heterojunction after the band-structure alignment under irradiation.482,1200 Similar results have also been observed for the hole cocatalysts on different n-type semiconductors during photocatalytic O2 evolution process.1201 The metallic IrOx and RuOx cocatalysts with higher electronic conductivities are prone to exhibit higher OER rates when they are loaded on BiVO4 with smaller OER overpotential due to facile and easy transfer of h+ to OER active sites, whereas the non-metallic CoOx, NiOx, and MnOx cocatalysts with poor electronic conductivity exhibit much higher OER rates when they are deposited on SnO2 and ZnO with higher OER overpotential, owing to the additionally higher driving force for hole transfer from a low-conductivity nonmetallic cocatalyst to the OER active sites.1201 Undoubtedly, the electrical conductivity of cocatalysts plays a decisive role in improving the activity of semiconductor/earth-abundant cocatalyst heterojunctions.1201 Therefore, improving electrical conductivity of both electron and hole cocatalysts should be a straightforward strategy to facilitate the effective electron separation, collection and transfer, and consequently, achieving the enhanced overall photocatalytic efficiency of the semiconductor/earth-abundant cocatalyst heterojunctions. The first strategy to increase the electrical conductivity of cocatalysts is to exploit the metallic structures for nonconductive materials. For instance, the layered MoS2 was

low activity (high overpotentials) low stability low selectivity low conductivity (semiconducting properties) interfacial coupling Fermi/CB level electrical conductivity electrocatalytic activity stability ad(de)sorption properties

Wang’s group compared the accelerated photocatalytic reduction performance of CO2 to CH4 over TiO2 doped with various noble metals, such as Pt, Rh, Pd, Ag, and Au.1160 It was found that the photocatalytic CH4 generation rates increase according to the following order: Ag < Au < Rh < Pd < Pt (Table 10). This sequence is very similar to that of the work function of different metal cocatalysts, suggesting that the higher metal work functions are favorable for extracting photogenerated electrons from TiO2.1160 Recently, it was considered that nitrogen-containing polyaniline (PANI) plays bifunctional role in boosting the CO2 photoreduction, owing to the both enhanced electron transfer and increased chemisorption of CO2.1176 Namely, the introduction of a proper amount of PANI would significantly boost the generation rates of CH4, CO, and H2 from CO2 photoreduction over the catalyst (Figure 78A and B). However, H2 was a major reduction product without CO2. The Mott−Schottky type measurements indicate that the switching atmosphere from N2 to CO2 has no effect on the Fermi level of TiO2 (−0.18 V vs RHE), but can obviously increase the PANI Fermi level from −0.42 to −0.15 V (vs RHE) (Figure 78C−F). Thus, the observed increase in the Fermi level of PANI makes the electron transfer from TiO2 to PANI more feasible in CO2 atmosphere (Figure 78G). This study demonstrate that the increased Fermi level of PANI cocatalyst improves the chargecarrier separation in the PANI-containing photocatalyst, thus

Table 10. Relationships between the Photocatalytic Activity toward CO2 Reduction over Noble Metal-Modified TiO2 and the Work Function of Noble Metals1160a formation rate (μmol g−1 h−1)

a

photocatalyst

CO

CH4

H2

R (electron) (μmol g−1 h−1)

selectivity for CO2 reduction (%)

work function (eV)

TiO2 Pt−TiO2 Pd−TiO2 Rh−TiO2 Au−TiO2 Ag−TiO2

1.2 1.1 1.1 0.62 1.5 1.7

0.38 5.2 4.3 3.5 3.1 2.1

2.1 33 25 18 20 16

10 110 85 66 67 51

10 40 42 45 41 39

5.65 5.12 4.98 5.10 4.26

Reprinted with permission from ref 1160. Copyright 2014 American Chemical Society. BS


Chemical Reviews

Review

Figure 78. Photoproduction rates of CH4, CO, and H2 under CO2 and N2 atmospheres: (A) 0.85% PANI−TiO2 and TiO2 and (B) Pt−0.85% PANI−TiO2 and Pt−TiO2. Mott−Schottky plots for TiO2 (C and D) and PANI (E and F) under N2 (C and E) and CO2 (D and F) atmospheres. (G) Proposed role of PANI in boosting the CO2 photoreduction.1176 Reprinted with permission from ref 1176. Copyright 2015 Royal Society of Chemistry.

Another simple method to improve electrical conductivity of graphene is the direct replacement of RGO by solventexfoliated graphene (SEG) with high conductivity.1221−1224 For example, Hersam and coworkers demonstrated that the electrical conductivity of SEG with smaller defect density is much higher than that of RGO.86 The resulting novel SEGTiO2 nanocomposites with low graphene defect densities are shown to possess higher photocatalytic activity for CO2 reduction to CH4 than those RGO/TiO2 nanocomposites (as shown in Figure 79A). It is believed that the superior electrical mobility of SEG with lower density of defects allows for more effective diffusion of photoexcited electrons to the adsorbed CO2 reactants via longer mean free paths (depicted as the yellow pathway in Figure 79B), thus facilitating the enhancement of CO2 photoreduction. Similarly, Xu’s group further confirmed the role of high-conductivity SEG in boosting visible-light photoactivity of TiO2 composites towards aerobic oxidation of alcohols in a liquid phase, in comparison to RGO.1221,1225,1226 Notably, the residual surfactant (Pluronic F127) stabilized zero-band gap SEG could show a much smaller increase in the visible-light efficiency of TiO2 for NOx removal than the semiconducting rGO.1227 Thus, it was believed that the balance between the high-conductivity zero-band gap SEG and the semiconducting rGO should be carefully optimized to substantially boost the photocatalytic activity in the practical applications. However, if considering the CO2 adsorption/ activation and the restacking of single-layer high-conductivity graphene, the synergistically boosted charge-carrier separation and transport and increased adsorption capacity should be critically important for constructing the high-efficiency CO2 photoreduction photocatalysts.1228 In this regard, the 3D porous graphene with the restacking-inhibited architectural morphology should be very appealing for the photoreduction of CO2.

shown to be an attractive H2-production cocatalyst for photocatalytic H2 evolution because of its low eelctrocatalytic H2-evolution overpotentials.524 However, semiconducting MoS2 (trigonal prismatic 2H phase) exhibits poor electrical conductivity, typically limiting the charge transport from the inert basal surface to the active sites located along the edges of 2D MoS2 layers.1202 Recently, the metallic 1T phase of MoS2 nanosheets with both high conductivity and density of active sites turned out to be better H2-production cocatalyst for photocatalytic applications than 2H phase of MoS2 nanosheets or semiconducting MoS2, owing to the increased number of basal plane active sites and accelerated charge transfer kinetics.1203−1207 However, there are only a few reports on the investigation of metallic 1T phase MoS2 or WS2 nanosheets in photocatalytic CO2 reduction, despite significant advances in the photocatalytic H2 evolution over these metallic nanosheets.1204,1208−1213 At this point, various kinds of metallic nanosheets (e.g., MoS2, WS2, CoS2, M2, and WSe2) with high conductivity and density of active sites seem to be the promising cocatalyst candidates for CO 2 photoreduction.1214−1219 The other strategy to increase the electrical conductivity of cocatalysts is to reduce structural defects in the conductive materials. It is well known that a larger number of structural defects in typical RGO-based cocatalysts may effectively disrupt the 2D π-conjugation of electronic structure and reduce the electrical conductivity of RGO in comparison to the defect-free, single-layer, non-oxygenated graphene, thus significantly hindering the photoexcited electron transfer and separation. It was shown that the improved electrical conductivity of RGO can efficiently promote the photocatalytic H2-evolution activities of the RGO/ZnIn2S4 nanocomposites through enhancing the reduction degree of RGO.1220 Therefore, various strategies to reduce defects and increase the electrical conductivity of RGO have been utilized in various applications. BT


Chemical Reviews

Review

Table 11. Summary of Work Function Values for Potential Cocatalysts1194,1196a

a

element

φ (eV)

C SWCNT DWCNT MWCNT SLG BLG Co Ni (100) (110) (111) Ge (111) Se Pd (111) Ir (110) (111) (100) (210) Pt (111) (110) (331) (320) Au (100) (110) (111) Be B Al (100) (110) (111) Si (100) (111)

5.0 5.051197 4.851198 4.951197 4.5−4.81199 4.65−4.751199 5.0 5.15 5.22 5.04 5.35 5.0 4.80 5.9 5.12 5.6 5.27 5.42 5.76 5.67 5.00 5.65 5.7 5.84 5.12 5.22 5.1 5.47 5.37 5.31 4.98 4.45 4.28 4.41 4.06 4,24 4.85n 4.91p 4.60p

element Ti V Cr Mn Fe (100) (111)

Cu (100) (110) (111) (112) Zn (0001) Ga Zr Rh In Sn Sb (amorph) (100) Re (1011) Os Nb (001) (110) (111) (112) (113) (116) (310) Mo (100) (110) (111)

φ (eV)

element

φ (eV)

4.33 4.3 4.5 4.1 4.5 4.67 4.81α 4.70α 4.62β 4.68γ 4.65 4.59 4.48 4.98 4.53 4.33 4.9 4.3 4.05 4.98 4.12 4.42 4.55 4.70 4.96 5.75 4.83 4.3 4.02 4.87 4.36 4.63 4.29 3.95 4.18 4.6 4.53 4.95 4.55

(112) (114) (332) Ru Ag (100) (110) (111) Cd Te Ta (100) (110) (111) W (100) (110) (111) (112) (113) (116) Hg Pb Bi Tc Mg Sc As(111) Y La Nd Gd Tb Lu Li Na K Ca Rb

4.36 4.50 4.55 4.71 4.26 4.64 4.52 4.74 4.22 4.95 4.25 4.15 4.80 4.00 4.55 4.63 5.25 4.47 5.01 4.18 4.30 4.49 4.25 4.22 4.88 3.66 3.5 3.75 3.1 3.5 3.2 3.1 3.0 3.3 2.93 2.75 2.30 2.9 2.16

Reprinted with permission from ref 1194. Copyright 1977 AIP Publishing.

the overall efficiency of photocatalysts. The poor interfacial adhesion and inadequate coupling could prevent the efficient charge transfer from photoexcited semiconductors to cocatalyst, thus leading to the limited cocatalyst utilization and insufficient improvement in the photoactivity of CO2 reduction. In other words, the high-quality semiconductor/cocatalyst interface should be advantageous for maximizing the charge transfer and separation efficiency. Thus, precise optimization and control of the key interfacial parameters offer a number of versatile strategies for achieving the efficient interfacial charge transfer and the improved overall surface photoreaction efficiency. Commonly, a random loading of cocatalysts on a portion of the surface of a semiconductor is disadvantageous for optimizing their properties to improve the photoactivity of heterojunctions. In contrast, the intimate semiconductor/ cocatalyst interface plays the dominant role in prolonging the electron−hole lifetime in the semiconductor and enhancing photoactivity of composite photocatalysts.362,482,1200 Thus, the research in this area has been directed toward reducing the

In addition, it is noteworthy that the combination of 2D dimensional confinement and defect engineering could be employed to enhance the electronic conductivity of semiconducting materials. For example, the 2D ultrathin nanosheets, including Bi2WO6,1229 SnNb2O6,765 Co3O4,1108 iron− nickel sulfide,1217 BiOCl,824 metal−organic frameworks,1230 and layered hydroxides,1231,1232 with remarkably enhanced electronic conductivity have been fabricated for different catalytic applications. In future, it is expected that these ultrathin nanosheet-based semiconductors and cocatalysts with superior electronic conductivity could be extensively applied in the field of CO2 photoreduction. 5.3. Interfacial Coupling of Semiconductor/Cocatalyst

In general, the semiconductor/cocatalyst interface is located where the charge transfer and separation occur. Both the activity of cocatalysts and the spatial charge separation in semiconductors are highly dependent on the charge-transfer efficiency across the cocatalyst/semiconductor interface. Absolutely, the interfacial coupling is the key factor to improve BU


Chemical Reviews

Review

interactions. This kind of vdW heterostructures with many unique electrical and optical properties seem to be promising for photocatalysis. Additionally, increasing the stiffness of heterojunction interfaces is advantageous for the charge separation and photocatalytic performance. For instance, to improve the intimate coupling between rGO and g-C3N4 for efficient transport of charge across the interface, Ong et al. fabricated the rGO-protonated g-C3N4 (pCN, protonated by HCl) 2D−2D heterojunction photocatalyst at relatively low temperatures by an electrostatic self-assembly strategy, followed by reduction with NaBH4 (Figure 80A).813 The optimized 15 wt % rGO/pCN (15rGO/pCN) heterojunction photocatalyst exhibited the largest CH4 yield of 13.93 μmol gcatalyst−1 with a quantum yield of 0.560% after 10 h of illumination, which was 1.7 and 5.4 times higher than those obtained for 15rGO/CN and pCN, respectively (Figure 80B). The results clearly show that the intimate 2D−2D interfacial coupling between rGO and pCN could be fabricated through the electrostatic self-assembly, which is advantageous for charge transfer across the rGO/pCN heterojunction and suppresses electron−hole recombination, thus resulting in the superior photoactivity toward reduction of CO2 to CH4. In addition to the interfacial electrostatic self-assembly strategy, the intimate heterojunctions with strongly coupled interfaces can be also fabricated through strong chemical (covalent) bonding or using an appropriate linker.176,1256−1260 More importantly, the covalent bonding could also reduce the band gap via favorable shifting the CB or VB edge potentials, enhance electrical conductivity and CO2 activation, all of which are helpful for more effective charge separation and visible-light-driven CO2 photoreduction.176,641,813,1184,1257 At this point, the formation of 2D−2D interface with strong covalent bonding seems to be an appealing strategy to boost the photoactivity of composite photocatalysts.

Figure 79. (A) Comparison of UV and visible CO2 photoreduction to methane over SEG/P25 and SRGO/P25 heterojunctions. (B) Proposed mechanism for CO2 photoreduction over graphene−TiO2 heterojunctions. The gray, white, red, blue, and green colors represent the carbon, hydrogen, oxygen, titanium, and hole, respectively. Under illumination, the photoexcited electrons and holes are confined in the graphene nanoplatelets and TiO2, respectively.86 Reprinted with permission from ref 86. Copyright 2011 American Chemical Society.

amount of cocatalysts and improving the interfacial coupling between cocatalyst and semiconductor. So far, several design strategies have been examined toward enhancing interfacial coupling and interactions between cocatalyst and semiconductor (such as introducing interfacial mediators, enhancing contact area and bonding strength) to rationally design and optimize the semiconductor/cocatalyst interface for achieving high-performance semiconductor/cocatalyst heterojunctions, which are presented below.177 The most straightforward strategy is to introduce interfacial mediators as conductive bridges and electron reservoirs between semiconductors and cocatalysts. The interfacial mediators not only significantly reduce the density of interfacial defects and enhance the transport of the photogenerated electrons from semiconductor to cocatalyst through strengthening the interfacial contact between them, but also greatly improve adsorption and activation of CO2 on the composite photocatalysts. Previously, various interfacial mediators, such as metal ions,1233 phosphate anions,1234 metallic nanocrystals,1200,1235−1237 nanocarbons,479,482,1238−1240 and semiconductors1241,1242 have been successfully employed to enhance photocatalysis over the semiconductor/cocatalyst heterojunction. Notably, the metallic Ni mediators in Ni/NiO core/shell structures undergo deactivation because of the continuous diffusion of Ni2+ from core into solution and the formation of an inactive hollow void/NiO shell.1243 Thus, the stability of interfacial mediators should be rationally manipulated. Apart from introduction of interfacial mediators, other strategies, such as enhancing interfacial contact area have attracted a significant attention in recent years. Clearly, the interfacial contact area between the semiconductor and cocatalyst could be obviously increased via their 2D−2D coupling. The application of 2D−2D heterojunctions in CO2 photoreduction is presented in section 6.4. Fabrication of the 2D van der Waals (vdW) heterostructures1244−1254 and Janus bilayer junctions1255 with 2D−2D interfaces is simple and involves stacking of different nanosheets via weak van der Waal

5.4. Surface Reactive Sites and Location of Cocatalysts

In general, it is widely recognized that the surface loaded cocatalysts are responsible for the oxidation/reduction reactions. Exactly, the reactive sites of a heterogeneous cocatalyst commonly consist of the thermodynamically unstable low-coordinated, low-population and high-energy surface atoms on high-index facets, kinks, terraces, edges, steps, corners, vertices, vacancies and holes.257,1261,1262 Furthermore, it is known that the adsorption/activation of CO2 and H2O and subsequent CO2 photoreduction activity/selectivity are significantly dependent on the surface chemical composition, exposed facets, specific phases, and micro/nanostructures (i.e., size and shape) of a cocatalyst.1263 To this end, the surface engineering of cocatalysts is the fundamental way to enhance the surface activation, adsorption, and photoreduction capacity for CO2 and H2O species.257 Thus, the CO2 photoreduction activity/selectivity could be improved through rational regulation of appropriate surface parameters (e.g., the composition, facets, phases, surface state, defects, vacancies, pores, and band bending) of cocatalysts, due to the increased number of surface reactive sites on cocatalysts.1262,1264 The dangling bonds in the surface defects or vacancies of cocatalysts are capable of capturing both charge carriers, CO2, H2O, and key intermediates, thus affecting catalytic activity and selectivity.1265−1268 For example, nitrogen-associated defects in inert nanocarbons could create an electrochemically active cocatalyst for different reactions without destroying their electric conductivities.1269,1271 The improvement in electroBV


Chemical Reviews

Review

Figure 80. (A) Schematic mechanism for fabricating rGO/pCN heterojunction via an electrostatic self-assembly strategy followed by reduction with NaBH4. (B) Total yield for CH4 production over rGO, pure g-C3N4, pCN, 15rGO/pCN, and 15rGO/CN photocatalysts after 10 h of illumination.813 Reprinted with permission from ref 813. Copyright 2015 Elsevier.

reaction.1190 Additionally, the exposed high-index facets and improved surface composition1112,1272−1279 of various metal electrocatalysts have also been confirmed to exhibit improved activity toward selective electrocatalytic CO 2 reduction.1076,1080,1113,1280−1282 For example, Xiong’s group demonstrated that the exposed (111) facets in Pd nanotetrahedrons

catalytic activity mostly stems from the carbon atoms with Lewis basicity next to pyridinic N, which have been proven to be the active sites for ORR and CO2 adsorption.1270 It was also found that the metal edges of transition metal dichalcogenides likely act as the reactive sites for electrocatalytic reduction of CO2 because of the high CO coverage during catalytic BW


Chemical Reviews

Review

Table 12. Photoreduction Selectivity of CO2 to H2O over C3N4-Based Catalysts1283a product rate (μmol gcat−1 h−1) catalyst 1 2 3 4 5 6 7 8 9 10c 11c

none bulk C3N4 C3N4 NSs C3N4−Pd NCs C3N4−Pd NCs C3N4−Pd NCs C3N4−Pd NTs C3N4−Pd NTs C3N4−Pd NTs C3N4−Pd NCs C3N4−Pd NTs

Pd loading (wt %)

2.9 5.7 11.9 3.1 5.8 11.6 5.7 5.8

Pd average size (nm)

4.0 4.5 5.9 4.2 4.9 5.8 4.5 4.9

H2

CO

b

n.d. 0.1 0.7 3.3 4.9 5.6 15.4 20.3 14.9 n.d. n.d.

n.d. 1.7 2.3 25.6 34.1 39.8 8.2 9.7 6.5 22.2 7.9

C2H5OH (×10−1)

CH4 (×10−1)

n.d.

n.d. n.d. n.d. n.d. n.d. n.d.

2.3 4.0 5.7 6.7 7.4 19.3 21.8 17.2 n.d. n.d.

selectivity for CO2 reduction (%) 46.5 57.4 20.8 20.7 20.1 76.9 78.1 80.0

0.7 2.8 1.8 n.d. n.d.

a

Reprinted with permission from ref 1283. Copyright 2014 Royal Society of Chemistry. Conditions: CO2 pressure, 0.15 MPa; photocatalysts, 10 mg; irradiation time, 4 h; H2O, 3.0 mL. bNot detected. cIn an Ar atmosphere. The nanosheets, nanotetrahedrons and nanocubes are denoted as NSs, NTs and NCs, respectively. The generated O2 was detected during the reactions.

Table 13. CO2 Photoreduction over ALa4Ti4O15 (A = Ca, Sr, and Ba)/Cocatalyst Heterojunctions85a activity (μmol h−1) photocatalyst

cocatalyst (wt %)

BaLa4Ti4O15 BaLa4Ti4O15 BaLa4Ti4O15 BaLa4Ti4O15 BaLa4Ti4O15 BaLa4Ti4O15 CaLa4Ti4O15 CaLa4Ti4O15 SrLa4Ti4O15 SrLa4Ti4O15 BaLa4Ti4O15 BaLa4Ti4O15 BaLa4Ti4O15 BaLa4Ti4O15 BaLa4Ti4O15 BaLa4Ti4O15 BaLa4Ti4O15 BaLa4Ti4O15 SrLa4Ti4O15 CaLa4Ti4O15

none NiOxb (0.5) Ru (0.5) Cu (0.5) Au (0.5) Ag (1.0) none Ag (1.0) none Ag (1.0) Ag (1.0) Ag (1.0) Ag (0.5) Ag (1.0) Ag (2.0) Ag (3.0) Ag (5.0) Ag (1.0) Ag (1.0) Ag (1.0)

loading method impregnation photodeposition photodeposition photodeposition photodeposition photodeposition photodeposition impregnationd impregnationd + H2 red.e liquid-phase reduction liquid-phase reduction liquid-phase reduction liquid-phase reduction liquid-phase reduction liquid-phase reduction liquid-phase reduction liquid-phase reduction

H2

O2

CO

HCOOH

5.3 58 84 96 110 10c 1.3 5.6 0.8 2.7 8.2 5.6 4.5 5.6 10 9.7 4.8 20f 4.8 3.2

2.4 29 41 45 51 7.0c 0.6 2.1 0.5 1.8 5.7 8.7 6.8 12 16 14 6.6 11f 5.8 6.6

0 0.02 0 0.6 0 4.3c 0.07 2.3 0.06 1.8 5.2 8.9 11 19 22 19 12 0f 7.1 9.3

0 0 0 0 0 0.3c 0 1.3 0 0.5 0.2 0.3 0.03 0.4 0.7 0.1 0.02 0f 0.8 0.4

Reprinted with permission from ref 85. Copyright 2011 American Chemical Society. Reaction conditions: water, 360 mL; catalyst, 0.3 g; CO2 flow system (15 mL min−1); an inner irradiation quartz cell with a 400 W high-pressure mercury lamp. bPretreatment: Reduced and subsequently oxidized at 673 and 473 K after impregnation (543 K for 1 h). cInitial activity. d723 K for 1 h. e473 K for 2 h. fAr flow. a

tion.106,555,560,588,670,1285−1287 However, in some cases, the CO2 photoreduction activity over Ag cocatalyst-loaded BaLa4Ti4O15 by the in situ photodeposition method is much smaller than those obtained by other loading methods, such as impregnation, impregnation and H2 reduction, and liquid-phase reduction (Table 13).85 It is believed that the liquid-phase reduction induced Ag cocatalysts show fine particles smaller than 10 nm on the edge of the BaLa4Ti4O15 plates and more efficient CO2 reduction, whereas the basal plane as oxidation site mainly drives O2 evolution (Figure 81).85 Accordingly, to maximize the CO2 reduction performance over photodeposited cocatalysts, the conditions of photodeposition, such as the presence or absence of (organic) sacrificial agents and an air/ inert atmosphere, applied pH, type and concentration of metal precursors, and applied temperature should be carefully

(NTs) favor the reduction of CO2, while Pd nanocubes (NCs) with Pd(100) facets facilitate the H2 generation from H2O splitting (Table 12).1283 However, studies about increasing the amount of surface reactive sites of cocatalysts by different strategies are still relatively limited. Furthermore, the suitable location of cocatalysts plays an important role in achieving the improved electrocatalytic CO2 reduction efficiency. Specifically, the loading of CO2 reduction cocatalysts at the exit position of photogenerated electrons (or the reduction sites) may shorten the transfer distance from semiconductor to cocatalysts, thus favoring the enhancement of photoactivity for CO2 reduction.1284 To this end, the in-situ photodeposition of various cocatalysts, including Pt, Ag, Au and Cu oxide cluster, especially for the structure-directed photodeposition, should be an ultimately promising approach to achieve high-efficiency CO2-photoreducBX


Chemical Reviews

Review

Table 14. Photoreduction Selectivity of CO2 to H2O over Cocatalyst Loaded KTaO3a product rate (ppm gcat−1 h−1) cocatalyst none Pt Ag

amount loaded (wt %) n/a 0.5 0.01

H2

CO

O2

1323.00 3780.92 1134.38

61.98 0.00 152.62

501.87 2038.80 499.98

a Reprinted with permission from ref 822. Copyright 2014 Royal Society of Chemistry.

and the semiconductor or cocatalysts could favor the further reduction of CO to CH3OH, CH4, and other products.642 More recently, Yu’s group further demonstrated the significant effect of Pd cocatalyst facets on the selective photoreduction of CO2 to CH3OH over graphitic carbon nitride (g-C3N4).1300 Cubic and tetrahedral Pd nanoparticles with exposed (100) and (111) facets were ex-situ deposited onto the surface of g-C3N4 via electrostatic assembly, respectively. The resulting T-CN exhibited the highest CH3OH-production rate (3.17 μmol h−1 g−1), which was 1.42 times larger than that on the C−CN hybrid photocatalyst, confirming a strong facet-dependent CO2 photoreduction over Pd cocatalyst deposited on g-C3N4 (Figure 82A). The in-situ FTIR results indicate that the intermediate products, such as HCOOH and HCHO, CH4 and CH3OH are involved in multi-step CO2 photoreduction process (Figure 82B). Furthermore, the calculated adsorption energies and the deformation energies revealed that CO2 can be more strongly adsorbed and activated at the bridge and the top1 positions on the Pd (111) surface, in comparison with those positions on the Pd (100) surface (Figure 82C and D). To reveal the effect of product desorption from the active sites on the photocatalytic CO2 reduction, the adsorption energies of CH3OH and CH4 molecules on different facets were also investigated. The results further confirm that the Pd (111) surface is more favorable for desorption of CH3OH molecule than the Pd (100) surface, despite the similar probability for desorption of CH4 molecule from two facets (Figure 82E and F). Hence, as compared to the Pd (100) surface, the Pd (111) surface on g-C3N4 acts as an electron sink that can more preferably capture photoexcited electrons from the CB of gC3N4 through such metal−semiconductor heterojunction, and is more beneficial for CO2 adsorption and CH3OH desorption, thus achieving the more efficient CO2 photoreduction. The study highlights the effect of cocatalyst facets on CO2 photoreduction. More importantly, the comprehensive investigation of the adsorption and deformation of CO2, as well as desorption of products offers a new strategy to rationally design and optimize composite CO2 photoreduction systems. Thus, to maximize the selective CO2 photoreduction, the ad(de)sorption and activation ability of CO2, H2O, and key intermediates on cocatalysts should be carefully optimized and improved. However, the adsorption/activation ability of H2O has been rarely investigated, which is the main oxidant and at the same time essential for the first step of CO2 activation.1301 Previously, it was shown that the surface groups and pore structures of adsorbents have significant effect on adsorption of water vapor.1302−1306 In this regard, the relationships between water vapor adsorption and the surface groups and pore structures of adsorbents should be carefully investigated in future studies.

Figure 81. Mechanism of photocatalytic CO2 reduction over BaLa4Ti4O15 with Ag cocatalysts decorated by different methods.85 Reprinted with permission from ref 85. Copyright 2011 American Chemical Society.

optimized and investigated to obtain the expected particle size distribution, oxidation states of metal atoms. 5.5. Stability and Ad(De)sorption Ability of Cocatalysts

In addition to the above mentioned design factors, the longterm stability of cocatalysts should be considered for rational fabrication of highly effective CO2 photoreduction photocatalysts for practical applications. Recently, graphite-like carbons, doped carbons, or graphene layers, have been coated on the surface of various electrocatalysts to significantly improve their stabilities for H2 evolution.1288−1296 Although the carbon-decorated semiconductors with improved photostability have been widely studied,797,1297,1298 there are limited reports on the stability improvement of cocatalysts through coating nanocarbon layers with suitable thickness. Therefore, it is interesting that the carbon-coated cocatalysts with high stability can be applied for photoreduction of CO2. The coated carbon layers could play the multifunctional role in improving CO2 photoreduction, which includes acceleration of the charge separation in semiconductors, increased amount of the active sites and higher stability of cocatalysts, enhanced CO 2 adsorption and activation, enhanced visible-light absorption and photothermal effects. Besides carbon layers, the suitable passivation layer could be also used to enhance the stability of cocatalysts, which deserves more attention. Additionally, the ad(de)sorption and activation ability of CO2, H2O, and key intermediates on cocatalysts should be also comprehensively considered, since these factors could substantially affect the overall CO2 photoreduction efficiency. For example, during the photocatalytic CO2 reduction process, the loading of Ag as a cocatalyst onto KTaO3 nanoflakes could significantly increase the selective formation rate of CO and decrease the rate of competitive H2 formation, whereas the Pt cocatalyst on KTaO3 catalyst decrease the formation of CO (Table 14).822 Previously, the studies on electrochemical reduction of CO2 have demonstrated that the poisoning effect of chemisorbed CO and too tight binding of CO with Pt lead to the small selectivity of Pt cocatalyst toward CO formation as compared with those observed on Ag and Au cocatalysts.49,703,1299 Similarly, the strong interaction between the CO intermediate BY


Chemical Reviews

Review

Figure 82. (A) Production rates of CH4 and CH3OH over CN, CN1, C−CN, and T−CN samples. (B) In-situ FTIR spectra over TACN sample. Optimized geometry of structures for CO2 adsorption on Pd (100) facets and Pd (111) facets at (C) bridge position and (D) top1 position, (E) CH3OH adsorption, and (F) CH4 adsorption on Pd (100) facets (bridge position) and Pd (111) facets (top1 position). (G) Schematic illustration of the mechanism for enhanced CO2 reduction over Pd-hybrids.1300 Reprinted with permission from ref 1300. Copyright 2017 Elsevier.

dimension,699 facets, kinks, edges, nanopores1308, and grain boundaries), bimetallic or binary nanostructures (e.g., strain effects,1309 electronic effects, and bifunctional effects), electrolyte properties (e.g., strong interactions of promoters, ligands, advanced electrolyte molecules with proper pH), and engineering of three-dimensional active sites at interfaces and in confined structures, could be also employed to tune adsorption energies of adsorbates on catalysts and create the favorable proton-coupled electron transfer pathways, thus enhancing the electrocatalytic activity of catalysts towards highly selective CO2 reduction (Figure 84).1310,1311 Besides these common principles, the interfacial coupling between semiconductors and cocatalysts is also crucial for improving the overall activity toward selective CO2 photoreduction. Here, some typical

6. MODIFICATION STRATEGIES OF CO2-PHOTOREDUCTION COCATALYSTS Improving properties of cocatalysts is beneficial for the bondmaking and bond-breaking reactions at the cocatalyst− semiconductor−electrolyte interface, which plays a key role in tuning their efficiency and selectivity towards CO2 reduction. So far, there are many available strategies to further improve the photocatalytic activity and selectivity of cocatalysts for photoreduction of CO2. Recently, Jaramillo and his coworkers summarized two typical strategies to improve the activity (or reaction rate) of electrocatalyst systems by increasing the number of active sites and/or the intrinsic activity of each active site (Figure 83).1307 Additionally, the different design strategies, including structural features (e.g., low-coordinated sites, BZ


Chemical Reviews

Review

Figure 83. Schematic illustration of various modification strategies of CO2 photoreduction cocatalysts for increasing the number of active sites and/ or the intrinsic activity of each active site.1307 Reprinted with permission from ref 1307. Copyright 2017 Science.

Figure 84. Underlying mechanisms for tuning the activity and selectivity of nanostructured catalysts towards CO2 electroreduction through the different design strategies.1311 Reprinted with permission from ref 1311. Copyright 2016 Springer Nature.

undesirable HER, thus resulting in the decreased activity and selectivity for CO2 photoreduction. Therefore, to suppress the surface back reactions, the rational design of different cocatalyst nanostructures is of great importance for selective CO2 photoreduction. It is known that the reduction of the particle size of metal electrocatalysts could result in improving the structure sensitivity during CO2 electroreduction and enhancing the Faradaic efficiency and current density.1058,1312,1313 For example, the significantly enhanced CO2 electroreduction activity could be observed for Au nanoparticles below 5 nm (Figure 85A), indicating the size-dependent properties. It is believed that the increase in low-coordinated sites on the

modification strategies available for designing efficient cocatalysts for selective CO2 photoreduction with water, such as controlling morphology and composition of cocatalysts, exploiting edge sites of cocatalysts for CO2 photoreduction, improving interfacial coupling between cocatalysts and semiconductors and loading dual cocatalysts on semiconductors, are thoroughly discussed in this section. Also, a special emphasis is given to the mechanism of these modification strategies assuring highly active and selective CO2 photoreduction. 6.1. Fabricating Nanostructured Cocatalysts

6.1.1. Optimizing the Size of Nanoparticles/Nanoclusters. Commonly, cocatalysts could also promote an CA


Chemical Reviews

Review

Figure 85. (A) Au NP size dependent CO2-electroreduction current densities on the micelle-synthesized Au nanoparticles supported on glassy carbon at E = −1.2 V vs RHE. (B) Au NP size dependent H2/CO product ratio at E = −1.2 V (vs RHE).1313 Reprinted with permission from ref 1313. Copyright 2014 American Chemical Society.

facilitate the competing HER. The density functional theory (DFT) calculations for Pt(111) with more terrace sites and Pt55 with more low-coordinated sites confirmed that Pt(111) exhibits much higher catalytic activity in the selective CH4 production than Pt55 because of its obvious lower energy barrier (0.74 eV) in the rate limiting steps (the hydrogenation of *CO and *COH) than latter (0.96 eV) (Figure 87B). Moreover, CO temperature-programmed desorption experiment (COTPD) on the fully and partially CO-covered 1.8PHTSO indicates the importance of separated terrace sites and low-coordinated sites in promoting CO2 photoreduction and HER, respectively (Figure 87C and D). As a result, the CO-1.8PHTSO and 1.8PHTSO show the CH4 selectivity of 62.9% and 39.1% (Figure 87E), respectively, clearly suggesting that the partial coverage of 1.8PHTSO with CO could suppress effectively the competitive HER, and promote the production yield of CH4. This work may provide an insight into the key roles of platinum’s size effect in semiconductor-based CO2 photoreduction. In another case, it was demonstrated that the cubic copper surface exhibits greatly improved selectivity for ethylene formation over methane via electrocatalytic CO2 reduction, implying that it is favorable for the C−C coupling and further generation of multicarbon products instead of methane formation through a complete reduction of a single carbon.1316 Accordingly, in the practical applications, the particle size and morphology of cocatalysts should be carefully controlled and optimized to achieve the best activity and selectivity for selective CO2 photoreduction. 6.1.2. Exploring 2D Ultrathin Nanosheets. Generally, the coordinatively unsaturated surface atoms are recognized as the active sites in heterogeneous catalysis. However, there is a challenge to tune the selectivity of nanoparticles because of the coexistence of the multiple active sites, such as low-index facets, edge sites, and corner sites. Fortunately, benefiting from the atomic thickness of a few nanometers, the 2D ultrathin nanosheets exhibit many advantages, including high CO2 adsorption capacity owing to the high specific surface area and unsaturated surface atoms, the remarkably enhanced intrinsic electronic conductivity with more delocalized electrons because of the dimensional confinement, the reduced reaction barriers for CO2 reduction via stabilizing a specific reaction intermediate, and rich active sites and facet effects for selective CO2 reduction because of the exposed specific facets.565,692 More importantly, the local atomic and electronic structures of atomically thin 2D solids at the atomic level could be successfully tailored by different surface modification strategies, such as surface molecular functionalization, surface heteroatom

surface of smaller nanoparticles with weaker COOH* binding leads to better selectivity for H2 evolution than CO2 reduction to CO under high H* coverage conditions (Figure 85B).1313 Similarly, tuning the particle size and morphology of cocatalysts is also one of the most viable options for achieving the optimum photocatalytic reduction of CO2. Typically, the size effect of Pt cocatalyst NPs has been well investigated during CO2 photoreduction.61,1160,1314,1315 For example, it should be pointed that the particle size of Pt nanoparticles has a great influence on the photocatalytic performance. Biswas and coworkers have demonstrated that the Pt nanoclusters deposited on TiO2 nanostructured films with a mean size of 1 nm could achieve the highest photocatalytic CH4 production via CO2 reduction (1361 μmol g−1 h−1, as displayed in Figure 86A).61 It

Figure 86. Size effect of Pt nanoclusters on TiO2 nanofilms on the CH4 formation rate during CO2 photoreduction and the proposed energy levels.61 Reprinted with permission from ref 61. Copyright 2012 American Chemical Society.

is shown that the Pt clusters with size smaller than 1 nm might exhibit much higher Fermi level than that of TiO2, which cannot create the favorable Schottky barrier, thus leading to the rapid decrease in activity (as shown in Figure 86B).61 More recently, Xing and his coworkers further demonstrated the Pt size-dependent activity and selectivity of CO2 photoreduction over various Pt NPs supported on hierarchically ordered TiO2− SiO2 porous materials (HTSO).1314 It was found that the smaller size of Pt NPs with greater metal−semiconductor interfacial area could exhibit higher charge transfer efficiency, and both the CO2 photoreduction and HER activity, but lower selectivity toward CH4 over H2 because of the lower fraction of terrace sites (Figure 87A and Table 15). Based on the experimental results and theoretical calculations, it was revealed that the terrace sites of Pt NPs could serve as the active sites for methane generation, whereas the low-coordinated sites could CB


Chemical Reviews

Review

Figure 87. (A) Surface site (Pt NPs)-dependent selectivity for CH4 in CO2 photoreduction with varying size of Pt NPs in xPHTSO (x = 1.8, 3.4, 4.3, and 7.0). (B) Free energy diagrams for selective CH4 production from CO2 reduction according to the thermochemical model on Pt(111) surface and Pt55. (C) Scheme illustrating the fabrication of the partially CO-modified 1.8PHTSO. (D) CO-TPD results for fully and partially CO-covered 1.8PHTSO. (E) Comparison of activity and selectivity for CO2 photoreduction on 1.8PHTSO and CO-1.8PHTSO.1314 Reprinted with permission from ref 1314. Copyright 2018 Springer Nature.

respectively (illustrated in Figure 88A).1319 The atomic force microscopy images exhibit the average sheet thickness of 0.84 nm, which is consistent with 0.82 nm thickness of a four-atomthick Co slab in the (001) direction, confirming the four-atom layer thickness of the partially oxidized Co sheets (Figure 88B and C). The resulting electrode of partially oxidized Co fouratom-thick layers shows the largest current density of 10.59 mA cm−2 and Faradaic efficiency of 90.1% at −0.85 V (vs SCE) (Figure 88D and E), for the formation of formate in CO2saturated 0.1 M Na2SO4 solution. Intriguingly, the partial oxidization afforded 10 times enhancement in the current density of the pure-Co four-atom-thick layer. It was shown that the remarkably boosted electrocatalytic activity can be ascribed to the combined effects of the increased electrochemical surface area (Figure 88F), surface oxidation state and CO2 adsorption capacity. In addition, the resulting electrodes also demonstrate excellent stability during long-term electrolysis (Figure 88G). More interestingly, the partially oxidized bulk Co and Co fouratom-thick layers exhibit the Tafel slopes of almost 118 and 59 mV per decade of current, respectively. The significantly reduced Tafel slopes clearly reveal that the confined Co atomic layers are favorable for CO2 activation through stabilizing the CO2•− intermediate, thus switching the rate-limiting steps from the formation of CO2•− intermediate to the subsequent slower chemical reaction of formate formation. Importantly, the partial oxidation could accelerate the H+ transfer step, thus facilitating the rate-determining formate-formation reaction. In a word, it is suggested that the combination of surface oxidation state and an atomic-scale metal catalyst could achieve the significantly improved intrinsic CO2 reduction activity, providing new facile strategies for developing highly efficient cocatalysts for

Table 15. Activity and Selectivity for CO2 Photoreduction over HTSO and Various Pt NPs in xPHTSO (x = 1.8,3.4, 4.3, and 7.0)a production rate (μmol g−1 h−1) in 4 h

sample

H2

CH4

CO

reacted electrons’ rate (μmol g−1 h−1)b

HTSO 1.8PHTSO 3.4PHTSO 4.3PHTSO 7.0PHTSO

0.39 58.7 29.7 16.2 1.1

0.045 9.7 7.1 7.2 1.1

0.44 1.8 0.80 0.40 0.062

2.02 198.6 117.8 90.8 11.1

selectivity for CH4 (%)c 17.8 39.1 48.2 63.4 79.1

a

Reprinted with permission from ref 1314. Copyright 2018 Springer Nature. bThe reacted electrons’ rate = 8r(CH4) + 2r(H2) + 2r(CO). c The selectivity toward CH4 = 100% [8r(CH4)]/[2r(CO) + 8r(CH4) + 2r(H2)].

incorporation, defect engineering, and so on.1317,1318 All these factors make the atomically thin 2D solids the well-defined model systems that draw intense attention in the field of selective electrocatalytic or photocatalytic CO2 reduction due to the combination of the advantageous features of both molecular and heterogeneous catalysts.565 To reveal the atomiclevel correlation and the crucial role of metals and their native oxides in enhancing electrocatalytic CO2-reduction activity and selectivity, Xie and coworkers proposed as a proof of concept the electrochemical CO2 reduction over atomically thin 2D nanosheets.1319 They achieved the fabrication of partially oxidized pure Co four-atom-layer through 3 and 48 h reactions between dimethylformamide and cobalt ions at 220 °C, CC


Chemical Reviews

Review

Figure 88. (A) Schematic illustration for fabricating the partially oxidized and pure-Co four-atom-layer, respectively. Atomic force microscopy image (B) and the corresponding height profiles (C) for the partially oxidized Co four-atomic-layers. (D) Linear sweep voltammetric curves in a N2saturated (dashed line) and CO2-saturated (solid line) 0.1 M Na2SO4 solution. (E) Faradaic efficiencies of formate for 4 h at each given potential. (F) Scan rate-dependent charging current density differences Δj. (G) Current densities at the corresponding potentials with the highest Faradaic efficiencies.1319 Reprinted with permission from ref 1319. Copyright 2016 Springer Nature.

with a high selectivity of 77.1% over competing H2 evolution in the initial 3 h, which are much better than those obtained for βCo(OH)2 and Co3O4 nanoparticles (Figure 89C). Moreover, based on the above results, the possible mechanism could be proposed: the excited photosensitizer [Ru(bpy)3]2+ transfers the photogenerated electrons to the Co3O4 HPs due to the favorable band alignment, and further activating the bound CO2

photocatalytic CO2 reduction. Inspired by the above work, Gao et al. synthesized the Co3O4 hexagonal platelets (Co3O4 HPs) of 4−5 μm lateral sizes and 50−60 nm thicknesses with the dominant exposed (112) facets by calcination of β-Co(OH)2 precursors (Figure 89A and B).1320 The resulting Co3O4 HPs could achieve the visible-light-driven CO generation rate of 2003 μmol h−1 g−1 (the external quantum efficiency of 0.069%) CD


Chemical Reviews

Review

Figure 89. (A) SEM images and (B) HRTEM images of Co3O4 hexagonal platelets (Co3O4 HPs) calcined at 400, (C) visible-light-driven generation rates of CO and H2 in first 3 h under the same conditions using β-Co(OH)2, Co3O4 nanoparticles (Co3O4 NPs), or Co3O4 HPs as catalysts, respectively (λ > 420 nm); the corresponding control experiments without cobalt-based catalysts, [Ru(bpy)3]Cl2 or CO2, respectively, (D) Proposed mechanism for the photoreduction of CO2 to CO, (E) Schematic electron-transfer mechanism from [Ru(bpy)3]Cl2 to Co3O4 HPs, and (F) DFT calculations for CO2 adsorption and reduction over Co3O4 surfaces. Free energy for the COOH* intermediate formation from CO2 reduction to CO on (111) and (112) surfaces of Co3O4 HPs.1320 Reprinted with permission from ref 1320. Copyright 2016 John Wiley & Sons, Inc.

exploiting the fabrication strategy of high-performance heterogeneous photocatalysts and better understanding the underlying factors affecting the photocatalytic properties for CO2 reduction.

molecule on the surface (Figure 89D and E). The further DFT calculations revealed that the (112) facets exhibit much larger adsorption energy of CO2* (−1.69 eV) and smaller reduction free energy of CO2* to COOH* (0.32 eV), as compared those of (111) facets, which favor the reduction of CO2* to COOH* and following CO*(Figure 89F), thus achieving the dramatically enhanced photocatalytic CO2 reduction. This study highlights that the crystal facet engineering is beneficial for

6.2. Designing Single-Atom Cocatalysts

In comparison to conventional catalysis, the deposition of metal single atoms on an appropriate supporting substrate through strong interactions has been shown to be a more advanced and CE


Chemical Reviews

Review

Figure 90. (A) LSV curves acquired in CO2-saturated 0.5 M KHCO3 solution.(B) TOF comparison between A-Ni-NSG and other state-of-the-art electrocatalysts for selective reduction of CO2 to CO. (C) Applied potential-dependent CO Faradaic efficiency. (D) Current−time response of A-NiNSG on the carbon fiber paper for CO2 reduction at an overpotential of 0.61 V.1087 Reprinted with permission from ref 1087. Copyright 2018 Springer Nature.

CO2 to CO.1087 The single Ni atom electrocatalyst could achieve a specific current of 350 A g catalyst−1 (Figure 90 A) and turnover frequency of 14 800 h−1 (Figure 90 B) at a mild overpotential of 0.61 V (vs RHE) for selective conversion of CO2 to CO with 97% Faradaic efficiency (Figure 90 C). Only 2% of its initial activity decreased after 100 h of continuous electrochemical reaction for selective reduction of CO2 to CO at the current densities of 22 mA cm−2 (Figure 90 D). Similarly, the experiments and DFT calculations verified that the atomically dispersed single-atom Co−N5 site anchored on polymer-derived hollow N-doped porous carbon spheres as the dominating active center could simultaneously achieve the CO2 activation, the rapid generation of key intermediate COOH*, as well as the desorption of CO product. Surprisingly, the nearly 100% CO selectivity and remarkable stability for electrochemical CO2 reduction could be obtained at −0.73 and −0.79 V.1088 More interestingly, Wang and coworkers explored Ni and Co single atoms dispersed on graphene nanosheets for electrocatalytic CO2 reduction, with or without neighboring N coordination (Figure 91A).1091 The results demonstrated that Ni−NG and Co−NG exhibited the excellent selectivity for CO and H2 (Figure 91 B and C), respectively. Theoretical analysis of Ni and Co sites suggests much lower *CO desorption barriers and the limiting HER potential for Ni and Co atomic sites (Figure 91D and E), respectively, in agreement with experimental observations, thus elucidating the mechanism for the excellent selectivity toward the CO2RR over those single atom active sites in the Ni−NG catalyst. Notably, the single-

desirable strategy to boost the heterogeneous catalytic activity and selectivity because of the unique electronic properties of a single active site, including the confinement of electrons and the unsaturated coordination environment.1321−1326 It has been demonstrated that the isolated metal atoms with well-defined and uniform single-atom dispersion on supports not only maximize the atom efficiency of scarce precious metals, but also possess the highest ratio of low-coordinated metal atoms as active sites for particular reactions, thus achieving the unexpected photocatalytic activity and selectivity.1327,1328 However, it should be noted that an appropriate support is necessary and important to fundamentally prevent the movement and aggregation of isolated atoms caused by the greatly increased surface free energy with the decreasing particle sizes, thus creating highly stable and finely dispersed active sites for heterogeneous catalysts.1329 Recently, considering the improvement of poor resistance to CO-poisoning (strong surface bonding) by modification of electronic structures of single atom metals, various kinds of single-atom noble and non-precious transition metals and bimetallic alloys embedded into different substrates with the tuned electronic properties, such as TiC, the doped porous carbon spheres and well-defined 2D graphene have been experimentally and theoretically proven to show the superior activity, stability a n d s e l e c t i v i t y f o r el e c t r o c a t a l y t i c C O 2 r e d u c tion.1087−1089,1091,1279,1330−1332 For example, Yang et al. loaded single Ni atoms on nitrogenated graphene to achieve a durable electrocatalyst for highly selective electrochemical reduction of CF


Chemical Reviews

Review

Figure 91. (A) Schematic illustration for metal−carbon and metal−nitrogen−carbon atomic configurations in a graphene matrix. (B) CO and (C) H2 Faradaic efficiencies over glassy carbon supported Ni−NG and Co−NG electrodes in 0.5 M KHCO3. (D) The *CO desorption barrier and (E) the limiting HER potential for model systems.1091 Reprinted with permission from ref 1091. Copyright 2018 Royal Society of Chemistry.

enhancement in the visible-light harvesting (Figure 92F) could be achieved because of an obvious red shift of the optical absorption spectra, thus leading to the excellent activity toward CO2 reduction over these photocatalysts. Recently, the DFT simulations1333 were used to show that the loading Pt/Pd single atoms occurs dominantly in g-C3N4 interlayer and these atoms serve as conductive bridges to accelerate the interlayer charge carrier transfer, whereas Au is mainly adsorbed in the six-fold cavity of g-C3N4 surface, which can only deliver a limited amount of charge carrier excited in the N-conjugated aromatic pore walls of g-C3N4. However, all these loaded single atoms of Pt/Pd/Au can significantly narrow the band gap of the photocatalyst. More recently, Ye and her coworkers developed the highly effective and selective ordered porphyrin-based MOF-525 composite photocatalysts for CO2 photoreduction

atom metal cocatalysts are expected to have great potential in the field of CO2 photoreduction. For example, Gao et al. first investigated the photocatalytic CO2 reduction over single-atom Pt and Pd decorated g-C3N4 photocatalysts, respectively, by density functional theory calculations. For these photocatalysts, metal single atoms and g-C3N4 are in charge of the CO2 reduction active sites and hydrogen (H*) generation, respectively. The Pd/g-C3N4 and Pt/g-C3N4 catalysts could predominantly generate HCOOH and CH4 via selective photoreduction of CO2 with the energy barriers of 0.66 (Figure 92A) and 1.16 eV (Figure 92B), respectively. More importantly, it was found that the band gaps of Pd/g-C3N4 and Pt/g-C3N4 are significantly decreased to 0.64 and 0.72 eV because of the occupied d bands of the metal atoms in the energy band of g-C3N4 (Figure 92C−E). As a result, an CG


Chemical Reviews

Review

Figure 92. Reaction pathways for CO2 reduction to CH3OH and CH4 on the single-atom Pd (A) and Pt (B) decorated g-C3N4 photocatalysts, respectively. (C−E) Energy bands and (F) optical absorption spectra of g-C3N4, Pt/g-C3N4, and Pd/g-C3N4.814 Reprinted with permission from ref 814. Copyright 2016 American Chemical Society.

6.3. Controlling Composition of Cocatalysts

through incorporating the coordinatively unsaturated singleatom Co sites into MOF matrix (Figure 93A).104 The Co Kedge extended X-ray absorption fine structure (EXAFS) further shows the local Co atom coordination environment upon insertion within the framework (Figure 93B and C). The asprepared porphyrin MOF-525-Co comprising of atomically dispersed catalytic centers achieve the significantly enhanced photoreduction rates of CO2 to both CO and CH4, which are about 3.13 (200.6 μmol g−1 h−1) and 5.93 (36.67 μmol g−1 h−1) fold larger than those obtained for the bare MOF-525, respectively (Figure 93D). The significant enhancement in the CO2 photoreduction could be mainly ascribed to the boosted hole−electron separation efficiency by directional migration of photogenerated electrons from porphyrin to catalytic Co centers and the increased CO2 adsorption (Figure 93E). Clearly, in this study, combining atomically dispersed active sites with material platforms at the molecular level, paves a new way to fabricate the practical and stable single-atom catalysts for diverse applications.104 Although it was shown that the insertion of single-atom Pt cocatalyst into g-C3N4 could tremendously enhance the photocatalytic H2 generation performance,1334 there are a few experimental reports on the photocatalytic CO2 reduction over the single-atom nanostructured photocatalysts because it is still a significant challenge to prepare the clusters with higher surface free energy and smaller particle size. Thus, it is expected that the potential single-atom photocatalysts could be experimentally developed and applied for effective conversion of CO2 into fuels using solar energy.

Apart from controlling the particle size and morphology and designing the single atom cocatalysts, the composition of cocatalysts can also have a great impact on the CO2 reduction activity and selectivity.1137,1277 In general, the ligand and strain effects could lead to the change in the electronic structure and the interatomic distance of the surface atoms, respectively, both of which could be achieved by creating the metal and oxide overlayers on a given metal surface and alloys.1335−1338 According to the d-band model, the interactions of the expanded and compressed lattice of the surface atoms with adsorbates could be enhanced and decreased, respectively. Reske et al.1339 found that increasing the film thickness from 1 to 40 MLs could enhance the relative Faradaic selectivity for CH4 because of the altered intermediate binding energies on the films of different thickness caused by the modified surface strain. Varela et al.,1340 found that the partially exposed Pt surface was achieved because of the high binding energy between CO and Pt, which could be related to the instability of 1-ML Cu on a Pt single crystal under reaction conditions. These results suggest that the low selectivity for CH4 on 1-ML Cu on Pt mainly results from the exposed Pt, which favors HER over CO2 reduction, instead of the Cu−CO binding energy. Similarly, Friebel et al.1341 showed that 7-ML Cu on Au(111) exhibits better oxidation resistance than 1-ML Cu/Au(111) under an applied potential, due to the incorporation of Cu into the Au surface. More interestingly, the surface Cu-rich composition of AuCu nanoalloy catalysts was able to selectively form the hydrocarbons1059,1342 and CO1343,1344 from CO2 electroreduction, respectively, owing to the alloying or segregation1344 of the surface Au atoms in AuCu alloys with CH


Chemical Reviews

Review

Figure 93. (A) Structure model for MOF-525-Co with incorporated single Co atoms as active sites. (B) The magnitude of Fourier transforms for the Co K-edge EXAFS spectra of samples (not corrected for phase shift). Key: Co foil (blue), Co@C (orange), MOF-525-Co (green). (C) Wavelet transform for the k3-weighted EXAFS signal of MOF-525-Co. (D) CO and CH4 generation rates of MOF-525-Co (green), MOF-525 (purple) and MOF-525-Zn (orange). (E) CO2 adsorption isotherms for MOF-525-Co (purple), MOF-525 (orange) and MOF-525-Zn (green) implanted with single atoms.104 Reprinted with permission from ref 104. Copyright 2016 John Wiley & Sons, Inc.

activity, selectivity and stability for electrochemical reduction of CO2. Indeed, tuning the surface composition of cocatalysts over semiconductors could play the crucial role in controlling the selectivity of the CO2 photoreduction reaction. For CO2 photoreduction, Guan et al. showed in 2003 that the combination of H2 evolution and CO2 hydrogenation catalysts can be an effective strategy for generating CH3OH from gaseous CO2 and water in the absence of H2 under concentrated sunlight.1350 In this system, the synergistic effect of dual cocatalysts of Pt and Cu was firstly demonstrated in the photocatalytic CO2 reduction. Since then, various kinds of alloy cocatalysts (such as Cu/Pt,60 Cu0.33Pt0.67,91 Au0.25/Pt0.75,1351

low surface energy or the lowered CO* binding energy. Additionally, it was demonstrated that oxide films grown on the Cu surface could switch the CO2 electroredcution selectivity from CH4 to C2H4 and C2H6, and substantially decrease the overpotential for CO2 electroreduction.1345−1349 Besides Cu, the much higher CO2 reduction activity and selectivity were found in the other oxide-derived metal nanostructures, such as Sn/SnOx,712,1048 SnO2 nanosheets/carbon cloth,1123 Au/ CeOx1086, and oxide-derived Au,702 as compared with the pristine metal nanostructures. These results thoroughly highlight the importance of controlling the surface composition of monometallic and bimetallic electrocatalysts in improving the CI


Chemical Reviews

Review

Figure 94. (A) HRTEM image of one Au−Cu alloy nanoparticle. (B) UV−vis analysis of the most active photocatalyst. (C) In situ time-resolved FTIR spectra in the 2250−1150 cm−1 region before (black spectrum) and after 30, 90, and 120 min of irradiation of the (Au, Cu)/TiO2 (Au/Cu ratio 1:2). (D) Proposed mechanism for the generation of different products over (Au, Cu)/TiO2 photocatalysts under different irradiation wavelength.62 Reprinted with permission from ref 62. Copyright 2014 American Chemical Society.

Au1Cu2,62 Au3Cu,1352 Cu5Zn8,13531354 and Pt@Cu2O92) have been widely investigated, all of which exhibited significantly enhanced activity and selectivity for CO2 photoreduction. For example, the plasmon Au−Cu alloy nanoparticles were decorated on P25 TiO2 by using two consecutive deposition steps.62 The optimized photocatalyst exhibited a relatively high methane-production rate (2000 μmol g−1 h−1) with a selectivity of about 97%, which is totally different from those obtained for Au/P25 (selective H2 generation) and Cu/P25 (selective methane evolution with a lower activity).62 The d-spacing value of 0.222 nm (Figure 94A) and the plasmonic absorption band at about 580 nm (Figure 94B) indicate the formation of Au−Cu alloy NPs, whereas the formation of CO precursor and the presence of surface bonded CO2•− intermediate species during reduction of CO2 on (Au, Cu)/TiO2 are also confirmed by in situ time-resolved FTIR spectra (Figure 94C). The multifunctional role of Au−Cu NPs as a cocatalyst and plasmon photosensitizer was essential for achieving tunable activity and selectivity towards CO2 photoreduction (Figure 94D). Apparently, the so-called “carbene pathway” could be employed to explain the selective formation of CH4 over (Au, Cu)/TiO2 photocatalysts (Figure 94D). These results constitute another example showing very selective materials for photocatalytic

production of CH4 at very high conversion based on the combination in the adequate proportions of two or more metals acting as cocatalysts on TiO2 semiconductor, managing electrons and controlling the process selectivity. It appears that the selectivity toward CH4 formation arises from the presence of CO bonded to Cu on the photocatalyst, while the surface plasmon band of Au introduces the visible light photoresponse. Impressively, Xiong’s group reported that the Pd7Cu1 alloys with Cu atoms isolated in Pd lattice can provide highly active sites for highly enhanced activity of TiO2 toward selective photoconversion of CO2 to CH4 due to the improved CO2 adsorption and activation (Figure 95A and B).1355 The CO2 photoreduction using a 13C isotopic label proved the formation of 13CH4 (m/z = 17) and 13CO (m/z = 29) originated from 13CO2 (Figure 95C). A continuous 20 h test suggests the high stability of the isolated Cu atoms (Figure 95D). In comparison to the in situ DRIFTS spectra of Pd1Cu1−TiO2 (Figure 95E) and Pd7Cu1−TiO2 (Figure 95F), it is clear that the monatomic Cu sites in Pd7Cu1 lattice are beneficial for the enhanced formation of important intermediate species, such as HCO3−, CO2−, and CO32−, which are more active sites for CO2 adsorption. More importantly, it was also revealed that the elevated Cu d-band center of Pd7Cu1 CJ


Chemical Reviews

Review

Figure 95. Average production rates of CH4 and CO calculated by the amount of (A) catalysts and (B) Cu atoms in the PdxCu1−TiO2 catalysts. (C) Mass spectra of 13CH4 (m/z = 17) and 13CO (m/z = 29) produced over Pd7Cu1−TiO2 in photocatalytic reduction of 13CO2. (D) Time-dependent photocatalytic CO2 reduction with H2O to CH4 and CO on Pd7Cu1−TiO2 up to 20 h. In situ DRIFTS spectra of (E) Pd1Cu1−TiO2 and (F) Pd7Cu1−TiO2 for adsorption and activation of CO2 in the presence of H2O under Xe-lamp irradiation at 1000−2250 cm−1. The structural models and Cu d-band centers for ordered (G) Pd7Cu1 and (H) Pd1Cu1 lattices.1355 Reprinted with permission from ref 1355. Copyright 2017 American Chemical Society.

Figure 96. (A) Faradaic efficiency and (B) mass activity (j) of Au nanowires 500, 100, and 15 nm in length supported on carbon toward selective electroreduction of CO2 to CO.1051 Reprinted with permission from ref 1051. Copyright 2014 American Chemical Society.

control of the cocatalyst composition can be achieved by using better fabrication technologies.

(−1.452 eV) favors the increased catalytic activity of Cu sites as compared to that of Pd1Cu1 (−1.161 eV) (Figure 95G and H). Thus, the monoatomic Cu sites in Pd matrix enhance CO2 adsorption and activation because of their elevated d-band center, whereas the Pd matrix suppresses the competitive H2 evolution. This study highlights that the lattice engineering at atomic level is a promising strategy for the design of efficient cocatalysts for highly selective photoconversion of CO2 to carbon-neutral fuels. In future, it is expected that more precise

6.4. Exploring Edge Sites and Facets of Cocatalysts

It is well known that the atoms on the edges and exposed facets, considered as special active centers, have different environments as compared to those in other parts of a nanomaterial, which leads to enhanced electrocatalytic activities for various kinds of reactions.711,1356 In general, these edge CK


Chemical Reviews

Review

Figure 97. Rates for (A) H2, (B) CO, and (C) CH4 production via CO2 photoreduction over TiO2, TiO2−PdNSs-L, TiO2−PdNSs-M, and TiO2− PdNSs-S. (D) Schematic illustration of the relationship between CO2 photoreduction activity and edge density of Pd NSs. (E) Rates for H2, CO, and CH4 production via CO2 photoreduction over TiO2−Pd NRs-S and referenced TiO2−Pd NSs-S. (F) Schematic mechanism for the enhanced CO2 reduction over TiO2−Pd NRs-S in comparison to that on TiO2−Pd NSs-S.108 Reprinted with permission from ref 108. Copyright 2017 Royal Society of Chemistry.

efficiency (FE) of 90% for selective generation of CO via CO2 reduction at less negative potential, much better as compared to that obtained for smaller Au nanoparticles with more active corner sites that are favorable for HER.1049 In contrast, the DFT calculations indicate that corner and edge sites are favorable for CO2 reduction to HCOOH because of the enhanced adsorption of CO2 and the formation of key reaction intermediate COOH*, while all three sites are beneficial to the formation of H* for competitive HER.1058 More recently, it was shown that the bulk defects, such as grain boundaries (GBs), can be employed to stabilize the catalytically active surfaces.1055 A quantitative correlation between GBs of Au NPs and their electrocatalytic CO2 reduction activity has also been established.1055 It is well known that the crystal facets of Cu single crystals determine both the reactivity and selectivity for

active sites on the CO2 reduction cocatalysts could also achieve the superior properties for improving adsorption and activation of CO2, stabilizing the key COOH intermediate, and suppressing side or back reactions.1357,1358 For example, Zhu et al. compared the Faradaic efficiency (Figure 96A) and mass activity (Figure 96B) of CO production for different nanowires with lengths in the range of 15−500 nm and found that longer nanowires were favorable for selective CO formation because of the much greater number of edge sites than that of corner sites.1051 The DFT calculations further revealed that the edge sites over Au NPs with the weak CO binding are much more reactive for electrochemical reduction of CO2 into CO as compared to terrace and corner sites, while competitive HER favors the surface corner sites.1051,1313 The 8 nm Au nanoparticles with optimal edge-site ratios showed the Faradaic CL


Chemical Reviews

Review

Figure 98. HRTEM (A and B) images of TiO2−Pd NPs and TiO2−Pd NWs. (C) Rates for H2, (D) CH4, (E) CO, and (F) C2H5OH production via CO2 photoreduction on bare TiO2, TiO2−Pd NPs, and TiO2−Pd NWs.1357 Reprinted with permission from ref 1357. Copyright 2017 Elsevier.

Figure 99. (A) TEM and (B) HRTEM images of C3N4 supported PtCu CNCs. (C) Rates for H2, CO, and CH4 production over C3N4, C3N4−PtCu NCs, and C3N4−PtCu CNCs. (D) Photocatalytic CO and CH4 generation rates and the CH4 selectivity over C3N4−PtCu CNCs under visible light (400 nm < λ < 780 nm). PDOS of CO2 on (E) Pt(100)/PtCu(100) and (F) Pt(730)/PtCu(730) models with free CO2 as a reference sample.1364 Reprinted with permission from ref 1364. Copyright 2017 Royal Society of Chemistry.

electrochemical CO2 reduction.1359 It was demonstrated that Cu(100) surfaces favor the selective C2H4 production through CO dimerization, whereas Cu(111) surfaces facilitate the selective CH4 formation via the CO protonation as a crucial step, despite C2H4 can also be produced by this pathway.682,687,711,1360,1361 Importantly, Hori and co-workers also showed that C2H4 selectivity could be significantly increased by the steps in the (100) surface of Cu nanocrystals due to the increased binding strength of reactants, thus achieving an optimal selectivity of 58.9% over Cu(711) surfaces.1359,1362 Clearly, the exposed edge active sites and facets of the metal cocatalysts on the semiconductor surface play also a crucial role in determining the overall CO2 photoreduction efficiency. To

disclose the relationship between the edge density of Pd cocatalysts and CO2 reduction performance, Zhu et al. decorated TiO2 nanosheets by using Pd nanosheets of different sizes.108 It was verified that the highest photoactivity for CO2 reduction increases with increasing the edge density of Pd nanosheets on the TiO2 nanosheets, indicating the crucial role of edge active sites in improving the CO2 reduction reaction (Figure 97A−D). Moreover, the edge-dependent photocatalytic performance was further improved through deposition of Pd nanorings on the TiO2 nanosheets due to the additional introduction of the exposed edge sites in the hollow interior rings (Figure 97E and F). This work highlights that the edge engineering of the surface cocatalysts seems to be a promising CM


Chemical Reviews

Review

strategy for improving performance of photocatalytic processes. Similarly, Zhu et al. loaded metal Pd nanowires with high density of grain boundaries (GBs) on TiO2 nanosheets (Figure 98A and B).1357 This study demonstrated that the suppressed competitive H2 evolution activity (Figure 98C) and promoted CO2 photoreduction activity and selectivity (Figure 98D−F), can be simultaneously accomplished by using the Pd nanowires with GBs, as compared with the corresponding metal NP cocatalysts without GBs. Accordingly, tailoring the density of GBs on the metal cocatalysts represents an important engineering route to enhance the photocatalytic performance. More recently, Lang et al. demonstrated that the Pd cocatalyst engineered with twin defects could greatly promote the photocatalytic CO2 reduction performance of g-C3N4 nanosheets.1363 The average CO and CH4 production rates gradually increase for C3N4−Pd NIs-L, C3N4−Pd NIs, and then C3N4− Pd NIs-S with decreasing size of Pd icosahedrons, thus leading to the higher CO2 reduction selectivity from 47.7% to 61.4% and then to 87.3%. It is believed that the increased amount of twin defects in cocatalysts as active sites play important roles in improving the photocatalytic activity and selectivity in CO2 photoreduction. More interestingly, to demonstrate the highindex facet engineering, the (730) facets covering PtCu concave nanocubes (CNCs) (Figure 99A and B) and (100) facets covering PtCu nanocubes (NCs) were in-situ grown on the C3N4 nanosheets.1364 It was found that PtCu CNCs exhibited much better photocatalytic CO2 reduction activity (3 times higher) and stability for selective CH4 evolution (increased selectivity from 85.9% to 90.6%) than the PtCu nanocubes (Figure 99C and D). The DFT calculations further revealed that the (730) high-index facets contain more low-coordinated metal active sites able to increase the CO2 activation and adsorption (Figure 99E and F), in comparison with the lowindex (100) facets on PtCu nanocubes. This work demonstrates that the rational design of cocatalysts with high-index facets can be effectively used to enhance photocatalytic CO2 conversion activity and selectivity for obtaining desired products. In addition, it is well known that the edge sites in MoS2 or graphene are excellent active sites for various electrocatalytic reactions. 1365 Namely, the defect-rich or porous MoS 2 nanosheets, which possess much more edges, usually exhibit higher electrocatalytic H2 evolution activity. Since much less is known about the effect of edge sites of cocatalysts on the selective CO2 photoreduction, further research in this area is highly desirable.

Figure 100. Schematic illustration of the contact (interfacial) area between solids of different morphology.1366 Reprinted with permission from ref 1366. Copyright 2014 Royal Society of Chemistry.

1D/2D composites, the unique 2D/2D heterojunction with intimate and large interface contact can show better improvement in the structure stability.1366 A logical strategy for improving interfacial coupling is via enlargement of the interfacial contact area, which has been somewhat successful in improving interfacial coupling between 2D H2 evolution cocatalysts (such as WS2, graphene, and MoS2) and 2D semiconductor nanosheets (such as g-C3N4 and TiO2), which resulted in improving interfacial transfer of the photogenerated electrons from semiconductors to cocatalysts, and consequently, improved the overall photocatalytic H2 evolution efficiency.1367−1372 Interestingly, it should be pointed out that the diversified 2D−2D layered heterojunctions have been also applied in the CO2 photoreduction, which is thoroughly discussed here. For example, to highlight the effect of carbon nanomaterial dimensionality on the interfacial charge transfer and photocatalytic CO2 reduction activity of carbon−titania nanosheet composites, Liang et al. constructed the 2D−1D TiO2 nanosheet−carbon nanotube (Figure 101A) and 2D−2D TiO2 nanosheet−graphene (Figure 101B) heterojunctions with low defect densities of nanocarbons, respectively.1373 Interestingly, it was demonstrated that the 2D−2D TiO2 nanosheet− graphene heterojunctions showed greater CO2 photoreduction activity under ultraviolet irradiation because of their superior interfacial electronic coupling (Figure 101C and E), whereas the 1D−2D carbon nanotube−titania nanosheet composites could achieve much higher visible-light CO2 reduction activity owing to more effective photosensitization (Figure 101D and E). It was proposed that the intimate 2D-2D interfaces favor much more the charge transfer from TiO2 nanosheets to RGO as compared to the 1D−2D interfaces between SWCNT and TiO2 nanosheets. This is because the increased contact area between graphene and semiconductor with face-to-face orientation can favor the charge separation, and consequently, significantly boost the activity for CO2 photoreduction.1373 In another example, Zou et al. synthesized the hierarchical G− Ti0.91O2 hollow spheres consisting of 2D/2D interfaces created by coupling between RGO nanosheets and Ti0.91O2 nanosheets via a layer-by-layer assembly (LBL) strategy using polymer beads as sacrificial templates (Figure 102A and B).90 As shown in Figure 102C and D, the resulting G−Ti0.91O2 hollow spheres could achieve five- and nine-times higher total generation rates of renewable fuels (CO and CH4) through photoreduction of CO2 with gaseous H2O, in comparison with those over blank Ti0.91O2 hollow spheres and commercial P25, respectively. The

6.5. Constructing 2D−2D Coupling Interfaces

As discussed above, the interfacial contact area plays a significant role in strengthening the interfacial coupling between semiconductor photocatalyst and cocatalyst. It is well recognized that the unique 2D−2D layered semiconductor−cocatalyst heterojunctions with much larger interfacial contact, intense physical and electronic coupling effects could provide sufficient channels for more efficient interfacial charge transfer, separation and trapping, thus enhancing the overall photoactivity (Figure 100).1366 Thus, the activity for selective photoreduction of CO2 can also be improved by the fabrication of 2D layered composite photocatalysts with tight heterojunction structure. Typically, the boosted CO2 photoreduction activity can be achieved via increasing the interfacial contact intimacy and area between graphene and semiconductors. For instance, as compared to the 0D/2D and CN


Chemical Reviews

Review

enhanced CO2 reduction photoactivity of G−Ti0.91O2 hollow spheres is attributed to the synergy of multiple factors, including the rapid spatial separation and transport of photoelectrons in the ultrathin Ti0.91O2 nanosheets and 2D/ 2D layered stacking heterojunction, and more efficient, permeable absorbance and scattering of light and adsorption/ activation of CO2 in the hierarchical hollow structures. Notably, the Ti0.91O2 photocatalyst and G−Ti0.91O2 composites have been shown to exhibit excellent selectivity toward CH4 and CO, respectively, indicating the importance of graphene in determining the selectivity for CO2 photoreduction products. As expected, the incorporated rGO with the lower Fermi level (−0.08 eV vs NHE) could accept the photogenerated electrons from Ti0.91O2 nanosheets because of its extremely high electron mobility and electrical conductivity. Then, the introduction of rGO sheets is disadvantageous for the accumulation of electrons and significantly reduces the local electron density, thus achieving the selective formation of CO through a twoelectron reaction mechanism. Additionally, novel ZnV2O6 nanosheets have been coupled with 2D RGO to construct the ZnV2O6 2D/2D nanosheets heterojunction through a solvothermal process (Figure 103A).1374 In comparison to pure ZnV2O6 nanosheets, the resulting 2D/2D ZnV2O6/RGO nanosheets exhibited much higher photoactivity for selective reduction of CO2 to CH3OH, HCOOH, and CH3COOH. The optimized ZnV2O6/4%RGO could achieve the yield of the main product (CH3OH) of 5154 μmol g-cat−1 with a selectivity of 68.89%, which is about 1.6 times higher than the generation of CH3OH over pure ZnV2O6 with a selectivity of 39.96% (Figure 103B). More importantly, the excellent photocatalytic stability for continuous 32 h of selective CH3OH production

Figure 101. SEM images of annealed (A) 1 wt % SWCNT−TiNS and (B) 1 wt % SEG−TiNS heterostructed ultrathin films. Schematic illustration of the (C) 2D−1D TiNS−SWCNT and (D) 2D−2D TiNS−SEG interfaces. The gray, red and blue atoms denote carbon, oxygen, and titanium, respectively. (E) CH4 production rates over SEG−TiNS and SWCNT−TiNS heterojunctions under ultraviolet (365 nm) and visible light.1373 Reprinted with permission from ref 1373. Copyright 2012 American Chemical Society.

Figure 102. (A) Schematic illustration for fabricating the LBL assembled multilayer-coated spheres composed of TiO2 and RGO nanosheets. (B) TEM images of G−Ti0.91O2 hollow spheres. (C) Photocatalytic generation rates of CO (squares) and CH4 (dots) over (G−Ti0.91O2)5 hollow spheres (a), (Ti0.91O2)5 hollow spheres (b), and P25 (c). (D) Comparison of the average product generation rates.90 Reprinted with permission from ref 90. Copyright 2012 John Wiley & Sons, Inc. CO


Chemical Reviews

Review

Figure 103. (A) TEM image of 2D−2D ZnV2O6/RGO (4%) nanosheets. (B) Activity and selectivity comparison for CH3OH production under visible light irradiation. (C). Schematic illustration of the charge separation mechanism for photoreduction of CO2 to CH3OH, HCOOH and CH3COOH over the ZnV2O6/RGO photocatalysts under visible light.1374 Reprinted with permission from ref 1374. Copyright 2018 Elsevier.

Figure 104. (A) Schematic illustration of the synthesis of g-C3N4/NiAl-LDH 2D−2D hybrid heterojunction. (B) CO2-photoreduction activity comparison for various hybrid heterojunctions. (C) Schematic illustration of charge-separation mechanism for CO2 photoreduction over the gC3N4/NiAl-LDH heterojunctions.1377 Reprinted with permission from ref 1377. Copyright 2018 American Chemical Society.

was also achieved due to the synergistic effects in ZnV2O6/ RGO 2D/2D nanosheets. The significant improvement in the photocatalytic activity, selectivity and stability is mainly attributed the excellent synergistic effects, efficient visible light absorption, and the enhanced charges separation originated from the strong interfacial interaction between

ZnV2O6 nanosheets and graphene nanosheets (Figure 103C). Clearly, these works reveal that the engineering of the welldefined RGO-based nanocomposite interfaces is a promising strategy for developing the low-cost and high-efficiency photocatalysts for CO2 reduction. In this regard, 2D g-C3N4 nanosheets are suitable for fabrication of the 2D−2D coupled CP


Chemical Reviews

Review

Figure 105. (A) Photocatalytic production rates of CH4 and CH3OH over TBx samples (x represents the the mass ratios of Ti3C2 to Bi2WO6). (B) GC-MS product analysis using 12CO2 and 13CO2 as carbon sources, respectively. (C) time-resolved photoluminescence (TRPL) spectra and (D) EIS plots of TB0 and TB2. (E) Energy level structure diagram of Bi2WO6 and Ti3C2. (F) Photoinduced electron transfer process at the ultrathin Ti3C2/ Bi2WO6 2D−2D heterojunction interface.1376 Reprinted with permission from ref 1376. Copyright 2016 John Wiley & Sons, Inc.

Bi2WO6 ultrathin nanosheets (Figure 105A). Furthermore, the CH4 (m/z = 17) could be mainly obtained by the gas chromatography-mass spectrometry (GC-MS) analysis using 13 CO2 as the carbon source, indicating that photocatalytic reaction products originate from CO2 conversion (Figure 105B). The significantly enhanced CO2 adsorption ability and excellent charge transfer and separation rates in both bulk and interface regions should be responsible for the boosted activity of photocatalytic CO2 reduction under simulated solar irradiation (Figure 105C and D). Clearly, the ultrathin Ti3C2/Bi2WO6 2D/2D heterojunction nanosheets play a crucial role in determining the CO2 photoreduction performance due to the short charge transport distance and the large interface contact area (Figure 105E and F). This study suggests that the 2D ultrathin Ti3C2 nanosheets are promising and cheap cocatalysts for fabrication of 2D/2D heterojunctions with improved photocatalytic CO2 reduction over different kinds of semiconductor nanosheets. It is anticipated that in future the strategy for fabricating 2D/2D layered heterojunctions with efficient charge separation can be extended to other semiconductor composite systems for highly efficient photocatalytic CO2 reduction. However, so far, there are only limited reports on the application of 2D−2D coupled semiconductor photocatalysts for CO2 reduction,90,614,641,813,1184,1374,1377 which is expected to be a hot topic for future studies. At this point, the further development of new 2D layered semiconductors and cocatalysts, such as black phosphorus,1378−1381 graphene,113,177 Bi-based semiconductors,1382−1384 transition-metal carbide,1385−1390 and dichalcogenide1391−1395 nanosheets is essential for fabrication of novel layered 2D−2D heterojunctions for CO2 photoreduction and other photocatalytic processes.

photocatalysts with other 2D materials, such as graphene. In 2011, Xiang et al. first fabricated the 2D−2D g-C3N4-graphene for photocatalytic H2 generation.1375 Since then, the layered gC3N4-based heterojunctions with 2D−2D interfaces have also been extensively explored in the CO 2 photoreduction.641,813,1184 As mentioned above, the optimized 2D−2D protonated g-C3N4 (pCN)/rGO interface exhibits the highest CH4 production of 13.93 mmol gcatalyst−1, which is almost 5.4fold higher than that obtained on pCN.813 Moreover, the total CH4 production over 15rGO/pCN photocatalyst was about 1.68 times higher that on 15rGO/CN, indicating the essential role of the intimate 2D/2D pCN/rGO interface in improving visible-light photoactivity of 15rGO/pCN heterostructures.813 Considering the enhanced CO2 adsorption and activation of semiconducting NiAl-layered double hydroxide (NiAl-LDH) cocatalysts, the g-C3N4/NiAl-LDH 2D−2D hybrid heterojunction was successfully fabricated through utilizing strong electrostatic interactions between positively charged 2D NiAlLDH nanosheets and the negatively charged 2D g-C3N4 nanosheets in the hydrothermal process (Figure 104A). The optimum g-C3N4/NiAl-LDH 2D/2D interface heterojunction showed the highest visible-light activity for selective photoreduction of CO2 to CO (8.2 μmol h−1 g−1), which is 5 and 9 times higher than those of single phase g-C3N4 and NiAl-LDH nanosheets, respectively (Figure 104B). Accordingly, the strong interfacial contact and improved separation and transfer of excited charge carriers are believed to be responsible for the significant enhancement of photocatalytic activity (Figure 104C). More interestingly, Cao et al. for the first time successfully constructed the 2D/2D heterojunction of ultrathin Ti3C2/Bi2WO6 nanosheets by in situ growth of Bi2WO6 ultrathin nanosheets on the surface of Ti3C2 ultrathin nanosheets.1376 The resultant 2D/2D Ti3C2/Bi2WO6 hybrids show 4- and 6-time improvements in the yields of CH4 and CH3OH, respectively, as compared with those over pristine

13

CQ


Chemical Reviews

Review

Figure 106. (A) TEM images of Au/BiOI/MnOx. (B) UV−vis driven production rates for BiOI, Au/BiOI, Au/BiOI/MnOx, and MnOx/BiOI for 2 h (inset shows the visible-light yields). (C) Cyclic photostability (Xe lamp irradiation) of Au/BiOI/MnOx. (D) The CO2-photoreduction enhancement of dual-cocatalyst loaded BiOI.1397 Reprinted with permission from ref 1397. Copyright 2016 Royal Society of Chemistry.

6.6. Loading Dual Cocatalysts on Semiconductors

to avoid the unexpected charge recombination because of the random dispersion of the dual cocatalysts, the spatially separated CoOx (hole collector) and Pt (electron trapper) nanoparticles were in situ deposited on the outer and inner skeleton surface of hierarchical TiO2−SiO2 (Pt/HCTSO), respectively.1315 This work revealed that the hierarchical TiO2− SiO2 structure with the spatially separated double cocatalysts exhibited the suppressed formation of H2 and CO, and promoted activity and selectivity for CH4 production, as compared with those achieved over hierarchical photocatalysts with single Pt cocatalyst and randomly deposited Pt−CoOx dual cocatalyst (Figure 107A−D). Two charge transfer routes for the composite photocatalysts with spatially separated dual cocatalysts were proposed, which is highlighted in Figure 107E and F, respectively. Clearly, the randomly loaded Pt−CoOx/ TiO2−SiO2 exhibits a poor photocatalytic performance owing to the unavoidable charge-carrier recombination at the interfaces of Pt and CoOx nanoparticles, whereas the spatially separated Pt/CoOx/TiO2−SiO2 displays the significantly enhanced photocatalytic activity because of much higher separation efficiency of charge carriers trapped in the spatially separated Pt and CoOx nanoparticles.1315 In another example, Akple et al. constructed the N-doped anatase TiO2 microsheets (NT) with optimized ratio of coexposed (001) and (101) facets via simple hydrothermal method using HF and TiN.106 Then, the separated Ag and MnOx nanoparticles as a dual cocatalyst were simultaneously photodeposited on the exposed (101) and (001) facets of the as-prepared NT microsheets, respectively (Figure 108A). The resulting Ag and MnOx modified NT microsheets exhibited good photocatalytic activity (0.53 μmol h−1 g−1) (Figure 108B) with excellent stability for the photoreduction of CO2 into methanol, which was about 2 times higher than that on pure NT microsheets. Clearly, the

It is known that loading dual cocatalysts into semiconductors has been shown to be an effective strategy to boost the photocatalytic water-splitting activity.925 Thus, it is natural to expect that the incorporation of both O2 evolution and CO2 reduction cocatalysts into semiconductors would further enhance the charge separation and accelerate kinetics of these two processes, and consequently, maximize the photocatalytic activity for CO2 reduction. So far, the dual cocatalysts, such as Pd/RuO2,1396 Au/MnOx,1397 Ag/MnOx,1398Pt/MnOx,3111399 Au/RuO2,1400 Pt/RuO2,78,618,1401,1402 CuxO/Co-Pi1403, and Pt/CoOx1315 have been used to efficiently enhance the selective formation of HCOOH, CH4, and CO, respectively. For example, Liu et al. synthesized the single-crystalline Zn2GeO4 nanobelts by a solvothermal route in the mixed ethylenediamine/water solvent.78 It was demonstrated that the CH4generation rate over the Zn2GeO4 nanoribbons during the first hour was enhanced 16-fold by random coloading of Pt and RuO2 as dual cocatalysts because of the significantly boosted separation efficiency of the photogenerated charge carriers.78 Similarly, Au and MnOx cocatalysts were simultaneously loaded on 2D BiOI by in-situ photodeposition (Figure 106A).1397 The UV−vis and visible-light driven CO production rates over Au/ BiOI/MnOx were 5.95 and 19 times higher, respectively, than those over pure BiOI (Figure 106B). This enhancement was associated with the excellent photostability (Figure 106C) and improved charge separation. Accordingly, the use of both, Au nanoparticles and MnO x layered cocatalysts not only significantly prevented the charge-carrier recombination, but also accelerated the surface CO2 reduction and water oxidation kinetics, respectively (Figure 106D), thus leading to the significantly enhanced CO2 photoreduction. More interestingly, CR


Chemical Reviews

Review

Figure 107. Formation rate of H2 (A), CH4 (B), and CO (C) and the selectivity of CH4 (D) over samples decorated with different amounts of Pt and CoOx. Schematic charge-transfer mechanism for randomly loaded Pt-CoOx/TiO2−SiO2(E) and spatially separated Pt/CoOx/TiO2− SiO2(F).1315 Reprinted with permission from ref 1315. Copyright 2016 Royal Society of Chemistry.

facet are believed to be the crucial for the spatial charge-carrier separation and activity enhancement (Figure 109B). The strategy for precise control of spatial distribution of dual cocatalysts may open a new way toward developing highly active and selective photocatalysts for advanced CO2 photoreduction. However, these dual cocatalysts are composed of noble metals, limiting their practical and large-scale applications. Thus, the dual cocatalysts consisting of earth-abundant cocatalysts, such as nanocarbons and the first-row transition metals, should be deeply exploited in future studies.

synergistic effects of various factors, such as nitrogen doping, design of coexposed facets, dual cocatalyst deposition, as well as surface plasmon resonance (SPR), improve often the charge separation (Figure 108C), increase visible-light harvesting, and improve activation and dissociation of CO2, thus achieving the significantly enhanced overall photocatalytic efficiency. This research paves a new way for rational design of highly active CO2 reduction photocatalysts with enhanced charge separation and light absorption/harvesting.106 More interestingly, Meng et al. integrated dual cocatalysts of MnOx and Pt on the (001) and (101) facets of TiO2 nanosheets (Figure 109A), respectively.1399 The resulting multiheterojunction photocatalysts could achieve the high activity (over 3-fold enhancement) and durable photoreduction of CO2 to CH4 and CH3OH (Figure 109B and C). The excellent cooperative and synergistic effects of the surface heterojunction between (001) and (101) facets, p−n junction between MnOx and TiO2 (001) facet and metal−semiconductor junction between Pt and TiO2 (101)

7. SELECTIVE CO2 PHOTOREDUCTION OVER DIFFERENT COCATALYSTS The continuous efforts have been directed toward exploiting various kinds of highly active and selective cocatalysts for selective photoreduction of CO2. Taking into account the chemical composition, the cocatalysts used in photocatalysis CS


Chemical Reviews

Review

Figure 108. FESEM images of TiO2 (NT, Ag−N-self-doped anatase microsheets)-Mn (A), selective formation rates of methanol over different samples for 2 h (B), and proposed photocatalytic mechanism for CO2 reduction over Ag-NT-Mn sample (C).106 Reprinted with permission from ref 106. Copyright 2016 Elsevier.

can be classified into five main categories: biomimetic cocatalysts, noble metal cocatalysts, earth-abundant metal cocatalysts, metal-free cocatalysts, and multifunctional cocatalysts. In this section, the development of different types of efficient cocatalysts for selective CO2 photoreduction is highlighted. So far, it is known that the metal-based cocatalysts loaded on photocatalysts have been proven to be the most widely used cocatalysts in the field of photocatalytic CO2 reduction; thus, their diversified applications are firstly highlighted and summarized in Table 16. Then, each category of cocatalysts is discussed in detail.

composite photocatalysts has been developed by attaching a small amount of CO dehydrogenase (CODH, 0.1 nmol) to dye-sensitized TiO2 nanoparticles1579,1580 (Figure 110) or CdS nanocrystals,4 which resulted in the significant enhancement of CO production. However, the stability of composite photocatalysts over long periods is poor due to unfavorable detachment of enzyme from semiconductors, which should be improved through binding the enzyme to the surface of semiconductors or constructing enzyme/semiconductor core/ shell structures. Recently, Yadav et. al reported a novel formate dehydrogenase (FDH) enzyme−graphene-based photocatalyst hybrid system for HCOOH production via CO2 photoreduction (as illustrated in Figure 111A).1580 It is demonstrated that both the transient photocurrent and photoregeneration of nicotinamide adenine dinucleotide (NADH) on the CCGCMAQSP photocatalyst are much larger than those on multi-anthraquinone-substituted porphyrin (MAQSP) (Figure 111B and C). In this system, the novel visible-light-driven CCGCMAQSP photocatalyst was constructed through covalent coupling of the chemically converted graphene (CCG) with the MAQSP chromophore. This study shows clearly that the photocatalytic HOOCH production activity of the graphene-based photocatalyst−formate dehydrogenase (FDH) enzyme coupled system (110.55 μmol over 2 h) is better than those obtained for other photocatalytic systems (14.25 and 46.53 μmol for W2Fe4Ta2O17 and multi-anthraquinone substituted porphyrin, respectively) (Figure 111D).1580 The DFT calculations using CCG consisting of 30 hexagon rings and MAQSP saturated by amine and carboxyl groups further revealed the easy and irreversible transfer of photoexcited electrons from MAQSP to CCG (Figure 111E and F) because of the matching energy level alignment between LUMO of MAQSP and the CB edges of CCG. To improve the rather poor activity, an integrated photocatalyst/biocatalyst system via

7.1. Biomimetic Cocatalysts

7.1.1. Biocatalysts (Enzymes). The enzyme-based biocatalysts provide a facile route for conversion of atmospheric CO2 into valuable chemicals at ambient conditions.1571 Such biocatalytic reduction reactions are promising because they are extremely active and can take advantage of low concentration reactants and resist toxicity of many impurities to chemical catalysts. Meanwhile, to improve the stability of enzymes and, consequently, their catalytic performance, their immobilization in the different carriers has been explored.1572−1575 The utility of enzymes in electrochemical and photoelectrochemical CO2 reduction has been demonstrated in the past decade.704,1095,1131,1576 Since the coupling of semiconductor photocatalysts and enzymes (or proteins) represents a new and effective strategy for improving photoactivity, it received a considerable attention nowadays.1577,1578 Since the pioneering work by Parkinson and Weaver in 1984,1131 there is also a great number of reports on the enzyme-assisted CO2 photoreduction systems. For example, the methanol production rate over ZnS microcrystallite/methanol dehydrogenase composites can increase to 0.25 mmol dm−3 with the quantum efficiency of 5.9% (at 280 nm), which so far is the largest reported value for the photochemical reduction of CO2 to methanol.1404 A series of CT


Chemical Reviews

Review

Figure 109. (A) Schematic illustration for selectively photodepositing MnOx and Pt cocatalysts on (001) and (101) facets of anatase TiO2 nanosheets. (B) Activity and (C) stability for CO2 photoreduction of different samples under irradiation for 3 h. (D) Proposed mechanisms for CO2 photoreduction over TMP. The TiO2 nanosheet, TiO2−MnOx, TiO2−Pt, and TiO2−MnOx−Pt samples were denoted as T, TM, TP, and TMP, respectively.1399 Reprinted with permission from ref 1399. Copyright 2018 American Chemical Society.

112E and F). Thus, the dense 3D immobilization of the appropriate enzyme/catalyst in the nanopores represents an effective and novel strategy to develop more efficient artificial photosynthesis systems for the multiple-step catalytic reactions. To further address the lack of direct interface for effective transferring the photoexcited electrons and chemicals into the redox active sites of biocatalysts, Zhang’s group integrated polyelectrolyte-doped hollow nanofibers and a bioinspired highly integrated artificial photosynthetic system (including photocatalyst and biocatalyst) for enhanced methanol formation by combination of LBL self-assembly and co-axial electrospinning/electrospray (Figure 113A). The enhanced CO2 reduction to methanol was fully demonstrated in this integrated artificial photosynthesis system, owing to the cascade of three dehydrogenases (alcohol, formaldehyde and formate dehydrogenases) and the photoinduced NADH regeneration under visible light. The photoinduced NADH generation efficiency over the fully integrated hollow nanofibers or microcapsules with a photocatalyst, photosensitizer (EY), and electron mediator (M), is nearly close to that of free solution

combining the graphene-based visible-light-driven CCG-IP photocatalyst (through covalent bonding of the isatinporphyrin chromophore to CCG) was prepared and sequentially coupled with enzymes (formate, formaldehyde, and alcohol dehydrogenase).1581 The resulting integrated photocatalytic system exhibited a 2-fold activity enhancement in selective photoconversion of CO2 to methanol as compared to that on the reference graphene/multi-anthraquinone-substituted porphyrin (CCGCMAQSP) photocatalyst integrated with enzymes. Besides the graphene-based photocatalysts, the molecular Ru(bpy)32+ complex as a photosensitizer has been also coupled with FDH enzyme in a photoreduction nanoporous glass reactor using methyl viologen (MV2+) as an electron mediator (Figure 112A−C).1582 The resulting overall HCOOH production efficiency in this reactor was 14 fold larger than that achieved in an equivalent solution (Figure 112D). It was shown that the nanopores inside Ru(bpy)32+/ MV2+/FDH/PGP50 could achieve a 22-fold increase in the electron transfer efficiency from MV•+ to FDH, which was the limiting factor in the Ru(bpy)32+/MV2+/FDH solution (Figure CU


Chemical Reviews

Review

Table 16. Summary of the Selective CO2 Photoreduction Systems with Metal-Based Cocatalysts semiconductor

cocatalysts

selective products

activity (μmol g−1 h−1)

ZnS Re-complex Re-complex Ru-complex

methanol dehydrogenase Ru-complex Ru-complex Re-complex

biomimetic cocatalysts QY(280) = 5.9% CH3OH CO TNCO = 110 CO TNCO = 190 CO TN = 180

N-doped Ta2O5 Re-complex

Ru-complex Ru-complex

HCOOH CO

70 (QY(405) = 1.9%) 4.16 μmol h−1

Re-complex

Ru-complex

CO

2.3 μmol h−1

p-Si photocathode N-doped Ta2O5


CO HCOOHCO

η = 9.3% TN = 118 TN = 67

Cu2ZnSnS4 photocathode triple-stranded β-helix nanotubes p-InP photocathode TiO2 nanotubes

Ru-complex Ru−Re complex

HCOOH CO

TOF = 62


HCOOH CH3OHCH4

η = 0.04% 746130

Ru-complex

Ru-complex

HCOOH

TON = 671

p-InP photocathode N-doped Ta2O5


HCOOH HCOOH

C3N4 Mn-complex


HCOOH HCOOH

η = 0.14% Faradaic efficiency of >75% AQY(400) = 1.5% TON = 149

g-C3N4

Ru-complex

HCOOH

46.425

kaolin

Re-complex

CO

150

g-C3N4 TiO2 bifunctional MOF-253 g-C3N4

Ru-complex Re-complex, dye Ru-complex Ru-complex

C3N4

Ru-complex

HCOOH CO CO CO HCOOH HCOOH

1100 TNCO ≥ 570 42.5 181.25 93.75 TON = 175

yttrium−tantalum oxynitride TiO2 (anatase)

Ru-complex

HCOOH

TON = 18

Ru-complex

CH4

Ag/TaON

Ru-complex

HCOOH

mesoporousC3N4 Co3O4

Ru-binuclear complex, Ag Ru-complex

Fe-complex Co-complex g-C3N4−TiO2

Ru-complex

HCOOH CO H2 CO

80 μL g−1 h−1 QY = 0.56% TON = 750 QY(400) = 0.48% TON = 3110 2003 595 TONCO = 2660

Ru−Re complex

CO

TON = 72

g-C3N4

Ru-complex

HCOOH

675

periodic mesoporous organosilica Ni-complex TiO2 (P25)

Ru-complex

CO

TON = 10.4

Ru-complex TDQD

CO CH4

TONCO > 700 162

Re-complex

Ir-complex

CO

TON = 1700

Fe-complex

Cu-complex

CO

CeO2 TiO2

N-doped graphene Cu-complex Co-complex

CH3OH CO

TON = 273 QY(436) = 6.7% 507.3 TONCO = 20

CV

conditions

ref (year)

G-L/λ ≥ 270 nm, pH = 7.0 G-L/high-pressure Hg lamp λ > 500 nm G-L/λ > 500 nm G-L/high-pressure Hg lamp, λ < 500 nm/ DMF-TEOA G-L/410 < λ < 750 nm G-L/λ = 365 nm 1.27 × 10−8 Einsteins−1/ DMF, TEOA G-L/λ = 365 nm, 8.5 × 10−9 Einsteins−1/ DMF, TEOA G-L/661 nm G-L/410 < λ < 750 nm

1404 1405 1406 1407

G-L/400 < λ < 800 nm G-L/high pressureHg lamp, λ > 500 nm/ DMF G-L/AM1.5G, NaHCO3 solution G-L/500 W, 24 V xenon lamp, 0.85 W/ cm2/323 K, 1.1−1.2 bar G-L/λ = 480 nm, 4.8×10−8 einstein s−1/ DMF, TEOA G-L/AM1.5G,NaHCO3 solution G-L/500W−Xe lamp is 45 mW/cm2

1411 (2011) 1412 (2011)

G-L/450 W Xe lamp G-L/λ = 480 nm, 4.3×10−8 einstein s−1/ TEOA G-L/λ > 400 nm, 20 vol% TEOA in acetonitrile visible-light irradiation (λ > 425 nm)/ 100 mW/cm2/DMF/TEOA G-L/λ > 400 nm, DMA (20 vol % TEOA) G-L/Xe lamp, λ > 420 nm G-L/Xe lamp/MECN, TEOA G-L/λ > 400 nm, DMA (20 vol % TEOA)

(1994) (2008) (2009) (2009)

79 (2010) 124 (2010) 1408 (2008) 1409 (2010) 1410 (2011)

54 (2011) 1413 (2012) 1414 (2012) 1415 (2013) 1416 (2013) 1417 (2013) 1418 (2014) 1419 (2014) 1420 (2014) 1421 1422 1423 1424

(2015) (2015) (2015) (2016)

G-L/400 W high-pressure Hg lamp λ > 400 nm/MeCN/TEOA G-L/400 W high-pressure Hg lamp/DMA, TEOA G-L/λ > 420 nm

1427 (2016)

G-L/λ>400 nm

1428 (2016)

G-L/λ > 400 nm/4:1 (v:v) DMA−TEOA G-L/λ > 420 nm/TEOA/15 °C, 1 atm CO2

1429 (2016) 1320 (2016)

G-L/blue LED centered at 460 nm

1430 (2016)

G-L/400 W mercury lamp, λ > 400 nm/ DMF, TEOA G-L/400 W Hg lamp, λ > 400 nm/4:1(v:v) DMF−TEOA G-L/500 W super-high-pressure mercurylamp; λ > 430 nm/DMA G-L/λ = 425 nm/DMA G-S/mercury lamps, 6.0 W cm−2, 365 nm/ 303 K, 1.0 atm G-L/Hg lamp, λ > 500 nm/DMA-TEOA/ BIN G-L/436 nm monochromic light/4:1(v:v) CH3CN−TEOA

735 (2017)

G-L/250 W Xe lamp/298 K TEOA

1425 (2016) 1426 (2016)

1431 (2017) 1432 (2017) 1433 (2017) 1434 (2016) 1435 (2016) 1436 (2016) 1437 (2016) 1438 (2014)


Chemical Reviews

Review

Table 16. continued semiconductor

cocatalysts

mesoporous SiO2

Co-complex

La-modified NaTaO3

Co-complex

C3N4 Ru complex

selective products


biomimetic cocatalysts CO TON = 141.8

Co-complex Co-complex

CH3OH C2H5OH CO CO

36.2 21.4 17 TON = 62

g-C3N4 nanosheets

Co−porphyrin

HCOOH

mpg-C3N4

Fe quaterpyridine

CO

g-C3N4 titanate nanosheets Ru-complex

amine internal pyridyl amine

CH4CH3OH CH3OH CH3OH

154.4 μmol (TON = 137) TON = 155 AQY(400) = 4.2% 0.340.28

Ru-complex Rh-doped TiO2

rhenium Bi-complex light-harvesting complex

Ru-complex

Re-complex

CO CO CH3CHO HCOOCH3 HCOOH

TNCO = 240 2.8 5.5 5.5 TON = 25

Ru-complex zirconium MOF Os-complex

Re-complex Re-complex, Ag Re-complex

CO CO CO

TON = 180

TiO2 nanoparticles

Pd Pt Pd

TiO2

TiO2 nanoparticles nafion-coated TiO2 particles

Pd Pd and RuO2 1.0 wt % Pd

TiO2

0.5% Pd

Al2O3 TiO2

PdxAuy 3 wt % Pd

TiO2

PdH0.43

TiO2 nanosheets

Pd nanosheets

TiO2 nanosheets

Pd nanorings

g-C3N4 CsPbBr3 NC

Pd Pd

ex-Ti-oxide/Y-zeolite Ti-MCM-48 (Si/Ti = 80) zeolites TiO2

2.1

TON = 1138

noble metal cocatalysts CH4 0.329 0.133 CH4 CH4 0.37 0.06 C2H6 CO 0.04 HCOOH 3765 ppm g−1 3435 ppm g−1 CH4 2 μmol g−1 h−1 1 μmol g−1 h−1 C2H6 CH4 4.3 CO 1.1 CH4 669.0 μmol g−1 min−1 CO 0.144 1.643 CH4 CH4 20.6

Pt 1 wt % Pt

H2 CO CH4 H2 CO CH4 CH3OH CH4 CO H2 CH4 CH4

20.7 12.6 3.0 13.7 15.5 4.1 3.17 3.48 1.92 1.1 12 ̀ 12

Pt

CH4

4.8

NaNbO3 nanowires TiO2 nanotubes

Pt ultrafine Pt NPs

CH4 CO

653 ppm g−1 h−1 25 ppm

self-doped SrTiO3 δparticles mesoporous Zn2GeO4

0.3% wt Pt

CH4

QE = 0.21%

1 wt % Pt

CH4

28.9 ppm g−1 h−1 QE = 0.2% CW

conditions

ref (year)

G-L/200-W mercury lamp, 100 mW/cm2/ TEOA, methanol G-L/77W Hg lamp

1439 (2016)

G-L/300W Xe lamp, 400 < λ < 800 nm G-L/300 W mercury lamp, λ > 415 nm/ ACN, TEOA G-L/500W−Xe lamp, 100 mW/cm2/KCl (−0.6 V, PEC) G-L/λ > 400 nm/CH3CN/TEOA (4:1 v/v)

1441 (2017) 1442 (2017)

1440 (2016)

1443 (2017) 1444 (2018)

G-S/300 W Xe lamp G-L/λ = 470 nm/DMF G-S/300 W Xe lamp, λ > 400 nm, 150 W/cm2 G-L/λ = 480 nm/DMF/TEOA G-L/300 W xenon lamp, 362 mW/cm2

653 (2015) 1445 (2014) 655 (2015)

G-L/high-pressure Hg lamp, λ > 500 nm/ DMA, TEOA G-L/λ= 480 nm Xe lamp/DMF, TEOA G-L/300 Wk Xe lamp/(5vol% TEA) G-L/300 W Xe lamp, λ = 600 nm/DMF, TEOA

1448 (2015)

G-L/>300 nm, 5 °C

1452 (1993)

G-L/>310 nm, 5 °C, pH 4.1

1453 (2001)

G-L/Xe lamp, 0.05 M Na2SO3

1396 (2001)

G-L/Xe lamp

1454 (2012)

G-S/320 < λ < 780 nm, 580 mW/cm2, 0.2 MPa, 323 K

1160 (2014)

G-S/visible light 0.21 W cm−2/500 °C G-S/Xe lamp

1455 (2016) 1456 (2017)

G-L/300 W xenon lamp, λ > 400 nm, 2.7 mW cm−2 G-S/300 W Xe lamp, λ < 400 nm, 2.7 mW/cm2

109 (2017)

G-S/300 W Xe lamp, λ < 400 nm, 2.7 mW/cm2

108 (2017)

G-S/300 W Xe lamp G-S/150 W Xe lamp, λ > 420 nm, 150 mW/cm2

1300 (2017) 1457 (2018)

G-S/λ > 280 nm, 328 K G-S/λ> 280 nm, 328 K

68 (1997) 56 (1998)

L-S/300 W high-pressure Hg lamp (wavelength 365 nm) G-S/Xe lamp G-S/300 W xenon lamp, 100 mW cm−2, AM 1.5G

1458 (2009)

1446 (2005) 1447 (2014)

1449 (2016) 1450 (2016) 1451 (2013)

108 (2017)

1459 (2011) 1460 (2011) 1461 (2011)

G-S/Xe lamp

1462 (2011)


Chemical Reviews

Review


cocatalysts

selective products

TiO2 rods with dominant (010) P25

1% Pt

CH4

Ti2O single crystals TiO2 thin film N-doped mesoporous TiO2 In2Ge2O7 nanowires ZnAl2O4-modified mesoporous ZnGaNO mesoporous (Zn1+xGe) (N2Ox) SiO2-pillared HNb3O8 NaNbO3 mesoporous In(OH)3 ZIF-8/Zn2GeO4 nanorods Fe2V4O13 nanoribbons g-C3N4/NaNbO3 Bi2WO6

Pt (ultrafine nanoparticles) 1.04 nm Pt 0.2 wt. % Pt

CH4 CH4 CH4

1% Pt 0.5 wt % Pt

CO CH4

1 wt % Pt

TiO2 nanotube films g-C3N4


noble metal cocatalysts 2.5 2.0 1361 1361 2.85

conditions

ref (year) 1463 (2011)

G-S/Xe lamp, 19.6 mW/cm2 G-S/λ > 420 nm, 38.2 mW/cm2, 60 °C

61 (2012) 61 (2012) 568 (2012)

0.51 9.2

G-S/Xe lamp G-S/λ > 420 nm

763 (2012) 1464 (2012)

CH4

2.68 ppm g−1 h−1

G-S/λ > 400 nm

575 (2012)

0.4 wt % Pt 0.5 wt % Pt 0.5 wt % Pt 1 wt % Pt 0.5 wt % Pt Pt Pt

CH4 CH4 CH4 CH3OH CH4 CH4 CO

2.90 12.6 μmol m−2 h−1 0.8 0.22 2.75 6.4 0.5 μmol/gcat

G-S/Xe lamp, 34.8 mW/cm2, 60 °C G-S/λ > 300 nm, 80 kPa G-S/Xe lamp, 80 kPa G-L/Xe lamp, Na2SO3 G-S/λ > 420 nm

1465 (2012) 1466 (2013) 576 (2013) 1467 (2013) 1468 (2013) 971 (2014) 558 (2014)

g-C3N4 g-C3N4 Cu2S

Pt, MgO 1 wt % Pt 0.75 wt % Pt 0.75 wt % Pt Pt 2 wt % Pt Pt

GaN nanowires

Pt

oxygen-vacancy-rich Ga2O3 TiO2 photonic crystals hydrogen-doped, bluecolored reduced titania reduced anatase TiO2 β-SiC hollow spheres C-In2O3

Pt

CH4 CH4 CH3OH HCHO CH4 CH4 CO CH4 CH4 CO CO

100.22 ppm h−1 cm−2 0.3 0.25 0.125 0.025 μmol h−1 1.302 3.02 0.13 14.8 47.4 21.0 μmol·h−1

Pt Pt

CH4 CH4

Pt Pt Pt

TiO2 nanofibers

1% Pt, 1% CdSe

TiO2 TiO2 films

Pt@Ag plasmonic Au NPs

carbon nanoparticles of sub-10 nm leaf-architectured SrTiO3

Au

ZnO

Au

TiO2 particles

0.5% Au

TiO2 TiO2 nanowires

3.5 wt. % In 0.2 wt. % Au 0.5 wt. % Au

TiO2 TiO2 g-C3N4/BiOBr

Au Au Au

BiOI

Au, MnOx

1 wt % Au

G-S/300 W Xe arc lamp 420 nm < λ < 620 nm G-L/300 W Hg lamp G-S/Xe lamp

1469 (2014) 1470 (2014)

G-S/300 W simulated solar Xe arc lamp G-S/daylight bulb, 8.5 mW cm−2 447 nm blue laser, 30 mW/cm2

1470 (2014) 1471 (2015) 1472 (2015)

G-S/300 W Xe lamp

1473 (2015)

G-L/300 W Xe lamp/1.01 bar, 25 °C

906 (2016)

3.22 80.35 (QE = 12.40%)

G-L/320 nm < λ < 780 nm/20 °C, 5 MPa G-S/100 W Xe lamp/AM1.5 filter

611 (2017) 1474 (2017)

CH4 CH4 CO CH4 CH3OH HCOOCH3 CH4 CH4 C2H6 HCHO CH3OH HCOOH

1.13 16.8 126.6 μmol h−1 27.9 μmol h−1 90 ppm g−1·h−1 225.4 ppm g−1·h−1 160.3 2.31 1.63 1.36 0.86 QE = 0.3%

G-S/100 W xenon solar simulator/AM1.5 G-S/300 W xenon lamp/298 K G-L/300 W Xe lamp/TEOA

1475 (2017) 639 (2017) 797 (2017)

G-S/6 W UV−B lamp, 2 mW/cm2

792 (2016)

G-S/500 W Xe lamp

1476 (2018) 84 (2011)

G-L/425 < λ < 720 nm

83 (2011)

CO CH4 CO CH4 CH4 CO CO CH4 CO CH4 CH4 CH4 CO CH4 CO CH4

0.35 0.25 4 1.2 3.1 1.5 8982 82.65 1237 12.65 2.8870 2.52 6.67 0.92 42.9 1.36

G-S/Xe lamp, 80 kPa

648 (2013)

G-S/2.5 × 105 W m−2

1477 (2013)

G-S/320 < λ < 780 nm, 580 mW/cm2, 0.2 MPa, 323 K

1160 (2014)

G-S/Hg lamp, 100 °C, M(CO2:H2) = 1.5

538 (2015)

G-S/Hglamp/100 °C, M(CO2:H2) = 1.0

539 (2015)

G-S/300 W xenon arc lamp G-S/300 W xenon arc lamp G-S/300 W Xe lamp, 380 nm monochromatic light

1478 (2015) 1479 (2015) 1480 (2016)

G-S/300 W Xe lamp/20 °C

1397 (2016)

CX


Chemical Reviews

Review


cocatalysts

C3N4-ZIF-9

Au

TiO2 nanosheets Pt/TiO2 TiO2 nanotubes TiO2

Au nanoplate Au Au@SiO2 Au 0.5 wt % Au

La2Sn2O7

1 wt % Au

TiO2

Au, montmorillonite

TiO2 g-C3N4

Au/Ag Au

hierarchical TiO2−SiO2 framework BaLa4Ti4O15 SrTiO3 nanocrystals AgX TaON−RuBLRu′

Au, RuO2 Ag 7 wt % Ag Ag Ag

TiO2 TiO2

Ag Ag

TiO2 (anatase)

3 wt % Ag

AgIO3 zinc−gallium layered CdS nanowires

Ag Ag/Au Ag nanowire RGO

La2Ti2O7 ZnGa2O4 TiO2 Ga2O3 BaCeO3 Ag2SO3

Ag Ag Ag Ag Ag 5% Ag

N-doped TiO2 (anatase) N-doped TiO2 microsheet TiO2

1.5 wt % Ag 1.5 wt % MnOx Ag, MnOx nanoparticle Ag, MgO

TiO2

Ag, MgO

Ga2O3−ZnGa2O4 layer ZnTa2O6 TiO2 TiO2

Ag Ag Ag Ag-NPs

TiO2/PU TiO2 nanorods

2 wt % Ag 4 wt % Cu Ag NPs

TiO2 CdS g-C3N4/TiO2 UiO-67 (Ren-MOF)

Ag Ag Ag Ag nanocubes

selective products


noble metal cocatalysts H2 7.66 CO 0.52 CH3OH 3.5 CH4 2.3 2.9 CH4 58.47 CO 4144 CH4 CO CO CH4 C2H6 CO CH4 CO H2COCH4

4 2 199 42 2.08 1813 1.55 6.11 2.51.25.9

CO HCOOH CH3OH HCOOH CO CH3OH CH4

63 3006 38 TN = 41 TN = 2.8 405.2 μmol/g 2.64

H2 CO CH4 CH4 CO H2 CO CH4 CO CO CH4 CO CH4 CH4 CO CH3OH

71.2 10.2 8.9 6 0.201 35.3 μmol·h−1 0.912 0.288 12 μmol h−1 155 μmol h−1 1.8 2.0 μmol h−1 0.56 3.01 1.24 0.53

CH3OH CH4

0.53 18.8

CH4 CH3OH CO CO CH3OH CO

0.86 0.06 110 19.3 μmol h−1 11.1 983

CO CH4 CO CH4 CH4 CO CO CO

183 220 12.5 1.1 80 ppm 1.30 μmol/gcat 87.3 7-fold enhancement

CY

conditions

ref (year)

G-S/300 W Xe lamp

1481 (2016)

G-L/300 W Xe lamp, UV-visible light G-L/two 5 W LED lamps, 365 and 530 nm

808 (2016) 597 (2016)

G-S/AM1.5 G-S/200 W Hg lamp, 150 mW/cm2/ M(CO2:H2) = 1.0 G-L/125 W mercury lamp/20 °C

1482 (2016) 1483 (2016)

G-S/solar simulator LCS-100 (Newport), 100 mW/cm2, visible light

1485 (2017)

G-S/35W HID Xe lamp G-S/300 W Xe lamp

536 (2017) 1486 (2018)

G-S/300 W Xe lamp, AM 1.5

1400(2018)

G-L/Xe lamp, 2800 μW/cm2, 25 °C G-L/300 W Xe arc lamp, λ > 420 nm G-L/λ > 400 nm

85 (2011) 922 (2012) 1487 (2012) 94 (2013)

1484 (2017)

G-L/500 W xenon arc lamp, λ > 400 nm G-S/8 W UVA lamps , 365 nm, average intensity = 3.25 mW cm−2 G-S/8W fluorescent tube/2 bars , 50 °C

1488 (2013) 1489 (2013)

G-S/UV−vis light G-L/500 W xenon arc lamp 3.25 mW cm−2 G-S/λ > 420 nm

1491 (2014) 1492 (2015) 1182 (2015)

G-L/400 W high-pressure mercury lamp G-L/400 W high-pressure mercury lamp G-S/300 W xenon arc lamp, λ > 420 nm G-L/5 h G-S/300 W xenon lamp G-S/500 W Xe lamp, λ > 400 nm, 10.75 mW/cm2/M(CO2:H2) = 1.0

1493 1494 1495 1167 1496 1497

G-S/300 W Xe lamp, λ > 400 nm

106 (2016)

G-S/300 W Xe lamp, λ > 400 nm G-S/mercury lamp (365 nm), 35.0 mW/cm2, 200 nm < λ < 400 nm/ 45 °C G-S/350 W Xe lamp

106 (2016) 1498 (2016)

G-L/400 W high-pressure mercury lamp G-L/400 W high-pressure mercury lamp G-S/300 W xenon arc lamp G-S/35 W car HID lamp, light intensity 20 mW/cm2 G-S/two 20 W bulbs, 50 mW/cm2, 400 nm < λ < 700 nm/45 °C

551 (2016) 1500 (2016) 1501 (2016) 1502 (2017)

1490 (2013)

(2015) (2015) (2015) (2015) (2015) (2016)

1499 (2018)

1503 (2017)

G-L/300 W xenon lamp, λ>420 nm

1504 (2017)

G-L/5 °C G-S/300 W Xe lamp with a 420 nm G-S/300 W Xe arc lamp, 45 °C G-L/300 W xenon, 700>λ>400 nm/ acetonitrile,triethylamine

1505 (2017) 1285 (2017) 957 (2017) 1506 (2017)


Chemical Reviews

Review


cocatalysts

CdS nanorods SrTiO3 N-doped TiO2 nanosheets K2Ti6O13 particles

Ag/RGO Ag-NPs Ag/Pd nanoalloys Pt and Cu

N-doped TiO2 nanotube arrays

Cu and Pt

TiO2 multiwalled nanotube arrays

Cu0.33Pt0.67

TiO2 g-C3N4

CuPt nanoclusters PtCu concave nanocubes

TiO2

Pt, Cu2O

TiO2 NFs TiO2 film

Au0.25/Pt0.75 Au1Cu2

SrTiO3/TiO2 coaxial nanotube arrays

Au3Cu

TiO2

Pt@Cu2O

mesoporous ZnGa2O4 Zn2GeO4 nanorods

1 wt % RuO2 3 wt % RuO2

CuxAgyInzZnkS solid solutions hollow TiO2 single crystals with (101) facets ZnGa2O4 nanocubes Cu2O Cd2Ge2O6 nanowires Na(1−x)LaxTaO(3+x)

RuOx 1% RuO2 RuO2

Zn2GeO4 nanoribbons Zn1.7GeN1.8O nanosheaves Zn2SnO4 nanosheetmicrooctahedrons Na2 V6O16 nanoribbons TiO2

1% RuO2 + 1% Pt 1% RuO2 + 1% Pt 1% RuO2 + 1% Pt 1% RuO2 + 1% Pt 0.5% Ru

ZnS

Ru NPs

TiO2 single-crystalline nanosheets (brookite)

Ti3+

GaN nanowires

Rh/Cr2O3

TiO2 nanosheets

Rh nanowires

hierarchical P-doped TiO2 nanotube array

Ti plate

g-C3N4 Ta3N5 Bi4O5I2

11.4 wt % Bi4O5I2 Bi Bi

g-C3N4

Mg

selective products


noble metal cocatalysts CO 1.61 μmol·h−1 CO 2 CH4 79.0 H2 102.1 μmol g−1 1.64 μmol g−1 CH4 HCHO 3.42 μmol g−1 HCOOH 18.26 μmol g−1 hydrocarbon 111 ppm cm−2 h−1 160 ppm cm−2 h−1 H2 CH4 116 21 C2H6 CH4 11.35 7.47 CH4 CO 3.07 CH4 1.42

RuO2 or Rh1.32Cr0.66O3

CH4 CH4 H2 CH4 CO CH4 CO H2 CH4 CO CH4 CH3OH

114 2200 286 421.2 3770 33 8.3 25 50.4 ppm h−1 17.9 ppm h−1 3.5 ppm h−1 118.5

1 wt % RuO2

CH4

0.5 wt % RuO2

conditions

ref (year)

G-S/300 W Xe lamp, λ > 420 nm G-S/300 W xenon, λ > 400 nm, 0.2 W cm−2 G-L/300 W xenon/triethylamine G-L/Hg lamp, 77 kPa

1507 1508 1509 1350

G-S/Xe lamp

60 (2009)

G-S/Xe lamp

91 (2012)

150 W Xe lamp/313 K, 1.2 atm G-S/300 W Xe lamp , 100 mW/cm2, λ > 400 nm/0.15 MPa CO2

1278 (2016) 1364 (2017)

G-S/300 W Xe lamp, 20.5 mW/cm2, 300 nm < λ < 400 nm/20 °C, 71 kPa

1186 (2017)

(2018) (2018) (2018) (2003)

G-S/Xe lamp

1351 (2013) 62 (2014)

G(N2H4·H2O)-S/Xe lamp

1352 (2015) 92 (2013)

G-S/Xe lamp G-S/Xe lamp

81 (2010) 1510 (2011)

G-L/λ > 400 nm

1511 (2011)

1.8

G-S/Xe lamp

1512 (2012)

CH4 O2 CO CH4 CH3OH C2H5OH CH4 CH4 CH4

0.16 μmol h−1 1.2 μmol h−1 0.293 0.72 49.6 16.2 6.7 4.4 36 ppm g−1 h−1

G-S/Xe lamp

1513 (2013)

G-L/Xe lamp, 0.7 M Na2SO3

1181 (2014) 1514 (2014) 1515 (2016)

CH4 CH4 CO HCOOH CO CO CH4 CH4 CO H2 CO CH4 C2H5OH CH3OH

0.18 3.5 0.62 0.75 mol dm−3 0.45 mol dm−3 23.5 11.9 3.5 47.1 10.6 13.5 4.5 12.1 286.8

earth-abundant CO CH4 CO CH4 CH4

metal cocatalysts 45.6 0.57 40.02 7.19 5.35

CZ

G-L/77 W Hg lamp/NaOH, pH 13

78 (2010) 618 (2012) 1402 (2012)

>420 nm

G-S/320 < λ < 780 nm, 580 mW/cm2, 0.2 MPa, 323 K

1401 (2014) 1160 (2014)

G-L/150 W XBO arc lamp, λ > 320 nm

1516 (2015)

G-S/300 W Xe lamp, 216 mW/cm2, λ > 420 nm/45 °C

807 (2016)

G-S/300 W Xe lamp

1473 (2015)

G-S/300 W Xe lamp, λ < 400 nm, 2.7 mW/cm2

1357 (2017)

G-L/Xe lamp/353 K

1517 (2016)

G-L/300 W Xe lamp, λ > 400 nm G-S/300 W Xe lamp G-S/300 W Xe lamp, λ > 400 nm

977 (2016) 1518 (2018) 1519 (2018)

G-S/300 W Xe lamp

1520 (2018) DOI: 10.1021/acs.chemrev.8b00400 Chem. Rev. XXXX, XXX, XXX−XXX

Chemical Reviews

Review


cocatalysts

ZnS microcrystals

Cd

ZrO2 TiO2

1 wt % Cu Cu powders

TiO2 powders

5% Cu

porous TiO2−SiO2

0.5 wt % Cu

TiO2

2 wt % Cu

TiO2 nanorod films TiO2 nanoparticle wafer

plasmonic Cu nanoparticles Cu nanoparticles

TiO2

1% Cu

In2O3/TiO2

0.5% Cu 1% Cu plasmonic Cu nanoparticles Cu, C 3% Cu

TiO2 nanoflower films TiO2 g-C3N4/TiO2 nanoporous TiO2 TiO2 NPs

0.4 wt % Cu 0.75 wt % Cu 0.25 wt % Bi2O3 Cu2O 2.0 wt % Cu2O 2.0 wt % Cu2O 3.0 wt % CuO 1.2 wt % Cu2O clusters

selective products


earth-abundant CO HCOOH H2 CO CO HCHO CH3OH CH4 C2H4 C2H6 CO CH4 CO CH4 H2 CH4 CH4 CO CO H2 CH4 CH3OH CH3OH CO CH3OH HCOOH CH4 CH4 CO CH3OH CH3OH CH3OH CH3OH CH3OH

metal cocatalysts 0.69 QE = 32.5% QE = 5% 2.5 0.27 0.28 0.55 0.65 μL g−1 h−1 0.92 μL g−1 h−1 0.13 μL g−1 h−1 60 10 1.1 2 15 0.18 36 ppm cm−2 h−1 24 ppm cm−2 h−1 334 452 181 68 1.8 μmol cm−2 h−1 2.526 445 2260 8.04 11.90 5.74

CH3OH CH4 C2H4 CH4 CH4 CH3OH CO CH4 CH3OH C2H5OH CH3OH CH3COCH3 CO

38.2 0.024 80 ppm 8.68 100 ppm h−1 0.59 14.5 2.2 60.5 15.9 137.48 335.93 1981 μmol/gcat 27.9 47.0 0.017 μmol cm−2 h−1 160

TiO2 nanoparticles TiO2 nanoparticles P25 TiO2 nanoparticles TiO2 coated on optical fibers SiC TiO2 nanoparticles Cu TiO2-(001) TiO2 nanotube arrays TiO2-pillared K2Ti4O9 TiO2

3.13% Cu2O 0.03 wt % Cu2O Cu2O (p-type) 1 wt % Cu2O octahedral Cu2O Cu2O CuO

Na(1−x)LaxTaO(3+x)

CuO

NaTaO3 nanocubes

3 wt % CuO

N-doped TiO2

CuO

GO−TiO2

CuO

SrTiO3 N-doped InTaO4

CuxO Ni@NiO

CH3OH C2H5OH CO CH3OH

InTaO4 (SSR) InTaO4 particles

1 wt % NiO 1 wt % NiO

CH3OH CH3OH

1.394 (QE = 2.45%) 11.1 (QE = 0.063%)

InNbO4 (SSR)

1 wt % NiO 1 wt % Co3O4 Ni Ni

CH3OH CH3OH CH4 CO

1.577 1.503 4200 900 μmol g−1 min−1

SiO2−Al2O3 SiO2

19.75 (QE = 10%) 10 (QE = 5.35%) 442 (QE = 19.23%) 0.45

DA

conditions

ref (year)

G-L/Xe lamp, 2-propanol

1521 (1995)

G-L/Hg lamp G-L/Hg lamp

55 (1993) 1522 (1992)

G-L/Hg lamp, pH 5.45, 28 kgf/cm2

1029 (1994)

G-S/Xe lamp, 2.4 mW/cm2

1523 (2010)

G-L/8 WHg lamp, pH 5.45, 120 kPa

1524 (2018)

G-L/UVAlamp, 3.25 mW/cm2 G-S/AM 1.5G, 100 mW/cm2

1525 (2012) 1526 (2014)

G-S/8 W UV−C lamp, 4.40 mW/cm2

1527 (2016)

G-S/500 W Hg lamp, 25 mW/cm2/1.2 bar/ M(CO2:H2:He) = 1:1:3

540 (2016)

G-L/λ > 420 nm G-L/32 W Hg lamp, λ = 253.7 nm/25 °C G-L/500 W Xe lamp

1528 (2015) 1529 (2016) 1530 (2017)

G-S/500 W Xe lamp G-S/300 W Xe lamp

1531 (2017) 1159 (2016)

G-S/Xe lamp, 2.4 mW/cm2 G-L/Hg lamp, 138 μW/cm2, 50 °C

684 (1994) 69 (2002)

G-L/Hg lamp, 2450 μW/cm2, 50 °C G-S/Hg lamp, 16 W/cm2

1179 (2005) 1532 (2005)

G-L/λ > 400 nm, Na2SO3 G-L/UVAlamp, 3.25 mW/cm2 G-L/blue LED light, 435 nm < λ < 450 nm G-S/Xe lamp, 298 K G-L/Xe lamp, 103 kPa G-S/AM 1.5, 100 mW/cm2/0.69 bar, 70 °C G-S/40 W Hg UV lamp, 20 mW cm−2

1533 (2011) 89 (2012) 1534 (2014) 670 (2015) 1535 (2015) 1536 (2016) 634 (2015)


1515 (2016)

G-L/250 W mercury lamp, λ = 360 nm/ 25 °C/isopropanol

1537 (2016)

G-S/200 W Hg reflector lamp 150 mW cm−2, 254 nm G-S/mercury vapor lamp/25 °C, pH 4

537 (2016) 1538 (2016)

G-L/Hg−Xe lamp G-L/390 < λ < 770 nm, 100 mW/cm2, 25 °C G-L/halogen lamp, KHCO3 G-L/400 < λ < 1100 nm, 327 mW/cm2, 25 °C G-L/500 < λ < 900 nm, 143 μW/cm2

1403

G-S/300 W Xe lamp, 1 KW/m2 G-S/300 nm < λ < 800 nm, 1.07 W cm−2, 550 °C

1542 (2016) 1543 (2017)

(2017) 844 (2011)

1539 (2007) 1540 (2010) 1541 (2012)


Chemical Reviews

Review


cocatalysts

InTaO4

1% Ni

black TiO2 TiO2 nanofibers

Ni-nanocluster Ni(OH)2 nanosheets

Na(1−x)LaxTaO(3+x)

NiO

TiO2

selective products


earth-abundant metal cocatalysts CH3OH 2.78 (QE = 1.85%) 1.67 0.71 2.20 0.11 0.15 59.6 18.8 240

KTaO3 ZnO TixSiMCM-41

1 wt %NiO 3 wt % In2O3 1 wt % NiO 3 wt % In2O3 2 NiO NiO 5.0 wt. % CaO

CH3CHO CO CH4 CH3OH C2H5OH CH3OH C2H5OH CH4 CO CH4 CH3OH CH3OH CH4

243 208 1815 1.57 82.0 μmol g−1 L−1

porous TiO2 microspheres

MgO

CO

TiO2 microspheres (spray pyrolysis) TiO2 Ga2O3

5% MgO

CO

21.3 (150 °C) 2.8 (150 °C) 30 (150°C)

0.2% porous MgO Mg−Al−LDH, Ag

CH4 CO

TiO2

0.5% Pt−1.0% MgO

TiO2 TiO2

MgO Pt−0.85% PANI

TiO2

3% NaOH

g-C3N4 g-C3N4 g-C3N4 CdS

0.5% Pd, 10 wt % Mg−Al−LDH Co-ZIF-9 UiO-66 Co-ZIF-9

TiO2 Ru-complex

Co-ZIF-9 Co-ZIF-67

g-C3N4 nanosheets

ZIF-20

[Ru(bpy)3]2+ (bpy = 2,2′-bipyridine) LaPO4 CdS

conductive Ni3(hexaaminotriphenylene)2 MOFs CoCl2 1 wt % CuCO2O4 nanoplates

CH4 H2 CO CH4 CH4 H2 CH4 H2 CH4 CO CO CO H2 CO CO H2 CH4 CO CO

1.87 211.7 μmol h−1 (TON = 75.4) 11 11 0.03 100.22 ppm/h cm2 50 320 8.7 19 QE = 0.093% 25 10 2520 555 17.58 74.8 μmol h−1 26 μmol h−1 15.524 53.869 34500

[Ru(bpy)3]Cl2

carbon coating on cobalt metal

CH4 CO H2 CO

1.6 μmol h−1 40 μmol h−1 7.5 μmol h−1 1258.30 μL

TiO2

NiS

CH4

6.65

TiO2 quasi-nanocubes (brookite)

g-C3N4 nanodots

ZnO TiO2

ZIF-8 CuSx

CO CH4 CH3OH CH4

3.8 31.8 0.83 6.65

mesoporous WO3

Mo

CdS NPs Bi2WO6

Mo2C nanowires MoS2

MoS2

Co-doped MoS2

CH3OH CH4 CO CH3OH C2H5OH CH3OH

1.15 0.50 29.2 μmol h−1 20.5 μmol g−1 17.9 μmol g−1 35 mmol L−1

TiO2

DB

conditions

ref (year)

G-L/20 W white LED, acetonitrile/water/ TEOA G-S/300 W halogen lamp G-S/300 W Xenon lamp, 40 mW cm−2

1544 (2017) 1545 (2018) 1546 (2018)


1515 (2016)

G-S/500 W Hg lamp, 25 mW/cm2/1.2 bar /H2O

1547 (2016)

G-S/500 W Hg lamp, 25 mW/cm2/ M(CO2:H2:He) = 1:1:3

1547 (2016)

G-L/250 W Hg lamp, isopropanol G-S/300 W Xe lamp G-S/Hg lamp, 6 W/cm2, 0.1 MPa, 303 K, M(CO2:H2O) = 1:2 G-L/200 < λ < 1000 nm, 420 mW/cm2

1548 (2018) 637 (2018) 581 (2015) 1163 (2013)

G-L/200 < λ < 1000 nm, 420 mW/cm2

1162 (2014)

G-S/300 W Xe lamp G-L/400 W Hg lamp, quartz filter/NaHCO3

610 (2016) 1549 (2017)

G-S/320 < λ < 780 nm, 580 mW/cm2, 0.2 MPa, 323 K

95, 1160 (2013)

G-L/300 W Hg lamp/room temperature G-S/320 < λ< 780 nm, 0.2 MPa, 323 K

1161 (2014) 1176 (2015)

G-S/Xe lamp, 80 kPa

1164 (2014)

G-L/Xe lamp, 200 Torr CO2 G-L/λ > 420 nm, 30 °C, TEOA in MeCN G-L/400 < λ < 800 nm, 80 kPa G-L/λ > 420 nm, 30 °C, TEOA in MeCN

1174 (2014) 1171 (2014) 965 (2015) 1172 (2015)

G-S/300 W Xenon lamp, 494 mW cm−2 G-L/300 W Xe lamp, λ > 420 nm/ M(TEOA:H2O:DMA = 1:2:3)

1550 (2016) 1551 (2017)

G-L/300 W Xe lamp, λ > 400 nm/ M(MeCN/TEOA = 4:1)

1552 (2018)

G-L/100 W LED light (MeCN/H2O/TEOA solution = 10:2:4 v/v/v) G-L/UV light G-L/300W Xe lamp, λ > 420 nm/TEOA /30 °C, 1 atm CO2

1553 (2018)

G-L/300 W Xe lamp, λ > 420 nm/ M(MeCN/TEOA/H2O = 3:1:1) G-S/mercury lamp, 6 W/m2/ M(CO2:H2O) = 1:4 G-S/300 W Xe lamp

1554 (2016) 1555 (2016) 1556 (2018) 945 (2017) 955 (2017)

G-S/300 W Xe lamp G-S/6 W Hg lamp, 365 nm/25 °C, 1.0 atm/ M(CO2:H2O) = 1:4 G-S/300 W Xe lamp, 340 mW/cm2/ 420 < λ < 780 nm

1297 (2016) 1557 (2017)

G-L/300 W Xe lamp, λ > 420 nm/TEOA G-L/300 W Xe lamp, λ > 420 nm

1559 (2018) 632 (2017)

G-L/500 W Xenon lamp, 100 mw cm−2

1560 (2015)

1558 (2016)


Chemical Reviews

Review


cocatalysts

selective products


CdS

WO3

earth-abundant metal cocatalysts CH4 1.02

ZnO nanorods

ZIF-8

CH3OH

0.83

MWCNT@TiO2 TiO2

transition metal oxide CeO2

CdS

CeO2

Mn-complex

zinc porphyrin photosensitizer

Zn0.75Mg0.25O

basalt fiber

CH4 CO CH4 CH4 CH3OH CO HCOOH CO

0.93 μmol g−1 7.83 5.12 2.3 305 TON = 64 TON = 16 5

TiO2 g-C3N4

ZrO2 AgX

CH4 CH4

0.48 10.92 μmol gcat−1

C3N4

AgCl

CH4

1

C3N4

B4C

CH4

0.85

P25

Ti3C2

Bi2WO6 nanosheets

Ti3C2 nanosheets

TiO2 MnCO2O4 B−P codoped g-C3N4 TiO2

Ti3C2 Ru-complex SnO2 SrTiO3

CO CH4 CH4 CH3OH CH4 CO CH4 CH4

11.74 16.61 1.78 0.44 4.4 9.2 μmol h−1 7.5 μmol h−1 20.83 ppm

TiO2

Cu2ZnSnS4

CH4

118.75 ppm

conditions

ref (year)

G-S/300 W Xe lamp, λ > 420 nm, 150 mW/cm2 G-S/300 W Xe lamp/atmospheric pressure and room temperature G-S/15 W energy saving light bulb G-S/300 W Xe lamp/298 K

101 (2015)

G-S/300 W Xe arc lamp

624 (2015)

G-L/500 W Xe lamp/TEA

1563 (2016)

G-S/UV lamp, 6.0 W/cm2 × 2 ea, total power = 12.0 W/cm2 G-L/UV 8 W Hg lamps G-S/15 W energy-saving daylight lamp, 8.5 mW cm−2 G-S/15 W energy-saving daylight lamp, 8.5 mW cm−2 G-L/300 W xenon short arc lamp, 405 nm < λ < 723 nm/295 K G-S/300 W xenon lamp

1564 (2017)

G-S/300 W xenon lamp

1376 (2018)

G-S/300 W xenon lamp G-L/300 W Xe lamp, λ > 420 nm/TEOA G-S/300 W xenon lamp, λ > 420 nm G-S/300 W high-pressure Hg lamp, 10.4 mW/cm2 G-S/AM1.5G sunlight

1568 (2018) 1569 (2015) 949 (2017) 1570 (2015)

1297 (2016) 1561 (2014) 1562 (2016)

1565 (2013) 969 (2016) 1566 (2016) 960 (2016) 1567 (2018)

934 (2016)

of control experiments without CdS or light were performed to further confirm photosynthesis of acetic acid through selfphotosensitization of a nonphotosynthetic bacterium (Figure 114C and D). A quantum yield of 85 ± 12% could be achieved for the M. thermoacetica−CdS hybrids (Figure 114E). It was shown that the acetic acid concentrations increased under lowintensity simulated sunlight and in the dark through several light−dark cycles (Figure 114F), implying that the accumulated biosynthetic intermediates under illumination could be then utilized in the dark cycle. The duration of the light cycle further confirmed that 12 h of illumination could lead to the saturated accumulation of intermediate for formation of acetic acid during the dark cycle (Figure 114F). Subsequently, Nocera and his coworkers developed a biological-inorganic hybrid CO2 reduction system with overall efficiency exceeding photosynthesis.1584 In this scalable system, the biocompatible earthabundant Co−P alloy and Co−Pi artificial leaf were in charge of water splitting into H2 and O2 at low driving voltages (Figure 115A), whereas the bacterium Ralstonia eutropha (R. eutropha) was used to generate the biomass, chemicals, or fuels via the low-concentration CO2 hydrogenation in the presence of O2. The resulting Co−Pi|Co−P|R. eutropha hybrid system exhibited the CO2 reduction energy efficiency of ∼50% at low Eappl of 2.0 V (Figure 115B). More interestingly, it was found that the linear growth of biomass accumulation is similar to that at the amount of charge passed under pure CO2 (Figure 115C) and ambient CO2 levels (Figure 115D), indicating the biosynthesis rate-limiting step of H2 oxidation rather than CO2 reduction. The observed accumulation of poly(3-hydroxybutyrate) (PHB) and liquid fuels exhibited similar trends to those obtained for

Figure 110. Schematic illustration of CO2 photoreduction over the anaerobic organism, Carboxydothermus hydrogenoformans (Ch) modified CODH, and RuP co-decorated TiO2 NPs.

system under visible light (Figure 113B). The integrated hollow nanofiber-based and microcapsule-based artificial photosynthesis systems could achieve the methanol yields of 90.6% and 92.97%, respectively, much larger than that obtained in a free solution system (35.6%) (Figure 113C and D). This integrated artificial photosynthesis platform shows a new direction for efficient and sustainable production of a considerable number of fuels and chemicals through the photoenzymatic reactions. More interestingly, Sakimoto et al. developed a hybrid system for photoconversion of CO2 through direct precipitation of CdS nanoparticles on the surface of the nonphotosynthetic CO2-reducing bacterium Moorella thermoacetica as cocatalyst (Figure 114A).1583 Under light irradiation, the photoexcited holes in CdS can oxidize cysteine (Cys) and generate the H+, whereas the photoexcited electrons in CdS can generate [H] equivalents via reduction outside or inside the cell, which participates in the formation of acetic acid from CO2 via the well-known Wood−Ljungdahl pathway (Figure 114B). A series DC


Chemical Reviews

Review

Figure 111. (A) Photoreduction of CO2 to formic acid over a graphene-based photocatalyst−formate dehydrogenase (FDH) enzyme coupled system under visible light. (B) Transient photocurrent of CCGCMAQSP and MAQSP samples under simulated sun light (1 sun). Photoactivity of CCGCMAQSP, W2Fe4Ta2O17, and MAQSP, for (C) NADH photoregeneration and (D) visible-light-driven generation of formic acid via CO2 photoreduction. The DFT calculated LUMO and HOMO orbitals of the (E) CCG and (F) MAQSP at the DFT-GGA level of approximation.1580 Reprinted with permission from ref 1580. Copyright 2012 American Chemical Society.

photosynthesis (Figure 115I).1584 The native integration of semiconductor nanoparticles with bacterial metabolic processes presents a new way toward rational design of hybrid organisms for solar-to-chemical carbon dioxide reduction, which is of great interest for future exploration. In addition, it is also interesting that the efficient multienzyme cascade systems can be used to enhance the selectivity

PHB synthesis (Figure 115E−H), confirming the necessity of digestion and tolerance of R. eutropha toward isopropanol. The energy efficiency of ∼10% for CO2 reduction was achieved via combining this hybrid device with an existing photovoltaic device of ηsolar = 18%. This approach provides an excellent platform for developing the distributed solar production of chemicals with efficiencies well beyond that of natural DD


Chemical Reviews

Review

Figure 112. (A) Schematic of a leaf and Ru(bpy)32+/MV2+/formate dehydrogenase (FDH)-immobilized PGP50 (a porous glass plate with a nanopore diameter of 50 nm) and (B) PGP50. (C) Formic acid production via electron transfer between Ru(bpy)32+ (photosensitizer), MV2+ (electron mediator), and FDH immobilized in PGP50. (D) Time evolution of light-induced formic acid production by Ru(bpy)32+/MV2+/FDH/ PGP50 (●) and the Ru(bpy)32+/MV2+/FDH solution (■). Photo-driven formic acid production mechanism in the (E) Ru(bpy)32+/MV2+/FDH solution as compared with (F) Ru(bpy)32+/MV2+/FDH/PGP50.1582 Reprinted with permission from ref 1582. Copyright 2017 American Chemical Society.

of photocatalytic CO2 reduction. Although enzymes have the ability to promote the multielectron and multistep CO2 electroreduction to valuable chemicals, such as methanol at low overpotentials, their rarity, and high prices significantly limit industrial applications. Consequently, the design of inexpensive catalysts for mimicking natural enzymes is very urgent. 7.1.2. Biomimetic Complexes. Inspired by the active site structures of enzymes, many metal complexes (biology-inspired molecular catalysts) have been available for photocatalytic or electrocatalytic water splitting and reduction of CO2.123,473,690,1414,1586−1589 Metal complexes with fine-tuned structures in homogeneous molecular systems are well known redox photosensitizers, electrocatalysts or photocatalysts for highly active and selective CO2 reduction.122,690,1414,1590

However, the low durability and inconvenient separation of metal complexes significantly restrict their practical application. Accordingly, the fabrication of the advanced photocatalysts for selective CO2 reduction via combining photoactive semiconductors and metal complexes as cocatalysts is a highly appealing strategy.473,1591−1593 In these complex/semiconductor hybrids, a favorable photoelectron transfer from the semiconductor to the complex can be accomplished, leading to a significant boost in the CO2 photoreduction activity. Considering the high selectivity of metal complexes and the high stability of semiconductor photocatalysts in water, so far, there are many interesting reports on the use of complex/ semiconductor hybrid systems as photocatalysts for CO2 photoreduction. Sato et al. reported that [Ru-dcbpy]/N− Ta2O5 showed the highest rate for production of HCOOH via DE


Chemical Reviews

Review

Figure 113. (A) Process of integrating the polyelectrolyte-doped hollow nanofibers and biocatalysts for generation of methanol via CO2 photoreduction.(B) Time-dependent photoinduced NADH regeneration in different systems. (C) Hollow nanofibers-based and (D) microcapsulesbased artificial photosynthesis systems for methanol generation via photoenzymatic CO2 reduction by biocatalysis (FateDH/FaldDH/ADH/ NADH) without NADH photoregeneration in solution (□), with NADH photoregeneration (M and EY) in solution (○), with integrated photocatalysts (▲), with biocatalysis and photocatalysts in solution (▼), or with integrated biocatalysis and photocatalysts (●).1585 Reprinted with permission from ref 1585. Copyright 2016 John Wiley & Sons, Inc.

TiO2/Fe2O31605 heterojunctions, for achieving the selective CO2 photoreduction. Notably, integration of hybrid semiconductors/metal complexes for photocatalytic CO2 reduction and water oxidation in a single device is of great interest.1606 Particularly, the hybrid systems consisting of metal complexes and particulate g-C3N4 semiconductor seem to be very promising for visible-light-driven CO2 reduction because of the excellent combination effects between the electrochemical (or photocatalytic) ability of metal complexes and the high efficiency of semiconductors for water oxidation.1431 In addition, since overall water splitting has rarely been achieved over a single metal oxide photocatalyst with visiblelight activity, in 1979, Bard first proposed the Z-scheme concept mimicking natural photosynthesis of green plants for water splitting,471 which was experimentally achieved by Abe et al. in 2001 through coupling two visible-light semiconductors and an appropriate shuttle redox mediator.1607,1608 For the photoreduction of CO2, there are also some reports on the Zscheme system containing complexes. Sato et al. first reported that the visible-light generation of HCOOH vis CO2 photoreduction can be achieved over a p-type N-doped Ta2O5/Ru complex photocatalyst.79 Next, they combined a p-type InP/Ru complex hybrid and TiO2 for CO2 reduction and water oxidation, respectively,54 thus achieving the so-called bias-free Z-scheme (or two-step photoexcitation) system for photoelectrochemical reduction of CO2 to HCOO− in aqueous solution (as shown in Figure 117). The selectivity and solarchemical energy conversion efficiency for HCOO production were >70% and 0.03−0.04%, respectively.54 Furthermore, Sekizawa et al. constructed the first visiblelight-driven artificial Z-scheme photocatalytic system for CO2

CO2 photoreduction among all the active photocatalysts. The HCOOH generation selectivity and quantum efficiency were more than 75% and 1.9% at 405 nm for the [Ru-dcbpy]/N− Ta2O5 photocatalyst, respectively.79 Li and coworkers reported that the covalently bonded Re(I) complex/mesoporous silica demonstrated higher activity and stability than its homogeneous counterpart for CO2 photoreduction.1594 Arai et al. reported that solar bias-free formate production from CO2 and H2O was achieved in a PEC system consisting of reduced SrTiO3 (r-STO) photoanode and InP/[RuCP] complex photocathode.1415 The solar-chemical energy conversion efficiency was enhanced from 0.03 to 0.14% as compared to the TiO2 photoanode system. Very recently, Maeda and his coworkers constructed the g-C3N4/Ru complex photocatalysts through direct hybridization in a methanol solution at room temperature.1421 The resulting heterogeneous photocatalysts showed the maximum visible-light apparent quantum yield of 5.7% (400 nm) for producing formic acid via CO2 photoreduction (as shown in Figure 116).1421 Additionally, it was found that two different ruthenium complexes used as photosensitizing and catalytic sites have been strongly immobilized on the periodic mesoporous organosilica (PMO) framework for photoreduction of CO2 to formate and CO in a CO2-saturated N,N-dimethylacetamide/water solution containing 1-benzyl-1,4-dihydronicotinamide.1432,1595,1596 Interestingly, to date, various metal complex cocatalysts have been covalently or non-covalently immobilized on a variety of semiconductor photocatalysts/photocathodes, such as gC3N4,1417,1424,1431 TiO2,735,1438,1597 metal sulfides,1598,1599 Cu2O,1600 MOFs,1423 doped graphene,953,1601,1602 InP,54,1415 TaON,1428,1603 N−oped Ta2O5,845,1410,1604 TiO2/C3N4735, and DF


Chemical Reviews

Review

Figure 114. (A) Schematic illustration of the CdS−M. thermoacetica hybrid photosynthesis system for generation of acetic acid via CO2 photoconversion and (B) two possible routes for generation of reduction equivalents, [H]: direct electron transport to the cell (solid line) or outside the cell (dashed line). (C) Photosynthesis of acetic acid and (D) colony-forming units (CFU) for the hybrid and deletion controls. (E) Photosynthesis rates and quantum yields of acetic acid with increasing photon flux and concentrations of hybrids. (F) Photosynthesis of acetic acid under low-intensity simulated sunlight with light-dark cycles. (G) Acetic acid production under dark conditions for varying illumination times.1583 Reprinted with permission from ref 1583. Copyright 2016 Science.

RuRu′’ (approximately 70%) was firmly attached to the surface of g-C3N4 nanosheets through the hydrogen bonding. More interestingly, rutile TiO2 nanoparticles with the size of 5−10 nm were employed as interfacial modifiers to construct the hybrid RuRe′ complex/TiO2/g-C3N4 nanosheets, resulting in a 4-fold enhancement in the photoactivity toward selective visible-light reduction of CO2 into CO (λ > 400 nm).735 The boosted photoactivity was primarily attributed to prolonged lifetime of free or shallowly trapped electrons and the suppressed undesirable desorption of the complex because of the introduction of TiO2 as an interfacial modifier. Clearly, the principle of tandem photoelectrode systems for solar fuels production is very similar to that of the Z-scheme system.1610 The main difference between them is that the conductive material in the former was replaced by the redox pairs in the Zscheme system. Therefore, the semiconductors used in tandem photoelectrochemical cells may be used in the Z-scheme systems. Especially, new semiconductors loaded with appropriate metal complexes or other cocatalysts seem to be well suited for the Z-scheme CO2 reduction systems, interesting for future exploration.1611

reduction through hybridization of a supramolecular CO2 reduction metal complex and methanol oxidation semiconductor particles.94 The structure of the as-synthesized hybrid is shown in Figure 118. The formic acid as a reduction product was mainly generated over the Ag/TaON−RuBLRu′ photocatalyst. The pure TaON particles cannot reduce CO2. However, after the RuBLRu′ was deposited on the Ag/TaON surface, the hybrid photocatalyst exhibited about 30-fold enhancement in the HCOOH yield in comparison with that over pure RuBLRu′ under the same conditions.94 Surprisingly, the ternary plasmonic Ag/mesoporous g-C3N4/binuclear Ru(II) complex hybrid showed a quite high turnover number of >33 000 with a selectivity of 87−99% (with respect to the amount of RuRu′) for HCOOH generation in an organic media because of the excellent synergism of Z-scheme charge transfer and plasmonic Ag (as shown in Figure 119).1429 More recently, they also demonstrated that the hybrid Z-scheme RuRu′/Ag/gC3N4 nanosheets as a photocatalyst could achieve the highest activity toward selective photoreduction of CO2 to formate in aqueous media, with a good TON (>2000, with respect to the loaded Ru complex) and high CO2 reduction selectivity (>90%) under visible light,1609 because a large portion of DG


Chemical Reviews

Review

Figure 115. (A) Schematic reaction and SEM images of Co−P alloy cathode and Co−Pi anode. Scale bar is 10 μm. (B) Energy efficiencies (ηelec) for production of chemicals and biomass at different Eappl and configurations. (C and D) Optical density at 600 nm (OD600; represents the biomass accumulation) and the amount of charge passed, plotted versus the experiment times with 100% CO2 (C) and air (D) in the headspace at room pressure. (E and F) Averaged ηelec values after and before excluding the light scattering for PHB accumulation. Averaged ηelec values for isopropanol (C3) (G), and C4 and C5 alcohols (H). (I) Schematic of hybrid bioelectrochemical system for CO2 fixation.1584 Reprinted with permission from ref 1584. Copyright 2016 Science.

Figure 116. Schematic of CO2 reduction over a g-C3N4/Ru complex hybrid photocatalyst.

Figure 118. Artificial Z-scheme for photocatalytic CO2 reduction.

applications, the earth-abundant Mn, 1 5 6 3 , 1 6 1 2 − 1 6 1 6 Cu,1437,1617−1619 Ni,1433,1599,1620−1622 Bi,1623 Co,1430,1624−1629 and Fe1430,1436,1627,1630−1635 complexes as cocatalysts of CO2 photoreduction deserve more attention in future studies.122,690,1627,1636−1638 Importantly, the integration/self-assembly of the earth-abundant biomimetic complex cocatalysts (such as cobaloximes, cobalt, and iron porphyrin) with colloidal quantum dot (QD) and MOFs sensitizers can be valuable for future studies to better understand the CO2-reduction

Figure 117. CO2 reduction mechanism for the Z-scheme photocatalytic system.

It is known that the Ru-based complexes are expensive for widespread adoption. Thus, from the viewpoint of practical DH


Chemical Reviews

Review

Figure 119. Schematic of Z-scheme CO2 reduction over a ternary Ag/ g-C3N4/binuclear Ru(II) complex hybrid. 1429 Reprinted with permission from ref 1429. Copyright 2016 American Chemical Society.

mechanism at the molecular level, which may inspire some new ideas for design of other cocatalyst systems.1062,1631,1639 However, many complexes suffer from several obvious disadvantages such as two-electron reduction of CO2 to CO, formate, and oxalate pathways, low reaction rates and high costs for the large-scale utilization.1586 Moreover, such metal complexes as photocatalysts require a suitable electron donor for photocatalysis in the photoexcited states because they cannot directly capture electrons from H2O.79,1640

Figure 120. (A) FE-SEM image, (B) AFM image (3D view), (C) elemental mapping image (green and red denotes Ti and Pt, respectively), (D) TEM and HRTEM (inset) images, and (E) CH4 and CO production rates for Pt (20 s) deposited on TiO2 thin film. (F) CO and CH4 production rate over P25, pristine TiO2 films, and Pt−TiO2 films with different Pt deposition times.61 Reprinted with permission from ref 61. Copyright 2012 American Chemical Society.

7.2. Noble Metal Cocatalysts

7.2.1. Monometallic Cocatalysts. Generally, noble metal Pt, Pd, and Au cocatalysts can selectively reduce CO2 to CH4 in gas-solid systems under light illumination (as shown in Figure 67). For example, Ishitani et al. first systematically investigated the CO2 photoreduction over TiO2 with deposited various kinds of metals in aqueous solutions. They found that the deposition of metals (Au, Pt, Rh, Pd, etc.) on TiO2 can significantly boost their CO2 reduction photoactivity for CH4 generation.1452 The highly dispersed Pt nanoparticles on TiO2 photocatalysts dominantly promote the charge separation and selective generation of CH4 instead of CH3OH.57 Feng et al. also reported that Pt nanoparticle/TiO2 nanotube hybrid significantly boosted the photoconversion of CO2 with gaseous H2O into CH4 because of a vast majority of homogeneously distributed active metal cocatalyst nanoparticles on the surface of TiO2 nanotube array.1460 After Pt deposition, a selective methane generation rate of about 25 ppm/(cm2 h), or (36 mL g−1 h) via photoreduction of CO2 with H2O vapor was obtained.1460 More surprisingly, a unique 1D single-crystalline TiO2 nanostructured films decorated with ultrafine Pt NPs (0.5−2 nm) were fabricated by various gas-phase deposition strategies (Figure 120A−D).61 The resulting Pt−TiO2 thin film with Pt deposition time of 20 s exhibited the highest selective photoreduction activity of CO2 to CH4 reported to date (the maximum CH4 yield of 1361 μmol/g/h) (as shown in Figure 120E and F).61 The activity enhancement could be assigned to the synergism of high surface area, unique 1D structure of the single-crystalline TiO2 film and size of Pt NPs, demonstrating the important role of tailored morphology in boosting the CO2 photoreduction efficiency. In addition, irregular Pt cocatalyst NPs of about 3−7 nm diameter were deposited on g-C3N4 via a NaOH-assisted impregnation followed by NaBH4-assisted reduction (Figure 121A and B).100 It was also found that the

Figure 121. (A) TEM and (B) HRTEM images of the 1 wt % Pt/gC3N4 sample. (C) CH4, CH3OH, and HCHO yields obtained via CO2 photoreduction over Ptx-modified g-C3N4 (x = the weight ratio of Pt to g-C3N4 were 0, 0.25, 0.5, 0.75, 1.0, and 2.0 wt %) after 4 h of simulated solar irradiation. (D) CO2 photoreduction over the Pt/gC3N4 photocatalysts.1470 Reprinted with permission from ref 1470. Copyright 2014 Royal Society of Chemistry.

loading of Pt nanoparticles (NPs) could achieve the selective CO2 photoreduction with enhanced activity of the reaction. The resulting Pt−C3N4 systems obtained by loading about 1 and 0.75 wt % Pt on g-C3N4 exhibited the highest yield of CH4 and CH3OH/HCHO, respectively (Figure 121C). Clearly, the loaded Pt cocatalysts facilitate not only the highly efficient DI


Chemical Reviews

Review

Figure 122. (A) Fabrication of copper deficient Cu2−xS NRs through a novel light-induced cation exchange method for selective photoreduction of CO2 to CO and CH4. Selective production rates of CO over Cu2S NRs (prepared via CdS-assisted process) after illumination with (B) a 447 nm laser or (C) a broad spectrum Xe lamp.1472 Reprinted with permission from ref 1472. Copyright 2015 American Chemical Society.

could be well designed and precisely controlled to maximize the selective CO2 photoreduction to target products. Meanwhile, Yui et al. found that the deposited Pd (>0.5 wt %) over TiO2 can promote the generation of CH4, instead of CO (as shown in Figure 123). Experimental data further

collection of photoexcited electrons for CO2 reduction (Figure 121D) but also promote the oxidation of the reduction products (the surface back reaction).100 Recently, it was demonstrated that the synergism of Pt2+ lattice doping and metallic Pt deposition could effectively enhance the selective production yields of H2 and CH4 over TiO2 without significant effect on the CO evolution.1641 The highest yield of CH4 over Pt2+−Pt0/TiO2 photocatalyst reached 264.5 and 138.6 μmol gcat−1 under UV and visible light for 7 h, respectively, due to the improved separation of photogenerated charge carriers, enhanced absorption of visible light and increased surface area induced by the synergistic effect of Pt nanoparticles and Pt2+ ions. Similarly, the 2 wt % Pt-loaded g-C3N4 nanocomposites by chemical reduction process in ethylene glycol exhibited a 5.1-fold enhancement in the CH4 generation via CO2 photoreduction with water vapor, in comparison to pure g-C3N4.1471 Thus, the optimal Pt loading contents are very crucial for achieving the highest activity toward the target product. In addition, the selective CO2 photoreduction can be significantly affected by location sites of Pt cocatalysts on colloidal semiconductor nanocrystals. Manzi et al. proposed a novel cation exchange reaction in which the photogenerated electrons in CB of CdS could in situ reduce the Cu(II) precursors to fabricate copper deficient Cu2−xS nanorods under an aqueous aerobic conditions (Figure 122A).1472 The formation of a thin copper-based shell around Pt NPs should be responsible for the enhanced photoreduction of CO2 and the decreased competitive H2 evolution. The as-prepared Cu2S NRs tip-decorated with Pt exhibited a suppressed competing H2 evolution and a high CO generation rate of 31.04 nmol h−1 g−1 (Figure 122B) during the 30 mW cm−2 illumination with a 447 nm blue laser. Under the illumination of IR wavelengths, the CO evolution rate (3.02 μmol h−1 g−1) of Pt tip-decorated Cu2S NRs is about 7.7 times higher than that observed on Cu2S NRs randomly decorated with Pt (39.48 nmol h−1 g−1) (Figure 122C), indicating the key role of Pt location sites in boosting the selective photoreduction of CO2 to CO.1472 In future, it is expected that the size, location, and facets of Pt nanocrystals

Figure 123. Photocatalytic CH4 and CO generation over Pd/TiO2 with different Pd amounts after 1.5 h of irradiation (>310 nm) under CO2 (650 Torr).1453 Reprinted with permission from ref 1453. Copyright 2011 American Chemical Society.

indicated that the CH4 formation was mainly derived from CO2 and CO32− adsorbed on the active Pd sites of Pd/TiO2. However, the long-time irradiation led to obvious deactivation of Pd/TiO2 photocatalysts because of the partial oxidation of the deposited Pd to PdO.1453 Furthermore, Au and Ag cocatalysts have also been widely investigated for selective photochemical reduction of CO2. Recently, Zhou et al. demonstrated that Au and Ag are highly active cocatalysts for photochemical reduction of CO2 to CO and CH4 over the leaf-architectured SrTiO3. These cocatalysts exhibit similar selectivity for both CO and CH4, in the following order: Au > Ag > Cu.648 Gold nanoparticles on Ti/ SBA-15 can also enhance the rate of photocatalytic CO2 reduction to short hydrocarbons, such as CH4.588 Surprisingly, the evolution of hydrocarbons was observed under irradiation in humid He (Figure 124A), suggesting the formation of the carbon pool. For Au/Ti/SBA-15, a slower formation of CxHy in humid He indicates less pronounced effects of a carbon pool DJ


Chemical Reviews

Review

Figure 124. (A) Photocatalytic yields for production of CH4 over the photocatalysts in the reaction gas mixture and subsequently performed in humid He. (B) Photocatalytic yields of CH4 over the photocatalysts in the reaction gas mixture and in CO2. (C) Hydrocarbon yields after 5 h of irradiation for the Au/Ti/SBA-15 and Ti/SBA-15 samples within the reaction sequence depicted in panel B. (D) Difference DRIFT spectra of Ti/ SBA-15 before and after CO2 photoreduction obtained after heating to 120 and 400 °C.588 Reprinted with permission from ref 588. Copyright 2013 Elsevier.

light irradiation. For instance, Kudo’s group showed that Agloaded ALa4Ti4O15 (A = Ca, Sr, and Ba) photocatalysts exhibited much higher activities for CO2 photoreduction to CO and HCOOH without any sacrificial reagents.85 It was also found that the method of cocatalyst loading and the Ag particle size have important effects on the activity toward CO2 photoreduction. This work demonstrates that Ag loaded by liquid phase reduction had the smallest particle size and exhibited the highest photoactivity, as compared with cocatalysts obtained by impregnation/H2 reduction and photodeposition.85 The selective CO production could be also achieved by loading Ag NPs onto other semiconductors.1500,1642−1644 In addition, Ag/TiO2 photocatalysts obtained by an ultrasonic spray pyrolysis strategy showed much better photoactivity toward H2 generation and CO2 photoreduction to CO than those fabricated by a wet-impregnation method.1645 However, some studies also indicate that methanol can also be selectively produced over Ag cocatalysts. Wu et al. found that the maximum yield of methanol, 4.12 μmol/(g h), could be achieved over 1.0 wt % Ag/TiO2 photocatalyst under the low intensity light (10 W/cm2).1646 Clearly, the increased yield was due to the better charge separation of the metal−TiO2 heterojunction. The decreased yield at high Ag loading was due to the shielding light absorption on TiO2 by Ag particles. Similarly, Pathak et al. also demonstrated that nanoscale TiO2 NPs embedded in the hydrophilic Nafion films significantly enhanced CO2 photoconversion to CH3OH when coated with silver.1647 The enhancement was primarily attributed to the

over catalysts on hydrocarbon formation. The results obtained in the absence of gas-phase water indicate that the significant effect of the former on the carbon chain growth; the amount of adsorbed water in mesopores is sufficient to achieve CO2 reduction and convert CO2 mainly to methane (Figure 124B and C). The photodeposited Au nanoparticles were shown to improve the selective CO2 photoreduction to short hydrocarbons over titanate species in SBA-15 (Figure 124C). Without Au, the observed active carbon pool accumulation over the photocatalyst mainly resulted in the generation of higher hydrocarbons. Infrared spectroscopy was used to identify formaldehyde (1685 and 2853 cm−1 for the ν(C O) and ν(CH2) stretching modes of adsorbed formaldehyde) and paraformaldehyde (2972 cm−1 for the asymmetric stretching νa(CH2) of paraformaldehyde) as major compounds of the carbon pool (Figure 124D). These results might inspire new thoughts for rational design and optimization of the CO2 reduction photocatalysts. Recently, Kanan and coworkers demonstrated that Au nanoparticles prepared with assistance of oxides exhibited high stability and selectivity for CO2 electroreduction to CO at extremely low overpotentials of 140 mV in water owing to the increased stabilization of the CO2•− intermediate as compared to other polycrystalline or nanostructured Au electrodes.702 This approach may offer new opportunities for the design of Au cocatalysts for photocatalytic reduction of CO2. Silver as an interesting noble metal cocatalyst has been shown to convert CO2 to CO or methanol selectively under DK


Chemical Reviews

Review

Figure 125. (A) Schematic illustration of photocatalytic mechanisms for CO2 conversion to fuels and (B) Generation rates of products over the Ndoped nanotube array films decorated with Cu and Pt NPs as dual cocatalysts.60 Reprinted with permission from ref 60. Copyright 2009 American Chemical Society.

Figure 126. (A) HAADF (high-angle annular dark field) TEM image of 1.2 nm CuPt−TiO2; production rate of CH4 over CuPt−TiO2 samples with varying metal cocatalysts (B) and CuPt size (C) under a 150 W Xe lamp. (D) Mechanism of the selective photoconversion of CO2 on small and large CuPt nanoclusters over TiO2.1278 Reprinted with permission from ref 1278. Copyright 2016 Royal Society of Chemistry.

improved charge carrier separation. The noble metal as electron sink could greatly reduce the recombination rate of the photogenerated charge carriers, while holes remained on the TiO2 surface.1647 In addition, Koči ́ et.al pointed out that the main factor affecting the methane and methanol yields obtained via CO2 photoreduction over Ag modified TiO2 is the Ag content, rather than the specific surface area. Two mechanisms were used to explain the yield increase over Ag modified TiO2. Ag, as an impurity dopant, can reduce the band gap of TiO2, and thus increase generation of the photoexcited e−−h+ pairs when the Ag content in TiO2 is below 5%, whereas the Schottky barrier between metallic Ag clusters and TiO2 crystals will strengthen the separation efficiency and prolong the lifetime of photogenerated electrons and holes, and thus increase the photocatalytic activity when the content of Ag in TiO2 is above 5%.76 Jiao and coworkers also reported that a nanoporous Ag electrocatalyst was capable of reducing CO2 to CO with about 92% selectivity. Surprisingly, its current was more than 3000-fold larger than that on the polycrystalline counterpart under moderate overpotentials ( 420 nm, 5 h, and 50 mg of catalyst) formation rates of C1−C3 hydrocarbons, (B) DRIFT spectra (after loading CO2), and (C) EPR spectra of DMPO−OH and DMPO−CH3 adducts observed at room temperature after 3 min of visible-light irradiation on CdS/(Cu-TNTs) with low (0.093), medium (0.143), and high (0.507) Na/Ti ratios in TNTs (i.e., NaxH2−xTi3O7). (D) Photocatalytic CO2 reduction mechanism over CdS/(Cu-TNTs).1660 Reprinted with permission from ref 1660. Copyright 2015 American Chemical Society.

transition bands of Cu2+ species, respectively. In comparison to three selected reference catalysts, the Cu2+-modified Nb3O8 nanosheets exhibited the highest CO-production activity due to the excellent synergy of the light-driven formation of mixed Cu2+/Cu+ cocatalysts and high CB level originating from the quantum confinement effect of Nb3O8 nanosheets (Figure 129D). The isotope-labeling experiments (H218O and 13CO2) and ESR analysis further demonstrated that excited holes and electrons trapped in the Cu2+ nanoclusters are responsible for water oxidation and reduction of CO2 to CO, respectively (Figure 129E). The strategy of grafting cocatalytic nanoclusters is expected to be applicable in developing highly efficient and selective artificial photosynthesis systems. Additionally, I and Cu codoped TiO2 NPs (Cu−I−TiO2) were shown to achieve the selective reduction of CO2 with water vapor into CO with trace amounts of CH4.1657 Through varying the Cu precursors, it was also shown that the Cl ions as the hole scavenging reagent promote CO2 photoreduction.1657 Besides selective formation of CO, both CuO-loaded TiO2 and Cu2+-doped anatase TiO2 NPs exhibited much higher photoactivity toward selective reduction of CO2 to HCOOH in CH3OH solution containing a sacrificial electron donor (e.g., Na2S),9211658 whereas the heterostructured CuO−TiO2−xNx hollow nanocubes1659 and Cu2O/S-TiO2 (sulfur-doped TiO2)/CuO947 showed the excellent activity for selective methane production via photoreduction of gaseous CO2 with water vapor. Furthermore, it is well known that the metallic Cu electrocatalysts could selectively convert CO2 to hydrocarbons. Usually, CH4 can be selectively formed over diverse semiconductors decorated with Cu cocatalysts. Cook et al. reported that CH4 was continuously generated on Cu-SiC sites in CO2 saturated KHCO3 electrolyte upon mercury UV lamp illumination.1028 Methane evolution increased as the electrolyte

Re-cluster sensitization and Cu-cluster cocatalyst leads to the significantly enhanced activity toward selective methanol formation (Figure 128C). Accordingly, further exploration of earth-abundant Cu-based cocatalysts for the selective CO2 photoreduction to methanol is highly desirable. Besides the selective formation of methanol, other products were also detected over various semiconductors modified with copper species. Recently, the formation of surface defect sites on the H2-pretreated Cu/TiO2 was shown to promote CO2 adsorption and subsequent activation, thus resulting in the significantly boosted CO and CH4 production.897 An electron attachment to CO2 leads to the generation of CO2− species, which can be spontaneously activated to CO over defective Cu(I)/TiO 2−x at room temperature even under dark conditions.672 The in situ X-ray absorption and infrared spectroscopies thoroughly revealed that the H2-pretreated Cu/TiO2 exhibited >50% activity enhancement toward CO2 photoreduction to CO in comparison to that of Cu/Ti(air) because of the increased amount of CO2 adsorption sites, better electron transfer, and accelerated activation/conversion of the adsorbed CO2 (HCO3− and CO2−) induced by the synergy of Cu+, OH groups, and VO (oxygen vacancy).1656 Adding hole scavengers (e.g., methanol) could decrease deactivation of the H2-pretreated Cu/TiO2 and keep or even increase the amount of active Cu+ sites via the single-electron photoreduction of Cu2+, thus leading to the highly active and durable photoreduction of CO2 into CO.1656 More interestingly, Yin et al. synthesized the earth-abundant Cu2+ nanocluster on Nb3O8 nanosheets by a facile wet chemical method (Figure 129A and B).820 The UV−visible spectra in Figure 129C exhibit three obvious absorption peaks at 300, 430 and 600-800 nm, associated with the direct band-to-band transition of the Nb3O8 nanosheets, the interfacial charge transfer (IFCT) and the d−d DP


Chemical Reviews

Review

Figure 131. Time-dependent production rates of (A) methanol and (B) acetaldehyde on the pristine GO, Cu/GO-1 (5 wt % of Cu), Cu/GO-2 (10 wt % of Cu), and Cu/GO-3 (15 wt % of Cu). (C) Average production rates of methanol and acetaldehyde during 2 h light irradiation. (D) UPSmeasured work functions and (E) band-edge positions of pristine GO and Cu/GO hybrids. (F) Schematic illustration of CO2 photoreduction over Cu/GO hybrids.1662 Reprinted with permission from ref 1662. Copyright 2014 American Chemical Society.

became more acidic, reaching a maximum rate of 14.9 μL h−1 g−1 (62 μL m−2 h−1) at pH 5. Under the same conditions, ethylene and ethane were also observed as hydrocarbon products with formation rates of 3.9 (16.25 μL m−2 h−1) and 2.3 μL h−1 g−1 (9.6 μl m−2 h−l), respectively.1028 Electron transfer to adsorbed CO2 on copper sites was suggested to be the rate determining step. Further acidification of electrolyte below pH 5 could lead to a dramatic decrease in the CH4 evolution rate because of increased SiO2 formation on SiC or hydrogen formation. Adachi et al. reported that methane and ethylene can be generated via photoreduction of CO2 in Cu− TiO2 suspended solution under CO2 pressure of 28 kgf/cm2 and a Xe lamp illumination. The yields for methane, ethylene, and ethane were 21.8, 26.2, and 2.7 μL/g, respectively, under optimum conditions.1029 In another example, Park et al. constructed a ternary photocatalyst through assembling both metallic copper (Cu 0 ) and CdS quantum dots on NaxH2−xTi3O7 nanotubes (TNTs) for selective photoconversion of CO2 and water into C1−C3 hydrocarbons.1660 It was found that the CO2 photoreduction activity of ternary hybrid samples obviously increased with increasing level of intercalated Na+ within a titanium nanotube framework (Figure 130A),

indicating the importance of the stoichiometric Na+ in TNTs in the formation of C1−C3 hydrocarbons, which is consistent with the previous report.1164 The improved generation of surface-absorbed CO2 and relevant carbonate species on the ternary catalyst could be verified by the DRIFT spectra (Figure 130B). The significant EPR signals of DMPO−CH3 and DMPO−OH adducts and ESR spin trapping probe molecule further confirm the formation of methyl radical intermediate, which is originated from the predominant reaction between one-electron reduced CO2 (CO2•−) and multiple hydrogen atoms (Figure 130C). More importantly, it was also revealed that the deposited metallic copper on the surface of TNTs could favor the transient trapping of methyl radical and the production of ethane through the self-reactions. Thus, it is clear that the trapped electrons on elemental Cu and photogenerated holes are in charge of the selective reduction of CO2 to C1−C3 hydrocarbons and the oxidization of water (Figure 130D), respectively. Similarly, the metallic copper (Cu)-decorated microsized, nanoporous TiO2 with optimal 0.4 wt.% of Cu2+ ions exhibited the best photocatalytic activity toward selective formation of CH4 at a rate of 8.04 μmol g−1 h−1, which is 21fold higher than that obtained on P25.1661 The metallic Cu DQ


Chemical Reviews

Review

Figure 132. (A) SEM and TEM (inset) images of Ni@NiO cocatalysts on N-doped InTaO4. (B) Formation rate of methanol and (C) UV−visible diffuse reflectance spectra of a series of InTaO4-based samples. (D) Schematic illustration of photoreduction mechanism of CO2 over Ni@NiO cocatalysts deposited on InTaO4−N.844 Reprinted with permission from ref 844. Copyright 2011 American Chemical Society.

In addition, Cu2O and CuO can be easily reduced to metallic Cu(0) because of the poor stability and unavoidable selfphotocorrosion if the photogenerated electrons in them cannot be quickly extracted and utilized in the surface reduction reactions.221,1668 Therefore, a protective layer is very important to isolate Cu2O from the electrolyte solution and minimize selfphotoreduction occurring at the Cu2O/electrolyte interface.1669 Recently, Gratzel and coworkers reported a highly active and stable photocathode consisting of electrodeposited Cu2O, nanolayers of Al-doped zinc oxide and titanium oxide and Pt nanoparticles.221 They also found that the Cu2O photoelectrodes protected by TiO2 layer and RuO2 exhibited much better stability versus those protected by TiO2 and platinum nanoparticles.1670 The photocorrosion of Cu2O photocatalysts can be suppressed by reduced graphene oxide, which acts as an electron sink to extract photogenerated electrons from Cu2O.1671 The improved activity and enhanced stability of Cu2O/RGO for CO2 photoreduction have been recently verified.1180 Consequently, multilayer metal oxide221 and carbon layer-coated Cu2O or CuO1669,1671 may offer a new approach for design and fabrication of highly durable Cu2O (or CuO)-based photocatalysts for photoreduction of CO2 with H2O. 7.3.2. NiOx and CoOx Cocatalysts. The p-type NiO semiconductor exhibits a band gap ranging from 3.4 to 4.0 eV.1672 The photoreduction of CO2 to CH3OH over pure NiO was demonstrated in the CO2-saturated water solution under irradiation of 355 nm UV laser.547 It was first reported that the Ni/NiO core−shell cocatalysts exhibited improved photocatalytic activities for water splitting by Domen’s research group because of the inhibited surface back reaction and enhanced

nanoparticles loaded as cocatalysts on TiO2 can not only increase the visible light absorption and crystallization of TiO2, but also serve as electron traps to significantly suppress unwanted photogenerated electron-hole recombination and improve the selective CH4 production rates.1661 However, the metallic Cu NPs on graphene oxide (GO) could selectively reduce CO2 into methanol and acetaldehyde.1662 Particularly, Cu/GO-2 (10 wt % of Cu) exhibited more than 60 and 240fold improvement in the CO2 reduction efficiency in comparison with those on pristine GO and commercial P-25 under visible light (Figure 131A−C), respectively. The strong interaction between Cu-NPs and graphene could not only increase its work function (Figure 131D) and reduce the GO bandgap (Figure 131E), but also promote electron−hole pair separation (Figure 131F), resulting in the enhanced photoreduction of CO2. Additionally, the main products of the CO2 photoreduction over ZrO2, are H2, O2, and CO.55 The addition of metal Cu cocatalyst can obviously suppress the activity of H2 evolution but has no significant influence on the rate of CO evolution. Similarly, decoration of g-C3N4 nanosheets with Cu NPs afforded a good selective photocatalyst for generation of CO from gaseous CO2 in the presence of H2O vapor.1663 The reason why the Cu−ZrO2 and Cu−g-C3N4 nanosheets show no selectivity for CH4 is still not clear.55,1663 Furthermore, it has been shown that the roughness,1345 porosity,1664 surface morphology,1665 particle size,1666 atomic-scale thickness,1339 and impurities1667 of Cu electrodes have significant impact on the overpotential and selectivity of CO2 electroreduction. Thus, these factors should be considered when designing and optimizing the Cu-based cocatalysts for selective photoreduction of CO2. DR


Chemical Reviews

Review

Figure 133. (A) Schematic illustration for fabrication of hierarchical TiO2/Ni(OH)2 hybrid photocatalysts. (B) Selective CO2 photoreduction activities of the T, N, and TNx (x = 0.5, 1, 1.5, 2, and 15) samples after 1 h irradiation. (C) Schematic illustration of CO2 photoreduction over the TiO2/Ni(OH)2 nanofiber.1546 Reprinted with permission from ref 1546. Copyright 2018 Royal Society of Chemistry.

charge carrier separation.1673,1674 Thus, NiO nanoparticles, especially in the case of Ni/NiO core-shell cocatalysts, loaded on different semiconductors are expected to boost the photoactivity for CO2 reduction. For example, Chen’s group reported the improved activity toward selective photoreduction of CO2 with water to CH3OH over InTaO4 and InVO4 with incorporated NiO cocatalysts.1539,1675 The photocatalytic reaction was performed in a Pyrex reactor under illumination of 500 W halogen lamp. The Ni@NiO core-shell structure was created on the InTaO4 surface. The obtained CH3OH yield over 1.0 wt. % NiO−InTaO4 was about 1.394 μmol h−1 g−1 within the first 20 h. The CH3OH yield increased with increasing loading of NiO cocatalyst, which acts an electron trap and suppresses the recombination of electron and holes due to the formation of surface Schottky barrier.1539 Meanwhile, Wang et al. further increased the quantum efficiency of CO2 photoreduction over NiO/InTaO4 thin film in the opticalfiber reactor.1540 Tsai et al. incorporated Ni@NiO core-shell cocatalyst into N-doped InTaO4 for highly efficient CO2 photoreduction to CH3OH (Figure 132A).844 The photoactivity for methanol production was enhanced three times due to the synergism of N-doping and the loading of Ni@NiO cocatalyst (Figure 132B). It is believed that the nitrogen doping can significantly enhance the visible-light absorbance because the formation of N 2p-orbital effectively lowers the band gap of InTaO4 photocatalyst (Figure 132C and D), thus resulting in the improved photocatalytic reduction efficiency. More importantly, the Ni@NiO core-shell cocatalysts not only dramatically increase light absorbance, but also efficiently

boost electron-hole separation in the crystal for CO2 photoreduction (Figure 132D).844 Thus, it is desirable to extend the above strategy, which combines doping and cocatalysts, to other semiconductor systems for efficient photoreduction of CO2. Additionally, considering the good adsorption and activation capacity of basic Ni(OH)2 toward the acidic CO2 molecules, and the easy transformation from Ni(OH)2 to Ni clusters under illumination, the earth-abundant Ni(OH)2 was also employed as an effective cocatalyst, to be utilized in a photocatalytic CO2 reduction reaction.1546 The vertically aligned Ni(OH)2 nanosheets/TiO2 nanofiber hierarchical composite was fabricated via a simple electrospinning and solution precipitation method (Figure 133A). As a result, the loading of 0.5 wt % of Ni(OH)2 on TiO2 nanofiber could achieve a 2-fold increase in the yield of selective methane production (2.20 μmol h−1 g−1) without changing the CO yield (Figure 133B). More interestingly, the TiO2/Ni(OH)2 hybrid was found to exhibit the good selectivity for production of alcohols (methanol and ethanol) (Figure 133B). Accordingly, the load of Ni(OH)2 cocatalysts could significantly enhance both charge separation efficiency and CO2 capture capacity, thus achieving the improved activity and the altered product selectivity upon photocatalysis (Figure 133C). This work opens a new pathway for improving both the CO2 photoreduction efficiency and selectivity through rational design and exploration of novel noble metal free cocatalysts. Unfortunately, the molecular O2 and H2 had not been quantitatively determined in the above reports, which is crucial for the Ni-based cocatalysts because NiOx is also good DS


Chemical Reviews

Review

Figure 134. (A) TEM images of ZnO@Co3O4 fabricated from ZIF-8@ZIF-67. (B) Photoactivities of different photocatalysts after 6 h of UV−vis irradiation. Schematic of CO2 photoreduction over ZnO (C) and ZnO@Co3O4 (D).1681 Reprinted with permission from ref 1681. Copyright 2016 Royal Society of Chemistry.

photoreduction of CO2 to CO with the aid of Ru-dye photosensitizer. At this point, it is highly desirable to extend the studies of cost-affordable spinel cobalt-based ternary metal oxide cocatalysts to improve the CO2 photoreduction activity of nanostructured semiconductor photocatalysts, beyond the complex dyes. More importantly, a possible mechanism of the MnCO2O4-promoted CO2 photoreduction at molecular levels should be revealed by various modern techniques to further improve and optimize these cocatalysts for efficient artificial photosynthesis. 7.3.3. Mixed Oxide Cocatalysts. Nguyen reported photoreduction of CO2 with gaseous H2O over Cu−Fe/TiO2 photocatalyst (containing Cu and Fe respectively in the form of Cu2O and Fe2O3) deposited on optical fibers under UV irradiation. Methane and ethylene were observed as the main products.1683 The presence of this binary cocatalyst on TiO2 photocatalyst was shown to synergistically reduce CO2 with H2O to ethylene with the total energy efficiency and quantum yield of 0.016% and 0.024%, respectively, owing to the boosted charge transfer from TiO2 to Cu2O and Fe2O3. Methane was formed more favorably than ethylene on Cu/TiO2. Meanwhile, Fe species were found to suppress the methane formation. Cu(0.5 wt %)−Fe(0.5 wt %)/TiO2 photocatalysts seem to give the best performance.1683 Luo et. al extensively investigated photoreduction of CO2 with H2O over Cu and Ce codoped TiO21684 and showed that Cu/Ce−TiO2 photocatalysts can evidently boost the photoreduction efficiency of CO2. The CH3OH yield could rapidly reach 180.3 μ mol/gcat. This study indicates that Ce species improve more the reaction in comparison to Cu species. Clearly, the former promote the activation of both H2O and CO2 molecules, while the latter only facilitate the photoelectron transfer and prevent the recombination of holes and

multifunction cocatalyst for H2 and O2 evolution from water splitting. Thus, it is necessary that the evolution of H2 and O2 over core−shell Ni/NiO cocatalysts is carefully investigated when they are used in the systems for photocatalytic reduction of CO2. Meanwhile, other core−shell cocatalysts, such as M@ Cr2O3 (M = Rh, Ir, Pt) developed by Domen et al.1023,1676−1679 could be worthy of exploration for photoreduction of CO2, especially for the earth-abundant metal core@Cr2O3 cocatalysts. Better understanding and investigation of these cocatalysts might extend their use in the field of CO2 photoreduction. Recently, another earth-abundant cocatalyst, CoOx has attracted a considerable attention. For example, it was shown that cobalt oxide (CoOx) nanoparticles on C3N4 as reductive and oxidative promoters can greatly enhance the activity of photocatalytic reduction of CO2 to CO because of the enhanced reaction rate of the oxidative partner and better charge-carrier separation and transfer kinetics.1680 Similarly, Wang et al. fabricated the porous ZnO@Co3O4 composites by calcination of the core−shell ZIF-8@ZIF-67 crystals (Figure 134A).1681 Among all corresponding single and composite photocatalysts, the as-prepared porous ZnO@Co3O4 photocatalysts exhibited the highest CH4 generation rate of 0.99 μmol g−1 h−1, which is approximately 66 and 367 folds larger than those obtained for commercial ZnO and P25, respectively (Figure 134B). The enhanced photoactivity can be attributed to the advantageous porous structure and effectively suppressed photocorrosion of ZnO because of the promoted water oxidation on the surface of Co3O4 cocatalysts (Figure 134C and D).1681 Thus, the application of CoOx in photoreduction of CO2 deserves more attention in future studies. Notably, stable MnCO2O41569 and ZnCO2O41682 with a spinel structure have been demonstrated to be excellent cocatalysts for selective DT


Chemical Reviews

Review

Figure 135. Production rates of CH4 (A) and CO (B), XPS valence band spectra (C), diffuse reflectance UV−vis spectra (D) and photoluminescence spectra (E) of different photocatalysts, and (F) illustration of the mechanism for photocatalytic CO2 reduction over TiO2−Pd− Mn photocatalyst.1687 Reprinted with permission from ref 1687. Copyright 2017 American Chemical Society.

synergetic effect.1685 More interestingly, it was first revealed by theoretical calculations and experiments that the introduction of surface O−Pd−O, O−Cu−O, and O−Mn−O species resulted in matching energy levels with the potentials of water oxidation (Pd and Cu) and CO2 photoreduction to CH4(Mn), respectively, thus assuring the improved visible light response, charge-carrier separation and photocatalytic CO2 reduction activity.1686 To further improve the synergetic effect of different metal species, Cao et al. first prepared the novel TiO2 photocatalyst comodified with the −O−Pd−O− and −O−Mn−O− species via a simple sol−gel method.1687 The resulting TiO2−Pd−Mn sample exhibited the highest photocatalytic activity for CH4 generation (5.51 μmol), which is nearly 3.6-fold larger than that obtained on pure TiO2 (Figure

electrons.1684 Recently, to enhance the surface area and CO2 adsorption, Pham et al. synthesized the Cu and V codoped TiO2 on polyurethane (Cu@V-TiO2/PU) toward selective CO 2 photoreduction to CH 4 with H 2 O vapor as a reductant.1685 On the one hand, the CuO, Cu2O, and V2O5 oxides fabricated on the TiO2 surface could serve as effective cocatalysts to significantly promote the electron−hole separation of TiO2 and selectively reduce CO2 to CH4, rather than CO. On the other hand, Ti3+ and oxygen vacancies created in the doped TiO2 lattice could increase both visible-light absorption and CO2 adsorption/activation. As a result, the highest production rates of CH4 and CO over the optimized 2Cu@4V-TiO2/PU photocatalyst reached 933 and 588 μmol g−1 cat. h−1 under visible light, respectively, due to the excellent DU


Chemical Reviews

Review

Figure 136. (A) Comparison of the CO2 photoreduction activity of pure TiO2 nanosheets and MoS2/TiO2 hybrid nanosheets with different MoS2 amounts and (B) TiO2 nanosheets with 0.5 wt % of Pt, Au, and Ag. (C) Schematic illustration of the charge-separation mechanism for selective photoreduction of CO2 to CH3OH over the MoS2/TiO2 photocatalysts.1696 Reprinted with permission from ref 1696. Copyright 2017 Royal Society of Chemistry.

Mn−O− species match well the redox potential for photoreduction of CO2 to CH4 and band gap of TiO2, which results in the enhanced visible response, better charge separation and better separation of redox reactive sites, thus achieving the improved CO2 reduction photoactivity (Figure 135F). This work provides new ideas for the design of the selective photocatalysts for CO2 reduction by introducing the mixed oxide cocatalysts, which are able to create the new energy levels above VB level, below CB level or in the middle band gap of the semiconductor. Recently, Kanan et al. reported that a Sn/SnOx electrode exhibited an enhanced activity for electroreduction of CO2 to CO and HCO2H as compared to a Sn electrode.1048 Similar selectivity of Sn/SnOx electrode was also observed in the PEC CO2 reduction.1048 It is especially noteworthy that a Ti electrode with simultaneous electrodeposition of Sn0 and SnOx could enhance the partial current density (or Faradaic efficiency) for CO2 reduction by a factor of 8 (or 4) as compared to a native SnOx layer-protected Sn electrode. It was suggested that the SnOx plays a significant role in stabilizing CO2−, leading to an enhanced production rate of HCO2H and CO. Thus, it is expected that the metal/metal oxide composite materials could be used as potential cocatalysts for solar fuel synthesis via CO2 photoreduction.

135A). The enhanced activity for CO intermediate product was also detected (Figure 135B). The calculated density of states and energy-band structure demonstrates that the Pd or Mn modified TiO2 photocatalyst exhibited the unchanged VB and CB, in comparison to those of pure TiO2. However, the mixed Pd 4d or Mn 3d state with Ti 3d and O 2p states could introduce new energy levels above VB, below CB or in the middle band gap of TiO2, thus favoring the charge separation and improving the visible-light absorption. The XPS valence band spectra of different samples exhibit almost the same onset edge as that of pure TiO2, indicating the valence band of TiO2 was hardly affected by the introduced surface Pd or/and Mn species (Figure 135C). For XPS valence band spectra of TiO2− Pd and TiO2−Pd−Mn, the small humps close to VB of TiO2 could be attributed to the additional energy level of −O−Pd− O− species, which is consistent with the DFT calculations. The diffuse reflectance UV−vis absorbance spectra in Figure 135D confirm that the synergetic effect of −O−Pd−O− and −O− Mn−O− species on the surface could cause an increase in the visible-light absorption, owing to the created new energy states in the band gap of TiO2. The decreased PL intensity confirms that the introduced Pd or/and Mn can distinctly boost the charge-carrier separation, facilitating the overall photoactivity (Figure 135E). The energy levels of the −O−Pd−O− or −O− DV


Chemical Reviews

Review

Figure 137. Binding energies Eb(COOH) (A) and Eb(CHO) (B) vs Eb(CO) for the S and metal sites of doped S edges in MoS2, as well as the bare (211) and (111) surfaces. (C) Limiting-potential difference for CO/H2 and CO2 reduction to CO over various doped sulfur edges in MoS2. The CO2 reduction free-energy changes over the Ni-doped (D) and Co-doped (F) sulfur edges in MoS2 without applied potential (0 V).1695 Reprinted with permission from ref 1695. Copyright 2016 American Chemical Society.

film showed the highest photocurrent and photoactivity for selective CH4 formation via CO2 reduction, owing to the enormously enhanced visible-light absorption and boosted charge separation. Recently, it was shown that p-type Cu2S and n-type CuS semiconductor nanorod and platelet arrays on both copper foil and copper-coated flexible Kapton substrates exhibit the excellent selectivity toward photoconversion of CO2 into CH4, implying that CuSx is also the potential cocatalyst for selective CO2 photoreduction.1692 In fact, it was recently shown that introducing an optimal amount of CuSx cocatalyst onto the

7.3.4. Sulfide, Carbide, and Other Cocatalysts. Recently, layered metal sulfides, such as MoS2,483,1202,1370 CuSx, WS2,1371 NiSx,1240 CoSx,1238,1688−1690and their composites1691 have been extensively employed in the photo-(or electro-)catalytic H2 evolution, because their unique 2D and electrical structures feature small overpotentials, relatively large amount of active sites and good charge separation. For example, Lee et al. decorated a highly aligned n-type TiO2 film by a ptype semiconductor, nickel sulfide, as a cocatalyst.945 The optimized p−n heterojunction NiS (0.1 M)-sensitized TiO2 DW


Chemical Reviews

Review

Figure 138. (A) TEM image and schematic illustration (inset) of the sandwich structure of TT550 (the dried Ti3C2 was calcined at 550 °C). (B) HRTEM image of TT550 (red rectangle in A). (C) CH4 production rate of TTx samples (x represents the calcination temperature) and P25. (D) Photocatalytic CO2 reduction stability test for TT550.1568 Reprinted with permission from ref 1568. Copyright 2018 Elsevier.

patterned TiO2 film with a 3D network microstructure could lead to 2.94- and 7.3-fold activity enhancement for selective photoreduction of CO2 to CH4 as compared with those observed on pure TiO2 and CuSx films under the same reaction conditions, respectively.1557 Additionally, the few layered MoS2 cocatalyst has been formed on the hierarchical flower-like Bi2WO6 microspheres, which resulted in the significant enhancement of photoactivity toward the selective CO2 photoreduction to methanol and ethanol in CO2 aqueous solution, in which the generated CO32−, HCO3− and H2CO3 would be the reactive species.632 The photocatalytic CO2 reduction activity over optimal MoS2(0.4 wt %)/Bi2WO6 nanocomposites is about 1.94 higher than that over pure Bi2WO6, which could be ascribed to the highly boosted visible light harvesting and better separation and transfer of electronhole pairs. In another example, the ternary hierarchical structure of mesoporous TiO2 on macroporous 3D graphene aerogel with few-layered MoS2 cocatalysts has been demonstrated to be a highly active, robust, low-cost photocatalyst for selective photoreduction of CO2 to CO.1693 These examples imply that MoS2 is a very promising cocatalyst candidate for design of highly active and earth-abundant composite photocatalysts for CO2 photoreduction. More interestingly, MoS2 has been theoretically and experimentally identified to be a promising cost-effective electrocatalyst with superior CO2 electroreduction performance, which is strongly related with its electronic structure, including the type of edges, phase and composition of the MoS2 nanosheets.1052,1560,1694,1695 The catalytic performance is mainly derived from the Mo edges of MoS2 owing to their high d-electron density and metallic nature. Interestingly, it was found that the CO2 electrocatalytic reduction ability of the MoS2-rods/TiO2 nanotube arrays could be greatly enhanced by the assistance of light, though the photocatalytic reduction of CO2 could not be achieved over the

MoS2-rods/TiO2 nanotube arrays because of the unsuitable conduction band.1143 It is believed that the combination of the enhanced electron transfer ability, decreased overpotential, and p−n heterojunction is responsible for the light enhanced electrocatalytic reduction of CO2 to methanol.1143 Note that the Co-doped MoS2 NPs with low overpotential and matched energy band exhibited high efficiency for photoelectrocatalytic reduction of CO2 to methanol, showing an excellent synergism between electrocatalysis and photocatalysis.1560 Recently, Tu et al. constructed 2D MoS2−TiO2 ultrathin nanosheet heterojunctions for photoreduction of CO2 in aqueous solution.1696 The results demonstrate that MoS2 nanosheets as efficient cocatalysts, exhibit much better UV−vis activity for selective reduction of CO2 to CH3OH in aqueous solution in comparison with the conventional metal cocatalysts (e.g., Pt, Au, and Ag) (Figure 136A and B). It was revealed that the metallic Mo-terminated edges with high d-electron density could facilitate the electron transfer and stabilize CHxOy intermediates (Figure 136C), thus resulting in the highly boosted CO2-photoreduction activity and selectivity. More interestingly, based on the DFT calculated adsorption energies of CO2 reduction intermediates, it was found that CO* on the doping metallic sites exhibits stronger binding energies, whereas CHO*, COOH*, and COH* show much stronger interactions with the Co- and Ni-doped S edge in MoS2 without the applied potential (Figure 137A and B).1695 As a result, the Co- and Nidoped MoS2 exhibited much higher selectivity and activity for CO2 reduction than for H2 evolution as compared to other metal-doped MoS2 because of the combined effect of the two binding sites (Figure 137C).1695 The CO2 reduction freeenergy changes for Ni-doped (Figure 137D) or Co-doped (Figure 137E) MoS2 were evaluated to further confirm the improved catalytic performance through optimizing the binding of the reduction intermediates. More importantly, it was shown DX


Chemical Reviews

Review

Table 17. Photoreduction of CO2 over Nanocarbon-Based Heterojunction Photocatalysts semiconductor

cocatalysts

selectivity (by-product)

enhanced factor (conditiona)

ref

TiO2 (anatase) TiO2 (rutile)

MWCNTs

TiO2 (anatase)

MWCNTs

MWCNTs and nanofibers C2H5OH 1.61 (G-S/0.1 MPa/365 nm) (G-S/0.1 MPa/365 nm) (HCOOH, CH4) HCOOH (CH4, C2H5OH) CH4 (G-S/0.1 MPa/15 W energy saving light bulb)

TiO2(anatase)

Ni, MWCNTs

CH4

(G-S/0.1 MPa/75 W visible daylight lamp)

AgBr

Ag, MWCNTs

(L-S/7.5 MPa)

carbon fibers

Ag

CH4 (CH3OH, CO, C2H5OH) CH3OH

ZnO nanorods

carbon fibers

CH3OH

7.5(G-S/UVlamp, λ = 420 nm, 12 mW/cm2/353 K)

Co complex Ru complex g-C3N4

MWCNTs

CO, H2

(L-S/xenon arc lamp, λ > 420 nm, 298 K/TEA)

OMC/MWCNTs

CO/CH4

2(G-S/300 W xenon arc lamp)

1729 (2018)

TiO2 Ti0.91O2 nanosheets titania nanosheets

RGO RGO RGO

CH4 CO(CH4) CH4

4-UV/7(G-S/UV or visible light) (G-S/300 W xenon arc lamp) (G-S/365 nm, 110 W/m2)

TiO2 TiO2

RGO RGO, Pt

C2H6(CH4) CH4

2 (G-S/300 W xenon arc lamp) 1.93 (G-S/tungsten−halogen lamp)

TiO2 nanosheets

SEG

CH4

3.7 (G-S/60 W daylight bulb)

N-TiO2 P25 TiO2

SEG SEG RGO, Pt55

CH4 CH4 CH4

10.9 (G-S/15 W daylight bulb) 7.2 (G-S/60 W daylight bulb) 13.5 (G-S/15 W daylight bulb)

HNb3O8 nanosheets

RGO

CO

8.6 (G-S/300 W xenon arc lamp)

CsPbBr3 perovskite QDs CdS nanorods CdS nanowires

GO RGO RGO, Ag

CO/CH4 CH4 CO(CH4)

1.19/1.29 (G-S/500 W xenon lamp, λ ≥ 400 nm) 12 (G-S/λ ≥ 420 nm, 150 mW/cm2) 1.4 (G-S/λ ≥ 420 nm, 150 mW/cm2)

AgBr/g-C3N4

RGO

C2H5OH(CH3OH)

1.7 (G-S/λ ≥ 420 nm, 150 mW/cm2)

WO3 Fe2V4O13−CdS TiO2−CdS g-C3N4 nanosheets g-C3N4 nanosheets TiO2

GO RGO RGO RGO RGO B-doped RGO

CH4 CH4 CH4 CH4 CH4 CH4(NaSO3)

∞ (G-S/λ ≥ 400 nm) 1.5 (G-S/λ ≥ 420 nm, 300 W Xe) 1.5 (G-S /λ ≥ 420 nm, 300 W Xe) 2.3 (G-S/15 W daylight bulb) 5.4 (G-S/15 W daylight bulb) 5.2 (L-S/300 W xenon arc lamp)

GO

Cu

CH3OH, CH3CHO

62 (L-S/300 W halogen lamp)

Cu2O microspheres

RGO

CO

5 (L-S/150 W Xe lamp)

Cu2O nanoparticles

RGO

CH3OH

1.5 (L-S/500 W Xe lamp)

Cu2O

RGO, Au−Cu

CH3OH

7.78 (L-S/500 W Xe lamp)

Ta2O5

RGO, NiOx

CH3OH(H2)

3.4 (L-S/400 W halogen lamp)

ZnO

RGO

CH3OH

1.75 (L-S/500 W Xe lamp)

CoPc BODIPY

GO RGO

CH3OH HCOOH

2 (L-S/500 W xenon lamp/TEOA) 11.4 (L-S/450 W xenon lamp/TEOA)

MAQSP

RGO

HCOOH

2.4 (L-S/450 W xenon lamp/TEOA)

86 (2011) 90 (2012) 1730 (2012) 614 (2013) 1731 (2015) 1373 (2012) 841 (2014) 86 (2011) 1732 (2015) 1733 (2016) 30 (2017) 98 (2014) 1182 (2015) 1184 (2015) 554 (2013) 981 (2015) 982 (2015) 641 (2015) 813 (2015) 1734 (2014) 1662 (2014) 1180 (2014) 1735 (2014) 1736 (2015) 1737 (2013) 1738 (2013) 954 (2014) 1739 (2014) 1580 (2012)

4 (G-S/350 W Xe,λ ≥ 420 nm)

72 (2007)

1725 (2014) 1725 (2014) 1183 (2013) 1726 (2017) 1727 (2016) 1728 (2016)

RGO

DY


Chemical Reviews

Review


cocatalysts



ref

RGO Ru(II) trinuclear complex

GO

CH3OH

1.8 (L-S/20 W LED/TEA)

rhenium complex TiO2

RGO

CO

6 (L-S/xenon lamp/TEOA)

TiO2 nanotube

GO, Cu2O

CH3OH

10.8 (L-S/300 W Xe arc lamp, λ > 400 nm, 100 mW/cm2)

CuZnO@Fe3O4 microspheres

RGO

CH3OH

9.6 (L-S/20 W LED, λ ≥ 400 nm, 85 W/m2)

nano-TiO2

N-doped RGO

CO

4.4 (G-S/400 W xenon lamp, λ > 400 nm)

TiO2

RGO

CH4, CH3OH

(L-S/250 W high-pressure mercury lamp)

ZnO nanorods

GO

CH3OH

2.81 (G-S/UV lamp, λ = 420 nm, 12 mW/cm2/353 K)

TiO2 TiO2

amine-RGO RGO

CO(CH4) CH4, CH3OH

4 (G-S/450 W xenon lamp, 11.5 mW/cm2) (L-S/150 W middle visible lamp, 1358 W/m2)

tourmaline co-doped TiO2

graphene

CH3OH

20.7 (L-S/500 W xenon lamp, λ > 400 nm)

CuO

RGO

CH3OH

hexamolybdenum clusters

GO

CH3OH

7.02 (L-S/20 W white cold LED flood light, 85 W/m2/ DMF) (L-S/20 W white cold LED flood light, 75 W/m2/DMF)

Cu2O/graphene/TiO2 nanotube array CeO2, Cu complex

graphene

CH3OH

10 (G-S/300 W xenon lamp, λ > 400 nm, 100 mW/cm2)

N-doped graphene

CH3OH

87.5 (L-S/250 W xenon lamp/298 K)

porphyrin

graphene

C2H4

(L-S/solar simulator/100 mW/cm2)

TiO2

RGO

CH4

5.2 (G-S/15 W energy-saving daylight bulb)

oxygen-rich TiO2 oxygen-rich TiO2

GO GO

CH4 CH4

(G-S/500 W xenon lamp, λ > 400 nm) 14 (G-S/15 W energy-saving daylight bulb, 8.5 mW/cm2)

Fe2O3

N-doped graphene

CO

TiO2

graphene

CO, CH4

(G-S/300 W xenon arc lamp, 300 nm < λ < 400 nm, 20.5 mW/cm2) (G-S/450 W xenon arc lamp, 19.6 mW/cm2)

Si nanowires

graphene quantum sheets

CO

(L-S/300 W xenon lamp, 100 mW/cm2)

ZnO

RGO

CH3OH

5 (L-S/300 W xenon lamp)

CdS nanorods

RGO, Ag

CO

8 (G-S/300 W xenon lamp, λ > 420 nm)

GQDs CdS NPs

CH3OH CH4

3 (L-S/300 W xenon lamp, 100 mW/cm2/TEOA, H2O) 3.5 (G-S/300 W xenon lamp, λ > 420 nm, 100 mW/cm2)

Ru-complex

BNPTL, Pt amine-functionalized graphene GO

CO

4.25 (L-S/visible light/DMF)

Cu-complex

nitrogen-doped graphene

CH3OH

6.2 (L-S/20 W white cold LED flood light, 75 W m−2/ DMF)

Ru-complex

graphene

CO

TiO2

RGO

CH4, CH3OH

(L-S/150 W middle visible lamp, 1358 W/m2)

titania photoanode

GO

HCOOH

0.02 V (SCE)

carbon nanodots carbon nanodots

Au or Pt Au

ultrathin Bi2WO6 nanosheets

carbon nanodots

CH4

3.1(G-S/500 W xenon lamp, λ ≥ 400 nm)

Cu2O

carbon nanodots

CH3OH

8.6 (G-S/300 W Xe lamp)

g-C3N4

carbon nanodots

CO/CH4

2.28/3.6 (G-S/500 W xenon lamp, λ ≥ 400 nm)

carbon nanodots and amorphous carbons HCOOH (L-S/425−720 nm) HCOOH(CH3COOH) (L-S/425−720 nm)

DZ

1602 (2014) 1740 (2016) 1741 (2016) 1742 (2017) 1743 (2017) 1744 (2016) 1745 (2017) 656 (2016) 1746 (2015) 1747 (2014) 1748 (2016) 1749 (2015) 1741 (2016) 1437 (2016) 1750 (2016) 1751 (2013) 848 (2017) 1752 (2015) 1753 (2015) 1754 (2014) 1755 (2016) 1756 (2015) 1507 (2018) 1757 (2018) 1758 (2017) 1601 (2015) 953 (2015) 1759 (2017) 1746 (2015) 1760 (2014) 83 (2011) 1761 (2014) 1762 (2017) 1763 (2015) 1764 (2017)


Chemical Reviews

Review


cocatalysts



ref

carbon nanodots and amorphous carbons CO, CH4 2 (G-S/500 W Xe lamp/30 °C/110 KPa)

hybrid g-C3N4

carbon

Cu2O nanorod

carbon

CH4, C2H4

2.5 (L-S/350 W Xe lamp, λ ≥ 420 nm, 1.16 mW/cm2)

SiO2

carbon nanodots

HCOOH

2.91 (L-S/350 W Xe lamp, λ ≥ 420 nm)

TiO2 hollow spheres

carbon

CH4CH3OH

3 (G-S/300 W Xe lamp)

ZnO1−x

carbon nanodots

CO

54.7/pristine ZnO (G-S/300 W Xe lamp)

Fe MOF

carbon layers

CO, CH4

(G-S)

1765 (2016) 1298 (2016) 1766 (2017) 1767 (2017) 1768 (2018) 1769 (2016)

a

G-S: Gas−solid system. L-S: Liquid−solid system. OMC: Ordered mesoporous carbon. GQDs: Graphene quantum dots. BNPTL: 1,1′-Bi(2naphthalene).

conductive MXene Ti3C2 nanosheets via in situ calcination method (Figure 138A and B).1568 The resultant TiO2/Ti3C2 heterojunction could achieve the better activity and stability for selective reduction of CO2 to CH4 (Figure 138C and D). The highest CH4-production rate of 0.22 μmol h−1 over the optimized sample was about 3.7 times higher than that of commercial TiO2 (P25). This extraordinary enhancement in the CO2-photoreduction performance was attributed to large population of the surface-active sites due to the fluffy rice crustlike structure and the facilitated transfer and separation of photogenerated charge carriers owing to the ultrahigh conductivity of Ti3C2 and the intimate interfacial contact. This work highlights the potential application of conductive Ti3C2 cocatalyst for efficient CO2 photoreduction. More interestingly, to improve further the photocatalytic CO2 reduction activity, Ye et al. developed the surface-alkalinized Ti3C2 through replacing −F with −OH.1567 As a result, the loading of surface-alkalinized Ti3C2 cocatalyst on P25 could achieve the 3- and 277-fold enhancements in the average evolution rates of CO (11.74 μmol·g−1·h−1) and CH4 (16.61 μmol·g−1·h−1) and typical selectivity for CH4 evolution during the photocatalytic CO2 reduction, respectively.1567 Apparently, the surface-alkalinized Ti3C2 cocatalyst could facilitate the charge carrier separation and transfer because of the superior electrical conductivity and suitable thermodynamic energy level. Moreover, the introduced hydroxyl groups as abundant basic sites could also favor adsorption and activation of the acidic CO2 molecules. Consequently, the synergistic effects result in the significant enhancement in the CO2 photoreduction. This study further confirms that new noble metal-free Ti3C2 cocatalysts should be a promising alternative to traditional noble metals for highly efficient photocatalytic CO2 reduction. Besides introduction of surface −OH, other modification strategies, such as reducing the size and optimizing the number of Ti3C2 layers, are highly expected to boost further the activity for CO2 photoreduction. Additionally, despite that metal phosphides as cocatalysts have been extensively used in the fields of photocatalytic H2 evolution,285,489,490,503 there are a few reports on the electrocatalytic or photocatalytic CO2 reduction over various earth-abundant metal phosphides,1710−1715 borides,1716 and nitrides,1712 which deserve more attention.

that the potential-limiting steps for the Ni-doped and Codoped MoS2 are the conversion of CHO to formaldehyde with only 0.28 eV overpotential and the CO2 reduction to COOH with the overpotential of 0.54 eV, respectively, both of which are much smaller than those for pure transition-metal surfaces, which results in boosting photoefficiency. Additionally, (Mo− Bi)Sx supported on mesoporous CdS has been found to be very active for highly selective photoreduction of CO2 to HCOOH in 1-butyl-3-methylimidazolium tetrafluoroborate ([Bmim]BF4)−acetonitrile (MeCN) mixed solvent under visible light.1697 Thus, in principle, doped MoS2 can also act as a potential cocatalyst in the photoreduction of CO2, which could be coupled with various semiconductors with sufficiently negative conduction band level, such as CdS, g-C3N4 and ZnS. In addition, non-precious molybdenum carbide (Mo2C) has been demonstrated to be an active and selective electrocatalyst for CO2 conversion to CO in H2,1698−1701 which holds great potential for the electrocatalytic CO2 reduction by water.1559 In particular, another promising class of noble-metal-free 2D layered cocatalysts, MXenes, have been attracting intensive interest in photocatalytic and elctrocatalytic applications since their discovery by Gogotsi and Barsoum in 2011,1702 due to their excellent structural stability, abundant exposed metal sites, the special photothermal conversion feature, the unique 2D structure, superior electrical conductivity and controllable surface functional groups. Impressively, it has been demonstrated that the metallic or semiconducting Ti3C2 (TC), one of the most studied MXenes, have been found to serve as good electrocatalysts or photocatalysts for photocatalytic H 2 evolution/water splitting.1385,1386,1388−1390,1703−1708 Interestingly, the terminated −O−, −OH, and −F groups on the planar surface offer more facile modification opportunities for promising and distinctive 2D MXene cocatalysts in the earthabundant photoreduction of CO2.31 Thus, MXenes represent a promising class of cocatalysts for photoreduction of CO2.31,1376,1567,1568,1709 In 2017, Zhang et al. first investigated the reduction of CO2 at the oxygen vacancies on Ti2CO2, V2CO2, and Ti3C2O2 MXene monolayers by means of firstprinciple computations.31 The results show that the Ti2CO2 exhibits the best catalytic activity and selectivity for the reduction of CO2 to HCOOH because of the favorable energy barrier of 0.53 eV. It was proposed that the sufficient oxygen vacancies on O-terminated MXene can be fabricated by CO and H2 treatment. Recently, Low et al. fabricated a unique rice crust-like structure TiO2/Ti3C2 composite through the uniform distribution of TiO 2 nanoparticles (NPs) over highly

7.4. Metal-Free Cocatalysts

In addition to complex electrocatalysts,1586,1717 metal-based electrocatalysts,681,1345 and highly active cocatalysts consisting EA


Chemical Reviews

Review

Figure 139. Photoconversion of CO2 to CH4 and CO over different photocatalysts (A, B) in water (pH 7) and (C) in NaOH solution (pH 9) under identical conditions. (D) Schematic illustration of photoinduced electron transfer in rutile TiO2 nanorods/carbon nanotubes in the presence of chloride and phosphate anions under light illumination.1234 Reprinted with permission from ref 1234. Copyright 2016 Royal Society of Chemistry.

eV).1771,1772 Meanwhile, CNTs can be used as photosensitizers and co-adsorbents because of their high specific surface area (>150 m2 g−1), mesoporous nature, and black color.1773−1775 Importantly, CNTs are widely used as good electrocatalysts because of their superior electrochemical performance.1185,1271,1776−1778 Thus, as a good conducting scaffold or cocatalyst, the hybridization of the cheap and nontoxic CNTs and other semiconductors has become a popular strategy to rationally develop multifunctional photocatalysts applied in different fields, such as photodegradation of organic pollutants and photochemical water splitting.1151,1153 Surprisingly, a few semiconductor−CNT nanocomposite photocatalysts have been reported so far for photocatalytic CO2 reduction.72,1234,1725,1779 Typically, the most of hybrid semiconductors for CO2 photoreduction are TiO2−CNT nanocomposite photocatalysts. CNTs in these composite photocatalysts play key role in trapping the photogenerated electrons in semiconductors and prolonging their lifetime for highly efficient CO2 photoreduction. It was first reported that the efficiency of CO2 photoreduction could be remarkably enhanced by addition of a proper amount of multiwalled carbon nanotubes (MWCNTs) as cocatalysts and support for TiO2. The MWCNT-supported anatase TiO2 nanoparticles fabricated by the sol−gel strategy were shown to selectively generate C2H5OH, whereas HCOOH was the major product over the composites of rutile TiO2 nanorods and MWCNTs synthesized by a hydrothermal method. The different crystal phases of TiO2 are responsible for the final selectivity toward CO2 photoreduction. Clearly, MWCNTs in these composite photocatalysts play very

of only earth-abundant elements, which are still very rare, the metal-free electrocatalysts for CO2 reduction (e.g., carbon nanotubes, graphene, carbon nanodots, carbon nanofibers, and pyridinium derivatives) continue to attract attention for heterogeneous CO2 photoreduction.73,1018,1040,1047,1718−1720 7.4.1. Nanocarbon Cocatalysts. Another strategy for selective photoreduction of CO2 is to construct various semiconductor/nanocarbon composite photocatalysts. The nanocarbon materials as cost-effective cocatalysts can not only greatly boost separation and transfer of photogenerated charge carriers, but also increase the reactant adsorption and the visible-light absorption.351 Importantly, the larger amount of active sites could result in the significant enhancement of the selective photoreduction of CO2. Although various kinds of nanocarbon materials as cocatalysts have been extensively utilized to design carbon-based heterojunctions for photocatalytic H2 production and degradation of pollutants in the gaseous and liquid phases,113,351,479,1238,1240,1721−1723 only a limited number of reports devoted to the photocatalytic CO2 reduction is available.350,352,1724 Table 17 lists the major nanocarbon cocatalysts, such as carbon nanotubes (CNTs), graphene, carbon nanodots, and carbon nanofiber, which are discussed in section 7.4. 7.4.1.1. Carbon Nanotubes and Nanofibers. Generally, CNTs can be employed as electron collector and transfer medium to promote the charge separation,1152,1770 because of their large electron storage capacity, good electron conductivity due to the long range π electronic conjugation, and favorable Fermi levels (work functions ranging from 4.3 to 5.1 EB


Chemical Reviews

Review

important role in reducing the unexpected agglomeration of TiO2 NPs and boosting the separation of photogenerated h+/e− pairs, thus leading to the improved photoactivity of TiO2 for CO2 reduction.72 Chai and coworkers reported that the core− shell MWCNT/TiO2 heterojunctions exhibited an excellent photoactivity for CH4 synthesis as compared to TiO2 under visible light, on which the highest CH4 yield was 0.17 μmol gcat−1 h−1.1725 The enhanced photoreactivity was ascribed to the enhanced visible-light absorbance and promoted electron−hole pair separation through the introduction of MWCNT core. More recently, to reveal the multifunctional role of phosphate bridges, Cl− and CNTs in photocatalysis, Jing’s group investigated the effects of the aforementioned species on the selective CO2 photoreduction to CH4 and CO over rutile TiO2 nanorods.1234 This study confirmed that the phosphate groups and CNTs are advantageous for improving the hole trapping and CO2 photoreduction efficiency over Cl-decorated TiO2 (Cl-R), respectively (Figure 139A and B). The optimized Cl-R sample modified with 2 wt % of CNTs and 0.2 M phosphoric acid solution exhibited a 4-fold enhancement in the CO2 photoreduction activity as compared to that on pure rutile TiO2 nanorods (Figure 139C). Thus, it is clear that CNTs and chloride/phosphate anions serve as the electron acceptors and donors, respectively, whereas the phosphate groups could act as effective functional bridges in the heterojunction TiO2/CNTs interface, which results in synergistically boosted photocatalytic CO2 reduction performance (Figure 139D). This work suggests that the simultaneous optimization of electron/hole separation and interfacial charge transfer could provide a feasible strategy to fabricate efficient nanosized CNT-based photocatalysts for selective CO2 conversion, which can also lead to better understanding of the CO2 photoreduction process. In addition to TiO2, the coupling of CNTs and non-TiO2 semiconductors has also been reported. For example, Ag@AgBr nanoparticles were loaded onto the surface of CNTs with different lengths of carbon tubes by successive depositionprecipitation and photoreduction methods (Figure 140A). The resulting Ag@AgBr/CNT nanocomposites containing CNTs with different lengths exhibited good selectivity for photoreduction of CO2 to CH4 and methanol through 8e and 6e pathways, respectively. Moreover, it was found that the product yields over Ag@AgBr/CNT heterojunctions were not only larger than those obtained on Ag@AgBr under the same conditions, but also their values increased with increasing length of CNTs (Figure 140B). The electrochemical impedance spectroscopy measurements further confirm that the longer CNTs can exhibit much lower charge transfer resistance, which results in more efficient charge separation and CO2 photoreduction. This study showed that the longer CNTs with a long-range order are beneficial for promoting transport of charge over longer distances, thus more efficiently suppressing recombination of the hole and electron pairs (Figure 140C).1183 Additionally, the introduction of CNTs might improve the CO2 adsorption/activation, which also enhances the yield of CO2 photoreduction. Furthermore, the N-doped CNTs or graphene have been extensively demonstrated to be active and durable electrocatalysts for hydrogen or oxygen evolution,1271,1780,1781 because nitrogen impurities can serve as active sites. More interestingly, it was shown that the presence of graphitic and pyridinic nitrogen in nitrogen-doped CNT arrays significantly increases the catalytic CO evolution activity (with small overpotential of −0.18 V) and selectivity (∼80%),1265 suggesting that the nitrogen-doped CNT

Figure 140. (A) TEM image of Ag@AgBr decorated with long CNTs. (B) Visible-light-driven CO2 reduction yields (after 5 h of illumination) over Ag@AgBr and Ag@AgBr/CNT heterojunctions with CNTs of different lengths in aqueous solution at pH 8.5. (C) Schematic illustration of electron transfer in Ag@AgBr/CNT during CO2 photoreduction.1183 Reprinted with permission from ref 1183. Copyright 2013 Elsevier.

cocatalysts might have promising prospects for fabrication of highly selective CO2 reduction photocatalysts. Interestingly, the N-containing sites are also excellent adsorption sites toward CO2. Thus, it is highly anticipated that the promising N-doped graphene or CNTs can be thoroughly studied and applied for CO2 photoreduction owing to the synergy between their superior electric conductivity and excellent CO2 adsorption ability. Recently, carbon nanofibers are also excellent cocatalysts that have been widely applied in electrocatalysis and photocatalysis because of their superior electrochemical properties, easy electrospinning fabrication, and unique 1D nanostructure.1782−1784 Furthermore, other amorphous nanocarbon materials such as carbon black and acetylene black as electron conductive cocatalysts have also been applied in the photocatalytic H2 evolution.479,1240 More interestingly, it was shown that the carbon nanofibers exhibited the extremely low overpotential (0.17 V) for electrocatalytic CO2 reduction and over 10-fold higher current density in comparison with that obtained for Ag electrocatalyst under similar operation conditions.1018 However, there are few available studies about the utilization of metal-free carbon nanofibers or amorphous nanocarbon materials in photocatalytic reduction of CO2. Consequently, the metal-free carbon nanofibers and other amorphous nanocarbon materials as cocatalysts are expected to be utilized for CO2 photoreduction in near future. 7.4.1.2. Graphene. Graphene, as a shining star of twodimensional layered materials, has attracted a lot of attention because of its high conductivity (∼5000 W m−1 K−1), extremely large surface area (∼2600 m2 g−1), excellent electron mobility (∼200 000 cm2 V−1 s−1) and low cost.1375,1721,1722,1785 Since the pioneering reports on the photocatalytic application by Kamat and coworkers,1786,1787 semiconductor/graphene heterojunctions have been extensively used in the photo(electro)catalytic water splitting,113,1370,1722,1788,1789 degradation of pollutants1224,1722,1790,1791 and CO2 reduction,349,350,352,1792 because of their good structural, optical and electronic EC


Chemical Reviews

Review

Figure 141. HRTEM image of (A) CsPbBr3 QDs and (A) CsPbBr3 QD/GO. (C) Photocatalytic production yields of CO and CH4 after 12 h of illumination, (D) UV−vis absorption spectra and the external quantum efficiency plots, (E) Steady-state PL spectra after excitation at 369.6 nm, (F) PL decay spectra after pulsed excitation at λ = 369.6 nm and (b) EIS Nyquist plots recorded under 150 mW cm−2 illumination at a bias of −0.4 V Ag/AgCl of the individual CsPbBr3 QDs and CsPbBr3 QD/GO composite. (H) Schematic diagram of CO2 photoreduction over the CsPbBr3 QD/ GO photocatalyst.30 Reprinted with permission from ref 30. Copyright 2017 American Chemical Society.

properties.264,1370,1721,1789,1793 On the one hand, the earthabundant RGO as a cocatalyst can significantly boost the separation and transport of photoexcited electrons from CB of a semiconductor to RGO due to its favorable graphene/ graphene•− potential (−0.08 V vs SHE, pH 0).1794 On the other hand, GO can directly function as an excellent photocatalyst for CO2 photoconversion to methanol.1662,1795 The largest reported visible-light generation rate of methanol via CO2 photoreduction over modified GO is approximately 0.172 μmol g cat−1 h−1, which is 6-time higher than that on pure TiO2.1795 Additionally, the CO2 adsorption capacity could be also enhanced through coupling RGO/GO with semiconductors,1796−1798 which has become an appealing strategy to boost their photoactivity for conversion of CO2 to valuable hydrocarbons.90,98,614,1180 First, the large 2D structures of RGO/GO provide sufficient opportunities to anchor different dimensions of nanostructured 0D, 1D, 2D, and 3D semiconductors onto them at separate sites. As a catalyst nanomaterial, the importance of RGO/GO in hybrid photocatalysts is in storing and shuttling electrons on demand to adsorbed species.1786 The fabrication of 2D RGO supported semiconductor heterojunctions paves the promising road to design highly feasible non-noble metal CO2 reduction photocatalysts. For example, Kuang’s group loaded CsPbBr3 halide perovskite QDs onto 2D GO and successfully constructed a 0D-2D hybrid junctions for CO2 photoreduction.30 This is the first report on the use of CsPbBr3 perovskite QDs as novel photocatalysts for photocatalytic reduction of CO2 into solar fuels in nonaqueous media. Both CsPbBr3 QDs (about 6 nm) and CsPbBr3 QD/GO composite

were synthesized by a simple room-temperature antisolvent precipitation method (Figure 141A). The resulting CsPbBr3 QDs exhibited the steady photocatalytic activity for selective reduction of CO2 to CO (49.5μmol g−1) and CH4 (22.9μmol g−1) with a selectivity over 99.3% (Figure 141B) after 12 h of photocatalytic reaction. Additionally, the heterostructured CsPbBr3 QD/graphene oxide (CsPbBr3 QD/GO) composite also featured a 25.5% enhancement in the rate of photocatalytic CO2 reduction. The CsPbBr3 QD/GO composite showed better external quantum efficiency (EQE) than the individual CsPbBr3 QDs in the entire EQE test range, despite the similar absorption behavior of their UV−vis absorption spectra (Figure 141C). The improved electron extraction and transport of conductive GO were verified by steady-state PL spectra and PL decay spectra (Figure 141D and E). Thus, the favorable charge transport from CsPbBr3 QD to GO is mainly responsible for the enhancement in the CO2 photoreduction (Figure 141F).30 Similarly, to simultaneously achieved higher CO2 adsorption and efficient light absorption and charge-transfer properties for CO2 photoconversion, Cho et al. developed an aminefunctionalized graphene/CdS NPs (AG/CdS) 2D/0D photocatalysts via an N,N′-dicyclohexylcarbodiimide coupling reaction between the carboxylic group of GO and the amine group of ethylenediamine.1758 As a result, the increased visiblelight photocurrent and CO2 adsorption capacity of the AG/ CdS clearly confirmed the enhanced charge separation and CO2 activation, respectively, leading to high methane formation rate of 2.84 μmol/(g h) under visible light and CO2 at 1 bar, corresponding to 3.5 times that observed for rGO/CdS (Figure 142A). Clearly, AG as a bifunctional cocatalyst could more ED


Chemical Reviews

Review

Figure 142. (A) CO2 photoreduction and CH4/CO ratio over different samples under CO2 at 1 bar (40 °C). (B) Schematic illustration of the proposed CO2 photoreduction mechanism over AG/CdS.1758 Reprinted with permission from ref 1758. Copyright 2017 American Chemical Society.

boosting the photoreduction of CO2 to CH4, including the enriched electron density, increased adsorption, destabilization and activation of CO2 molecules through strong π−π conjugation interactions (Figure 143D). Clearly, although the CO2 adsorption capacity and electron conductivity of nanocomposite photocatalysts increase with increasing content of graphene, the light shielding caused by its excess could lead to a decreased activity for CO2 photoreduction. Therefore, the optimized amount of graphene in composite photocatalysts is very crucial for boosting the efficiency for CO2 photoreduction. Moreover, the interesting and emerging 2D−2D graphenebased hybrids have been thoroughly discussed in the section 6.4. Additionally, 3D semiconductor microspheres have been also coupled with 2D RGO/GO nanosheets to construct the 2D/3D hierarchical photocatalysts for efficient CO2 photoreduction. For instance, the 3D−2D Cu2O microspheres/RGO nanosheets hybrids could be simply fabricated by a one-step microwave-assisted chemical method. 1180 The optimized Cu2O/0.5%RGO heterojunctions showed a nearly 6 and 50 times higher photoactivity for selective conversion of CO2 into CO, than those obtained for the optimized Cu2O and Cu2O/ RuOx junctions after 20 h of illumination, owing to reduced h+−e− recombination, efficient charge transfer, and protective function of RGO.1180 Furthermore, defect densities and heteroatom doping of graphene also play an important role in boosting the photoactivity toward reduction of CO2.1226,1233 In other words, the electron conductivity and electrocatalytic activity of graphene could be improved through decreasing defect density and doping the suitable heteroatoms into graphene, thus leading to the promoted separation of photogenerated electron−hole pairs and enhanced photoactivity for CO2 reduction. On the one hand, the selective photoreduction of CO2 could be significantly enhanced through decreasing the defects of graphene due to the improved electron conductivity and accelerated electron transfer to the active sites for reduction reaction. As mentioned above, an approximately 7fold visible light activity improvement was achieved over the composites with less defective solvent-exfoliated graphene (SEG) and TiO2 as compared to P25 alone.86 On the other hand, the visible-light-driven CO2 photoreduction could be significantly boosted through simultaneously optimizing graphene and semiconductor.614,841 For example, the assynthesized TiO2-graphene 2D sandwich-like nanosheets in a binary ethylenediamine(En)/H2O solvent exhibited good selectivity for C2H6 production owing to the synergy between the surface-Ti3+ abundant TiO2 and graphene.614 Importantly,

efficiently promote the charge separation/transfer and activate CO2 molecules (Figure 142B) in comparison to rGO, which should be exploited for other heterogeneous GO-based photocatalysts for high-efficiency CO2 photoconversion. Besides 0D−2D hybrids, 1D−2D hybrid graphene-based photocatalysts have also been widely fabricated, which could be effectively overcome both the unwanted agglomeration of 1D nanostructures and restacking of 2D RGO/GO nanosheets, thus leading to the remarkably enhanced photocatalytic efficiency.98,1182,1745 Yu’s group successfully fabricated RGO/ CdS nanorod heterojunctions via a facile one-step microwavehydrothermal strategy in a mixed ethanolamine−water solution (Figure 143A and B).98 The optimized RGO−CdS nanorod heterojunctions showed a high CH 4-generation rate of 2.51μmol g−1 h−1 at an RGO content of 0.5 wt % (as shown in Figure 143C), 10 times higher as that obtained on pure CdS nanorods, which was even much larger than that on the optimized Pt-loaded CdS nanorods under the same conditions.98 It is believed that RGO plays multifunction role in

Figure 143. TEM (A) and HRTEM (B) images of the 0.5 wt % RGO−CdS nanorods.(C) Visible-light CH4-generation rate over the Gx, P0.5, and RGO photocatalysts. (D) Schematic illustration of visible-light CO2 photoreduction over the RGO−CdS nanorod heterojunctions.98 Reprinted with permission from ref 98. Copyright 2014 Royal Society of Chemistry. EE


Chemical Reviews

Review

Figure 144. (A) High magnification, (B)TEM, and (C) HRTEM images of N−TiO2-001/GR. (D) Total visible-light CH4 yield over TiO2-001, N− TiO2-001, and various TiO2-based/GR heterojunctions. (E) Schematic illustration of photoreduction of CO2 with gaseous H2O to CH4 using N− TiO2-001/GR heterojunctions.841 Reprinted with permission from ref 841. Copyright 2014 Springer Nature.

Figure 145. (A) Fabrication of Vo-NaTaON and N-GQDs/Vo-NaTaON nanocubes. (B) UV−vis diffuse reflectance spectra, (C) EPR, and (D) PL spectra of (i) NaTaO3 and (ii) Vo-NaTaON crystals. (E) Solar-driven CH4 and CO generation rate measured for NaTaO3, NaTaON, Vo-NaTaON, GQDs/Vo-NaTaON, and N-GQDs/Vo-NaTaON. (F) Schematic illustration of solar-driven CO2 photoreduction over N-GQDs/Vo-NaTaON heterojunctions.1799 Reprinted with permission from ref 1799. Copyright 2016 Elsevier.

facets lead to the high visible-light absorption, effective charge separation, and high catalytic activity, respectively, thus achieving the significant activity enhancement (Figure 144E). Similarly, a new GO-doped-O-rich TiO 2 (GO-OTiO2 ) heterojunctions with an optimum GO loading of 5 wt % could achieve the highest total CH4 yield of 1.718 μmol/g(cat) after 6 h of reaction, which is about 14 times larger that that on P25.1752 More interestingly, Hou et al. fabricated the N-doped graphene quantum dots (N-GQDs) on Vo-NaTaON nanocubes.1799 As expected, the EPR (Figure 145A) and PL spectra (Figure 145B) reveal that the created nitrogen and oxygen-

it was also shown that the intimate coupling achieved via in situ growth process also played an important role in enhancing the photoactivity toward selective conversion of CO2 to C2H6.614 Similarly, Ong et al. demonstrated that the formation of Ti− O−C bonds in the composite of TiO2 NPs (10−17 nm, Ndoped with ∼35% (001) facets) and graphene (GR) nanosheets (N-TiO2-001/GR) (Figure 144A−C) could successfully narrow the band gap from 3.23 to 2.9 eV and reach the highest visible-light CH4 yield of 3.70 μmol·gcatalyst−1, which is about 11 fold larger than that on TiO2-001 (Figure 144D).841 It is believed that N-doping, graphene loading, and exposed (001) EF


Chemical Reviews

Review

Figure 146. (A) PEG-modified CQDs before (left, fluorescent) and after (right, CO2 photoreduction) metal deposition. (B) TEM and HRTEM (inset) images of Au coated PEG-CQDs. (C) Absorption spectra of PEG-CQDs (dashed line) and Au coated PEG-CQDs (solid line) in an aqueous solution. (D) 1H NMR spectra of (a) HCOONa generated via CO2 photoreduction and (b) CH3COONa as an internal standard in D2O.83 Reprinted with permission from ref 83. Copyright 2011 American Chemical Society.

separation (Figure 146A). The resulting CQDs functionalized by both PEG and Au show the average diameter of 9 nm (Figure 146B) and the enhanced surface plasmon absorption (405−720 nm, Figure 146C), and could serve as photocatalysts for visible-light photoreduction of CO2 in aqueous solutions.83 Formic acid, as a main product, was selectively produced via CO2 photoreduction with a quantum yield of 0.3% (Figure 146D), which was an order of magnitude larger than that over P25 under UV light. The surface-modified CQDs are a new kind of visible-light photocatalysts for CO2 photoreduction.83 More recently, the formation of acetic acid via CO 2 photoreduction was also confirmed by using gold-doped carbon dots as aqueous soluble photocatalysts.1761 Thus, it is highly desirable that the metal-doped carbon dots could be combined with other semiconductors to achieve an improved activity and selectivity for photocatalytic reduction of CO2 under visible light irradiation. More interestingly, CQDs could be also employed as metal-free cocatalysts to boost the photocatalytic CO2 reduction over diverse semiconductors, due to the improved electrical conductivity, rapid interfacial electron transfer, the suppressed electron−hole recombination rate and higher work function of CQDs.1762,1764 Li et al. synthesized a novel CQDs/Cu2O heterojunction with a direct bandgap of 1.96 eV through loading 5 nm CQDs cocatalysts over the surface of the 2 μm Cu2O particles (Figure 147A).1763 The resulting heterojunction exhibited excellent visible-lightdriven activity (55.7 μmol g−1 h−1) and stability for selective photoconversion of CO2 to CH3OH (Figure 147B). It is believed that the loaded CQDs cocatalysts could improve the light absorption, charge separation and transfer, resulting in the enhanced activity and stability (Figure 147C) of Cu2O for CO2

vacancies could effectively narrow the wide bandgap and promote the charge separation of perovskite NaTaO3. Consequently, the optimized Vo-NaTaON catalyst exhibited superior broad spectrum photoreduction of CO2 to CO and CH4. Moreover, the CO2 photoreduction could be further improved through fabricating N-GQDs/Vo-NaTaON heterojunctions, due to the boosted light absorption and charge separation (Figure 145C and D). These works highlight that the optimization of graphene and semiconductors pave the way for designing new efficient graphene-based photocatalysts for CO2 photoreduction. In future, it is also expected that the heteroatom doped1800 and 3D hierarchical macro/mesoporous1798,1801−1804 graphene could be utilized in the selective photoreduction of CO2 because of their unique electrical conductivity and adsorption properties. 7.4.1.3. Carbon Nanodots and Amorphous Carbon. Recently, aqueous-soluble carbon quantum dots (CQDs) were considered to be excellent alternatives to traditional semiconductor NPs and attracted increasing attention because of their superior electron reservoir and transfer ability, chemical stability, and their facile and low cost synthesis, and nontoxicity.1523,1805,1806 Recently, the surface-functionalized CQDs as photocatalysts were also applied in visible-light photoreduction of CO2.83 However, CQDs alone could not act as effective photocatalysts owing to the ultrafast charge recombination. Consequently, to enhance their photostability, the sub-10 nm CQDs were first passivated by poly(ethylene glycol) diamine (PEG1500N) (Figure 146A).1807 Au or Pt as a cocatalyst was then coated on the PEG-functionalized CQDs through in-situ photodeposition, thus further promoting the photogenerated charge EG


Chemical Reviews

Review

Figure 147. (A) HRTEM images of CQDs/Cu2O heterojunction. (B) Time dependence of selective ethanol yield (black, continuous; other colors, solution replacement every 3 h; green: accumulation after 3 h runs), (C) The XRD pattern of the CQDs/Cu2O catalyst before and after reaction, (D) A schematic diagram illustrating the photocatalytic reduction of CO2 to methanol over CQDs/Cu2O.1763 Reprinted with permission from ref 1763. Copyright 2015 John Wiley & Sons, Inc.

to synergistically achieve the enhanced CO2 photoreduction over the vis−NIR broad spectrum. The present work provides an unprecedented proof-of-concept, which might inspire further exploration toward developing the next-generation active and cost-effective Vis−NIR wide-spectrum-responsive photocatalysts for various applications. Besides carbon nanodots, amorphous carbons have also been employed as metal-free cocatalysts to boost the photocatalytic reduction of CO2. In general, the carbon coating layer as a perfect chemical protection can not only remarkably improve photostability of narrow-band semiconductors, such as Cu2O and CdS, through passivating the surface traps, but also can favor adsorption ability and reaction of reactants because of its large specific area and porous structure.1298,1809 To fully utilize the advantage and address the unfavorable factors of bulk gC3N4, Wang et al. fabricated the hybrid composites of crumpled multilayer and mesoporous thin g-C3N4 nanosheets and amorphous carbon (H-g-C3N4/C) through a facile one-pot pyrolysis of melamine powder and soybean oil (Figure 149A).1765 The resulting H-g-C3N4/C composites exhibited more favorable formation of carbon monoxide than that of methane (Figure 149B and C). The optimal H-g-C3N4/C-6 sample with a 3.77 wt % C achieved the visible-light CO and CH4 yields of 22.60 and 12.5 μmol g−1 after irradiation for 9 h, respectively, both of which were 2 fold higher than those over bulk g-C3N4. The EIS profiles (Figure 149D) and PL spectra (Figure 149E) of bulk g-C3N4 and H-g-C3N4/C-6 heterojunctions further confirm the boosted photogenerated charge separation due to the synergy of amorphous carbon and gC3N4, reflected by the remarkably improved photoactivity for CO2 photoreduction with H2O (Figure 149F). Similarly, Liu et

conversion to methanol. As previously reported for photocatalytic water splitting over CQD-semiconductor composite,1808 CQDs could mainly accept the photogenerated holes from Cu2O and further oxidize H2O to O2 on their surface via a two-electron pathway, thus inhabiting the instability problem of Cu2O (Figure 147D). However, the additional photoexcitation of CQDs for this enhanced photocatalytic process was not directly evidenced in this work. Accordingly, the exact underlying mechanism for the retarded charge recombination in Cu2O through loading CQDs is still indistinct, and should be further studied. More importantly, the intriguing up-conversion photoluminescence behavior of CQDs could make them harvest the long wavelength near-infrared (NIR) light to visible light, thus achieving the CO2 photoreduction under the lowenergy NIR light, which contains almost 50% of the solar spectrum. For instance, Kong et al. first constructed an active and cost-effective Vis−NIR wide-spectrum-responsive photocatalyst through coupling the 0D CQDs of 5−10 nm diameters and 2D ultrathin (001) facet-exposed Bi2WO6 nanosheets (UBW) by a one-pot hydrothermal process (Figure 148A and B).1762 Impressively, the optimized visible-light CH4 production yield of 1CQDs/UBW (1 wt % CQD) could reach up to 7.19 μmol/gcat after 8 h of irradiation, which is about 9.5 and 3.1 times higher than those obtained on pristine Bi2WO6 nanoplatelets (PBW) and bare UBW, respectively (Figure 148C). It is also noteworthy that 1CQDs/UBW showed the highest CH4 production yield of 0.41 μmol/gcat after 8 h of NIR-light irradiation, verifying the NIR-driven CO2 reduction (Figure 148D). Thus, the up-conversion properties and electron-withdrawing nature of the CQDs and the ultrathin nanosheets and highly exposed (001) facets of UBW were able EH


Chemical Reviews

Review

Figure 148. HRTEM image of (A) 1 CQDs/ultrathin Bi2WO6 nanosheets and (B) CQDs (inset, the solution color of CQDs under daylight lamp (left) and UV light (right)). (C) Visible-light (λ > 400 nm) and (D) NIR-light (λ > 700 nm) CH4 yields obtained via CO2 photoreduction over different samples after 8 h of irradiation.1762 Reprinted with permission from ref 1762. Copyright 2017 Springer Nature.

al. fabricated the ZnO nanoparticles coated by amorphous carbon layers through direct high-temperature treatment of ZIF-8 (zeolitic imidazolate framework) (Figure 150A and B).1297 The resulting mesoporous ZnO@C core/shell photocatalysts exhibited significantly enhanced CH3OH formation via CO 2 photoreduction (Figure 150C) and higher CO 2 adsorption capacity under full-spectrum Xe lamp. Notably, the highest CO2 photoreduction activity (0.83 μmol h−1 g−1) was achieved over the 500 °C-calcined sample, about 6 fold higher than that obtained on ZnO nanorods (Figure 150C). Furthermore, the enhanced visible light absorption was also verified. Accordingly, it is clear that the in situ doping and coating of amorphous carbon could lead to the increased visible light harvesting, CO2 capture, and charge separation because of the high specific surface area and porous framework (Figure 150D), thus achieving the superior CO2 photoreduction activity over mesoporous ZnO photocatalyst. This work further demonstrates that the coated amorphous carbon layers could play the multifunctional role in boosting the CO2 photoreduction performance. Furthermore, the amorphous carbon could be utilized to address the fateful photocorrosion of some visible-light-driven semiconductors, such as Cu2O and CdS. For example, to enhance the CO2 adsorption and charge carrier transfer of mesoporous Cu2O nanorods, the thin carbon layer coated mesoporous Cu2O nanorods were constructed through annealing the glucose-coated Cu(OH)2 nanotubes on a Cu foil at 500 °C under N2 atmosphere.1298 The resulting C-2/Cu2O sample exhibited a 2.5-times higher the total production of CH4

and C2H4, as compared to that over pure Cu2O (Figure 151AC). Additionally, the durability of C-2/Cu2O was demonstrated to be much better than that of pure Cu2O (Figure 151D). Consequently, the synergetic effects of enhanced CO 2 adsorption (Figure 151E), decreased charge transfer resistance and abundant amount of electrons (Figure 151F) are believed to be the key factors for the significantly high selective CO2 photoreduction to hydrocarbons over C-2/Cu2O. However, the reaction mechanism and intermediates in this study were not fully discussed. The selectivity of Cu2O in this study is obviously different from the previously reported CH3OH selectivity for CO2 photoreduction in aqueous solutions. The above studies highlight an important role of the amorphous carbon layer in boosting the stability and activity of Cu2O for CO2 reduction in artificial photosynthesis under visible light. More recently, to suppress the main competitive H2-formation process for the photoreduction of CO2 over In2O3, Pan et al. fabricated the In2O3 nanobelts coated by a 5 nm-thick carbon layer (C−In2O3, Figure 152A).797 It was shown that the Pt/C− In2O3 exhibited better activity for selective formation of CO and CH4, while H2 evolution was significantly suppressed as compared to that on Pt loaded pure In2O3(Pt/P−In2O3) (Figure 152B and C). The improved photoinduced charge separation (Figure 152D) and increased chemisorption of CO2 (Figure 152E) were also further verified. More importantly, the DFT calculations revealed that the Pt/C−In2O3 catalyst favors the reduction of the adsorbed CO2 to CO and CH4, whereas the Pt/P−In2O3 catalyst is advantageous for the exothermic H2 EI


Chemical Reviews

Review

Figure 149. (A) TEM images of H-g-C3N4/C-6. Time-dependent yields of (B) CO and (C) CH4 over all catalysts. (D) EIS profiles and (E) PL spectra of the bulk g-C3N4 and H-g-C3N4/C-6 composite catalyst (F) CO2-photoreduction mechanism over the hybrid g-C3N4/carbon composites.1765 Reprinted with permission from ref 1765. Copyright 2016 American Chemical Society.

and CH3OH generation rates of 4.2 and 9.1 μmol g−1 h−1, respectively, which are dramatically higher than those obtained on pure TiO2(Figure 153B). The significantly improved photoactivity could be attributed to the enhanced specific surface area (110 m2 g−1), remarkably enhanced visible-light absorption, CO2 uptake (0.64 mmol g−1) and charge separation efficiency. In addition, an interesting local photothermal effect around the photocatalyst caused by carbon has been also proposed to explain the enhanced photoactivity. In situ DRIFTS spectra further confirmed the formation of adsorbed intermediates, such as carbonate, adsorbed formate (HCOO),

formation (Figure 152F). Thus, the photocatalytic CO2 reduction to both CO and CH4 is achieved over the catalytic active sites (i.e., Pt particles) with the adsorbed CO2, the trapped electrons through the carbon coating and the asgenerated protons (Figure 152G). Apart from loading the amorphous carbon on the outer surface, it can be also fabricated on the inner surface of hollow semiconductors. Recently, Wang et al. constructed the hybrid carbon@TiO2 hollow spheres through a facile and green calcination method of carbon nanospheres coated by TiO2 shell (Figure 153A).1767 The optimized carbon@TiO2 heterojunctions show the CH4 EJ


Chemical Reviews

Review

Figure 150. TEM (A) and HRTEM (B) images of the sample Z-500. (C) Methanol formation rates of different photocatalysts. (D) Schematic illustration of enhanced CO2 photoreduction over ZIF- derived porous carbon on ZnO photocatalysts.1297 Reprinted with permission from ref 1297. Copyright 2016 Royal Society of Chemistry.

overpotential73 In 2008, Barton et al. first reported that the highly active and selective photoelectroreduction of CO2 to methanol in water on a p-GaP semiconductor electrode could be achieved using pyridine as a cocatalyst.73 However, during the past several years, the role of Py, the electrode surface and acidic solution in catalyzing CO2 reduction to formic acid on GaP electrodes is still under debate.1817 Keith and Carter thought that the adsorbed dihydropyridine (DHP*) intermediate controls the formation of formic acid by transferring protons and electrons to CO2 (Figure 154A).1818,1819 Similarly, Musgrave and coworkers proposed that the aqueous dihydropyridine (DHP(aq)) intermediate could also achieve the selectively reduction of CO2 to formic acid through hydrogenation reaction and proton transfer (Figure 154B).1820 However, due to the high instability of the aqueous pyridinyl radical (1-PyH•(aq)) over the GaP(110) surface and higher computed reduction potential of homogeneous PyH+(aq) than CBmin of bare GaP(110) in vacuum,1720,1821 Lessio and Carter proposed an alternative mechanism for the formation of DHP* by coupling Py* and reduced H*.1821 Interestingly, considering the explicit solvation of the GaP(110) surface covered with adsorbed water molecules,1822−1824 Carter and coworkers proposed an alternative heterogeneous mechanism for explaining CO2 reduction on p-GaP photoelectrodes by adsorbed 2pyridinyl species (2-PyH•*) (Figure 154C).1817,1825 In addition, theoretical studies showed that the pyridinium radical as a strong reductant could yield a carbamate intermediate through a one-electron reduction step, thus resulting in the formation of HCOOH, formaldehyde, and finally CH3OH (as shown in Figure 155).1040 The further quantum chemical calculations demonstrated that pyridine could favor the PEC reduction of CO2 without formation of high-energy Py− and

methoxyl group (CH3O), and molecularly adsorbed formaldehyde (HCHO), indicating the multistep reduction process of CO2 to CH4 through the typical intermediate products, such as HCOOH, HCHO, and CH3OH. The electrons accumulated in the carbon from the excited TiO2 could promote the charge separation and reduction of adsorbed CO2, allowing for the enhanced overall photocatalytic activity (Figure 153C). In future, it is expected that various hybrid nanostructures could be widely constructed with the multifunction amorphous carbon/CQDs and applied in other semiconductor systems for CO2 reduction.1810 For example, Varela et al. demonstrated that amorphous carbon blacks codoped with N and Fe or Mn ions were more active catalysts toward highly selective electroreduction of CO2 to CO than a polycrystalline Au benchmark with low surface area.1811 It was further revealed that the nitrogen functionalities could function as both active CO-production and competing H2-evolution sites, which were evidenced by CO protonation and hydrocarbon generation owing to the sufficiently strong binding of CO to doped metal. Notably, N-doped graphene with the high specific surface area generally exhibits abundant Lewis basic nitrogen sites, which can readily coordinate various kinds of metal ions.565 Especially, some active nitrogen sites with coordinated metals, structurally similar to porphyrin and phthalocyanine complexes, could achieve the high activity for selective electrocatalytic CO2 reduction.1087,1088,1091,1812−1815 At this point, the emerging and promising metal and nitrogen-doped carbon cocatalysts should be highly effective for selective reduction of CO2 under visible light illumination.646,1816 7.4.2. Molecular Cocatalysts. It is worth noting that the simple pyridinium (Py) cation showed the good selectivity for methanol generation via CO2 reduction at very modest EK


Chemical Reviews

Review

Figure 151. Time-dependent yield over (A) pure Cu2O and (B) C-2/Cu2O. (C) Total yield and (D) stability study of photocatalytic evolution (CH4 and C2H4) on pure Cu2O and C-2/Cu2O under visible light irradiation. (E) CO2 adsorption isotherm curves and (F) electrochemical impedance spectra (EIS) measured in 0.02 M Na2SO4 solution (in dark and under illumination for pure Cu2O and C-2/Cu2O.(L) Schematic illustration of visible-light CO2 photoreduction over CCMNRs.1298 Reprinted with permission from ref 1298. Copyright 2016 American Chemical Society.

CO2− anionic radicals.1826 Although there is still debate on the mechanism of reducing CO2 to methanol in a system containing a soluble pyridinium component, the good reduction selectivity of CO2 has the potential for application in photocatalytic reduction of CO2 using pyridine as a cocatalyst. Additionally, it should be pointed out that, in these systems, the strong photocorrosion of p-GaP and the required external bias voltage for the CO2 reduction need to be further improved in future studies. Furthermore, it was found that the silver cathode could selectively reduce CO2 to CO at an applied potential of 1.5 V (overpotential below 0.2 V) and Faradaic efficiency greater than

96% in an ionic liquid, 1-ethyl-3-methylimidazolium tetrafluoroborate (EMIM-BF4).1047 It was shown that the ionic liquid electrolyte used as a cocatalyst plays a significant role in reducing the (CO2)− intermediate energy, thus leading to the lowered CO2 reduction barrier and improved efficiency. This work may suggest that the solvents or electrolytes have great impact on the selective electroreduction of CO2, which may provide a new idea to boost the activity and selectivity toward CO2 photoreduction through the addition of metal-free ionic liquid electrolyte into the reduction systems. EL


Chemical Reviews

Review

Figure 152. (A) SEM and TEM (inset) images of C−In2O3. (B) Product formation rates via CO2 photoreduction over Pt/C−In2O3 and Pt/P− In2O3. (C) CO2 photoreduction product distribution on Pt/C−In2O3 after 4 h irridiattion. (D) EIS of In2O3 and C−In2O3. (E) CO2 adsorption capacity at 1.01 bar as a function of the glucose amount used for coating a thin carbon layer on In2O3 nanoblets. (F) DFT-calculated relative energy profiles for the proton reduction to H2 and proton transfer to O atom of CO2 on Pt2/P−In2O3(110) and Pt2/C−In2O3(110). (G) Schematic illustration of the photoreduction of CO2 with water on Pt/C−In2O3, using TEOA as the electron donor.797 Reprinted with permission from ref 797. Copyright 2017 American Chemical Society.

7.5. Multifunctional Cocatalysts

catalysts for highly efficient reduction reaction, and inhibited H2 evolution reaction for highly selective CO2 reduction. First, nanocarbon materials are generally employed to improve the interface contact between the cocatalysts and semiconductors because of their excellent conductivity. Thus, a combination of nanocarbons and other cocatalysts offers a powerful and practical strategy to enhance the activity and selectivity of semiconductors for CO2 photoreduction. For example, Tan et al. successfully synthesized a series of ternary noble metal (Pt, Pd, Ag, and Au)/RGO/TiO2 (GT) nanocomposites through the solvothermal and subsequent polyol process (Figure 156A).1732 The resulting ternary Pt/RGO/ TiO2 nanocomposites could achieve the highest total CH4 yield of 1.70 μmol/gcat after 6 h of irradiation, which was 2.6 and 13.2

7.5.1. Hybrid Cocatalysts. In most cases, it is impossible to achieve high enough activity and selectivity for photocatalytic CO2 reduction using a single cocatalyst because of the complexity of CO2 photoreduction. Thus, the multifunctional composite cocatalysts would provide some new opportunities for the design of highly active and selective photocatalysts for CO2 photoreduction. Generally, several factors that influence the overall efficiency and selectivity of CO2 photoreduction should be considered in designing and optimizing the cocatalysts, such as improved interfaces between cocatalysts and semiconductors for fast transfer of photogenerated electrons, enhanced CO2 adsorption, and stability of photoEM


Chemical Reviews

Review

Figure 153. (A) Formation mechanism for the carbon@TiO2 composite hollow structure. (B) Photocatalytic generation rates of CH4 and CH3OH over carbon@TiO2 heterojunctions and P25. (C) Photoexcitation process of the carbon@TiO2 composite hollow structure.1767 Reprinted with permission from ref 1767. Copyright 2017 Royal Society of Chemistry.

Figure 154. Proposed mechanism for Py-catalyzed CO2 reduction over p-GaP photoelectrodes through different intermediates: (A) a surfacebinding DHP*, (B) an aqueous 1-PyH• radical and an aqueous DHP, and (C) a surface-binding 2-PyH•* radical. An asterisk (*) represents the adsorbed species on the electrode surface.1817 Reprinted with permission from ref 1817. Copyright 2016 American Chemical Society.

the greatly enhanced activity for CH4 production. However, the commonly used RGO in composite photocatalysts was prepared through the facile chemical reduction of exfoliated graphite oxide, whose electronic conductivity is still much lower than that of mechanically exfoliated GR or the ideal GR because of the presence of domain defects, boundaries and residual O-containing functional groups. Therefore, 1D metallic Ag nanowires were employed for the first time to further

fold larger than those on GT and P25, respectively(Figure 156B). Clearly, in comparison to Pt-TiO2 binary nanocomposite (path 1 in Figure 156C), the introduction of the rGO sheets with a large specific surface area and superior electrical conductivity could achieve more efficient electron collection and transfer to highly dispersed Pt active sites for photoreduction of adsorbed CO2, due to favorable equilibrium Fermi-level positions (path 2 in Figure 143B), thus leading to EN


Chemical Reviews

Review

Figure 155. Proposed mechanism for the pyridinium-induced reduction of CO2 to HCOOH, CH2O, and CH3OH.1040 Reprinted with permission from ref 1040. Copyright 2010 American Chemical Society.

Figure 156. (A) Schematic illustration of the synthesis of ternary heterojunctions by a two-step strategy. (B) Total CH4 yield over anatase TiO2, P25, GT, and various NM-GT heterojunctions obtained after 6h of reaction. (B) Schematic illustration of the photoreduction of CO2 to CH4 over Pt-GT composite.1732 Reprinted with permission from ref 1732. Copyright 2015 Elsevier.

enhance the mechanical flexibility and electrical conductivity of RGO.1182 It was reported that Ag NWs−RGO−CdS NWs (ACG) ternary heterojunctions could be facilely constructed via

a fast and easy electrostatic self-assembly strategy, followed by a hydrothermal treatment (Figure 157A and B).1182 The photocatalytic CO and CH4 production over these ternary EO


Chemical Reviews

Review

Figure 157. (A) Schematic illustration of the fabrication of the Ag NWs−RGO−CdS NWs (ACG) ternary heterojunctions. (B) SEM images of ACG. (C) Selective CH4 and CO generation rates over different photocatalysts under visible light (λ > 420 nm).1182 Reprinted with permission from ref 1182. Copyright 2015 Royal Society of Chemistry.

Figure 158. (A) TEM image of NiOx deposited on Ta2O5−rG. (B) CH3OH generation rate over different photocatalysts in CO2-saturated or NaHCO3 solution,(C) H2 production rate over different photocatalysts (20 mg) after 6 h of irradiation in CO2 and N2-saturated aqueous solutions. (D) Schematic illustration of CO2 photoreduction and charge separation/transfer over the NiOx−Ta2O5−rG heterojunctions under UV−vislight.1737 Reprinted with permission from ref 1737. Copyright 2013 Royal Society of Chemistry.

electronic conductivity capability of RGO and prolonging lifetime of photogenerated charge carriers. The present work provides a promising strategy to construct highly conductive

composites are 1.17 and 2.77 times higher than those on binary photocatalysts without Ag NWs (Figure 157C), respectively, suggesting the key role of doped Ag NWs in increasing EP


Chemical Reviews

Review

Figure 159. Typical (A) HRTEM and (B) TEM images of Rh/Cr2O3 core/shell decorated GaN nanowires. Time-dependence production rates of (C) CH4 and (D) CO on bulk GaN nanowires and Rh/Cr2O3 decorated GaN nanowires. (E) H2 evolution rate over GaN nanowires, Rh/Cr2O3, and Pt-decorated GaN nanowires. Schematic illustration of CO2 photoreduction mechanism on (F) Rh/Cr2O3-decorated GaN nanowires.1473 Reprinted with permission from ref 1473. Copyright 2015 American Chemical Society.

and efficient CO2 photoreduction cocatalysts through coupling RGO and other conductive metallic and metal-free nanomaterials. In this regard, the composite cocatalysts composed of RGO and other nanocarbons, such as CNTs and carbon QDs, are also highly expected to be applied in the sustainable artificial photosynthesis.1827−1830 Similarly, it was demonstrated that the ternary 2 wt % Ag-doped MWCNT@TiO2 core-shell nanocomposites could achieve the highest total C2H4 and CH4 generation of ∼0.68 and 6.34 μmol/g−1 after 7.5 h of reaction, respectively.1831 In particular, the 2 wt % Ag loading showed a 1.60-fold enhancement in the methane yield over MWCNT@ TiO2 nanocomposites, indicating the synergistic effect of Ag and MWCNT in enhancing the activity in CO2 photoreduction. To reduce the utilization of noble metals in the practical applications, the earth-abundant metal compounds have been extensively coupled with nanocarbons to obtain highly efficient composite cocatalysts. For example, Lv et al. loaded RGO and NiOx onto Ta2O5 as dual cocatalysts for photoreduction of CO2 to CH3OH and H2 in an aqueous solution (Figure 158A). The as-designed ternary NiOx−Ta2O5−RGO(1%) photocatalysts displayed the highest CO2 photoreduction rate for the generation of CH3OH, producing 3.4 times more CH3OH than the corresponding sample without graphene (G0) under the same conditions (Figure 158B).1737 More interestingly, it was also found that the ternary composite photocatalysts exhibited much higher formation rate of methanol in aqueous NaHCO3 solution, than that in the CO2-saturated water solution. Notably, the competing reaction for hydrogen evolution in the aerated CO2 aqueous solution was obviously higher than that under N2 because of the increased concentration of H+ (Figure 158C). It is believed that the excellent electrical conductivity and transfer, and CO 2

adsorption capability of RGO are beneficial for the stable formation of useful chemicals through multielectron reduction of CO2 (Figure 158D). In particular, the synergistic effects of RGO and NiOx dual cocatalysts played a significant role in achieving the evidently boosted activity for CH 3 OH production. Similarly, the ternary CNT@Ni/TiO2 and CuOMWCNT@TiO2 nanocomposites showed much higher visiblelight activity towards CH4 synthesis via CO2 photoreduction as compared to TiO2 and binary Ni (or CuO)/TiO2, owing to the synergism of CNTs and Ni (or CuO) cocatalysts.1561,1832 Besides metal and metal oxides, other cocatalysts such as metal complexes, enzymes and their mimics have been also covalently attached to the nanocarbons to improve their stability and reduce the overvoltages. For instance, a very high electrocatalytic activity for H2 evolution (more than 100,000 turnovers) could be achieved by binding a nickel bisdiphosphine-based hydrogenase mimic enzyme to CNTs.1833 Recently, it was found that the water-stable iridium dihydride pincer complexes exhibit excellent selectivity for electroreduction of CO2 to HCOOH.1834,1835 Very interestingly, in CO2-saturated aqueous solutions containing HCO3−, the high turnover frequencies (∼15 s−1) and numbers (∼54 000) for electroreduction of CO2 to HCOOH could be achieved on the CNT-coated gas diffusion electrodes with immobilized iridium pincer complexes.1776 For photocatalytic reduction of CO2, the coupling of graphene and enzymes as cocatalysts also exhibits an excellent selectivity for photosynthetic production of formate from CO2.1580 Thus, the covalent immobilization of enzymes or metal complexes on the nanocarbon materials provides a facile approach to fabricate highly selective photocatalysts for CO2 photoreduction. EQ


Chemical Reviews

Review

Figure 160. (A) SEM images of the Cu3(BTC)2@TiO2 core−shell photocatalysts. (B) CO2 adsorption isotherms for Cu3(BTC)2@TiO2 core−shell photocatalysts and Cu3(BTC)2, respectively. (C) Selective formation rate of CH4 and H2 via CO2 photoproduction using Cu3(BTC)2@TiO2 coreshell photocatalysts after 4 h of UV irradiation. (D) CH4 generation yields over Cu3(BTC)2@TiO2 in recycling tests. (E) Delay time-dependent ultrafast transient absorption signal for Cu3(BTC)2 (probed at 600 nm), TiO2 (probed at 450 nm), and Cu3(BTC)2@TiO2 core−shell photocatalysts (probed at 600 nm). (F) Schematic illustration of the electron transfer in the femtosecond pump−probe measurements.1855 Reprinted with permission from ref 1855. Copyright 2014 John Wiley & Sons, Inc.

Furthermore, the electrocatalytic activity of nanocarbons and CO2 adsorption could be further boosted by synergy because of nitrogen doping and grafting polyethylenimine.1104,1836 Recently, it was founded that the polyethylenimine (PEI) overlayer film on nitrogen-doped carbon nanotubes functions as a cocatalyst can evidently enhance the CO2 adsorption, reduce the catalytic overpotential and stabilize CO2•−, thus leading to the enhanced current density and efficiency for electrochemical reduction of CO2.1104 This work may inspire further developments in nanocarbon hybrid cocatalysts with

Importantly, nanocarbons in these heterojunctions could enhance the CO2 adsorption capacity.98 It was verified that the CO2 adsorption capacity has a strong linear relationship with RGO content, instead of the specific surface area. Namely, 2 wt % of RGO on CdS nanoparticles could lead to a 3-fold enhancement of CO2 adsorption capacity due to the π−π conjugation interaction between CO2 and graphene.98 Interestingly, the CO2 adsorption sites also serve as CO2 photoreduction active sites, thus facilitating the fast activation of adsorbed CO2 and improving the CO2 photoreduction activity. ER


Chemical Reviews

Review

Figure 161. (A) Design of the disordered spongy Ni(TPA/TEG) structures by partial replacement of the Ni(TPA) framework by soft Ni-TEG building units through laser-chemical reaction. (B) TEM images of Ni(TPA/TEG) deposited with Ag nanocrystals. (C) Selective formation of HOOH, CO and CH3COOH via CO2 photoreduction over Ni(TPA/TEG)-Rh, Ni(TPA/TEG) and Ni(TPA/TEG)-Ag. (D) Visible light reduction of the photosensitizer [Ru(bpy)3]2+, (E) photoconversion of CO2 to CO over the Ni(TPA/TEG) catalyst, and (F) CH3COOH, HCOOH, and CH3CH2OH production achieved by further CO reduction over Ni(TPA/TEG)-(Ag/Rh) catalysts.111 Reprinted with permission from ref 111. Copyright 2017 Science.

boosted CO2 adsorption and cocatalytic activity for CO2 photoreduction. In addition, it represents an advanced strategy to boost the selectivity of CO2 reduction via loading the core/shell composite cocatalyst on the surface of semiconductors.92,1473 As above mentioned, a Pt@Cu2O core−shell cocatalyst over TiO2 has been demonstrated to be capable of suppressing the H2 evolution reaction on Pt cocatalysts.92 More recently, AlOtaibi et al. constructed the Rh/Cr2O3 core/shell cocatalyst on gallium nitride (GaN) nanowire arrays (Figure 159A and B).1473 The resulting Rh/Cr2O3-deocrated nanowires exhibited a 3-fold enhancement in the activity for selective CO2 photoreduction with H2O to CH4 (3.5 μmol gcat−1 h−1, Figure 159C) and suppressed CO evolution (Figure 159D), in comparison with that over the bulk nanowire arrays. It was proposed that the formate pathway may dominate the

formation of CH4 after producing a sufficient amount of H2 (Figure 159E), thus suppressing the CO evolution in an H2 environment. More interestingly, Pt nanoparticles on GaN nanowires could achieve the CH4-formation rate of 14.8 μmol gcat−1 h−1, which is about nearly ten-fold as high as that of bulk nanowires. The CO2 photoreduction mechanism on Rh/Cr2O3 decorated GaN nanowires are schematically displayed in Figure 159F. Accordingly, engineering the nanostructures as well as the surface charge properties of both cocatalysts and semiconductors is a good strategy to manipulate and control the CO2 photoreduction pathways over the cocatalyst/semiconductor composite systems. 7.5.2. Metal−Organic Frameworks. For enhancing the CO2 activation and adsorption over the photocatalyst surface, metal−organic frameworks (MOFs) with excellent CO2 capture and storage capacity have gained a lot of attention ES


Chemical Reviews

Review

recombination in the semiconductor and distinctly enhanced photocatalytic reduction of adsorbed CO2 over MOFs (Figure 160E and F).1855 The present knowledge in this area implies that MOFs as cocatalysts could achieve the improved CO2 adsorption, activation and charge separation, which opens a new way to design and fabricate various MOF-based composite photocatalysts for gaseous CO2 reactions.1856 More interestingly, it was recently found that the partial substitution of the rigid terephthalic acid (TPA) linkers in traditional MOFs with soft triethylene glycol (TEG) molecules via laser-induced solution reactions, may damage the crystal growth of ordered Ni-TPA MOFs, thus leading to the formation of defective and disordered metal−organic Ni(TPA/TEG) hybrid cocatalysts for controlled photocatalytic CO2 reduction reactions in dimethylformamide (DMF) solvent(Figure 161A).111 The resulting spongy Ni(TPA/TEG) cocatalysts could achieve almost 100% selective CO generation over H2 evolution, whereas further decoration of metallic Rh or Ag nanocrystals on these cocatalysts could switch their selectivity for generation of formic acid and acetic acid (Figure 161B and C). It is suggested that the Ni-TPA coordination structures are disadvantageous for proton transfer and formation of H2 because of the unfavorable binding of H• on the surface active sites, while the open and defective structure in flexible Ni-TEG units with more accessible Ni2+ sites could favorably stabilize and capture the CO2•− intermediates, resulting in the highly active and selective generation of CO (Figure 161D and E). Subsequently, the evolved CO can be further converted to formic acid and acetic acid through proton-coupled multielectron reduction processes (Figure 161F). Impressively, the proper “tandem cocatalyst” system could selectively reduce CO2 to CO, which can directly serve as an intermediate gas reactant for further production of acetic acid and ethanol. This study suggests that the proper concentration of defects in MOFs is beneficial for improving their activity for selective reduction of CO2. Thus, further developments in this area are highly desirable for practical generation of value-added multicarbon fuels by taking advantage of the sustainable solar energy. Furthermore, besides as CO2 photoreduction cocatalysts, MOFs are good supports and can be also used to boost the selectivity and activity of photocatalysts for CO2 photoreduction. A 3.8-fold improvement in the amount of dissolved CO2 in water was reported, which led to a 62% photoactivity enhancement for reduction of CO2 to CH3OH by loading 25 wt % of ZIF-8 to Zn2GeO4 nanorods.1467 Similarly, the optimized Co-ZIF-9/TiO2 composite photocatalysts fabricated via an in situ synthetic procedure could achieve a 2.1-fold enhancement in the CO2 photoreduction activity after 10 h of irradiation in comparison to that on pure TiO2.1550 Linear sweep voltammetry in a CO2 saturated solution and photoluminescence spectra revealed the decreased onset potential of CO2 reduction and promoted charge separation efficiency by loading the suitable amount of Co-ZIF-9 cocatalysts, respectively, both of which are favorable for enhancing photocatalytic CO2 reduction activity. Thus, the use of MOFs cocatalysts with tunable structures and chemistry for CO2 photoreduction should be accelerated in future studies. However, the improvement in the stability of MOFs and the use of conductive 2D MOFs should be also taken into account in designing the MOF-based photocatalysts.1839,1857,1858 7.5.3. Plasmonic Cocatalysts. An additional function of Ag and Au cocatalyst nanoparticles is their superior surface plasmon resonance (SPR) effect. The plasmonic metal nanoparticles can function as alternative sensitizers to boost

during the past decades because of their super high porosity and tunable interactions with CO2 molecules.44,87,88,671,855,1837−1845 Importantly, metal centers and organic linkers in MOFs could serve as inorganic semiconductor quantum dots and antenna-like visible-light sensitizers, respectively, paving the way toward the MOF-based photocatalysis for CO2 reduction.87,88,1844−1850 For example, various MOFs containing Ti and Zr, such as NH2-MIL125(Ti), NH2-UiO-66(Zr), and UiO-67 with Re complexes exhibit good activity for selective photoreduction of carbon dioxide to formate anion and CO under visible light irradiation, respectively.44,87,88 Importantly, Logan et al. successively prepared a family of Ti-based MOFs isoreticular to MIL-125NH2, in which the amine functionality was modified by alkyl chains with varying connectivity and length.1850 It was found that the as-prepared MIL-125-NHCy materials display the decreased optical bandgaps related to the increased electron donor ability of the alkyl substituent and the destabilized valence band in small steps, thus achieving higher photocatalytic activity towards selective reduction of carbon dioxide under blue illumination. This study shows that the photocatalytic and photophysical properties of MOFs can be readily tuned through small modifications of organic linkers. Xu et al., for the first time, designed an active visible-light-responsive metal−organic framework (MOF), PCN-222, through the assembly of a photoactive porphyrin molecular system, which exhibited higher CO2 uptake capacity and better visible-light activity for selective photoconversion of CO2 to formate anion as compared to the corresponding porphyrin ligand alone.1846 It is believed that the presence of an extremely long-lived electron trap state in PCN-222 effectively enhances the favorable electron−hole separation, thereby boosting the efficiency of the CO2 photoreduction.1846 However, as compared to the conventional inorganic semiconductors, MOFs as photocatalysts suffer from low visible-light efficiency and stability, and fast charge recombination. More recently, it was demonstrated that the thin films of nanosized cobalt− porphyrin MOFs could achieve a highly selective (> 76%), active (with a per-site TON of 1400) and durable (>7 h) electrocatalytic reduction of CO2 to CO production.1851 Thus, it is highly probable that MOFs can be extensively employed as cocatalysts for improving adsorption and activation of CO2 and thus significantly boosting the photocatalytic performance of CO 2 reduction over various inorganic semiconductors.32,1844,1852,1853 For example, Wang et.al reported that a cobalt-containing zeolitic imidazolate framework (Co-ZIF-9) cocatalyst could boost the CO2 capture and concentration and improve electron transfer in the semiconductors, such as a Rubased dye, C3N4, or CdS,1171,1172,1854 thus improving the activity and selectivity for CO2 photoreduction to CO. Recently, Li et al. prepared novel Cu3(BTC)2@TiO2 coreshell structures using a hydrolysis method for photocatalytic CO2 conversion in gaseous reactions (Figure 160A).1855 The CO2 adsorption isotherms show that the resulting microporous cores in Cu3(BTC)2@TiO2 photocatalysts still exhibit comparable adsorption capacity towards CO2 molecules through porous TiO2 shells (Figure 160B). In comparison to the bare TiO2 nanocrystals, the resulting Cu3(BTC)2@TiO2 core−shell photocatalysts showed superior activity and stability for selective photoreduction of CO2 to CH4 (Figure 160C and D). The ultrafast spectroscopy further demonstrated the favorable charge transfer from inorganic semiconductors to MOFs, substantially leading to the suppressed charge ET


Chemical Reviews

Review

Figure 162. (A) TEM and HRTEM (inset) images of Au@TiO2 yolk−shell hollow spheres. (B) Photoactivity for CO2 reduction to CH4 and C2H6 over P25, TiO2 hollow spheres, and Au@TiO2 yolk−shell hollow spheres. (C) Light intensity-dependent photocurrent responses and transient decay lifetime of TiO2 and Au@TiO2 yolk−shell hollow spheres. (D) The spatial distribution of enhanced local EM field on the x−y plane for Au@TiO2 yolk−shell hollow spheres based on an FDTD simulation.1479 Reprinted with permission from ref 1479. Copyright 2015 Royal Society of Chemistry.

generation and subsequent separation of charge carriers, whereas the rapid decay in the surface trap states of the Au@ TiO2 yolk−shell spheres implies the improvement in the transfer of photoexcited holes to the TiO2 surfaces due to the effective removal of surface trap states (Figure 162C). The 3D finite difference time domain (FDTD) simulation showed much higher the electric field strength at the place closer to Au NPs, confirming the spatial distribution of increased electric field intensity around Au NPs on the TiO2 surface (Figure 162D). This work offers a new viewpoint for developing unique LSPR induced-semiconductors for the enhanced UV−vis-light CO2 photoreduction to hydrocarbon fuels. Similarly, the plasmonic Ag dispersed uniformly in the double-shell of TiO2 hollow spheres could also achieve a visible light CH4 production of about 7.6 μmol/g in the first hour, which was about 20 times larger than that obtained on TiO2 alone.1495 It seems that SPR of Ag NPs, hollow structure and large specific surface area synergistically contribute to the enhanced visible light harvesting and multi-scattering process and increase the amount of surface reaction sites, respectively, all of which are synergistically responsible for the enhanced photocatalytic activity for CO2 reduction. Except for the TiO2-based photocatalysts, the loading Ag or Au nanoparticles on nonTiO2 semiconductors could distinctly enhance their visible-light absorption owing to the strong SPR of Ag or Au NPs.969,1167,1477,1480,1484,1487,1491,1497,1566,1862 Surprisingly, the maximum visible−light methanol yields of 188.68 and 108.70 μmol g−1 were observed over the plasmonic-shaped AgCl:Ag and AgBr:Ag, respectively.1487 Besides modification of single Au or Ag nanoparticles, the combination of plasmonic Ag and Au nanoparticles, or other noble metals, such as Pt, has also attracted much attention, due

the visible−light absorption of photocatalysts due to the SPR effects. Recently, the promising SPR effects have been directly observed for the visible-light CO2 photoreduction by using the technology with the single-nanoparticle spatial resolution.1859 In the past several years, the Au or Ag nanoparticles on TiO2 were successfully used to enhance the photoactivity for visiblelight production of CH4 or methanol via CO2 reduction.84,808,1478,1488−1490,1495,1498,1501,1502,1860,1861 Clearly, the strong local electromagnetic fields induced by plasmonic Ag or Au NPs over the TiO2 surface play a significant role in improving the photoactivity. Recently, the SPR effect of deposited Ag NPs in the inner space of TiO2 nanotube arrays (TNTAs) was explored for enhancing photocatalytic performance,1861 which was mainly attributed to two aspects: (i) promoting the generation and effective transfer of “hot electrons” from Ag NPs to TNTAs and (ii) boosting the charge carrier migration on the TNTAs surface via a unique near field effect. As a typical example, the Au@TiO2 yolk−shell hollow spheres were fabricated via a facile three-step process: hydrothermal treatment of glucose and HAuCl4 mixed solutions (formation of Au-encapsulated carbon spheres), controlling the tetrabutyl titanate (TBOT) hydrolysis/condensation in mixed ammonia/ethanol solution (formation of amorphous TiO2 shell layer), and the thermal annealing treatment (Figure 162A).1479 The as-fabricated Au@TiO2 yolk−shell hollow spheres exhibited much higher photoreduction yields of CO2 to CH4 (2.52 μmolg−1 h−1) and C2H6 (1.67 μmolg−1 h−1) in comparison to those obtained on P25 and bare TiO2 hollow spheres (Figure 162B). The Au@ TiO2 yolk−shell spheres featured the linearly increased photocurrent with light intensity, clearly indicating that the LSPR-induced local EM field could distinctly boost the EU


Chemical Reviews

Review

Figure 163. Rates of CH4 and CO production over 5 mg of different NFs under UV−vis light irradiation:(A) TiO2, (B) Au1/TiO2, (C) Au0.25/Pt0.75/ TiO2, and (D) Pt1/TiO2. (E) Schematic illustration of the photocatalytic CO2 reduction over Au/Pt/TiO2 NFs.1351 Reprinted with permission from ref 1351. Copyright 2013 American Chemical Society.

to the excellent synergistic effects between different metals. For example, it was found that the bimetallic Ag−Pt cocatalysts on TiO2 could improve product selectivity. A selectivity of CH4 of about 80% can be obtained by combining both bimetals and Ag@SiO2 NPs.1650 Similarly, co-deposition of Au and Pt NPs of 5−12 nm on TiO2 nanofibers could switch the selectivity from CO to CH 4 production (Figure 163A−D). 1351 More importantly, the Au0.25/Pt0.75/TiO2 NFs (Figure 163C) showed a 1.35 times higher CH4 production activity (0.57 μmol h−1) than that obtained on Pt1/TiO2 NFs (Figure 163D), demonstrating that the surface plasmon excitation of Au nanoparticles could give an additional improvement in the photoactivity of CO2 reduction. Clearly, the synergy of SPR of Au NPs and surface electron sink of Pt could distinctly boost the charge separation of photoexcited TiO2, and remarkably enhance the photocatalytic activity and selectivity for CO2 reduction to CH4 (Figure 163E).1351 This study offers a more powerful way to harvest solar light through the SPR effect to boost the photoactivities of semiconductors for fuel production. More recently, to further study the size-dependent SPR effect

of Au NPs in the CO2 photoreduction reaction, Au NPs of 4, 8, 18, and 26 nm, as well as their corresponding Au@SiO2 core− shell NPs, were selectively loaded onto Pt/TiO2 for the CO2 photoreduction (Figure 164A).597 Under 365 nm LED lamp irradiation, the photoactivities of Pt/TiO2 decorated with Au or Au@SiO2 NPs showed no appreciable increase as compared to that of bare Pt/TiO2, confirming that the LSPR effect of the Au and Au@SiO2 NPs is of significant importance in determining the CO2 conversion activity. Surprisingly, under simultaneous irradiation using 530 and 365 nm LED lamps, Pt/TiO2/Au18@ SiO2 exhibited the largest activity for CH4 production, which was estimated to be 3.1 fold (18 nm) higher than that achieved on Pt/TiO2 (Figure 164B), implying that the optimum size of Au NPs and their coverage with SiO2 shells can be used to synergistically maximize the plasmonic effects for photoconversion of CO2 to CH4. Hence, it is believed that the local electric field of Pt/TiO2/Au18@SiO2 could be further enhanced due to the coverage of Au NPs by SiO2 shells, resulting in the improved photocatalytic CO2-reduction efficiency (Figure 164C and D). These studies are beneficial EV


Chemical Reviews

Review

Figure 164. (A) TEM images of Pt/TiO2/Au18@SiO2. The scale bar is 20 nm. (B) Formation rates of CH4 in 2 h under simultaneous irradiation by using 530 and 365 nm LED lamps. The blue and red colors refer to the Pt/TiO2/Au@SiO2 and Pt/TiO2/Au samples, respectively. Schematic illustration of the SPR effects over Pt/TiO2/Au (C) and Pt/TiO2/Au@SiO2 (D) under simultaneous irradiation by using 530 and 365 nm LED lamps.597 Reprinted with permission from ref 597. Copyright 2016 Elsevier.

of visible and NIR photon energy and its further conversion into heat, which could selectively kill cancer cells, leaving the healthy cells unaffected. Recently, motivated by these interesting applications, the emerged photothermal effects were also employed to enhance the photocatalytic activity.367,1892−1897 More importantly, the photothermal effects can also extend photocatalysis from visible-light to NIR (accounting for ∼52% of solar spectrum) region, thus significantly boosting the utilization efficiency of solar energy.1895 Notably, the photothermal effects have also attracted a considerable attention in the photocatalytic reduction of CO2.96,556,1898−1901 On the one hand, the photothermal effects could be achieved through direct light-irradiation absorption by metal nanoparticles and induced rapid rise in temperature. For example, to fully utilize the excellent photothermal effect and H2 activation ability of Group VIII NPs (Ru, Ni, Rh, Pd, Co, Ir, Pt, and Fe) over the whole range of the solar spectrum, Ye and her coworkers impregnated Group VIII metal nanocatalysts into inert mesoporous Al2O3 support and independently studied their photothermal CO2-conversion performance.96 Surprisingly, it was found that all of the group VIII NPs exhibited excellent photothermal CO2-conversion rates (mol h−1 g−1, Table 18), which are several orders of magnitude higher than the corresponding photocatalytic CO2-conversion rates (μmol h−1 g−1). Particularly, Ru/Al2O3 and Rh/Al2O3 showed the highest reaction rates for photothermal CO2 conversion for selective production of CH4 (ca.99%) (as shown in Table 18), due to their intense absorption of broad solar spectrum and significantly induced photothermal effect. As can be seen from Table 18 the low-cost Ni/Al2O3 is even more active than several noble-metal-based (Pd, Pt, and Ir) catalysts, suggesting its promising application in practical systems for photothermal CO2 conversion. Both temperature and CO2 conversion increased with increasing Ni loading. The

for designing highly efficient plasmonic photocatalysts through coating metal NPs with a passivation layer, and for enriching our knowledge about the role of strong localized plasmonic effect in promoting the CO2 conversion reactions. Additionally, the SPR effect of plasmonic non-noble Cu nanoparticles has been also studied for the CO2 photoreduction.1525,1528 For instance, the final CH4 production rate over the Cu−TiO2 nanorod films was found to be twice higher than that on TiO2 films owing to the promoted separation of photogenerated holes and electrons and mild LSPR effect.1525 In addition, it was found that the CH3OH production rate over plasmonic non-noble Cu nanoparticles deposited on TiO2 nanoflower films was about 6 times higher than that on TiO2 film, due to the excellent synergistic effect between SPR properties of Cu nanoparticles and unique nanostructure of TiO2 film.1528 Beside Cu, the study of other non-precious metals, such as Bi149,150,152,154,1863 and Al,1864−1867 and nonmetal plasmonic W18O49,1868−1870 Cu2−xS,1871,1872 and MoO3−x1873−1875 showed their substantial plasmonic effect on the visible-light photoactivity. Thus, further studies on the activity and selectivity of plasmonic NPs deposited on various photocatalysts are needed to better understand the CO2 photoreduction in these systems by suitable engineering of plasmonic nanoparticles.137,1876,1877 7.5.4. Photothermal Cocatalysts. In 2002, Boyer et al. first demonstrated a significant temperature rise by about 15 K for 5 nm gold particles by analyzing photothermal images.1878 It was also found that the temperature rise decreased by 3 K at a distance of 13 nm from the particle’s center. Since then, many gold nanospheres/nanorods,1879−1881 CNTs,1882,1883 CuSx nanostructures,1884−1886 and functionalized graphene nanosheets1887−1891 have been extensively utilized as multifunctional theranostic or contrast agents in photothermal cancer therapy because of the wavelength-dependent scattering and absorption EW


Chemical Reviews

Review

CO2 conversion due to the potential synergism between photochemical and thermochemical catalytic processes. Ha et al. successfully synthesized double perovskites LaSrCoFeO6−δ (LSCF) and a three-dimensionally ordered macroporous LSCF (3DOM-LSCF) by a facile calcination process at 550−950 °C for 4 h (Figure 166A).1898 Under photothermal conditions (350 °C + vis-light) in 8 h, LSCF and 3DOM-LSCF catalysts could selectively reduce CO2 with H2O to CH4 with the rates of 351.32 and 557.88 μmol g−1 (Figure 166B and C), respectively. The suitable band structures of double perovskites LSCF and 3DOM-LSCF and energetically favorable adsorption/dissociation (Figure 166D) of CO2 and H2O on the defective surfaces synergistically lead to the significantly enhanced catalytic performance under photothermal reaction conditions. More importantly, it should be noted that the CH4production rate in the photothermal mode is 5 times higher than that for the thermal reduction mode, suggesting that the photothermal effect plays a critical role in improving conversion of CO2 into CH4 over active oxygen vacancies.1898 Similarly, it was also demonstrated that hydrogen-treated mesoporous WO3 with suitable oxygen vacancies exhibited the improved photothermal coupling performance for selective conversion of CO2 into CH4.556 These findings may further provide new strategies for efficient photothermal conversion of CO2 into solar fuels and offer new insights into the prominent role of self-formed oxygen vacancies in improving the CO2 and H2O absorption and reaction. 7.5.5. Water Oxidation Cocatalysts. In theory, the oxygen-evolution half-reaction is an important accompanying reaction for photoreduction of CO21902−1906 because an improvement of water oxidation must have positive effects on the separation of photogenerated electrons and holes and, thus, can enhance the photocatalytic activity for reduction of CO2. However, the four-electron water oxidation reaction is very difficult and complicated.412,1907 Therefore, to avoid the complicated and slow water oxidation reaction, some highly efficient sacrificial reagents for trapping holes in the semiconductor have been extensively used in many systems. So far, there are a few reports on the application of water oxidation cocatalysts in the photocatalytic reduction of CO2. Recently, a robust electrocatalyst for water oxidation, a cobalt phosphate system (Co−Pi), showed a great potential to replace noble metal oxides, which was first reported by Kanan and Nocera in 2008.412 Since then, cobalt-based electrocatalysts, such as Co−Pi, CoOx, Co3O4, Co(OH)2, and Fe100−y−zCoyNizOx, have attracted a lot of attention.1908−1914 Thus, it is highly expected that these water oxidation cocatalysts

Table 18. Selectivities and Activities of the Group VIII Catalystsa sample Ru/ Al2O3 Rh/ Al2O3 Ni/ Al2O3 Co/ Al2O3 Pd/ Al2O3 Pt/ Al2O3 Ir/ Al2O3 Fe/ Al2O3 TiO2 Pt/ TiO2 Ru/ TiO2

metal loading (wt %)

Rmax (mol h−1 g−1)

conversionof CO2 (%)

selectivity for CH4 (%)

selectivity for CO (%)

2.4

18.16

95.75

99.22

0.78

2.6

6.36

96.25

99.48

0.52

2.1

2.30

93.25

99.04

0.95

2.5

0.90

92.58

99.51

0.49

2.0

0.53

93.43

98.64

1.36

2.4

0.47

60.42

15.55

84.45

2.8

0.05

14.94

63.25

36.74

2.4

0.02

7.27

4.04

95.96

2.5

9.04×10−7 8.01×10−9

68.23 100

31.77 0

2.5

5.31×10−9

100

0

a

Reprinted with permission from ref 96. Copyright 2014 John Wiley & Sons, Inc.

activity of a 7.3 wt % Ni/Al2O3 catalyst is comparable to that of a 2.6 wt %Rh/Al2O3 catalyst. All of the Group VIII catalysts could achieve a rapid rise in temperature because of the obvious photothermal effect (Figure 165A). In theory, the overall waterbased CO2 conversion process (the combination of photocatalytic H2 production from water and photothermal CO2 reduction with H2) should possess much higher activity than that of the direct CO2 photoreduction with water over semiconductor photocatalysts (Figure 165B). To achieve the simultaneous activation of CO2 and H2 on active supports and metals, the nanostructured Pd@Nb2O51900 and Ru-loaded ultrathin LDHs1899 as visible and near-infrared photothermal catalysts were examined and showed the highest CO generation rate of 1.8 mmol gcat−1 h−1 and CH4 generation of 230 mol h−1 m−2, respectively. Therefore, future studies on direct photothermal CO2 conversion mechanism can not only pave a new avenue for design of rational carbon cycling systems with zero carbon dioxide emission, but also provide a novel low-cost and highly-effective technology to develop sustainable solar fuels. On the other hand, a suitable combination of photocatalysis and thermal catalysis could be used to boost the photothermal

Figure 165. (A) Monitoring the temperature of different catalysts. (B) Solar energy driven two-step water-based CO2 conversion.96 Reprinted with permission from ref 96. Copyright 2014 John Wiley & Sons, Inc. EX


Chemical Reviews

Review

Figure 166. (A) Synthesis route of the 3DOM perovskites LaSrCoFeO6−δ (LSCF) catalyst. Thermal and photothermal catalytic activity of (B) LSCF and (C) 3DOM-LSCF. (D) Possible binding configurations of adsorbed CO2 (a−e) and H2O (f−j) molecules on the double perovskite LSCF surface.1898 Reprinted with permission from ref 1898. Copyright 2016 Royal Society of Chemistry.

sites on the powdered photocatalysts in liquid water solution, the PEC reduction of CO2 to fuel seems to be more promising for practical applications. In the PEC systems for CO2 reduction, the two half-reactions of CO2 reduction and water oxidation are spatially separated through the proton conducting membranes, thus efficiently avoiding the direct contact of reduction products and oxidation sites (Table 19).13 In 2010, a newly-designed PEC reactor consisting of the separated photoanode (an ordered TiO2 nanotube arrays supported on the porous Ti foil) and electrocathode (Pt(or Fe)/CNT supported on carbon cloth) for water oxidation and CO2 reduction to liquid fuels (mainly isopropanol) has been first proposed and tested (Figure 167).1927 Inspired by this work, the TiO2 nanotube (TNT) photoanode driven photoelectrocatalytic (PEC) cells have been widely fabricated for efficient CO2 reduction to solar fuels.1928,1931 For example, Li et al. constructed a light-driven dual-chamber reactor using the monolithic two-side Cu2O/graphene/TNT heterostructure as separated dual-function oxidation and reduction catalysts for CO2 photoreduction (Figure 168A).1741 The resulting Cu2O/ graphene/TNT heterostructure could achieve a methanol generation rate of 45 μmol cm−2 h−1 with the quantum efficiency of 5.71% at 420 nm, which is obvious higher than those of the previously reported TNT-based photocatalysts (Figure 168B). It is believed that the improved photocatalytic activity is attributed to the increased light absorption, electron− hole separation and promoted electron transfer across the heterojunction interfaces (Figure 168C). Besides TNT, other n-type semiconductors, such as WO3,1048 ZnO,1932 SiC,1933 and BiVO4,1934 were also extensively employed as photoanodes for OER. Correspondingly, some p-type semiconductors,1935−1939 m e t a ls , 1 9 3 2 , 1 9 4 0 c a r b o n s , 1 9 2 8 o r m o l ec u l a r c o m plexes,1603,1934,1941,1942 have been used as photocathodes to

could be used to accelerate the kinetics of water oxidation, thus leading to an enhanced activity for CO2 photoreduction. Meanwhile, water oxidation cocatalysts were also generally used to improve the stability of photocatalysts. For example, it has been reported that CoOx cocatalysts could greatly enhance stability of some photocatalysts, such as LaTiO2N,1915 Sm2Ti2S 2O5,1916 TaON, 1917 Ta3N 51918, and g-C3N 41919, because of the improved water oxidation reaction. For CO2 photoreduction, photocorrosion widely exists in many photocatalysts, such as nitrogen-doped TiO2 and TiO2 nanotubes (NTNTs),60,568,842 Zn1.7GeN1.8O,575,618 nitrogen-doped Ta2O5, and InTaO4. On the basis of the valence band level, the loading of cobalt-based water oxidation cocatalysts is capable to improve the stability of these photocatalysts, which results in boosting activity for CO2 photoreduction. Therefore, water oxidation cocatalysts may offer a feasible way for improving the photoactivity for CO2 reduction. Furthermore, since the initial reports by Graetzel and his coworkers1920 on the decoration of the same photocatalyst with both O2 and H2 production cocatalysts for water splitting, the photocatalyst systems with dual cocatalysts have also been proposed for water splitting during the past decade.1921−1924 However, there are only a few reports on the CO 2 photoreduction through loading dual cocatalysts for CO2 reduction and water oxidation. Therefore, there is a need to study the systems with two separated cocatalysts for CO2 reduction and water oxidation.1925 It may open a new direction for synchronous improvement of the photoactivity for water oxidation and CO2 reduction. In addition, to avoid the re-oxidation of products during CO2 photoreduction, it is crucial to physically separate the reduction and oxidation active sites.1926 Since it is a considerable challenge to spatially separate the reduction and oxidation EY


Cu2O

Pt−RGO/Cu foam

Pt−RGO/Ni foam

Cu−ZnO Cu CuFeO2/CuO Cu Cu

Cu

p-Si/TiO2/Pt

TiO2 NRs

TiO2 nanotubes

Pt−TiO2 nanotube/Ti foil GaN/n+-p Si Cu2O Pt AlGaN/GaN AlGaN/GaN-SiNiO

Cu2O

Pt

EZ

TiO2 CoOx/TaON CuFeO2 BiVO4 RuRe complex

hierarchical CNTs− ZnO−Co3O4 NW SrTiO3 WO3 Si

−

Co3O4 ZnTe/ZnO-nanowires

Au3Cu NPs/Si NW mesoporous Pd7Cu3 alloy Cu5Zn8 alloy Cu nanoporous Au thin Films graphene NiO−RuRecomplex CuO Pd−Ti3C2/g-C3N4 NiO

CNT/Cu2O

hierarchical Co3O4 Ru-complex Au Cu3Nb2O8 Zn-doped p-InP

Pt

pyridinium

p-GaP

Cu-RGO−TiO2/ITO

Ru-complex

cathode or photocathode

p-InP-Zn

photoanode or anode

1929 (2014)

300W Xe lamp, 10 mW cm−2/2 V/1 M NaCl(anode), 1 M NaHCO3(cathod)

HCOOH CO (TON = 361) acetate (FE = 80%) HCOO−/CH3OH CO (TON = 255)

0.54 mA cm−2 −0.3 mA cm−2

HCOOH (FE = 79.11%) CH4(FE=71.6%) CO (FE = 91%)

0.6 mA cm−2 8 μA cm−2 40 μA cm−2 50.2 μM cm−2 h−1

0.5 M TEA, 0.2 V/AM1.5G, 100 mW cm−2 0.05 M NaHCO3, 0.3 V/λ = 400 nm 0.1 M NaHCO3/warm white-light LED 100 mW/cm2 300 W xenon lamp/200 mW cm−2/0.1 M KHCO3/pH 6.8 λ > 460 nm,1.2 V

0.1 M KHCO3, 0 V/Hg−Xe lamp (240−300 nm) 0.5 M KHCO3, 0.75 V/500 W Hg lamp, λ > 420 nm 0.2 M KHCO3, 0.45 V/100 mW cm−2

−0.20 V vs RHE/740 nm, 100 mW cm−2/AM1.5G/0.1 M KHCO3 −1.2 V/λ =340 nm

−5 mAcm−2 0.4 mA

CH3OH C2H5OH HCOOH CO (FE = 60%) CO (FE = 75%)

0.26 mA cm−2

300 W xenon lamp, 9 mW cm−2/−0.9 V (vs SCE)/0.1 M Na2SO4 −0.60 V (vs NHE)/0.1 M NaHCO3 −0.7 VRHE/AM1.5G/100 mW cm−2/0.5 M NaHCO3 AM 1.5 G solar light, 100 mW cm−2/0.5M NaHCO3 /−0.2 V vs Ag/AgCl xenon lamp/0.8 M LiOH in methanol (catholyte) 0.3 M KOH in methanol (anolyte)/−2.5 V vs Ag/AgCl/ 278 K solar simulator (100 W)/0.1 M Na2SO4/+0.05 V (vs Ag/AgCl)

−144.7 μA cm−2 −26 mA cm−2 −16 mA cm−2 −0.14 mA cm−2 6 mAcm−2

1956 (2015)

125 W UV−vis light, 21 mW cm−2/−0.8 V vs Ag/AgCl/0.1 M NaHCO3

1760 (2015) 1603 (2016) 1935 (2017) 1963 (2017) 1941 (2017)

1353 (2017) 1940 (2014) 1962 (2017)

1939 (2016) 1932 (2016)

1936 (2016)

1958 (2013) 1959 (2016) 1944 (2015) 1960 (2015) 1961 (2006)

1957 (2015)

1955 (2015)

1951 (2016) (2014) 1952 (2015) 1953 (2013) 1954 (2015) 1038

UV-Vis light 125W/0.1 M Na2CO3/NaHCO3/pH = 9.0/+0.2 V vs Ag/AgCl

10 mW cm−2/−0.61 V/0.1 M Na2SO4

1.0 mA

0.8 mA

11.6 mA 29 mA

300 W xenon lamp/0.18 V 125 W mercury lamp/0.2 V vs Ag/AgCl/0.1 M Na2CO3/NaHCO3/pH 8 +0.9 V vs RHE in CO2-purged NaHCO3 Xe lamp, 40 mW/cm−2/3 M KCl/1.4 V 300 W Xe lamp/H-type reactor/5.0M NaOH (anode), 3.0 M KCl (cathode)

1930 (2015)

Xe lamp, 320 < λ < 410 nm/2 V/0.5 M H2SO4(anode), 0.5 M NaHCO3 (cathode)

14.22 mA cm2

5 mA cm−2 6 mA

1950 (2016)

100 mW cm−2/AM 1.5G/0.75 V

1.34 mAcm−2

73 (2008)

Hg−Xe lamp 200 W/−0.6 V/pH 5.2

ref (year) 1949 (2010)

520 μA

conditions 400 < λ < 800 nm/−0.6 V/3 h

photocurrent 70 μA

1.31 mAcm−2

HCOOH (46.7 μmol h−1) CH3OH QY(365 nm) = 71% CH4 (rf = 54.63%) CO (rf = 30.03%) HCOOH (0.75 μmol h−1) CH3COOH (0.5 μmol h−1) CH3OH, HCOOH, C2H5OH, CH3COOH (∼4.200 μmol/h−1) CO (rf = 70%, TON = 1330) CH3OH (80 ppm) HCOOH (selectivity > 90%) C2H4, C2H5OH CH4 (285.3 ppm) C2H4 (251.8 ppm) CH3OH (82 ppm) CH2O (15 ppm) CH3OH (0.88 mmol L−1) C2H5OH (2.6 mmol L−1) CH3COCH3 (0.049 mmol L−1) CH3OH (189.06 μmol h−1 cm−2) HCOOH (255 μmol h−1 cm−2) HCOOH (48.1 μmolh−1) HCOOH (110 μmol cm−2 h−1) CO (37 μmol cm−2 h−1) CO (20 nmol h−1) HCOOH(rf = 14.7%)CO (rf = 42%)

selective products (activity, μmol g−1 h−1)

Table 19. Summary of the Photoelectrochemical CO2 Reduction Systems



1966 (2016) 1.1 V, 7 W excimer lamps, λ = 222 nm

1934 (2017)

CO (0.6 mg/cm2)

0.6 mA cm−2

achieve the PEC CO2 reduction. However, in these PEC systems, the water oxidation cocatalysts have been rarely applied for acceleration of the water oxidation kinetics on the photoanode. Recently, Lee and his coworkers first found that cobalt carbonate (Co−Ci) could be employed as a tailored electrocatalyst to boost both OER over BiVO4/WO3 composite photoanode and PEC CO2-reduction over a Cu cathode (Figure 169A and B).411 For water oxidation, an exceptional high photocurrent of 3.5 mA/cm2 at 1.23 V-RHE and an onset potential of 0.2 V-RHE were achieved over Co-Ci/BiVO4/WO3 in CO2-saturated KHCO3 (KCi, pH 7) electrolyte recording under 1 sun illumination (Figure 169C). In the photoanodedriven CO2 reduction, the Co−Ci cocatalyst assisted system showed stable photocurrent and 51.9% Faradaic efficiency (against water reduction) for CO and C-1-C-2 hydrocarbons (Figure 169D and E), which are much better than those of the popular Co-Pi cocatalyst-based system. As a result, the former achieved an 11-time enhancement in the CH4-production amount than the latter in a continuous operation (Figure 169F). The present study provides a promising earth-abundant OER coccatalyst for the advanced application in solar fuel production. Furthermore, the same group also demonstrated that a p-type zinc-blende zinc telluride (ZnTe) photocathode with the most negative CB edge exhibited an excellent PEC performance for selective reduction of CO2 to CO at −0.2 to −0.7 V (vs RHE) without an electron donor.1943 More interestingly, the CO formation rates over ZnTe photocathode could be further enhanced by direct coupling with plasmonic Au nanoparticles and a perovskite solar cell in tandem.1944,1945 More recently, Zhou et al. constructed a two-electrode solardriven CO2 reduction cell, in which the tandem GaAs/InGaP/ TiO2/Ni and Pd/C nanoparticle-coated Ti mesh served as photoanode in 1.0 M KOH(aq) (pH 13.7, OER) and a cathode in 2.8 M KHCO3(aq) (pH 8.0, CO2 reduction reaction) with the aid of a bipolar membrane, respectively (Figure 170A).107 The resulting cell exhibited the stable photocurrent density of 8.7 ± 0.5 mA cm−2 under AM1.5 illumination (100 mW cm−2) (Figure 170B). In particular, the overpotential (Figure 170C) and Faradaic efficiency of CO2 reduction to formate over the cathode were 94% in 2.8 M KHCO3(aq) (pH 8.0), respectively, corresponding to ∼10% solar-to-fuels

Pt-modified TiO2 nanotubes FeO(OH)/BiVO4

B-doped diamond

2 V, 0.5 M NaHCO3/300 W xenon lamp

1.3 V, 0.05 M Na2SO4/AM1.5G, 100 mW/cm2 CO (FE = 83%)

4 mA cm−2 C2H5OH (0.2 μmol cm−2 h−1)

Figure 167. Schematic illustration of the PEC device with the separated photoanode and electrocathode for water oxidation and CO2 reduction.1927 Reprinted with permission from ref 1927. Copyright 2010 Royal Society of Chemistry.

Co-complex/multiwalled carbon nanotubes Ag

1938 (2012) 1.5 V, 1 M NaHCO3/150 W xenon lamp (cathode), 25 W Hg arc lamp (anode) 3.6 mA cm−2 CH4 (201.5 nM/cm2)

1928 (2016)

1712 (2016) 100 mW/cm2 simulated sunlight, 1.23 V 1.5 mA cm−2

Si NWs@CoP/N-doped carbon Cu-p-type Si nanowire arrays Pt-RGO

1964 (2006) 1965 (2015)

Cu−Co3O4 nanotube arrays TiO2 NWs@CoP/Ndoped carbon n-type TiO2 nanotubes

conditions

2.5 V/5000 W xenon lamp, λ > 300 nm 0.9 V, 0.1 M Na2SO4/300 W xenon lamp, 10 mW cm−2

photocurrent

10 mA cm−2 1.2 mA cm−2 CO (rf = 80.4%) formate (6.75 mmol·L−1·cm−2)

selective products (activity, μmol g−1 h−1) cathode or photocathode photoanode or anode

Table 19. continued

Review

Ag-p-InP Pt

ref (year)

Chemical Reviews

FA


Chemical Reviews

Review

Figure 168. (A) Schematic illustration of the CO2 photoreduction reaction system, (B) Selective formation of methanol from CO2 photoreduction over TNA, graphene−TNA, Cu2O/TNA, and Cu2O/graphene/TNA catalysts under visible light irradiation (λ > 400 nm), (C) proposed mechanism for CO2 photoreduction over Cu2O/graphene/TNA photocatalysts under visible light irradiation.1741 Reprinted with permission from ref 1741. Copyright 2016 Elsevier.

Figure 169. (A) Schematic illustration of a PEC system for water oxidation and solar fuel production by CO2 reduction. (B) Energy diagram and reactions involved on Co-Ci/BiVO4/WO3 photoanode for oxygen evolution and on Cu cathode for CO2 reduction. (C) Photocurrent of Co-Ci/ BiVO4/WO3 and BiVO4/WO3 in various electrolytes (under 1 sun illumination, pH 7, (CO2 purged) 0.1 M KHCO3). (D) Photocurrent of the PA− Cu cathode for PEC CO2 reduction under chronoamperometry, Faradaic efficiency (E) at 60 min, and (F) amounts of CH4 production. With potential of 0.4 VRHE and CO2 purging, 0.5 M KCi was used for BiVO4/WO3−Cu, Co−Ci/BiVO4/WO3−Cu, and 0.5 M KPi was used for Co-Pi/ BiVO4/WO3−Cu.411 Reprinted with permission from ref 411. Copyright 2015 Elsevier.

respectively. The simulation results demonstrate that the Cu (Figure 172C) and Ag (Figure 172D) cocatalysts exhibit the obvious selectivity for alkanes (methane and ethylene) and CO, respectively. More importantly, the nonuniform selectivity for CO2 reduction products along the width of the corresponding electrodes were also demonstrated, and closely related to the illumination intensity as well as electrode dimensions. Additionally, the geometric parameters of the cell, the transport losses and current−voltage relationship of the light absorbers also play important role in determining the product selectivity. This work highlights the key role of water oxidation cocatalysts in improving the PEC activity and selectivity for CO2 reduction products. More interestingly, Singh et al. calculated the thermodynamic, achievable, and realistic STF efficiencies for CO2 reduction to fuels.1948 It was revealed that the maximum thermodynamic efficiency in the range of 32−42% could be achieved for adiabatic electrochemical production of various

conversion efficiency. Additionally, the photoanode exhibited minimal photocorrosion due to the loading of both protective TiO2 layer and Ni cocatalysts. Similarly, Grätzel and his coworkers designed a bifunctional, sustainable and all earthabundant SnO2 (by atomic layer deposition) modified CuO nanowires for the solar-driven splitting of CO2 into CO and oxygen (Figure 171A). Through combining with a GaInP/ GaInAs/Ge photovoltaic(Figure 171A and B), they surprisingly achieved an STH efficiency of 13.4% for predominantly selective conversion of CO2 to CO (Figure 171C).1946 It was the highest efficiency for the solar fuel production through coupling two separated electrodes for the CO2 reduction reaction and OER. More interestingly, Chen et al. designed an integrated PEC CO2 reduction cell to obtain the light-intensity dependent selectivity of spatially separated products (Figure 172A and B).1947 In this PEC system, Co−Pi and Cu/Ag were selected as the water oxidation and CO2 reduction cocatalysts, FB


Chemical Reviews

Review

maximum achievable STF efficiencies for synthesis gas (H2 and CO, 18.4%) and Hythane (H2 and CH4, 20.3%). Therefore, it is expected that the triple-junction light absorbers with a photovoltage >2 V and a photocurrent density >10 mA cm−2 should be developed through tuning the band-gaps and/or the catalyst-to-PV area ratio, thus achieving an artificial photosynthetic system with >10% efficiency.1948 In future, much effort should be directed toward application of the CO2-R/ OER cocatalysts and triple-junction light absorbers with optimal band gap combinations in both the powered and PEC systems for CO2 photoreduction.

8. CONCLUSIONS AND PERSPECTIVES In summary, this Review focuses on tailoring the selectivity for CO2 conversion to useful fuels over semiconductors using different kinds of cocatalysts. Although more and more new photocatalysts have been developed for photocatalytic CO2 reduction in the recent years,1496,1967 it is still challenging to improve the selectivity and yields of the desired products via CO2 photoreduction. Therefore, many problems such as the fabrication of highly active and durable multifunctional photocatalysts, the development of appropriate non-noble metal cocatalysts with high selectivity, the design of highly effective and stable CO2 photoreduction systems, and better understanding the underlying mechanisms in selective CO2 photoreduction, should be thoroughly studied in the future. First, it is clear that the fabrication of highly active, durable and low-cost multifunctional photocatalysts for visible-lightdriven or NIR-driven CO2 reduction remains a great challenge. This review shows that although the visible-light-driven semiconductor photocatalysts have been widely investigated for CO2 photoreduction, their activity, stability and selectivity should be further studied to meet the practical applications. At

Figure 170. (A) Schematic illustration of a 2-electrode configuration for CO2 electroreduction. (B) Operational time-dependent CO2 reduction current density over a GaAs/InGaP/TiO2/Ni photoanode and a Pd/C-coated Ti mesh cathode in a two-electrode system under AM1.5 illumination (100 mW cm−2). (C) The polarization curves for the OER and CO2R reaction using a p+-Si/TiO2/Ni anode and a Pd/ C-coated Ti mesh cathode.107 Reprinted with permission from ref 107. Copyright 2016 American Chemical Society.

solar fuels at 1-sun illumination (Figure 173A). Single-, double-, and triple-junction light absorbers were verified to be optimal for electrochemical load ranges of 0−0.9, 0.9−1.95, and 1.95− 3.5 V, respectively (Figure 173B). The realistic STF efficiencies of PECs, tandem PECs and photovoltaic PV-electrolyzers were estimated to be 0.8%, 7.2% and 7.2% under identical operating conditions (Figure 173C and D), which are far lower than the

Figure 171. (A) Schematic illustration of device for the photoelectrocatalytic reduction of CO2 over bifunctional SnO2 (by atomic layer deposition) modified CuO nanowires.(B) J−V behaviors of a GaInP/GaInAs/Ge photovoltaic under light (blue) and in the dark (green) and measured operating current density of the CO2 electrolysis system at different voltages (black squares).(C) Time-dependent selectivity toward CO, solar current density and solar-to-CO efficiency.1946 Reprinted with permission from ref 1946. Copyright 2017 Springer Nature. FC


Chemical Reviews

Review

Figure 172. (A) Schematic and (B) the simulated steady-state current distribution (white arrows) and electrolyte potential profile of an integrated PEC CO2 reduction cell, the simulated PEC selectivity of the CO2 reduction products with the normalized distance along 1 cm electrodes for the Cu (C) and Ag (D) cocatalysts in an integrated triple-junction cell under AM1.5 illumination (100 mW cm−2).1947 Reprinted with permission from ref 1947. Copyright 2016 American Chemical Society.

Figure 173. (A) Thermodynamic restrictions of STF efficiency for different CO2RR products, and (B) maximum current density for a single (blue), double (green), and triple (red) junction solar cell and their panels versus electrochemical load. (C) Schematic illustration of three electrochemical cell configurations for solar-driven CO2 reduction. (a) PEC, (b) tandem PEC, and (c) PV-electrolyzer. (D) STF efficiencies of fuels generated over Cu using Spectrolab’s triple junction light absorber in above three systems.1948 Reprinted with permission from ref 1948. Copyright 2015 American Chemical Society.

FD


Chemical Reviews

Review

Figure 174. Proposed timeline for CO2 utilization methods.1974 Reprinted with permission from ref 1974. Copyright 2018 Elsevier.

Second, more efforts should be made toward developing new noble-metal-free cocatalysts and investigating their electrocatalytic mechanism of selective CO2 photoreduction. The multifunctional core/shell structured, bimetallic/polymetallic and nanocarbon-based composites have been proven to be efficient cocatalysts for CO2 photoreduction, which is of great interest and worthy of further study in the field of CO2 photoreduction. The metal−organic complex cocatalysts seem to be very promising for the selective CO2 photoreduction because of their mutability, ready fabrication methods, tunable electronic properties for high-efficiency light harvesting, and multifunctional groups for more effective adsorption and activation of CO2.111 More importantly, all the factors affecting the cocatalyst performance, such as the Fermi level, electrical conductivity, stability, ad(de)sorption stability, surface reactive sites, and location of cocatalysts and their interfacial coupling with semiconductors, should be comprehensively considered when designing the highly effective and stable photocatalysts. At this regard, the 2D−2D coupling of van der Waals heterostructures or Janus bilayer junctions between layered semiconductor nanosheets and metallic cocatalyst nanosheets seems to be very promising for practical CO2 photoreduction. Impressively, the multifunctional photo/thermal catalysts have achieve the highest efficiency, so far, for selective reduction of carbon dioxide to target solar fuels, which should be further optimized and improved to develop practical photocatalytic CO2 reduction systems.96,556,1896,1898,1900,1971,1972 Also, some earth-abundant electrocatalysts for CO 2 reduction with excellent selectivity should be brought to the field of selective CO2 photoreduction. More importantly, identifying the active sites in cocatalysts for CO2 photoreduction remains a grand challenge. Despite the newly emerging, atomically precise metal nanocluster catalysts with the strong quantum confinement effect and molecular purity have been demonstrated to be promising in mechanistic insights for CO2 electroreduction at the atomic scale, the atomically precise nanocluster cocatalysts have been seldom applied in the fundamental studies of photocatalytic CO2 reduction.1973 Especially, the alloy nanoclusters with cheap metals could be further optimized by surface engineering and morphology control, which hold a great promise for investigation of their synergistic effects and the catalytic properties at the single-atom, single-electron level.1973 To this end, the electrocatalytic reduction of CO2 also

this end, the earth-abundant semiconductors with high CB levels, such as, CdS and Cu2O, are the most promising semiconductor candidates for CO2 photoreduction. Additionally, there are relatively a few reports on the study of SiC and Si for CO2 photoreduction. Thus, there is still large room for improving these two semiconductors for practical photocatalytic applications. Because of the major challenge in tuning the properties of highly crystalline inorganic semiconductors, the less-explored and soft organic semiconductors composed of light (and earth-abundant) elements, such as g-C3N4, ternary BCN compounds1968 and conjugated porous/linear polymers,1969,1970 seem to be more promising for CO2 photoreduction. More importantly, the properties of these organic semiconductors could be readily predicted by theoretical calculations. The great challenges in improving the carrier mobility and photostability of organic semiconductors should be addressed in future studies. As a rising star, MOFs also deserve more attention due to their excellent adsorption/ activation properties toward CO2 and readily tunable structures. Besides the development of visible-light-driven photocatalysts, the NIR-driven or wide-spectrum-response CO2 reduction photocatalysts should be more studied in near future, which might be the next-generation photocatalysts for CO2 reduction, because of the more effective utilization of solar spectrum.905,1762,1868,1895 More importantly, various thermodynamic and kinetics modification strategies, such as doping, coexposing different facets, exploiting ultrathin 2D nanosheets, fabricating 3D hierarchical architectures, utilizing the surface fluorination effects, creating surface overlayers, constructing surface vacancies, should be continuously explored to fundamentally improve the CO2 reduction activity and stability over these earth-abundant photocatalysts.113,177,178 Especially, more advanced multifunctional integrated photocatalysts with various junctions, such as bulk heterojunctions, phase junctions, surface heterojunctions and direct Z-scheme photocatalytic systems, should be exploited to enrich semiconductor candidates for CO2 photoreduction. The interface, electronic states and lattice mismatches of different material components should be thoroughly investigated to gain the underlying material−structure−property relationships, design and construct new, better heterojunction materials for robust, selective, and effective CO2 photoreduction. FE


Chemical Reviews

Review

CO2. Interestingly, more attention should be still paid to the PEC CRR systems with two spatially separated half-reactions of CO2 reduction and water oxidation through the proton conducting membranes because of the physically separated oxidation and reduction sites. Especially, much effort should be directed toward application of the CRR/OER cocatalysts and advanced triple-junction light absorbers with optimal band gap combinations in both the powered and PEC systems for CO2 photoreduction in future studies. So far, the mechanism of CO2 reduction on semiconductors has been investigated by a great number of groups using different analysis techniques such as electron spin resonance (ESR) spectra, in situ diffuse reflectance infrared Fourier transform spectroscopy (DRIFTS). However, the mechanism behind this reaction is still unclear and hotly debated, and most results are usually explained based on somewhat speculative analysis. Therefore, to study mechanisms in detail, the complicated intermediates and products should be analyzed by various experimental techniques such as online mass spectrometry682,1993 and isotope labeling of 13CO2.36,82 The combination of in-situ IR and Raman analyses and isotopic experiments is required to identify a key intermediate and ultimately reveal the comprehensive mechanism of the CO2 photoreduction system, thus obtaining an exact reaction pathway. Furthermore, it is very important to synchronously evaluate the reduction products both in the gas and aqueous media due to their complicated distribution and low selectivity.1994 A thorough and accurate determination of activity and selectivity for promising multicarbon Cx (x ≥ 2) organic compounds produced via CO2 photoreduction is highly needed, which has received far less attention than the extensively studied C1 products.676,682,1660,1995 More intermediates are involved in the multicarbon products, all of which could interact with the single active sites on the surface of cocatalysts. To address this issue, tandem catalysis and dual binding sites based on the cocatalyst heterostructures are highly expected, which, in theory, could achieve the improved catalytic activity and selectivity for multicarbon products.1695,1996 To guide further performance improvement of these emerging photocatalysts, the fundamental reaction pathways and catalytically active sites on photocatalysts (especially for organic semiconductors) should be carefully identified and revealed, which are especially critical factors determining the kinetics and product selectivity for multielectron CO2 photoreduction processes. Notably, under the working conditions, both semiconductors and cocatalysts typically undergo the indispensable dynamic changes, such as oxidation state, composition, and local structure, induced by the photogenerated electrons and holes. In this respect, to deeply understand the underlying mechanism, the nature of active sites and reaction intermediates under the working conditions should be thoroughly studied by in situ/operando spectroscopic techniques, including synchrotron-based X-ray absorption fine structure (XAFS) spectroscopy and in situ attenuated total reflectance infrared (ATR-IR) spectroscopy,1997 which can provide more information for rational design of the CO2 reduction cocatalysts and semiconductors. Importantly, the insight into the interaction between various reaction intermediates and cocatalysts and the challenging adsorption/ activation ability of H2O and CO2 should be carefully investigated in future studies. In addition, H2 and O2 should be also detected, which is beneficial for the evaluation of photocatalytic selectivity and the study of mechanism.

should be strongly encouraged in the next 5−10 years to better understand the mechanism of selective CO2 photoreduction and provide the potential and practical cocatalysts for the CO2 photoreduction (Figure 174).1974 Even so, for the next 10−50 years, the explored bioinspired and confined electrocatalysts could be employed as highly efficient cocatalysts to be applied for the design and fabrication of advanced molecular devices for CO2 photoreduction (Figure 174). Importantly, the electrocatalytic reduction of CO2 under a given applied voltage is much easier than the photocatalytic reduction of CO2. Additionally, the active sites and active phases in the thermal catalysts for the selective CO2 hydrogenation to desirable products can be employed to guide the rational construction and design of more efficient cocatalysts for the selective photoreduction of CO2 with H2O. Third, the design of highly effective and stable CO2 photoreduction systems is crucial for practical CO2 photoreduction. Beyond suppression of the competing H2 evolution and selective formation of CO and CH4, the visible-light-driven sustainable syngas generation from CO2 and H2O could be realized through synchronously optimizing H2 evolution and CO2 reduction,1975−1979 which seems to be more interesting, promising and appealing for the synthesis of various liquid fuels and chemicals. Considering the famous Fischer−Tropsch process capable of converting CO and H2 to liquid fuels or chemicals, selective formation of liquid sunshine (i.e., formate, methanol, carbon−carbon bonds, higher-order hydrocarbons, and alcohols) is highly expected via direct photoassisted CO2 hydrogenation with sustainable H2 from photocatalytic water splitting at ambient conditions.534,1980 In this regard, to fundamentally understand the effects of high temperature and surface chemistry on the CO2 reduction activity and selectivity, a direct coupling of thermo- or photothermal-catalysis for photoreduction of CO2 by H2O, H2, or CH4 into fuels is anticipated,96,1899,1981−1984 which should provide new strategies for boosting the CO2 reduction efficiency for practical applications. Moreover, it is more difficult to achieve sustainable artificial photosynthesis of fuels at low concentration of CO2 in the atmosphere, in comparison with the highconcentration and high-pressure CO2.1985 Accordingly, more efforts should be directed toward photoreduction of CO2 at low concentrations in future studies.1986 In this regard, one-pot fabrication of hydrocarbons from organic pollutants have been proven to be an advanced strategy to tackle energy and environments through coupling photocatalytic oxidation degradation with photoreduction of low-concentration CO2,1987−19881989 which would be desirable in future studies. Interestingly, coupling photocatalytic CO2 reduction with selective organic transformations should be a promising and appealing strategy to simultaneously produce valuable multicarbon organics and improve the photostability of narrow-band gap semiconductors.1990 Additionally, it is known that the lower valence band maximum of the commonly used visible-light photocatalysts, such as sulfides, oxynitrides, and metal−organic frameworks, cannot provide sufficient overpotentials for driving the water oxidation half-reaction to generate oxygen. Thus, to increase the solubility of CO2 and rule out more thermodynamically favorable and competitive overall water splitting, the readily available, highly efficient, abundant, and industrial electron donors (sacrificial reagents), such as NH3, NH4+, and hydrous hydrazine (N2H4·H2O),1352,1991,1992 should be explored to replace the water for achieving the significantly enhanced activity (mmol h−1 g−1) for selective reduction of FF


Chemical Reviews

Review

Furthermore, a combination of the experimental techniques such as in situ and operando spectroscopic tools and theoretical DFT analysis of CO2 electroreduction on the cocatalysts should be used to reveal some new and exciting insights to the design of highly selective cocatalysts. Therefore, although the photocatalytic conversion of CO2 into valuable energy-bearing hydrocarbons is very promising and attractive, it is unquestionable that there is still a long way to bring this technology to reality. This Review shows that the detailed mechanistic studies and the development of highly effective and selective cocatalysts are essential for achieving highly selective reduction of CO2. Fundamental studies should be undertaken to address the bottleneck problems in the field (i.e., water oxidation reaction, kinetic difficulties in multielectron reduction processes, low reduction selectivity and low quantum yield of photocatalysts). It is expected the breakthrough can take place in the near future when all these factors are comprehensively considered and studied.

Dr. Xiaobo Chen is an Associate Professor at the University of MissouriKansas City, Department of Chemistry. His research interests include nanomaterials, photocatalysis, electrocatalysis, electrochemistry, and light-materials interactions and their applications in energy, environment, and information protection. His renowned work includes the discovery of black TiO2 and new applications of black TiO2 nanomaterials along with other nanomaterials in microwave and terahertz absorption. Dr. Chen has published so far 140 peer-reviewed articles with about 37 000 citations.

ACKNOWLEDGMENTS X.L. would like to thank the National Natural Science Foundation of China (51672089 and 20906034), the Science and Technology Planning Project of Guangdong Province (2015B020215011), and the State Key Laboratory of Advanced Technology for Material Synthesis and Processing (Wuhan University of Technology) (2015-KF-7). J.Y. would like to thank the NSFC (51320105001, U1705251 and 21433007), 973 program (2013CB632402), the Natural Science Foundation of Hubei Province (2015CFA001), and Innovative Research Funds of SKLWUT (2017-ZD-4). X.C. appreciates the support from the U.S. National Science Foundation (DMR1609061) and the College of Arts and Sciences, University of MissouriKansas City.

AUTHOR INFORMATION Corresponding Authors

*E-mail: [email protected]. *E-mail: [email protected]. *E-mail: [email protected]. Notes

The authors declare no competing financial interest.

REFERENCES

Biographies

(1) Meinshausen, M.; Meinshausen, N.; Hare, W.; Raper, S. C. B.; Frieler, K.; Knutti, R.; Frame, D. J.; Allen, M. R. Greenhouse-Gas Emission Targets for Limiting Global Warming to 2 °C. Nature 2009, 458, 1158−1162. (2) Solomon, S.; Plattner, G.-K.; Knutti, R.; Friedlingstein, P. Irreversible Climate Change Due to Carbon Dioxide Emissions. Proc. Natl. Acad. Sci. U. S. A. 2009, 106, 1704−1709. (3) Vermeer, M.; Rahmstorf, S. Global Sea Level Linked to Global Temperature. Proc. Natl. Acad. Sci. U. S. A. 2009, 106, 21527−21532. (4) Chaudhary, Y. S.; Woolerton, T. W.; Allen, C. S.; Warner, J. H.; Pierce, E.; Ragsdale, S. W.; Armstrong, F. A. Visible Light-Driven CO2 Reduction by Enzyme Coupled CdS Nanocrystals. Chem. Commun. 2012, 48, 58−60. (5) Goeppert, A.; Czaun, M.; Jones, J.-P.; Surya Prakash, G. K.; Olah, G. A. Recycling of Carbon Dioxide to Methanol and Derived Products-Closing the Loop. Chem. Soc. Rev. 2014, 43, 7995−8048. (6) Kondratenko, E. V.; Mul, G.; Baltrusaitis, J.; Larrazabal, G. O.; Perez-Ramirez, J. Status and Perspectives of CO2 Conversion into Fuels and Chemicals by Catalytic, Photocatalytic and Electrocatalytic Processes. Energy Environ. Sci. 2013, 6, 3112−3135. (7) Song, C. Global Challenges and Strategies for Control, Conversion and Utilization of CO2 for Sustainable Development Involving Energy, Catalysis, Adsorption and Chemical Processing. Catal. Today 2006, 115, 2−32. (8) Centi, G.; Perathoner, S. Opportunities and Prospects in the Chemical Recycling of Carbon Dioxide to Fuels. Catal. Today 2009, 148, 191−205. (9) Kumar, B.; Llorente, M.; Froehlich, J.; Dang, T.; Sathrum, A.; Kubiak, C. P. Photochemical and Photoelectrochemical Reduction of CO2. Annu. Rev. Phys. Chem. 2012, 63, 541−569. (10) Sakakura, T.; Choi, J.-C.; Yasuda, H. Transformation of Carbon Dioxide. Chem. Rev. 2007, 107, 2365−2387. (11) Osterloh, F. E. Photocatalysis Versus Photosynthesis: A Sensitivity Analysis of Devices for Solar Energy Conversion and Chemical Transformations. ACS Energy Letters 2017, 2, 445−453. (12) Zhu, S.; Wang, D. Photocatalysis: Basic Principles, Diverse Forms of Implementations and Emerging Scientific Opportunities. Adv. Energy Mater. 2017, 7, 1700841.

Xin Li received his BS and PhD degrees in Chemical Engineering from Zhengzhou University in 2002 and South China University of Technology in 2007, respectively. Then, he joined South China Agricultural University as a faculty staff member, and became an associate professor of Applied Chemistry in 2011. In 2017, he became a Professor at the South China Agricultural University. During 2012− 2013, he worked as a visiting scholar at the electrochemistry Center, the University of Texas at Austin, USA. His research interests include photocatalysis, photoelectrochemistry, adsorption, and the development of nanomaterials and devices(see http://www.researcherid.com/ rid/A-2698-2011). Jiaguo Yu received his B.S. and M.S. in chemistry from Central China Normal University and Xi’an Jiaotong University, respectively, and his Ph.D. in materials science in 2000 from Wuhan University of Technology. In 2000, he became a Professor at Wuhan University of Technology. He was a postdoctoral fellow at the Chinese University of Hong Kong from 2001 to 2004, a visiting scientist from 2005 to 2006 at the University of Bristol, and a visiting scholar from 2007 to 2008 at the University of Texas at Austin. His current research interests include semiconductor photocatalysis, photocatalytic hydrogen production, CO2 reduction to hydrocarbon fuels, and so on. Mietek Jaroniec received his M.S. and Ph.D. from M. CurieSklodowska University (Poland) in 1972 and 1976; afterward, he was appointed as a faculty at the same University. Since 1991, he has been Professor of Chemistry at Kent State University, Kent, Ohio, USA. His research interests include interfacial chemistry and the chemistry of materials, especially adsorption at the gas/solid and liquid/solid interfaces and nanoporous materials. At Kent State, he has established a vigorous research program in the area of nanomaterials, such as ordered mesoporous silicas, organosilicas, inorganic oxides, carbon nanostructures, and nanostructured catalysts/photocatalysts, focusing on their synthesis, characterization, and environmental and energy-related applications. FG


Chemical Reviews

Review

(13) Habisreutinger, S. N.; Schmidt-Mende, L.; Stolarczyk, J. K. Photocatalytic Reduction of CO2 on TiO2 and Other Semiconductors. Angew. Chem., Int. Ed. 2013, 52, 7372−7408. (14) Halmann, M. Photoelectrochemical Reduction of Aqueous Carbon Dioxide on P-Type Gallium Phosphide in Liquid Junction Solar Cells. Nature 1978, 275, 115−116. (15) Inoue, T.; Fujishima, A.; Konishi, S.; Honda, K. Photoelectrocatalytic Reduction of Carbon Dioxide in Aqueous Suspensions of Semiconductor Powders. Nature 1979, 277, 637−638. (16) Ma, Y.; Wang, X. L.; Jia, Y. S.; Chen, X. B.; Han, H. X.; Li, C. Titanium Dioxide-Based Nanomaterials for Photocatalytic Fuel Generations. Chem. Rev. 2014, 114, 9987−10043. (17) Dhakshinamoorthy, A.; Navalon, S.; Corma, A.; Garcia, H. Photocatalytic CO2 Reduction by TiO2 and Related Titanium Containing Solids. Energy Environ. Sci. 2012, 5, 9217−9233. (18) Abdullah, H.; Khan, M. M. R.; Ong, H. R.; Yaakob, Z. Modified TiO2 Photocatalyst for CO2 Photocatalytic Reduction: An Overview. J. CO2 Util. 2017, 22, 15−32. (19) Shehzad, N.; Tahir, M.; Johari, K.; Murugesan, T.; Hussain, M. A Critical Review on TiO2 Based Photocatalytic CO2 Reduction System: Strategies to Improve Efficiency. J. CO2 Util. 2018, 26, 98− 122. (20) Yan, S.; Wang, J.; Gao, H.; Wang, N.; Yu, H.; Li, Z.; Zhou, Y.; Zou, Z. Zinc Gallogermanate Solid Solution: A Novel Photocatalyst for Efficiently Converting CO2 into Solar Fuels. Adv. Funct. Mater. 2013, 23, 1839−1845. (21) Nikokavoura, A.; Trapalis, C. Alternative Photocatalysts to TiO2 for the Photocatalytic Reduction of CO2. Appl. Surf. Sci. 2017, 391, 149−174. (22) Mohapatra, L.; Parida, K. A Review on the Recent Progress, Challenges and Perspective of Layered Double Hydroxides as Promising Photocatalysts. J. Mater. Chem. A 2016, 4, 10744−10766. (23) Iguchi, S.; Hasegawa, Y.; Teramura, K.; Hosokawa, S.; Tanaka, T. Preparation of Transition Metal-Containing Layered Double Hydroxides and Application to the Photocatalytic Conversion of CO2 in Water. J.CO2 Util. 2016, 15, 6−14. (24) Zhao, Y.; Chen, G.; Bian, T.; Zhou, C.; Waterhouse, G. I. N.; Wu, L.-Z.; Tung, C.-H.; Smith, L. J.; O’Hare, D.; Zhang, T. DefectRich Ultrathin ZnAl-Layered Double Hydroxide Nanosheets for Efficient Photoreduction of CO2 to CO with Water. Adv. Mater. 2015, 27, 7824−7831. (25) Teramura, K.; Iguchi, S.; Mizuno, Y.; Shishido, T.; Tanaka, T. Photocatalytic Conversion of CO2 in Water over Layered Double Hydroxides. Angew. Chem., Int. Ed. 2012, 51, 8008−8011. (26) Kumar, S.; Isaacs, M. A.; Trofimovaite, R.; Durndell, L.; Parlett, C. M. A.; Douthwaite, R. E.; Coulson, B.; Cockett, M. C. R.; Wilson, K.; Lee, A. F. P25@Coal Layered Double Hydroxide Heterojunction Nanocomposites for CO2 Photocatalytic Reduction. Appl. Catal., B 2017, 209, 394−404. (27) Zhao, H.; Xu, J.; Liu, L.; Rao, G.; Zhao, C.; Li, Y. CO2 Photoreduction with Water Vapor by Ti-Embedded Mgal Layered Double Hydroxides. J. CO2 Util. 2016, 15, 15−23. (28) Saliba, D.; Ezzeddine, A.; Sougrat, R.; Khashab, N. M.; Hmadeh, M.; Al-Ghoul, M. Cadmium−Aluminum Layered Double Hydroxide Microspheres for Photocatalytic CO2 Reduction. ChemSusChem 2016, 9, 800−805. (29) Hou, J.; Cao, S.; Wu, Y.; Gao, Z.; Liang, F.; Sun, Y.; Lin, Z.; Sun, L. Inorganic Colloidal Perovskite Quantum Dots for Robust Solar CO2 Reduction. Chem. - Eur. J. 2017, 23, 9481−9485. (30) Xu, Y.-F.; Yang, M.-Z.; Chen, B.-X.; Wang, X.-D.; Chen, H.-Y.; Kuang, D.-B.; Su, C.-Y. A CsPbBr3 Perovskite Quantum Dot/ Graphene Oxide Composite for Photocatalytic CO2 Reduction. J. Am. Chem. Soc. 2017, 139, 5660−5663. (31) Zhang, X.; Zhang, Z. H.; Li, J. L.; Zhao, X. D.; Wu, D. H.; Zhou, Z. Ti2CO2 Mxene: A Highly Active and Selective Photocatalyst for CO2 Reduction. J. Mater. Chem. A 2017, 5, 12899−12903. (32) Ma, Y. J.; Wang, Z. M.; Xu, X. F.; Wang, J. Y. Review on Porous Nanomaterials for Adsorption and Photocatalytic Conversion of CO2. Chin. J. Catal. 2017, 38, 1956−1969.

(33) Li, R.; Zhang, W.; Zhou, K. Metal-Organic-Framework-Based Catalysts for Photoreduction of CO2. Adv. Mater. 2018, 30, 1705512. (34) Fang, Y. X.; Wang, X. C. Photocatalytic CO2 Conversion by Polymeric Carbon Nitrides. Chem. Commun. 2018, 54, 5674−5687. (35) Marszewski, M.; Cao, S.; Yu, J.; Jaroniec, M. SemiconductorBased Photocatalytic CO2 Conversion. Mater. Horiz. 2015, 2, 261− 278. (36) Izumi, Y. Recent Advances in the Photocatalytic Conversion of Carbon Dioxide to Fuels with Water and/or Hydrogen Using Solar Energy and Beyond. Coord. Chem. Rev. 2013, 257, 171−186. (37) Zhao, Y.; Jia, X.; Waterhouse, G. I. N.; Wu, L.-Z.; Tung, C.-H.; O’Hare, D.; Zhang, T. Layered Double Hydroxide Nanostructured Photocatalysts for Renewable Energy Production. Adv. Energy Mater. 2016, 6, 1501974. (38) Wen, J.; Li, X.; Liu, W.; Fang, Y.; Xie, J.; Xu, Y. Photocatalysis Fundamentals and Surface Modification of TiO2 Nanomaterials. Chin. J. Catal. 2015, 36, 2049−2070. (39) Li, K.; An, X.; Park, K. H.; Khraisheh, M.; Tang, J. A Critical Review of CO2 Photoconversion: Catalysts and Reactors. Catal. Today 2014, 224, 3−12. (40) Mori, K.; Yamashita, H.; Anpo, M. Photocatalytic Reduction of CO2 with H2O on Various Titanium Oxide Photocatalysts. RSC Adv. 2012, 2, 3165−3172. (41) Fan, W. Q.; Zhang, Q. H.; Wang, Y. Semiconductor-Based Nanocomposites for Photocatalytic H 2 Production and CO2Conversion. Phys. Chem. Chem. Phys. 2013, 15, 2632−2649. (42) Navalon, S.; Dhakshinamoorthy, A.; Alvaro, M.; Garcia, H. Photocatalytic CO2 Reduction Using Non-Titanium Metal Oxides and Sulfides. ChemSusChem 2013, 6, 562−577. (43) Roy, S. C.; Varghese, O. K.; Paulose, M.; Grimes, C. A. Toward Solar Fuels: Photocatalytic Conversion of Carbon Dioxide to Hydrocarbons. ACS Nano 2010, 4, 1259−1278. (44) Sun, D. R.; Fu, Y. H.; Liu, W. J.; Ye, L.; Wang, D. K.; Yang, L.; Fu, X. Z.; Li, Z. H. Studies on Photocatalytic CO2 Reduction over Nh2-Uio-66(Zr) and Its Derivatives: Towards a Better Understanding of Photocatalysis on Metal-Organic Frameworks. Chem. - Eur. J. 2013, 19, 14279−14285. (45) Yuan, L.; Xu, Y.-J. Photocatalytic Conversion of CO2 into ValueAdded and Renewable Fuels. Appl. Surf. Sci. 2015, 342, 154−167. (46) Low, J. X.; Cheng, B.; Yu, J. G. Surface Modification and Enhanced Photocatalytic CO2 Reduction Performance of TiO2A Review. Appl. Surf. Sci. 2017, 392, 658−686. (47) Li, K.; Peng, B.; Peng, T. Recent Advances in Heterogeneous Photocatalytic CO2 Conversion to Solar Fuels. ACS Catal. 2016, 6, 7485−7527. (48) Tu, W.; Zhou, Y.; Zou, Z. Photocatalytic Conversion of CO2 into Renewable Hydrocarbon Fuels: State-of-the-Art Accomplishment, Challenges, and Prospects. Adv. Mater. 2014, 26, 4607−4626. (49) Xie, S.; Zhang, Q.; Liu, G.; Wang, Y. Photocatalytic and Photoelectrocatalytic Reduction of CO2 Using Heterogeneous Catalysts with Controlled Nanostructures. Chem. Commun. 2016, 52, 35−59. (50) Li, X.; Wen, J.; Low, J.; Fang, Y.; Yu, J. Design and Fabrication of Semiconductor Photocatalyst for Photocatalytic Reduction of CO2 to Solar Fuel. Sci. China Mater. 2014, 57, 70−100. (51) Chen, D.; Zhang, X.; Lee, A. F. Synthetic Strategies to Nanostructured Photocatalysts for CO2 Reduction to Solar Fuels and Chemicals. J. Mater. Chem. A 2015, 3, 14487−14516. (52) Ye, S.; Wang, R.; Wu, M.-Z.; Yuan, Y.-P. A Review on g-C3N4 for Photocatalytic Water Splitting and CO2 Reduction. Appl. Surf. Sci. 2015, 358, 15−27. (53) Tahir, M.; Amin, N. S. Advances in Visible Light Responsive Titanium Oxide-Based Photocatalysts for CO2 Conversion to Hydrocarbon Fuels. Energy Convers. Manage. 2013, 76, 194−214. (54) Sato, S.; Arai, T.; Morikawa, T.; Uemura, K.; Suzuki, T. M.; Tanaka, H.; Kajino, T. Selective CO2 Conversion to Formate Conjugated with H2O Oxidation Utilizing Semiconductor/Complex Hybrid Photocatalysts. J. Am. Chem. Soc. 2011, 133, 15240−15243. FH


Chemical Reviews

Review

(55) Sayama, K.; Arakawa, H. Photocatalytic Decomposition of Water and Photocatalytic Reduction of Carbon Dioxide over Zirconia Catalyst. J. Phys. Chem. 1993, 97, 531−533. (56) Anpo, M.; Yamashita, H.; Ikeue, K.; Fujii, Y.; Zhang, S. G.; Ichihashi, Y.; Park, D. R.; Suzuki, Y.; Koyano, K.; Tatsumi, T. Photocatalytic Reduction of CO2 with H2O on Ti-Mcm-41 and TiMcm-48 Mesoporous Zeolite Catalysts. Catal. Today 1998, 44, 327− 332. (57) Yamashita, H.; Fujii, Y.; Ichihashi, Y.; Zhang, S. G.; Ikeue, K.; Park, D. R.; Koyano, K.; Tatsumi, T.; Anpo, M. Selective Formation of CH3OH in the Photocatalytic Reduction of CO2 with H2O on Titanium Oxides Highly Dispersed within Zeolites and Mesoporous Molecular Sieves. Catal. Today 1998, 45, 221−227. (58) Ikeue, K.; Nozaki, S.; Ogawa, M.; Anpo, M. Characterization of Self-Standing Ti-Containing Porous Silica Thin Films and Their Reactivity for the Photocatalytic Reduction of CO2 with H2O. Catal. Today 2002, 74, 241−248. (59) Ikeue, K.; Yamashita, H.; Anpo, M.; Takewaki, T. Photocatalytic Reduction of CO2 with H2O on Ti−Β Zeolite Photocatalysts: Effect of the Hydrophobic and Hydrophilic Properties. J. Phys. Chem. B 2001, 105, 8350−8355. (60) Varghese, O. K.; Paulose, M.; LaTempa, T. J.; Grimes, C. A. High-Rate Solar Photocatalytic Conversion of CO2 and Water Vapor to Hydrocarbon Fuels. Nano Lett. 2009, 9, 731−737. (61) Wang, W.-N.; An, W.-J.; Ramalingam, B.; Mukherjee, S.; Niedzwiedzki, D. M.; Gangopadhyay, S.; Biswas, P. Size and Structure Matter: Enhanced CO2 Photoreduction Efficiency by Size-Resolved Ultrafine Pt Nanoparticles on TiO2 Single Crystals. J. Am. Chem. Soc. 2012, 134, 11276−11281. (62) Neatu, S.; Maciá-Agulló, J. A.; Concepcion, P.; Garcia, H. GoldCopper Nanoalloys Supported on TiO2 as Photocatalysts for CO2 Reduction by Water. J. Am. Chem. Soc. 2014, 136, 15969−15976. (63) Kamat, P. V. Semiconductor Surface Chemistry as Holy Grail in Photocatalysis and Photovoltaics. Acc. Chem. Res. 2017, 50, 527−531. (64) Singh, V.; Beltran, I. J. C.; Ribot, J. C.; Nagpal, P. Photocatalysis Deconstructed: Design of a New Selective Catalyst for Artificial Photosynthesis. Nano Lett. 2014, 14, 597−603. (65) Liu, H.; Meng, X.; Dao, T. D.; Zhang, H.; Li, P.; Chang, K.; Wang, T.; Li, M.; Nagao, T.; Ye, J. Conversion of Carbon Dioxide by Methane Reforming under Visible-Light Irradiation: Surface-PlasmonMediated Nonpolar Molecule Activation. Angew. Chem., Int. Ed. 2015, 54, 11545−11549. (66) Han, B.; Wei, W.; Chang, L.; Cheng, P.; Hu, Y. H. Efficient Visible Light Photocatalytic CO2Reforming of CH4. ACS Catal. 2016, 6, 494−497. (67) Li, Y.; Chan, S. H.; Sun, Q. Heterogeneous Catalytic Conversion of CO2A Comprehensive Theoretical Review. Nanoscale 2015, 7, 8663−8683. (68) Anpo, M.; Yamashita, H.; Ichihashi, Y.; Fujii, Y.; Honda, M. Photocatalytic Reduction of CO2 with H2O on Titanium Oxides Anchored within Micropores of Zeolites: Effects of the Structure of the Active Sites and the Addition of Pt. J. Phys. Chem. B 1997, 101, 2632− 2636. (69) Tseng, I. H.; Chang, W. C.; Wu, J. C. S. Photoreduction of CO2 Using Sol-Gel Derived Titania and Titania-Supported Copper Catalysts. Appl. Catal., B 2002, 37, 37−48. (70) Tseng, I. H.; Wu, J. C. S.; Chou, H. Y. Effects of Sol-Gel Procedures on the Photocatalysis of Cu/TiO2 in CO2 Photoreduction. J. Catal. 2004, 221, 432−440. (71) Lo, C. C.; Hung, C. H.; Yuan, C. S.; Wu, J. F. Photoreduction of Carbon Dioxide with H2 and H2O over TiO2 and ZrO2 in a Circulated Photocatalytic Reactor. Sol. Energy Mater. Sol. Cells 2007, 91, 1765− 1774. (72) Xia, X.-H.; Jia, Z.-J.; Yu, Y.; Liang, Y.; Wang, Z.; Ma, L.-L. Preparation of Multi-Walled Carbon Nanotube Supported TiO2 and Its Photocatalytic Activity in the Reduction of CO2 with H2O. Carbon 2007, 45, 717−721.

(73) Barton, E. E.; Rampulla, D. M.; Bocarsly, A. B. Selective SolarDriven Reduction of CO2 to Methanol Using a Catalyzed P-Gap Based Photoelectrochemical Cell. J. Am. Chem. Soc. 2008, 130, 6342−6344. (74) Wang, C.; Thompson, R. L.; Baltrus, J.; Matranga, C. Visible Light Photoreduction of CO2 Using CdSe/Pt/TiO2 Heterostructured Catalysts. J. Phys. Chem. Lett. 2010, 1, 48−53. (75) Kocí, K.; Obalová, L.; Matejová, L.; Plachá, D.; Lacný, Z.; Jirkovský, J.; Solcová, O. Effect of TiO2 Particle Size on the Photocatalytic Reduction of CO2. Appl. Catal., B 2009, 89, 494−502. (76) Kočí, K.; Matějů, K.; Obalová, L.; Krejčíková, S.; Lacný, Z.; Plachá, D.; Č apek, L.; Hospodková, A.; Šolcová, O. Effect of Silver Doping on the TiO2 for Photocatalytic Reduction of CO2. Appl. Catal., B 2010, 96, 239−244. (77) Li, Y.; Wang, W. N.; Zhan, Z. L.; Woo, M. H.; Wu, C. Y.; Biswas, P. Photocatalytic Reduction of CO2 with H2O on Mesoporous Silica Supported Cu/TiO2 Catalysts. Appl. Catal., B 2010, 100, 386− 392. (78) Liu, Q.; Zhou, Y.; Kou, J. H.; Chen, X. Y.; Tian, Z. P.; Gao, J.; Yan, S. C.; Zou, Z. G. High-Yield Synthesis of Ultralong and Ultrathin Zn2GeO4 Nanoribbons toward Improved Photocatalytic Reduction of CO2 into Renewable Hydrocarbon Fuel. J. Am. Chem. Soc. 2010, 132, 14385−14387. (79) Sato, S.; Morikawa, T.; Saeki, S.; Kajino, T.; Motohiro, T. Visible-Light-Induced Selective CO2 Reduction Utilizing a Ruthenium Complex Electrocatalyst Linked to a P-Type Nitrogen-Doped Ta2O5 Semiconductor. Angew. Chem., Int. Ed. 2010, 49, 5101−5105. (80) Woolerton, T. W.; Sheard, S.; Reisner, E.; Pierce, E.; Ragsdale, S. W.; Armstrong, F. A. Efficient and Clean Photoreduction of CO2 to Co by Enzyme-Modified TiO2 Nanoparticles Using Visible Light. J. Am. Chem. Soc. 2010, 132, 2132−2133. (81) Yan, S. C.; Ouyang, S. X.; Gao, J.; Yang, M.; Feng, J. Y.; Fan, X. X.; Wan, L. J.; Li, Z. S.; Ye, J. H.; Zhou, Y.; et al. A Room-Temperature Reactive-Template Route to Mesoporous ZnGa2O4 with Improved Photocatalytic Activity in Reduction of CO2. Angew. Chem., Int. Ed. 2010, 49, 6400−6404. (82) Yang, C.-C.; Yu, Y.-H.; van der Linden, B.; Wu, J. C. S.; Mul, G. Artificial Photosynthesis over Crystalline TiO2-Based Catalysts: Fact or Fiction? J. Am. Chem. Soc. 2010, 132, 8398−8406. (83) Cao, L. C. L.; Sahu, S.; Anilkumar, P.; Bunker, C. E.; Xu, J. A.; Fernando, K. A. S.; Wang, P.; Guliants, E. A.; Tackett, K. N.; Sun, Y. P. Carbon Nanoparticles as Visible-Light Photocatalysts for Efficient CO2 Conversion and Beyond. J. Am. Chem. Soc. 2011, 133, 4754−4757. (84) Hou, W. B.; Hung, W. H.; Pavaskar, P.; Goeppert, A.; Aykol, M.; Cronin, S. B. Photocatalytic Conversion of CO2 to Hydrocarbon Fuels Via Plasmon-Enhanced Absorption and Metallic Interband Transitions. ACS Catal. 2011, 1, 929−936. (85) Iizuka, K.; Wato, T.; Miseki, Y.; Saito, K.; Kudo, A. Photocatalytic Reduction of Carbon Dioxide over Ag CocatalystLoaded Ala4Ti4O15 (a = Ca, Sr, and Ba) Using Water as a Reducing Reagent. J. Am. Chem. Soc. 2011, 133, 20863−20868. (86) Liang, Y. T.; Vijayan, B. K.; Gray, K. A.; Hersam, M. C. Minimizing Graphene Defects Enhances Titania NanocompositeBased Photocatalytic Reduction of CO2 for Improved Solar Fuel Production. Nano Lett. 2011, 11, 2865−2870. (87) Wang, C.; Xie, Z.; deKrafft, K. E.; Lin, W. Doping MetalOrganic Frameworks for Water Oxidation, Carbon Dioxide Reduction, and Organic Photocatalysis. J. Am. Chem. Soc. 2011, 133, 13445− 13454. (88) Fu, Y. H.; Sun, D. R.; Chen, Y. J.; Huang, R. K.; Ding, Z. X.; Fu, X. Z.; Li, Z. H. An Amine-Functionalized Titanium Metal-Organic Framework Photocatalyst with Visible-Light-Induced Activity for CO2 Reduction. Angew. Chem., Int. Ed. 2012, 51, 3364−3367. (89) Liu, L.; Zhao, H.; Andino, J. M.; Li, Y. Photocatalytic CO2 Reduction with H2O on TiO2 Nanocrystals: Comparison of Anatase, Rutile, and Brookite Polymorphs and Exploration of Surface Chemistry. ACS Catal. 2012, 2, 1817−1828. (90) Tu, W. G.; Zhou, Y.; Liu, Q.; Tian, Z. P.; Gao, J.; Chen, X. Y.; Zhang, H. T.; Liu, J. G.; Zou, Z. G. Robust Hollow Spheres Consisting of Alternating Titania Nanosheets and Graphene Nanosheets with FI


Chemical Reviews

Review

High Photocatalytic Activity for CO2 Conversion into Renewable Fuels. Adv. Funct. Mater. 2012, 22, 1215−1221. (91) Zhang, X. J.; Han, F.; Shi, B.; Farsinezhad, S.; Dechaine, G. P.; Shankar, K. Photocatalytic Conversion of Diluted CO2 into Light Hydrocarbons Using Periodically Modulated Multiwalled Nanotube Arrays. Angew. Chem., Int. Ed. 2012, 51, 12732−12735. (92) Zhai, Q.; Xie, S.; Fan, W.; Zhang, Q.; Wang, Y.; Deng, W.; Wang, Y. Photocatalytic Conversion of Carbon Dioxide with Water to Methane: Platinum and Copper(I) Oxide Co-Catalysts with a Core− Shell Structure. Angew. Chem., Int. Ed. 2013, 52, 5776−5779. (93) Mao, J.; Peng, T.; Zhang, X.; Li, K.; Ye, L.; Zan, L. Effect of Graphitic Carbon Nitride Microstructures on the Activity and Selectivity of Photocatalytic CO2 Reduction under Visible Light. Catal. Sci. Technol. 2013, 3, 1253−1260. (94) Sekizawa, K.; Maeda, K.; Domen, K.; Koike, K.; Ishitani, O. Artificial Z-Scheme Constructed with a Supramolecular Metal Complex and Semiconductor for the Photocatalytic Reduction of CO2. J. Am. Chem. Soc. 2013, 135, 4596−4599. (95) Xie, S.; Wang, Y.; Zhang, Q.; Fan, W.; Deng, W.; Wang, Y. Photocatalytic Reduction of CO2 with H2O: Significant Enhancement of the Activity of Pt-TiO2 in CH4 Formation by Addition of MgO. Chem. Commun. 2013, 49, 2451−2453. (96) Meng, X.; Wang, T.; Liu, L.; Ouyang, S.; Li, P.; Hu, H.; Kako, T.; Iwai, H.; Tanaka, A.; Ye, J. Photothermal Conversion of CO2 into CH4 with H2 over Group Viii Nanocatalysts: An Alternative Approach for Solar Fuel Production. Angew. Chem., Int. Ed. 2014, 53, 11478− 11482. (97) Liao, Y.; Cao, S.-W.; Yuan, Y.; Gu, Q.; Zhang, Z.; Xue, C. Efficient CO2 Capture and Photoreduction by Amine-Functionalized TiO2. Chem. - Eur. J. 2014, 20, 10220−10222. (98) Yu, J.; Jin, J.; Cheng, B.; Jaroniec, M. A Noble Metal-Free Reduced Graphene Oxide-CdS Nanorod Composite for the Enhanced Visible-Light Photocatalytic Reduction of CO2 to Solar Fuel. J. Mater. Chem. A 2014, 2, 3407−3416. (99) Zhou, S.; Liu, Y.; Li, J.; Wang, Y.; Jiang, G.; Zhao, Z.; Wang, D.; Duan, A.; Liu, J.; Wei, Y. Facile in Situ Synthesis of Graphitic Carbon Nitride (g-C3N4)-N-TiO2 Heterojunction as an Efficient Photocatalyst for the Selective Photoreduction of CO2 to Co. Appl. Catal., B 2014, 158, 20−29. (100) Yu, J.; Low, J.; Xiao, W.; Zhou, P.; Jaroniec, M. Enhanced Photocatalytic CO2-Reduction Activity of Anatase TiO2 by Coexposed {001} and {101} Facets. J. Am. Chem. Soc. 2014, 136, 8839−8842. (101) Jin, J.; Yu, J.; Guo, D.; Cui, C.; Ho, W. A Hierarchical ZScheme CdS-WO3 Photocatalyst with Enhanced CO2 Reduction Activity. Small 2015, 11, 5262−5271. (102) Li, M.; Zhang, L.; Fan, X.; Zhou, Y.; Wu, M.; Shi, J. Highly Selective CO 2 Photoreduction to CO over g-C 3 N 4 /Bi 2 WO 6 Composites under Visible Light. J. Mater. Chem. A 2015, 3, 5189− 5196. (103) Qin, J.; Wang, S.; Ren, H.; Hou, Y.; Wang, X. Photocatalytic Reduction of CO2 by Graphitic Carbon Nitride Polymers Derived from Urea and Barbituric Acid. Appl. Catal., B 2015, 179, 1−8. (104) Zhang, H.; Wei, J.; Dong, J.; Liu, G.; Shi, L.; An, P.; Zhao, G.; Kong, J.; Wang, X.; Meng, X.; et al. Efficient Visible-Light-Driven Carbon Dioxide Reduction by a Single-Atom Implanted MetalOrganic Framework. Angew. Chem., Int. Ed. 2016, 55, 14310−14314. (105) Xia, P.; Zhu, B.; Yu, J.; Cao, S.; Jaroniec, M. Ultra-Thin Nanosheet Assemblies of Graphitic Carbon Nitride for Enhanced Photocatalytic CO2 Reduction. J. Mater. Chem. A 2017, 5, 3230−3238. (106) Akple, M. S.; Low, J.; Liu, S. W.; Cheng, B.; Yu, J. G.; Ho, W. K. Fabrication and Enhanced CO2 Reduction Performance of N-SelfDoped TiO2Microsheet Photocatalyst by Bi-Cocatalyst Modification. J. CO2 Util. 2016, 16, 442−449. (107) Zhou, X. H.; Liu, R.; Sun, K.; Chen, Y. K.; Verlage, E.; Francis, S. A.; Lewis, N. S.; Xiang, C. X. Solar-Driven Reduction of 1 atm of CO2 to Formate at 10% Energy-Conversion Efficiency by Use of a TiO2-Protected Iii-V Tandem Photoanode in Conjunction with a Bipolar Membrane and a Pd/C Cathode. ACS Energy Letters 2016, 1, 764−770.

(108) Zhu, Y.; Xu, Z.; Jiang, W.; Zhong, S.; Zhao, L.; Bai, S. Engineering on the Edge of Pd Nanosheet Cocatalysts for Enhanced Photocatalytic Reduction of CO2 to Fuels. J. Mater. Chem. A 2017, 5, 2619−2628. (109) Zhu, Y.; Gao, C.; Bai, S.; Chen, S.; Long, R.; Song, L.; Li, Z.; Xiong, Y. Hydriding Pd Cocatalysts: An Approach to Giant Enhancement on Photocatalytic CO2 Reduction into CH4. Nano Res. 2017, 10, 3396−3406. (110) Jiao, X.; Chen, Z.; Li, X.; Sun, Y.; Gao, S.; Yan, W.; Wang, C.; Zhang, Q.; Lin, Y.; Luo, Y.; et al. Defect-Mediated Electron−Hole Separation in One-Unit-Cell ZnIn2S4 Layers for Boosted Solar-Driven CO2 Reduction. J. Am. Chem. Soc. 2017, 139, 7586−7594. (111) Niu, K.; Xu, Y.; Wang, H.; Ye, R.; Xin, H. L.; Lin, F.; Tian, C.; Lum, Y.; Bustillo, K. C.; Doeff, M. M.; et al. A Spongy Nickel-Organic CO2 Reduction Photocatalyst for Nearly 100% Selective Co Production. Science Advances 2017, 3, No. e1700921. (112) Girish Kumar, S.; Koteswara Rao, K. S. R. Tungsten-Based Nanomaterials (WO3 & Bi2WO6): Modifications Related to Charge Carrier Transfer Mechanisms and Photocatalytic Applications. Appl. Surf. Sci. 2015, 355, 939−958. (113) Li, Q.; Li, X.; Wageh, S.; Al-Ghamdi, A. A.; Yu, J. CdS/ Graphene Nanocomposite Photocatalysts. Adv. Energy Mater. 2015, 5, 1500010. (114) Ma, S.; Deng, Y.; Xie, J.; He, K.; Liu, W.; Chen, X.; Li, X. Noble-Metal-Free Ni3C Cocatalysts Decorated CdS Nanosheets for High-Efficiency Visible-Light-Driven Photocatalytic H2 Evolution. Appl. Catal., B 2018, 227, 218−228. (115) Kuang, P. Y.; Zheng, P. X.; Liu, Z. Q.; Lei, J. L.; Wu, H.; Li, N.; Ma, T. Y. Embedding Au Quantum Dots in Rimous Cadmium Sulfide Nanospheres for Enhanced Photocatalytic Hydrogen Evolution. Small 2016, 12, 6735−6744. (116) He, R. a.; Cao, S.; Zhou, P.; Yu, J. Recent Advances in Visible Light Bi-Based Photocatalysts. Chin. J. Catal. 2014, 35, 989−1007. (117) Chen, X.; Mao, S. S. Titanium Dioxide Nanomaterials: Synthesis, Properties, Modifications, and Applications. Chem. Rev. 2007, 107, 2891−2959. (118) Rehman, S.; Ullah, R.; Butt, A. M.; Gohar, N. D. Strategies of Making TiO2 and ZnO Visible Light Active. J. Hazard. Mater. 2009, 170, 560−569. (119) Li, X.; Yu, J.; Low, J.; Fang, Y.; Xiao, J.; Chen, X. Engineering Heterogeneous Semiconductors for Solar Water Splitting. J. Mater. Chem. A 2015, 3, 2485−2534. (120) Chen, X.; Shen, S.; Guo, L.; Mao, S. S. Semiconductor-Based Photocatalytic Hydrogen Generation. Chem. Rev. 2010, 110, 6503− 6570. (121) Zhang, X. H.; Peng, T. Y.; Song, S. S. Recent Advances in DyeSensitized Semiconductor Systems for Photocatalytic Hydrogen Production. J. Mater. Chem. A 2016, 4, 2365−2402. (122) Morris, A. J.; Meyer, G. J.; Fujita, E. Molecular Approaches to the Photocatalytic Reduction of Carbon Dioxide for Solar Fuels. Acc. Chem. Res. 2009, 42, 1983−1994. (123) Esswein, A. J.; Nocera, D. G. Hydrogen Production by Molecular Photocatalysis. Chem. Rev. 2007, 107, 4022−4047. (124) Takeda, H.; Ishitani, O. Development of Efficient Photocatalytic Systems for CO2 Reduction Using Mononuclear and Multinuclear Metal Complexes Based on Mechanistic Studies. Coord. Chem. Rev. 2010, 254, 346−354. (125) Windle, C. D.; Perutz, R. N. Advances in Molecular Photocatalytic and Electrocatalytic CO2 Reduction. Coord. Chem. Rev. 2012, 256, 2562−2570. (126) Sprick, R. S.; Bonillo, B.; Clowes, R.; Guiglion, P.; Brownbill, N. J.; Slater, B. J.; Blanc, F.; Zwijnenburg, M. A.; Adams, D. J.; Cooper, A. I. Visible-Light-Driven Hydrogen Evolution Using Planarized Conjugated Polymer Photocatalysts. Angew. Chem., Int. Ed. 2016, 55, 1792−1796. (127) Muktha, B.; Madras, G.; Guru Row, T. N.; Scherf, U.; Patil, S. Conjugated Polymers for Photocatalysis. J. Phys. Chem. B 2007, 111, 7994−7998. FJ


Chemical Reviews

Review

(128) Li, L.; Cai, Z.; Wu, Q.; Lo, W.-Y.; Zhang, N.; Chen, L. X.; Yu, L. Rational Design of Porous Conjugated Polymers and Roles of Residual Palladium for Photocatalytic Hydrogen Production. J. Am. Chem. Soc. 2016, 138, 7681−7686. (129) Zhou, Q.; Shi, G. Conducting Polymer-Based Catalysts. J. Am. Chem. Soc. 2016, 138, 2868−2876. (130) Ghosh, S.; Kouame, N. A.; Ramos, L.; Remita, S.; Dazzi, A.; Deniset-Besseau, A.; Beaunier, P.; Goubard, F.; Aubert, P.-H.; Remita, H. Conducting Polymer Nanostructures for Photocatalysis under Visible Light. Nat. Mater. 2015, 14, 505−511. (131) Yeh, T.-F.; Syu, J.-M.; Cheng, C.; Chang, T.-H.; Teng, H. Graphite Oxide as a Photocatalyst for Hydrogen Production from Water. Adv. Funct. Mater. 2010, 20, 2255−2262. (132) Cao, S.; Low, J.; Yu, J.; Jaroniec, M. Polymeric Photocatalysts Based on Graphitic Carbon Nitride. Adv. Mater. 2015, 27, 2150−2176. (133) Wen, J.; Xie, J.; Chen, X.; Li, X. A Review on g-C3N4-Based Photocatalysts. Appl. Surf. Sci. 2017, 391, 72−123. (134) Ong, W.-J.; Tan, L.-L.; Ng, Y. H.; Yong, S.-T.; Chai, S.-P. Graphitic Carbon Nitride (g-C3N4)-Based Photocatalysts for Artificial Photosynthesis and Environmental Remediation: Are We a Step Closer to Achieving Sustainability? Chem. Rev. 2016, 116, 7159−7329. (135) Cao, S.; Yu, J. g-C3N4-Based Photocatalysts for Hydrogen Generation. J. Phys. Chem. Lett. 2014, 5, 2101−2107. (136) Ueno, K.; Misawa, H. Surface Plasmon-Enhanced Photochemical Reactions. J. Photochem. Photobiol., C 2013, 15, 31−52. (137) Linic, S.; Christopher, P.; Ingram, D. B. Plasmonic-Metal Nanostructures for Efficient Conversion of Solar to Chemical Energy. Nat. Mater. 2011, 10, 911−921. (138) Clavero, C. Plasmon-Induced Hot-Electron Generation at Nanoparticle/Metal-Oxide Interfaces for Photovoltaic and Photocatalytic Devices. Nat. Photonics 2014, 8, 95−103. (139) Zhang, X. M.; Chen, Y. L.; Liu, R. S.; Tsai, D. P. Plasmonic Photocatalysis. Rep. Prog. Phys. 2013, 76, 046401. (140) Long, R.; Prezhdo, O. V. Instantaneous Generation of ChargeSeparated State on TiO2 Surface Sensitized with Plasmonic Nanoparticles. J. Am. Chem. Soc. 2014, 136, 4343−4354. (141) Cushing, S. K.; Li, J.; Meng, F.; Senty, T. R.; Suri, S.; Zhi, M.; Li, M.; Bristow, A. D.; Wu, N. Photocatalytic Activity Enhanced by Plasmonic Resonant Energy Transfer from Metal to Semiconductor. J. Am. Chem. Soc. 2012, 134, 15033−15041. (142) Ha, E.; Lee, L. Y. S.; Wang, J.; Li, F.; Wong, K.-Y.; Tsang, S. C. E. Significant Enhancement in Photocatalytic Reduction of Water to Hydrogen by Au/Cu2ZnSnS4 Nanostructure. Adv. Mater. 2014, 26, 3496−3500. (143) Jiang, R.; Li, B.; Fang, C.; Wang, J. Metal/Semiconductor Hybrid Nanostructures for Plasmon-Enhanced Applications. Adv. Mater. 2014, 26, 5274−5309. (144) Mo, Z.; Xu, H.; Chen, Z. G.; She, X. J.; Song, Y. H.; Yan, P. C.; Xu, Y. G.; Lei, Y. C.; Yuan, S. Q.; Li, H. M. Gold/Monolayer Graphitic Carbon Nitride Plasmonic Photocatalyst for Ultrafast Electron Transfer in Solar-to-Hydrogen Energy Conversion. Chin. J. Catal. 2018, 39, 760−770. (145) Li, Y. R.; Guo, Y.; Long, R.; Liu, D.; Zhao, D. M.; Tan, Y. B.; Gao, C.; Shen, S. H.; Xiong, Y. J. Steering Plasmonic Hot Electrons to Realize Enhanced Full-Spectrum Photocatalytic Hydrogen Evolution. Chin. J. Catal. 2018, 39, 453−462. (146) Yang, X.; Wang, Y.; Xu, X.; Qu, Y.; Ding, X.; Chen, H. Surface Plasmon Resonance-Induced Visible-Light Photocatalytic Performance of Silver/Silver Molybdate Composites. Chin. J. Catal. 2017, 38, 260− 269. (147) Yang, J. J.; Liu, B. S.; Zhao, X. J. A Visible-Light-Active AuCu(I)@Na2Ti6O13 Nanostructured Hybrid Pasmonic Photocatalytic Membrane for Acetaldehyde Elimination. Chin. J. Catal. 2017, 38, 2048−2055. (148) Warren, S. C.; Thimsen, E. Plasmonic Solar Water Splitting. Energy Environ. Sci. 2012, 5, 5133−5146. (149) Dong, F.; Xiong, T.; Sun, Y.; Zhao, Z.; Zhou, Y.; Feng, X.; Wu, Z. A Semimetal Bismuth Element as a Direct Plasmonic Photocatalyst. Chem. Commun. 2014, 50, 10386−10389.

(150) Zhang, Q.; Zhou, Y.; Wang, F.; Dong, F.; Li, W.; Li, H.; Patzke, G. R. From Semiconductors to Semimetals: Bismuth as a Photocatalyst for NO Oxidation in Air. J. Mater. Chem. A 2014, 2, 11065− 11072. (151) Zhao, Z.; Zhang, W.; Sun, Y.; Yu, J.; Zhang, Y.; Wang, H.; Dong, F.; Wu, Z. Bi Cocatalyst/Bi2MoO6 Microspheres Nanohybrid with SPR-Promoted Visible-Light Photocatalysis. J. Phys. Chem. C 2016, 120, 11889−11898. (152) Sun, Y.; Zhao, Z.; Dong, F.; Zhang, W. Mechanism of Visible Light Photocatalytic NOx Oxidation with Plasmonic Bi CocatalystEnhanced Bi2CO3 Hierarchical Microspheres. Phys. Chem. Chem. Phys. 2015, 17, 10383−10390. (153) Dong, F.; Zhao, Z.; Sun, Y.; Zhang, Y.; Yan, S.; Wu, Z. An Advanced Semimetal-Organic Bi Spheres-g-C3N4 Nanohybrid with SPR-Enhanced Visible-Light Photocatalytic Performance for No Purification. Environ. Sci. Technol. 2015, 49, 12432−12440. (154) Dong, F.; Li, Q.; Sun, Y.; Ho, W.-K. Noble Metal-Like Behavior of Plasmonic Bi Particles as a Cocatalyst Deposited on Bi2CO3 Microspheres for Efficient Visible Light Photocatalysis. ACS Catal. 2014, 4, 4341−4350. (155) Xiong, T.; Dong, X. a.; Huang, H.; Cen, W.; Zhang, Y.; Dong, F. Single Precursor Mediated-Synthesis of Bi Semimetal Deposited NDoped Bi2CO3Superstructures for Highly Promoted Photocatalysis. ACS Sustainable Chem. Eng. 2016, 4, 2969−2979. (156) Zhai, Z.-Y.; Guo, X.-N.; Jin, G.-Q.; Guo, X.-Y. Visible LightInduced Selective Photocatalytic Aerobic Oxidation of Amines into Imines on Cu/Graphene. Catal. Sci. Technol. 2015, 5, 4202−4207. (157) Ni, Z. L.; Zhang, W. D.; Jiang, G. M.; Wang, X. P.; Lu, Z. Z.; Sun, Y. J.; Li, X. W.; Zhang, Y. X.; Dong, F. Enhanced Plasmonic Photocatalysis by SiO2@Bi Microspheres with Hot-Electron Transportation Channels Via Bi-O-Si Linkages. Chin. J. Catal. 2017, 38, 1174−1183. (158) Zhang, J.; Yu, J.; Zhang, Y.; Li, Q.; Gong, J. R. Visible Light Photocatalytic H2-Production Activity of CuS/ZnS Porous Nanosheets Based on Photoinduced Interfacial Charge Transfer. Nano Lett. 2011, 11, 4774−4779. (159) Zhang, J.; Xu, Q.; Qiao, S. Z.; Yu, J. Enhanced Visible-Light Hydrogen-Production Activity of Copper-Modified ZnxCd1‑XS. ChemSusChem 2013, 6, 2009−2015. (160) Chandra, D.; Tsuriya, R.; Sato, T.; Takama, D.; Abe, N.; Kajita, M.; Li, D.; Togashi, T.; Kurihara, M.; Saito, K.; et al. Characterization of Interfacial Charge-Transfer Photoexcitation of Polychromium-OxoElectrodeposited TiO2 as an Earth-Abundant Photoanode for Water Oxidation Driven by Visible Light. ChemPlusChem 2016, 81, 1116− 1122. (161) Feng, X.; Zhang, W.; Deng, H.; Ni, Z.; Dong, F.; Zhang, Y. Efficient Visible Light Photocatalytic NOx Removal with Cationic Ag Clusters-Grafted Bi2CO3 Hierarchical Superstructures. J. Hazard. Mater. 2017, 322, 223−232. (162) Miyauchi, M.; Irie, H.; Liu, M.; Qiu, X.; Yu, H.; Sunada, K.; Hashimoto, K. Visible-Light-Sensitive Photocatalysts: NanoclusterGrafted Titanium Dioxide for Indoor Environmental Remediation. J. Phys. Chem. Lett. 2016, 7, 75−84. (163) Zhang, H.; Guo, L.-H.; Wang, D.; Zhao, L.; Wan, B. LightInduced Efficient Molecular Oxygen Activation on a Cu(II)-Grafted TiO2/Graphene Photocatalyst for Phenol Degradation. ACS Appl. Mater. Interfaces 2015, 7, 1816−1823. (164) Liu, M.; Qiu, X.; Hashimoto, K.; Miyauchi, M. Cu(II) Nanocluster-Grafted, Nb-Doped TiO2 as an Efficient Visible-LightSensitive Photocatalyst Based on Energy-Level Matching between Surface and Bulk States. J. Mater. Chem. A 2014, 2, 13571−13579. (165) Irie, H.; Miura, S.; Kamiya, K.; Hashimoto, K. Efficient Visible Light-Sensitive Photocatalysts: Grafting Cu(II) Ions onto TiO2 and WO3 Photocatalysts. Chem. Phys. Lett. 2008, 457, 202−205. (166) Goeringer, S.; Chenthamarakshan, C. R.; Rajeshwar, K. Synergistic Photocatalysis Mediated by TiO2 Mutual Rate Enhancement in the Photoreduction of Cr(VI) and Cu(II) in Aqueous Media. Electrochem. Commun. 2001, 3, 290−292. FK


Chemical Reviews

Review

(167) Wang, P.; Xia, Y.; Wu, P.; Wang, X.; Yu, H.; Yu, J. Cu(II) as a General Cocatalyst for Improved Visible-Light Photocatalytic Performance of Photosensitive Ag-Based Compounds. J. Phys. Chem. C 2014, 118, 8891−8898. (168) Yu, H.; Irie, H.; Hashimoto, K. Conduction Band Energy Level Control of Titanium Dioxide: Toward an Efficient Visible-LightSensitive Photocatalyst. J. Am. Chem. Soc. 2010, 132, 6898−6899. (169) Qiu, X.; Miyauchi, M.; Yu, H.; Irie, H.; Hashimoto, K. VisibleLight-Driven Cu(II)-(Sr1‑YNay)(Ti1‑XMox)O‑3 Photocatalysts Based on Conduction Band Control and Surface Ion Modification. J. Am. Chem. Soc. 2010, 132, 15259−15267. (170) Feng, X.; Zhang, W.; Sun, Y.; Huang, H.; Dong, F. Fe(III) Cluster-Grafted (BiO)2CO3 Superstructures: In Situ Drifts Investigation on IFCT-Enhanced Visible Light Photocatalytic No Oxidation. Environ. Sci.: Nano 2017, 4, 604−612. (171) Wang, X.; Wang, K.; Feng, K.; Chen, F.; Yu, H.; Yu, J. Greatly Enhanced Photocatalytic Activity of TiO2‑XNx by a Simple Surface Modification of Fe(III) Cocatalyst. J. Mol. Catal. A: Chem. 2014, 391, 92−98. (172) Nishikawa, M.; Mitani, Y.; Nosaka, Y. Photocatalytic Reaction Mechanism of Fe(III)-Grafted TiO2 Studied by Means of Esr Spectroscopy and Chemiluminescence Photometry. J. Phys. Chem. C 2012, 116, 14900−14907. (173) Sun, W.; Zhang, H.; Lin, J. Surface Modification of Bi2O3 with Fe(III) Clusters toward Efficient Photocatalysis in a Broader Visible Light Region: Implications of the Interfacial Charge Transfer. J. Phys. Chem. C 2014, 118, 17626−17632. (174) Yu, H.; Irie, H.; Shimodaira, Y.; Hosogi, Y.; Kuroda, Y.; Miyauchi, M.; Hashimoto, K. An Efficient Visible-Light-Sensitive Fe(III)-Grafted TiO2 Photocatalyst. J. Phys. Chem. C 2010, 114, 16481−16487. (175) Yu, H.; Tian, J.; Chen, F.; Wang, P.; Wang, X. Synergistic Effect of Dual Electron-Cocatalysts for Enhanced Photocatalytic Activity: RGO as Electron-Transfer Mediator and Fe(III) as Oxygen-Reduction Active Site. Sci. Rep. 2015, 5, 13083. (176) Huang, Q.; Tian, S.; Zeng, D.; Wang, X.; Song, W.; Li, Y.; Xiao, W.; Xie, C. Enhanced Photocatalytic Activity of Chemically Bonded TiO2/Graphene Composites Based on the Effective Interfacial Charge Transfer through the C-Ti Bond. ACS Catal. 2013, 3, 1477−1485. (177) Li, X.; Yu, J.; Wageh, S.; Al-Ghamdi, A. A.; Xie, J. Graphene in Photocatalysis: A Review. Small 2016, 12, 6640−6696. (178) Li, X.; Yu, J.; Jaroniec, M. Hierarchical Photocatalysts. Chem. Soc. Rev. 2016, 45, 2603−2636. (179) Wood, P. M. The Potential Diagram for Oxygen at pH 7. Biochem. J. 1988, 253, 287−289. (180) Wang, C.; Zhang, X.; Liu, Y. Promotion of Multi-Electron Transfer for Enhanced Photocatalysis: A Review Focused on Oxygen Reduction Reaction. Appl. Surf. Sci. 2015, 358, 28−45. (181) Wu, G.; Zelenay, P. Nanostructured Nonprecious Metal Catalysts for Oxygen Reduction Reaction. Acc. Chem. Res. 2013, 46, 1878−1889. (182) Xia, W.; Mahmood, A.; Liang, Z.; Zou, R.; Guo, S. EarthAbundant Nanomaterials for Oxygen Reduction. Angew. Chem., Int. Ed. 2016, 55, 2650−2676. (183) Dai, L.; Xue, Y.; Qu, L.; Choi, H.-J.; Baek, J.-B. Metal-Free Catalysts for Oxygen Reduction Reaction. Chem. Rev. 2015, 115, 4823−4892. (184) Shao, M.; Chang, Q.; Dodelet, J.-P.; Chenitz, R. Recent Advances in Electrocatalysts for Oxygen Reduction Reaction. Chem. Rev. 2016, 116, 3594−3657. (185) Wang, D.-W.; Su, D. Heterogeneous Nanocarbon Materials for Oxygen Reduction Reaction. Energy Environ. Sci. 2014, 7, 576−591. (186) Duan, J.; Chen, S.; Jaroniec, M.; Qiao, S. Z. HeteroatomDoped Graphene-Based Materials for Energy-Relevant Electrocatalytic Processes. ACS Catal. 2015, 5, 5207−5234. (187) Karkas, M. D.; Verho, O.; Johnston, E. V.; Akermark, B. Artificial Photosynthesis: Molecular Systems for Catalytic Water Oxidation. Chem. Rev. 2014, 114, 11863−12001.

(188) Hisatomi, T.; Kubota, J.; Domen, K. Recent Advances in Semiconductors for Photocatalytic and Photoelectrochemical Water Splitting. Chem. Soc. Rev. 2014, 43, 7520−7535. (189) Jiao, Y.; Zheng, Y.; Jaroniec, M.; Qiao, S. Z. Design of Electrocatalysts for Oxygen- and Hydrogen-Involving Energy Conversion Reactions. Chem. Soc. Rev. 2015, 44, 2060−2086. (190) Singh, A.; Spiccia, L. Water Oxidation Catalysts Based on Abundant 1st Row Transition Metals. Coord. Chem. Rev. 2013, 257, 2607−2622. (191) Faber, M. S.; Jin, S. Earth-Abundant Inorganic Electrocatalysts and Their Nanostructures for Energy Conversion Applications. Energy Environ. Sci. 2014, 7, 3519−3542. (192) Hong, W. T.; Risch, M.; Stoerzinger, K. A.; Grimaud, A.; Suntivich, J.; Shao-Horn, Y. Toward the Rational Design of NonPrecious Transition Metal Oxides for Oxygen Electrocatalysis. Energy Environ. Sci. 2015, 8, 1404−1427. (193) Gong, M.; Dai, H. A Mini Review of NiFe-Based Materials as Highly Active Oxygen Evolution Reaction Electrocatalysts. Nano Res. 2015, 8, 23−39. (194) Wu, G.; More, K. L.; Johnston, C. M.; Zelenay, P. HighPerformance Electrocatalysts for Oxygen Reduction Derived from Polyaniline, Iron, and Cobalt. Science 2011, 332, 443−447. (195) He, R. A.; Xu, D. F.; Cheng, B.; Yu, J. G.; Ho, W. K. Review on Nanoscale Bi-Based Photocatalysts. Nanoscale Horizons 2018, 3, 464− 504. (196) Li, X.; Xie, J.; Jiang, C.; Yu, J.; Zhang, P. Review on Design and Evaluation of Environmental Photocatalysts. Front. Environ. Sci. Eng. 2018, 12, 14. (197) Guan, L.; Chen, X. Photoexcited Charge Transport and Accumulation in Anatase TiO2. ACS Applied Energy Materials 2018, 1, 4313−4320. (198) Zhang, J. Z. Interfacial Charge Carrier Dynamics of Colloidal Semiconductor Nanoparticles. J. Phys. Chem. B 2000, 104, 7239−7253. (199) Ravensbergen, J.; Abdi, F. F.; van Santen, J. H.; Frese, R. N.; Dam, B.; van de Krol, R.; Kennis, J. T. M. Unraveling the Carrier Dynamics of BiVO4A Femtosecond to Microsecond Transient Absorption Study. J. Phys. Chem. C 2014, 118, 27793−27800. (200) Kelzenberg, M. D.; Turner-Evans, D. B.; Kayes, B. M.; Filler, M. A.; Putnam, M. C.; Lewis, N. S.; Atwater, H. A. Photovoltaic Measurements in Single-Nanowire Silicon Solar Cells. Nano Lett. 2008, 8, 710−714. (201) Tang, H.; Prasad, K.; Sanjinès, R.; Schmid, P. E.; Lévy, F. Electrical and Optical Properties of TiO2 Anatase Thin Films. J. Appl. Phys. 1994, 75, 2042−2047. (202) Yoshihara, T.; Katoh, R.; Furube, A.; Tamaki, Y.; Murai, M.; Hara, K.; Murata, S.; Arakawa, H.; Tachiya, M. Identification of Reactive Species in Photoexcited Nanocrystalline TiO2 Films by WideWavelength-Range (400−2500 nm) Transient Absorption Spectroscopy. J. Phys. Chem. B 2004, 108, 3817−3823. (203) Wang, X.; Kafizas, A.; Li, X.; Moniz, S. J. A.; Reardon, P. J. T.; Tang, J.; Parkin, I. P.; Durrant, J. R. Transient Absorption Spectroscopy of Anatase and Rutile: The Impact of Morphology and Phase on Photocatalytic Activity. J. Phys. Chem. C 2015, 119, 10439− 10447. (204) Tamaki, Y.; Furube, A.; Murai, M.; Hara, K.; Katoh, R.; Tachiya, M. Dynamics of Efficient Electron−Hole Separation in TiO2 Nanoparticles Revealed by Femtosecond Transient Absorption Spectroscopy under the Weak-Excitation Condition. Phys. Chem. Chem. Phys. 2007, 9, 1453−1460. (205) Tamaki, Y.; Hara, K.; Katoh, R.; Tachiya, M.; Furube, A. Femtosecond Visible-to-Ir Spectroscopy of TiO2 Nanocrystalline Films: Elucidation of the Electron Mobility before Deep Trapping. J. Phys. Chem. C 2009, 113, 11741−11746. (206) Maruska, H. P.; Ghosh, A. K. Transition-Metal Dopants for Extending the Response of Titanate Photoelectrolysis Anodes. Sol. Energy Mater. 1979, 1, 237−247. (207) Forro, L.; Chauvet, O.; Emin, D.; Zuppiroli, L.; Berger, H.; Lévy, F. High Mobility N-Type Charge Carriers in Large Single Crystals of Anatase (TiO2). J. Appl. Phys. 1994, 75, 633−635. FL


Chemical Reviews

Review

(208) Grant, F. A. Properties of Rutile (Titanium Dioxide). Rev. Mod. Phys. 1959, 31, 646−674. (209) Yagi, E.; Hasiguti, R. R.; Aono, M. Electronic Conduction above 4 K of Slightly Reduced Oxygen-Deficient Rutile TiO2−x. Phys. Rev. B: Condens. Matter Mater. Phys. 1996, 54, 7945−7956. (210) Yamakata, A.; Vequizo, J. J. M.; Kawaguchi, M. Behavior and Energy State of Photogenerated Charge Carriers in Single-Crystalline and Polycrystalline Powder SrTiO3 Studied by Time-Resolved Absorption Spectroscopy in the Visible to Mid-Infrared Region. J. Phys. Chem. C 2015, 119, 1880−1885. (211) Moos, R.; Menesklou, W.; Härdtl, K. H. Hall Mobility of Undoped N-Type Conducting Strontium Titanate Single Crystals between 19 K and 1373 K. Appl. Phys. A: Mater. Sci. Process. 1995, 61, 389−395. (212) Lee, C.; Destry, J.; Brebner, J. L. Optical Absorption and Transport in Semiconducting SrTiO3. Phys. Rev. B 1975, 11, 2299− 2310. (213) Tufte, O. N.; Chapman, P. W. Electron Mobility in Semiconducting Strontium Titanate. Phys. Rev. 1967, 155, 796−802. (214) Ö zgür, Ü .; Alivov, Y. I.; Liu, C.; Teke, A.; Reshchikov, M. A.; Doğan, S.; Avrutin, V.; Cho, S.-J.; Morkoç, H. A Comprehensive Review of Zno Materials and Devices. J. Appl. Phys. 2005, 98, 041301. (215) Bauer, C.; Boschloo, G.; Mukhtar, E.; Hagfeldt, A. Ultrafast Relaxation Dynamics of Charge Carriers Relaxation in Zno Nanocrystalline Thin Films. Chem. Phys. Lett. 2004, 387, 176−181. (216) Soudi, A.; Dhakal, P.; Gu, Y. Diameter Dependence of the Minority Carrier Diffusion Length in Individual Zno Nanowires. Appl. Phys. Lett. 2010, 96, 253115. (217) Seager, C. H.; Myers, S. M. Quantitative Comparisons of Dissolved Hydrogen Density and the Electrical and Optical Properties of Zno. J. Appl. Phys. 2003, 94, 2888−2894. (218) Look, D. C.; Reynolds, D. C.; Sizelove, J. R.; Jones, R. L.; Litton, C. W.; Cantwell, G.; Harsch, W. C. Electrical Properties of Bulk Zno. Solid State Commun. 1998, 105, 399−401. (219) Lou, Y.; Yin, M.; O’Brien, S.; Burda, C. Electron-Hole Pair Relaxation Dynamics in Binary Copper-Based Semiconductor Quantum Dots. J. Electrochem. Soc. 2005, 152, G427−G431. (220) de Jongh, P. E.; Vanmaekelbergh, D.; Kelly, J. J. Photoelectrochemistry of Electrodeposited Cu2O. J. Electrochem. Soc. 2000, 147, 486−489. (221) Paracchino, A.; Laporte, V.; Sivula, K.; Grätzel, M.; Thimsen, E. Highly Active Oxide Photocathode for Photoelectrochemical Water Reduction. Nat. Mater. 2011, 10, 456−461. (222) de Jongh, P. E.; Vanmaekelbergh, D.; Kelly, J. J. Cu2O: Electrodeposition and Characterization. Chem. Mater. 1999, 11, 3512− 3517. (223) Cavaleri, J. J.; Colombo, D. P.; Bowman, R. M. Ultrafast Charge Carrier Dynamics of SnO2 Nanoclusters: A Refined Interpretation of the Electron−Hole Kinetics in Metal Oxides. J. Phys. Chem. B 1998, 102, 1341−1346. (224) Kar, A.; Stroscio, M. A.; Meyyappan, M.; Gosztola, D. J.; Wiederrecht, P. W.; Dutta, M. Tailoring the Surface Properties and Carrier Dynamics in SnO2 Nanowires. Nanotechnology 2011, 22, 285709. (225) Jarzebski, Z. M.; Marton, J. P. Physical Properties of SnO2 Materials: Ii. Electrical Properties. J. Electrochem. Soc. 1976, 123, 299C−310C. (226) Yan, H.; Yang, J.; Ma, G.; Wu, G.; Zong, X.; Lei, Z.; Shi, J.; Li, C. Visible-Light-Driven Hydrogen Production with Extremely High Quantum Efficiency on Pt−PdS/CdS Photocatalyst. J. Catal. 2009, 266, 165−168. (227) Mark, P. Ambipolar Diffusion of Free Carriers in Insulating CdS Crystals. Phys. Rev. 1965, 137, A203−A210. (228) Ebothé, J. Hole Diffusion Length and Transport Parameters of Thin CdS Films from a Schottky Barrier. J. Appl. Phys. 1986, 59, 2076−2081. (229) Waxman, A.; Henrich, V. E.; Shallcross, F. V.; Borkan, H.; Weimer, P. K. Electron Mobility Studies in Surface Space Charge

Layers in Vapor Deposited CdS Films. J. Appl. Phys. 1965, 36, 168− 175. (230) Bube, R. H.; MacDonald, H. E. Effect of Photoexcitation on the Mobility in Photoconducting Insulators. Phys. Rev. 1961, 121, 473−483. (231) Peyghambarian, N.; Fluegel, B.; Hulin, D.; Migus, A.; Joffre, M.; Antonetti, A.; Koch, S. W.; Lindberg, M. Femtosecond Optical Nonlinearities of CdSe Quantum Dots. IEEE J. Quantum Electron. 1989, 25, 2516−2522. (232) Bawendi, M. G.; Wilson, W. L.; Rothberg, L.; Carroll, P. J.; Jedju, T. M.; Steigerwald, M. L.; Brus, L. E. Electronic Structure and Photoexcited-Carrier Dynamics in Nanometer-Size CdSe Clusters. Phys. Rev. Lett. 1990, 65, 1623−1626. (233) Fowler, A. B. Photo-Hall Effect in CdSe Sintered Photoconductors. J. Phys. Chem. Solids 1961, 22, 181−188. (234) Godin, R.; Wang, Y.; Zwijnenburg, M. A.; Tang, J.; Durrant, J. R. Time-Resolved Spectroscopic Investigation of Charge Trapping in Carbon Nitrides Photocatalysts for Hydrogen Generation. J. Am. Chem. Soc. 2017, 139, 5216−5224. (235) Ye, C.; Li, J.-X.; Li, Z.-J.; Li, X.-B.; Fan, X.-B.; Zhang, L.-P.; Chen, B.; Tung, C.-H.; Wu, L.-Z. Enhanced Driving Force and Charge Separation Efficiency of Protonated g-C3N4 for Photocatalytic O2 Evolution. ACS Catal. 2015, 5, 6973−6979. (236) Ziani, A.; Nurlaela, E.; Dhawale, D. S.; Silva, D. A.; Alarousu, E.; Mohammed, O. F.; Takanabe, K. Carrier Dynamics of a VisibleLight-Responsive Ta3N5 Photoanode for Water Oxidation. Phys. Chem. Chem. Phys. 2015, 17, 2670−2677. (237) Furube, A.; Maeda, K.; Domen, K. Transient Absorption Study on Photogenerated Carrier Dynamics in Visible Light Responsive Photocatalysts GaN:ZnO. Proceedings Volume 8109, Solar Hydrogen and Nanotechnology VI 2011, 8109, No. 810904. (238) Suzuki, A.; Hirose, Y.; Oka, D.; Nakao, S.; Fukumura, T.; Ishii, S.; Sasa, K.; Matsuzaki, H.; Hasegawa, T. High-Mobility Electron Conduction in Oxynitride: Anatase Taon. Chem. Mater. 2014, 26, 976−981. (239) Patil, P. R.; Patil, P. S. Transient Photoconductivity Measurements of Ultrasonic Spray Pyrolyzed Tungsten Oxide Thin Films. Mater. Res. Bull. 2000, 35, 865−874. (240) Pesci, F. M.; Cowan, A. J.; Alexander, B. D.; Durrant, J. R.; Klug, D. R. Charge Carrier Dynamics on Mesoporous WO3 During Water Splitting. J. Phys. Chem. Lett. 2011, 2, 1900−1903. (241) Butler, M. A. Photoelectrolysis and Physical Properties of the Semiconducting Electrode WO2. J. Appl. Phys. 1977, 48, 1914−1920. (242) Miyakawa, M.; Ueda, K.; Hosono, H. Carrier Generation in Highly Oriented WO3 Films by Proton or Helium Implantation. J. Appl. Phys. 2002, 92, 2017−2022. (243) Kennedy, J. H.; Frese, K. W. Photooxidation of Water at ΑFe2O3 Electrodes. J. Electrochem. Soc. 1978, 125, 709−714. (244) Kudo, A.; Omori, K.; Kato, H. A Novel Aqueous Process for Preparation of Crystal Form-Controlled and Highly Crystalline BiVO4 Powder from Layered Vanadates at Room Temperature and Its Photocatalytic and Photophysical Properties. J. Am. Chem. Soc. 1999, 121, 11459−11467. (245) Kudo, A.; Ueda, K.; Kato, H.; Mikami, I. Photocatalytic O2 Evolution under Visible Light Irradiation on BiVO4 in Aqueous AgNO3 Solution. Catal. Lett. 1998, 53, 229−230. (246) Abdi, F. F.; Savenije, T. J.; May, M. M.; Dam, B.; van de Krol, R. The Origin of Slow Carrier Transport in BiVO4 Thin Film Photoanodes: A Time-Resolved Microwave Conductivity Study. J. Phys. Chem. Lett. 2013, 4, 2752−2757. (247) Rettie, A. J. E.; Lee, H. C.; Marshall, L. G.; Lin, J.-F.; Capan, C.; Lindemuth, J.; McCloy, J. S.; Zhou, J.; Bard, A. J.; Mullins, C. B. Combined Charge Carrier Transport and Photoelectrochemical Characterization of BiVO4 Single Crystals: Intrinsic Behavior of a Complex Metal Oxide. J. Am. Chem. Soc. 2013, 135, 11389−11396. (248) Zhong, D. K.; Choi, S.; Gamelin, D. R. Near-Complete Suppression of Surface Recombination in Solar Photoelectrolysis by “Co-Pi” Catalyst-Modified W:BiVO4. J. Am. Chem. Soc. 2011, 133, 18370−18377. FM


Chemical Reviews

Review

(249) Dong, Q. F.; Fang, Y. J.; Shao, Y. C.; Mulligan, P.; Qiu, J.; Cao, L.; Huang, J. S. Electron-Hole Diffusion Lengths > 175 μm in Solution-Grown CH3NH3PbI3 Single Crystals. Science 2015, 347, 967−970. (250) Dawlaty, J. M.; Shivaraman, S.; Chandrashekhar, M.; Rana, F.; Spencer, M. G. Measurement of Ultrafast Carrier Dynamics in Epitaxial Graphene. Appl. Phys. Lett. 2008, 92, 042116. (251) Du, X.; Skachko, I.; Barker, A.; Andrei, E. Y. Approaching Ballistic Transport in Suspended Graphene. Nat. Nanotechnol. 2008, 3, 491. (252) Zhang, Z.; Yates, J. T. Band Bending in Semiconductors: Chemical and Physical Consequences at Surfaces and Interfaces. Chem. Rev. 2012, 112, 5520−5551. (253) Zhang, L. P.; Jaroniec, M. Toward Designing SemiconductorSemiconductor Heterojunctions for Photocatalytic Applications. Appl. Surf. Sci. 2018, 430, 2−17. (254) Xu, Q.; Zhang, L.; Yu, J.; Wageh, S.; Al-Ghamdi, A. A.; Jaroniec, M. Direct Z-Scheme Photocatalysts: Principles, Synthesis, and Applications. Mater. Today 2018, 21, 1042. (255) Kumar, S. G.; Rao, K. S. R. K. Comparison of Modification Strategies Towards Enhanced Charge Carrier Separation and Photocatalytic Degradation Activity of Metal Oxide Semiconductors (TiO2WO3 and ZnO). Appl. Surf. Sci. 2017, 391, 124−148. (256) Bai, S.; Jiang, J.; Zhang, Q.; Xiong, Y. Steering Charge Kinetics in Photocatalysis: Intersection of Materials Syntheses, Characterization Techniques and Theoretical Simulations. Chem. Soc. Rev. 2015, 44, 2893−2939. (257) Bai, S.; Jiang, W.; Li, Z.; Xiong, Y. Surface and Interface Engineering in Photocatalysis. ChemNanoMat 2015, 1, 223−239. (258) Zhang, P.; Wang, T.; Chang, X.; Gong, J. Effective Charge Carrier Utilization in Photocatalytic Conversions. Acc. Chem. Res. 2016, 49, 911−921. (259) Gomathi Devi, L.; Kavitha, R. A Review on Plasmonic MetalTiO2 Composite for Generation, Trapping, Storing and Dynamic Vectorial Transfer of Photogenerated Electrons across the Schottky Junction in a Photocatalytic System. Appl. Surf. Sci. 2016, 360, 601− 622. (260) Song, S.; Cheng, B.; Wu, N.; Meng, A.; Cao, S.; Yu, J. Structure Effect of Graphene on the Photocatalytic Performance of Plasmonic Ag/Ag2CO3-RGO for Photocatalytic Elimination of Pollutants. Appl. Catal., B 2016, 181, 71−78. (261) Qi, L.; Yu, J.; Liu, G.; Wong, P. K. Synthesis and Photocatalytic Activity of Plasmonic Ag@AgCl Composite Immobilized on Titanate Nanowire Films. Catal. Today 2014, 224, 193−199. (262) Zhou, X.; Liu, G.; Yu, J.; Fan, W. Surface Plasmon ResonanceMediated Photocatalysis by Noble Metal-Based Composites under Visible Light. J. Mater. Chem. 2012, 22, 21337−21354. (263) Wang, X.; Li, S.; Ma, Y.; Yu, H.; Yu, J. H2WO4 Center Dot H2O/Ag/AgCl Composite Nanoplates: A Plasmonic Z-Scheme Visible-Light Photocatalyst. J. Phys. Chem. C 2011, 115, 14648−14655. (264) Low, J.; Yu, J.; Li, Q.; Cheng, B. Enhanced Visible-Light Photocatalytic Activity of Plasmonic Ag and Graphene Co-Modified Bi2WO6 Nanosheets. Phys. Chem. Chem. Phys. 2014, 16, 1111−1120. (265) Jiang, J.; Yu, J.; Cao, S. Au/PtO Nanoparticle-Modified g-C3N4 for Plasmon-Enhanced Photocatalytic Hydrogen Evolution under Visible Light. J. Colloid Interface Sci. 2016, 461, 56−63. (266) Yu, S.; Wilson, A. J.; Kumari, G.; Zhang, X.; Jain, P. K. Opportunities and Challenges of Solar-Energy-Driven Carbon Dioxide to Fuel Conversion with Plasmonic Catalysts. ACS Energy Letters 2017, 2, 2058−2070. (267) Madhusudan, P.; Zhang, J.; Yu, J.; Cheng, B.; Xu, D.; Zhang, J. One-Pot Template-Free Synthesis of Porous CdMoO4 Microspheres and Their Enhanced Photocatalytic Activity. Appl. Surf. Sci. 2016, 387, 202−213. (268) Lei, C. S.; Zhu, X. F.; Zhu, B. C.; Jiang, C. J.; Le, Y.; Yu, J. G. Superb Adsorption Capacity of Hierarchical Calcined Ni/Mg/Al Layered Double Hydroxides for Congo Red and Cr(VI) Ions. J. Hazard. Mater. 2017, 321, 801−811.

(269) Lei, C.; Zhu, X.; Zhu, B.; Yu, J.; Ho, W. Hierarchical NiO-SiO2 Composite Hollow Microspheres with Enhanced Adsorption Affinity Towards Congo Red in Water. J. Colloid Interface Sci. 2016, 466, 238− 246. (270) He, R.; Zhang, J.; Yu, J.; Cao, S. Room-Temperature Synthesis of BiOI with Tailorable (0 0 1) Facets and Enhanced Photocatalytic Activity. J. Colloid Interface Sci. 2016, 478, 201−208. (271) Chen, F.; Liu, S. W.; Yu, J. G. Efficient Removal of Gaseous Formaldehyde in Air Using Hierarchical Titanate Nanospheres with in Situ Amine Functionalization. Phys. Chem. Chem. Phys. 2016, 18, 18161−18168. (272) He, R.; Cao, S.; Yu, J.; Yang, Y. Microwave-Assisted Solvothermal Synthesis of Bi4O5I2 Hierarchical Architectures with High Photocatalytic Performance. Catal. Today 2016, 264, 221−228. (273) Chen, M.; Huang, Y.; Lee, S. C. Salt-Assisted Synthesis of Hollow Bi2WO6 Microspheres with Superior Photocatalytic Activity for No Removal. Chin. J. Catal. 2017, 38, 348−356. (274) Yang, J.; Wang, D.; Han, H.; Li, C. Roles of Cocatalysts in Photocatalysis and Photoelectrocatalysis. Acc. Chem. Res. 2013, 46, 1900−1909. (275) Ran, J.; Zhang, J.; Yu, J.; Jaroniec, M.; Qiao, S. Z. EarthAbundant Cocatalysts for Semiconductor-Based Photocatalytic Water Splitting. Chem. Soc. Rev. 2014, 43, 7787−7812. (276) Liu, C.; Zhang, Y.; Dong, F.; Reshak, A. H.; Ye, L.; Pinna, N.; Zeng, C.; Zhang, T.; Huang, H. Chlorine Intercalation in Graphitic Carbon Nitride for Efficient Photocatalysis. Appl. Catal., B 2017, 203, 465−474. (277) Chen, W.; Chu, M.; Gao, L.; Mao, L.; Yuan, J.; Shangguan, W. Ni(OH)2 Loaded on TaON for Enhancing Photocatalytic Water Splitting Activity under Visible Light Irradiation. Appl. Surf. Sci. 2015, 324, 432−437. (278) Xu, Y.; Xu, R. Nickel-Based Cocatalysts for Photocatalytic Hydrogen Production. Appl. Surf. Sci. 2015, 351, 779−793. (279) Zou, X.; Zhang, Y. Noble Metal-Free Hydrogen Evolution Catalysts for Water Splitting. Chem. Soc. Rev. 2015, 44, 5148−5180. (280) Yu, J.; Ran, J. Facile Preparation and Enhanced Photocatalytic H2-Production Activity of Cu(OH)2 Cluster Modified TiO2. Energy Environ. Sci. 2011, 4, 1364−1371. (281) Ran, J.; Yu, J.; Jaroniec, M. Ni(OH)2 Modified CdS Nanorods for Highly Efficient Visible-Light-Driven Photocatalytic H2 Generation. Green Chem. 2011, 13, 2708−2713. (282) Zhou, X.; Jin, J.; Zhu, X. J.; Huang, J.; Yu, J. G.; Wong, W. Y.; Wong, W. K. New Co(OH)2/CdS Nanowires for Efficient Visible Light Photocatalytic Hydrogen Production. J. Mater. Chem. A 2016, 4, 5282−5287. (283) Yu, J.; Hai, Y.; Cheng, B. Enhanced Photocatalytic H2Production Activity of TiO2 by Ni(OH)2Cluster Modification. J. Phys. Chem. C 2011, 115, 4953−4958. (284) Yu, J.; Zhang, J.; Liu, S. Ion-Exchange Synthesis and Enhanced Visible-Light Photoactivity of CuS/ZnS Nanocomposite Hollow Spheres. J. Phys. Chem. C 2010, 114, 13642−13649. (285) Wen, J.; Xie, J.; Shen, R.; Li, X.; Luo, X.; Zhang, H.; Zhang, A.; Bi, G. Markedly Enhanced Visible-Light Photocatalytic H2 Generation over g-C3N4 Nanosheets Decorated by Robust Nickel Phosphide (Ni12P5) Cocatalysts. Dalton Trans. 2017, 46, 1794−1802. (286) He, K.; Xie, J.; Yang, Z.; Shen, R.; Fang, Y.; Ma, S.; Chen, X.; Li, X. Earth-Abundant WC Nanoparticles as an Active Noble-MetalFree Cocatalyst for Highly Boosted Photocatalytic H2 Production over g-C3N4 Nanosheets under Visible Light. Catal. Sci. Technol. 2017, 7, 1193−1202. (287) Chen, F.; Yang, H.; Wang, X.; Yu, H. Facile Synthesis and Enhanced Photocatalytic H2-Evolution Performance of NiS2-Modified g-C3N4 Photocatalysts. Chin. J. Catal. 2017, 38, 296−304. (288) Ma, S.; Xu, X. M.; Xie, J.; Li, X. Improved Visible-Light Photocatalytic H2 Generation over CdS Nanosheets Decorated by NiS2 and Metallic Carbon Black as Dual Earth-Abundant Cocatalysts. Chin. J. Catal. 2017, 38, 1970−1980. (289) Ma, B. J.; Zhang, R. S.; Lin, K. Y.; Liu, H. X.; Wang, X. Y.; Liu, W. Y.; Zhan, H. J. Large-Scale Synthesis of Noble-Metal-Free FN


Chemical Reviews

Review

Phosphide/CdS Composite Photocatalysts for Enhanced H2 Evolution under Visible Light Irradiation. Chin. J. Catal. 2018, 39, 527−533. (290) Wang, Q. Z.; Niu, T. J.; Wang, L.; Huang, J. W.; She, H. D. NiFe Layered Double-Hydroxide Nanoparticles for Efficiently Enhancing Performance of BiVO4 Photoanode in Photoelectrochemical Water Splitting. Chin. J. Catal. 2018, 39, 613−618. (291) Xu, W. C.; Wang, H. X. Earth-Abundant Amorphous Catalysts for Electrolysis of Water. Chin. J. Catal. 2017, 38, 991−1005. (292) Liang, Q. S.; Shi, F. B.; Xiao, X. F.; Wu, X. F.; Huang, K. K.; Feng, S. H. In Situ Growth of CoP Nanoparticles Anchored on Black Phosphorus Nanosheets for Enhanced Photocatalytic Hydrogen Production. ChemCatChem 2018, 10, 2179−2183. (293) Chai, B.; Liu, C.; Wang, C. L.; Yan, J. T.; Ren, Z. D. Photocatalytic Hydrogen Evolution Activity over MoS2/ZnIn2S4 Microspheres. Chin. J. Catal. 2017, 38, 2067−2075. (294) Jiang, D. C.; Zhu, L.; Irfan, R. M.; Zhang, L.; Du, P. W. Integrating Noble-Metal-Free NiS Cocatalyst with a Semiconductor Heterojunction Composite for Efficient Photocatalytic H2 Production in Water under Visible Light. Chin. J. Catal. 2017, 38, 2102−2109. (295) Di, T.; Zhu, B.; Zhang, J.; Cheng, B.; Yu, J. Enhanced Photocatalytic H2 Production on CdS Nanorod Using CobaltPhosphate as Oxidation Cocatalyst. Appl. Surf. Sci. 2016, 389, 775− 782. (296) Low, J.; Yu, J.; Jaroniec, M.; Wageh, S.; Al-Ghamdi, A. A. Heterojunction Photocatalysts. Adv. Mater. 2017, 29, 1601694. (297) Moniz, S. J. A.; Shevlin, S. A.; Martin, D. J.; Guo, Z.-X.; Tang, J. Visible-Light Driven Heterojunction Photocatalysts for Water Splitting - a Critical Review. Energy Environ. Sci. 2015, 8, 731−759. (298) Wang, H.; Zhang, L.; Chen, Z.; Hu, J.; Li, S.; Wang, Z.; Liu, J.; Wang, X. Semiconductor Heterojunction Photocatalysts: Design, Construction, and Photocatalytic Performances. Chem. Soc. Rev. 2014, 43, 5234−5244. (299) Fu, J. W.; Yu, J. G.; Jiang, C. J.; Cheng, B. g-C3N4-Based Heterostructured Photocatalysts. Adv. Energy Mater. 2018, 8, 1701503. (300) Du, H.; Liu, Y. N.; Shen, C. C.; Xu, A. W. Nanoheterostructured Photocatalysts for Improving Photocatalytic Hydrogen Production. Chin. J. Catal. 2017, 38, 1295−1306. (301) Zhang, Z.; Huang, Y.; Liu, K.; Guo, L.; Yuan, Q.; Dong, B. Multichannel-Improved Charge-Carrier Dynamics in Well-Designed Hetero-Nanostructural Plasmonic Photocatalysts toward Highly Efficient Solar-to-Fuels Conversion. Adv. Mater. 2015, 27, 5906−5914. (302) Samsudin, E. M.; Hamid, S. B. A.; Juan, J. C.; Basirun, W. J.; Kandjani, A. E. Surface Modification of Mixed-Phase Hydrogenated TiO2 and Corresponding Photocatalytic Response. Appl. Surf. Sci. 2015, 359, 883−896. (303) Dai, J.; Yang, J.; Wang, X.; Zhang, L.; Li, Y. Enhanced VisibleLight Photocatalytic Activity for Selective Oxidation of Amines into Imines over TiO2 (B)/Anatase Mixed-Phase Nanowires. Appl. Surf. Sci. 2015, 349, 343−352. (304) Xu, F.; Xiao, W.; Cheng, B.; Yu, J. Direct Z-Scheme Anatase/ Rutile Bi-Phase Nanocomposite TiO2 Nanofiber Photocatalyst with Enhanced Photocatalytic H2-Production Activity. Int. J. Hydrogen Energy 2014, 39, 15394−15402. (305) Yu, J.; Xiong, J.; Cheng, B.; Liu, S. Fabrication and Characterization of Ag−TiO2 Multiphase Nanocomposite Thin Films with Enhanced Photocatalytic Activity. Appl. Catal., B 2005, 60, 211−221. (306) Wang, X.; Shen, S.; Feng, Z.; Li, C. Time-Resolved Photoluminescence of Anatase/Rutile TiO2 Phase Junction Revealing Charge Separation Dynamics. Chin. J. Catal. 2016, 37, 2059−2068. (307) Qiu, Y.; Ouyang, F. Fabrication of TiO2 Hierarchical Architecture Assembled by Nanowires with Anatase/ TiO2(B) Phase-Junctions for Efficient Photocatalytic Hydrogen Production. Appl. Surf. Sci. 2017, 403, 691−698. (308) Wang, Y. L.; Zhang, W.; Wang, Z. H.; Cao, Y. M.; Feng, J. M.; Wang, Z. L.; Ma, Y. Fabrication of TiO2(B)/Anatase Heterophase Junctions in Nanowires Via a Surface-Preferred Phase Transformation Process for Enhanced Photocatalytic Activity. Chin. J. Catal. 2018, 39, 1500−1510.

(309) Devaraji, P.; Jo, W. K. Two-Dimensional Mixed Phase LeafTi1‑xCuxO2 Sheets Synthesized Based on a Natural Leaf Template for Increased Photocatalytic H2Evolution. ChemCatChem 2018, 10, 3813−3823. (310) Hu, J. Y.; Zhang, S. S.; Cao, Y. H.; Wang, H. J.; Yu, H.; Peng, F. Novel Highly Active Anatase/Rutile TiO2 Photocatalyst with Hydrogenated Heterophase Interface Structures for Photoelectrochemical Water Splitting into Hydrogen. ACS Sustainable Chem. Eng. 2018, 6, 10823−10832. (311) Li, P.; Zhou, Y.; Zhao, Z.; Xu, Q.; Wang, X.; Xiao, M.; Zou, Z. Hexahedron Prism-Anchored Octahedronal CeO2Crystal Facet-Based Homojunction Promoting Efficient Solar Fuel Synthesis. J. Am. Chem. Soc. 2015, 137, 9547−9550. (312) Jiang, G.; Wei, M.; Yuan, S.; Chang, Q. Efficient Photocatalytic Reductive Dechlorination of 4-Chlorophenol to Phenol on {001}/ {101} Facets Co-Exposed TiO2 Nanocrystals. Appl. Surf. Sci. 2016, 362, 418−426. (313) Huang, M.; Yu, J.; Hu, Q.; Su, W.; Fan, M.; Li, B.; Dong, L. Preparation and Enhanced Photocatalytic Activity of Carbon Nitride/ Titania(001 Vs 101 Facets)/Reduced Graphene Oxide(g-C3N4/ TiO2/RGO) Hybrids under Visible Light. Appl. Surf. Sci. 2016, 389, 1084−1093. 3+

(314) Lu, D.; Zhang, G.; Wan, Z. Visible-Light-Driven g-C3N4/Ti TiO2 Photocatalyst Co-Exposed {001} and {101} Facets and Its Enhanced Photocatalytic Activities for Organic Pollutant Degradation and Cr(VI) Reduction. Appl. Surf. Sci. 2015, 358, 223−230. (315) Zhang, J.; Zhang, L. L.; Shi, Y. X.; Xu, G. L.; Zhang, E. P.; Wang, H. B.; Kong, Z.; Xi, J. H.; Ji, Z. G. Anatase Tio2 Nanosheets with Coexposed {101} and {001} Facets Coupled with Ultrathin SnS2 Nanosheets as a Face-to-Face N-P-N Dual Heterojunction Photocatalyst for Enhancing Photocatalytic Activity. Appl. Surf. Sci. 2017, 420, 839−848. (316) Zhao, Y.; Huang, X.; Tan, X.; Yu, T.; Li, X.; Yang, L.; Wang, S. Fabrication of BiOBr Nanosheets@ TiO2 Nanobelts P-N Junction Photocatalysts for Enhanced Visible-Light Activity. Appl. Surf. Sci. 2016, 365, 209−217. (317) Yang, S.; Xu, D.; Chen, B.; Luo, B.; Yan, X.; Xiao, L.; Shi, W. Synthesis and Visible-Light-Driven Photocatalytic Activity of P-N Heterojunction Ag2O/NaTaO3 Nanocubes. Appl. Surf. Sci. 2016, 383, 214−221. (318) Sun, B.; Zhou, G.; Gao, T.; Zhang, H.; Yu, H. Nio Nanosheet/ TiO2 Nanorod-Constructed P-N Heterostructures for Improved Photocatalytic Activity. Appl. Surf. Sci. 2016, 364, 322−331. (319) Li, Y.; Wang, B.; Liu, S.; Duan, X.; Hu, Z. Synthesis and Characterization of Cu2O/TiO2 Photocatalysts for H2 Evolution from Aqueous Solution with Different Scavengers. Appl. Surf. Sci. 2015, 324, 736−744. (320) Duo, F.; Wang, Y.; Mao, X.; Zhang, X.; Wang, Y.; Fan, C. A BiPO4/BiOCl Heterojunction Photocatalyst with Enhanced ElectronHole Separation and Excellent Photocatalytic Performance. Appl. Surf. Sci. 2015, 340, 35−42. (321) Tian, N.; Huang, H.; Zhang, Y. Mixed-Calcination Synthesis of CdWO4/g-C3N4 Heterojunction with Enhanced Visible-Light-Driven Photocatalytic Activity. Appl. Surf. Sci. 2015, 358, 343−349. (322) Feng, Y.; Yan, X.; Liu, C.; Hong, Y.; Zhu, L.; Zhou, M.; Shi, W. Hydrothermal Synthesis of CdS/Bi2MoO6 Heterojunction Photocatalysts with Excellent Visible-Light-Driven Photocatalytic Performance. Appl. Surf. Sci. 2015, 353, 87−94. (323) Cao, C.; Xiao, L.; Chen, C.; Cao, Q. Synthesis of Novel Cu2O/ BiOCl Heterojunction Nanocomposites and Their Enhanced Photocatalytic Activity under Visible Light. Appl. Surf. Sci. 2015, 357, 1171− 1179. (324) Guo, X.; Chen, Y. B.; Qin, Z. X.; Su, J. Z.; Guo, L. J. FacetSelective Growth of Cadmium Sulfide Nanorods on Zinc Oxide Microrods: Intergrowth Effect for Improved Photocatalytic Performance. ChemCatChem 2018, 10, 153−158. (325) Wang, B.; Zhang, J. T.; Huang, F. Enhanced Visible Light Photocatalytic H2 Evolution of Metal-Free g-C3N4/SiC Heterostructured Photocatalysts. Appl. Surf. Sci. 2017, 391, 449−456. FO


Chemical Reviews

Review

(326) Teng, W.; Tan, X. J.; Li, X. Y.; Tang, Y. B. Novel Ag3PO4/ MoO3 P-N Heterojunction with Enhanced Photocatalytic Activity and Stability under Visible Light Irradiation. Appl. Surf. Sci. 2017, 409, 250−260. (327) Zhou, P.; Yu, J.; Jaroniec, M. All-Solid-State Z-Scheme Photocatalytic Systems. Adv. Mater. 2014, 26, 4920−4935. (328) Zhu, C.; Zhang, L.; Jiang, B.; Zheng, J.; Hu, P.; Li, S.; Wu, M.; Wu, W. Fabrication of Z-Scheme Ag3PO4/MoS2 Composites with Enhanced Photocatalytic Activity and Stability for Organic Pollutant Degradation. Appl. Surf. Sci. 2016, 377, 99−108. (329) Luo, J.; Zhou, X.; Ma, L.; Xu, X. Rational Construction of ZScheme Ag2CrO4/g-C3N4 Composites with Enhanced Visible-Light Photocatalytic Activity. Appl. Surf. Sci. 2016, 390, 357−367. (330) Li, J.; Yuan, H.; Zhu, Z. Improved Photoelectrochemical Performance of Z-Scheme g-C3N4/Bi2O3/BiPO4 Heterostructure and Degradation Property. Appl. Surf. Sci. 2016, 385, 34−41. (331) Cui, M.; Yu, J.; Lin, H.; Wu, Y.; Zhao, L.; He, Y. In-Situ Preparation of Z-Scheme AgI/Bi5O7I Hybrid and Its Excellent Photocatalytic Activity. Appl. Surf. Sci. 2016, 387, 912−920. (332) Liu, X.; Jin, A. L.; Jia, Y. S.; Xia, T. L.; Deng, C. X.; Zhu, M. H.; Chen, C. F.; Chen, X. S. Synergy of Adsorption and Visible-Light Photocatalytic Degradation of Methylene Blue by a Bifunctional ZScheme Heterojunction of WO3/g-C3N4. Appl. Surf. Sci. 2017, 405, 359−371. (333) He, R. A.; Zhou, J. Q.; Fu, H. Q.; Zhang, S. Y.; Jiang, C. J. Room-Temperature in Situ Fabrication of Bi2O3/g-C3N4 Direct ZScheme Photocatalyst with Enhanced Photocatalytic Activity. Appl. Surf. Sci. 2018, 430, 273−282. (334) Hu, T. P.; Li, P. F.; Zhang, J. F.; Liang, C. H.; Dai, K. Highly Efficient Direct Z-Scheme WO3/CdS-Diethylenetriamine Photocatalyst and Its Enhanced Photocatalytic H2 Evolution under Visible Light Irradiation. Appl. Surf. Sci. 2018, 442, 20−29. (335) He, K.; Xie, J.; Luo, X.; Wen, J.; Ma, S.; Li, X.; Fang, Y.; Zhang, X. Enhanced Visible Light Photocatalytic H2 Production over ZScheme g-C3N4Nansheets/WO3 Nanorods Nanocomposites Loaded with Ni(OH)XCocatalysts. Chin. J. Catal. 2017, 38, 240−252. (336) Yu, W.; Chen, J.; Shang, T.; Chen, L.; Gu, L.; Peng, T. Direct Z-Scheme g-C3N4/WO3 Photocatalyst with Atomically Defined Junction for H2 Production. Appl. Catal., B 2017, 219, 693−704. (337) Xu, Q.; Zhu, B.; Jiang, C.; Cheng, B.; Yu, J. Constructing 2D/ 2D Fe2O3/g-C3N4 Direct Z-Scheme Photocatalysts with Enhanced H2Generation Performance. Solar RRL 2018, 2, 1800006. (338) Pan, L.; Zhang, J.; Jia, X.; Ma, Y.-H.; Zhang, X.; Wang, L.; Zou, J.-J. Highly Efficient Z-Scheme WO3‑X Quantum Dots/TiO2 for Photocatalytic Hydrogen Generation. Chin. J. Catal. 2017, 38, 253− 259. (339) Tang, H.; Fu, Y.; Chang, S.; Xie, S.; Tang, G. Construction of Ag3PO4/Ag2MoO4 Z-Scheme Heterogeneous Photocatalyst for the Remediation of Organic Pollutants. Chin. J. Catal. 2017, 38, 337−347. (340) Fu, Y. H.; Li, Z. J.; Liu, Q. Q.; Yang, X. F.; Tang, H. Construction of Carbon Nitride and MoS2 Quantum Dot 2D/0D Hybrid Photocatalyst: Direct Z-Scheme Mechanism for Improved Photocatalytic Activity. Chin. J. Catal. 2017, 38, 2160−2170. (341) Xia, P. F.; Zhu, B. C.; Cheng, B.; Yu, J. G.; Xu, J. S. 2D/2D gC3N4/MnO2Nanocomposite as a Direct Z-Scheme Photocatalyst for Enhanced Photocatalytic Activity. ACS Sustainable Chem. Eng. 2018, 6, 965−973. (342) Ma, Y. J.; Bian, Y.; Liu, Y.; Zhu, A. Q.; Wu, H.; Cui, H.; Chu, D. W.; Pan, J. Construction of Z-Scheme System for Enhanced Photocatalytic H2 Evolution Based on CdS Quantum Dots/CeO2 Nanorods Heterojunction. ACS Sustainable Chem. Eng. 2018, 6, 2552− 2562. (343) Lv, J. L.; Zhang, J. F.; Liu, J.; Li, Z.; Dai, K.; Liang, C. H. Bi Spr-Promoted Z-Scheme Bi2MoO6/CdS-Diethylenetriamine Composite with Effectively Enhanced Visible Light Photocatalytic Hydrogen Evolution Activity and Stability. ACS Sustainable Chem. Eng. 2018, 6, 696−706. (344) Lu, D. Z.; Wang, H. M.; Zhao, X. N.; Kondamareddy, K. K.; Ding, J. Q.; Li, C. H.; Fang, P. F. Highly Efficient Visible-Light-

Induced Photoactivity of Z-Scheme g-C3N4/Ag/MoS2 Ternary Photocatalysts for Organic Pollutant Degradation and Production of Hydrogen. ACS Sustainable Chem. Eng. 2017, 5, 1436−1445. (345) Xu, F. Y.; Zhang, L. Y.; Cheng, B.; Yu, J. G. Direct Z-Scheme TiO2/NiS Core-Shell Hybrid Nanofibers with Enhanced Photocatalytic H2-Production Activity. ACS Sustainable Chem. Eng. 2018, 6, 12291−12298. (346) Song, S.; Meng, A.; Jiang, S.; Cheng, B.; Jiang, C. Construction of Z-Scheme Ag2CO3/N-Doped Graphene Photocatalysts with Enhanced Visible-Light Photocatalytic Activity by Tuning the Nitrogen Species. Appl. Surf. Sci. 2017, 396, 1368−1374. (347) Meng, A. Y.; Zhu, B. C.; Zhong, B.; Zhang, L. Y.; Cheng, B. Direct Z-Scheme TiO2/CdS Hierarchical Photocatalyst for Enhanced Photocatalytic H2-Production Activity. Appl. Surf. Sci. 2017, 422, 518− 527. (348) Li, J.; Zhang, M.; Li, Q.; Yang, J. Enhanced Visible Light Activity on Direct Contact Z-Scheme g-C3N4-TiO2 Photocatalyst. Appl. Surf. Sci. 2017, 391, 184−193. (349) Low, J.; Yu, J.; Ho, W. Graphene-Based Photocatalysts for CO2 Reduction to Solar Fuel. J. Phys. Chem. Lett. 2015, 6, 4244−4251. (350) Xiang, Q.; Cheng, B.; Yu, J. Graphene-Based Photocatalysts for Solar-Fuel Generation. Angew. Chem., Int. Ed. 2015, 54, 11350−11366. (351) Cao, S.; Yu, J. Carbon-Based H2-Production Photocatalytic Materials. J. Photochem. Photobiol., C 2016, 27, 72−99. (352) Low, J.; Cheng, B.; Yu, J.; Jaroniec, M. Carbon-Based TwoDimensional Layered Materials for Photocatalytic CO2 Reduction to Solar Fuels. Energy Storage Materials 2016, 3, 24−35. (353) Chen, S. Y.; Wang, L. W. Thermodynamic Oxidation and Reduction Potentials of Photocatalytic Semiconductors in Aqueous Solution. Chem. Mater. 2012, 24, 3659−3666. (354) Bard, A. J.; Parsons, R.; Jordan, J. Standard Potentials in Aqueous Solution; CRC Press, 1985; Vol. 6. (355) Yang, X.; Cui, H.; Li, Y.; Qin, J.; Zhang, R.; Tang, H. Fabrication of Ag3PO4-Graphene Composites with Highly Efficient and Stable Visible Light Photocatalytic Performance. ACS Catal. 2013, 3, 363−369. (356) Zhang, D.; Tang, H.; Wang, Y.; Wu, K.; Huang, H.; Tang, G.; Yang, J. Synthesis and Characterization of Graphene Oxide Modified Agbr Nanocomposites with Enhanced Photocatalytic Activity and Stability under Visible Light. Appl. Surf. Sci. 2014, 319, 306−311. (357) Li, J.; Wei, L.; Yu, C.; Fang, W.; Xie, Y.; Zhou, W.; Zhu, L. Preparation and Characterization of Graphene Oxide/Ag2CO3 Photocatalyst and Its Visible Light Photocatalytic Activity. Appl. Surf. Sci. 2015, 358, 168−174. (358) Reddy, D. A.; Lee, S.; Choi, J.; Park, S.; Ma, R.; Yang, H.; Kim, T. K. Green Synthesis of AgI-Reduced Graphene Oxide Nanocomposites: Toward Enhanced Visible-Light Photocatalytic Activity for Organic Dye Removal. Appl. Surf. Sci. 2015, 341, 175−184. (359) Kudo, A.; Miseki, Y. Heterogeneous Photocatalyst Materials for Water Splitting. Chem. Soc. Rev. 2009, 38, 253−278. (360) Gu, J.; Yan, Y.; Krizan, J. W.; Gibson, Q. D.; Detweiler, Z. M.; Cava, R. J.; Bocarsly, A. B. P-Type CuRhO2 as a Self-Healing Photoelectrode for Water Reduction under Visible Light. J. Am. Chem. Soc. 2014, 136, 830−833. (361) Park, J. E.; Hu, Y.; Krizan, J. W.; Gibson, Q. D.; Tayvah, U. T.; Selloni, A.; Cava, R. J.; Bocarsly, A. B. Stable Hydrogen Evolution from an AgRhO2 Photocathode under Visible Light. Chem. Mater. 2018, 30, 2574−2582. (362) Chen, S. S.; Shen, S.; Liu, G. J.; Qi, Y.; Zhang, F. X.; Li, C. Interface Engineering of a CoOx/Ta3N5 Photocatalyst for Unprecedented Water Oxidation Performance under Visible-Light-Irradiation. Angew. Chem., Int. Ed. 2015, 54, 3047−3051. (363) Yu, H.; Xu, L.; Wang, P.; Wang, X.; Yu, J. Enhanced Photoinduced Stability and Photocatalytic Activity of AgBr Photocatalyst by Surface Modification of Fe(III) Cocatalyst. Appl. Catal., B 2014, 144, 75−82. (364) Yu, H.; Liu, L.; Wang, X.; Wang, P.; Yu, J.; Wang, Y. The Dependence of Photocatalytic Activity and Photoinduced Self-Stability FP


Chemical Reviews

Review

of Photosensitive AgI Nanoparticles. Dalton Trans. 2012, 41, 10405− 10411. (365) Wang, X.; Li, S.; Yu, H.; Yu, J.; Liu, S. Ag2O as a New VisibleLight Photocatalyst: Self-Stability and High Photocatalytic Activity. Chem. - Eur. J. 2011, 17, 7777−7780. (366) Tian, J.; Liu, R.; Wang, G.; Xu, Y.; Wang, X.; Yu, H. Dependence of Metallic Ag on the Photocatalytic Activity and Photoinduced Stability of Ag/AgCl Photocatalyst. Appl. Surf. Sci. 2014, 319, 324−331. (367) Yang, K.-H.; Hsu, S.-C.; Huang, M. H. Facet-Dependent Optical and Photothermal Properties of Au@Ag-Cu2O Core-Shell Nanocrystals. Chem. Mater. 2016, 28, 5140−5146. (368) Kuo, C.-H.; Yang, Y.-C.; Gwo, S.; Huang, M. H. FacetDependent and Au Nanocrystal-Enhanced Electrical and Photocatalytic Properties of Au-Cu2O Core-Shell Heterostructures. J. Am. Chem. Soc. 2011, 133, 1052−1057. (369) Pan, Y.; Deng, S.; Polavarapu, L.; Gao, N.; Yuan, P.; Sow, C. H.; Xu, Q.-H. Plasmon-Enhanced Photocatalytic Properties of Cu2O Nanowire-Au Nanoparticle Assemblies. Langmuir 2012, 28, 12304− 12310. (370) Yao, W.; Li, F.-L.; Li, H.-X.; Lang, J.-P. Fabrication of Hollow Cu2O@CuO-Supported Au-Pd Alloy Nanoparticles with High Catalytic Activity through the Galvanic Replacement Reaction. J. Mater. Chem. A 2015, 3, 4578−4585. (371) Peng, Y.; Ji, J.; Chen, D. Ultrasound Assisted Synthesis of ZnO/Reduced Graphene Oxide Composites with Enhanced Photocatalytic Activity and Anti-Photocorrosion. Appl. Surf. Sci. 2015, 356, 762−768. (372) Huang, M.; Yu, J.; Deng, C.; Huang, Y.; Fan, M.; Li, B.; Tong, Z.; Zhang, F.; Dong, L. 3D Nanospherical CdxZn1‑xS/Reduced Graphene Oxide Composites with Superior Photocatalytic Activity and Photocorrosion Resistance. Appl. Surf. Sci. 2016, 365, 227−239. (373) Chen, J.; Zhang, F.; Zhao, Y.-L.; Guo, Y.-C.; Gong, P.; Li, Z.Q.; Qian, H.-S. Facile Synthesis of CdS/C Core-Shell Nanospheres with Ultrathin Carbon Layer for Enhanced Photocatalytic Properties and Stability. Appl. Surf. Sci. 2016, 362, 126−131. (374) Cai, L.; Xiong, X.; Liang, N.; Long, Q. Highly Effective and Stable Ag3PO4-WO3/Mwcnts Photocatalysts for Simultaneous Cr(VI) Reduction and Orange Ii Degradation under Visible Light Irradiation. Appl. Surf. Sci. 2015, 353, 939−948. (375) Wang, H.; Li, J.; Huo, P.; Yan, Y.; Guan, Q. Preparation of Ag2O/Ag2CO3/Mwnts Composite Photocatalysts for Enhancement of Ciprofloxacin Degradation. Appl. Surf. Sci. 2016, 366, 1−8. (376) Miao, J.; Xie, A.; Li, S.; Huang, F.; Cao, J.; Shen, Y. A Novel Reducing Graphene/Polyaniline/Cuprous Oxide Composite Hydrogel with Unexpected Photocatalytic Activity for the Degradation of Congo Red. Appl. Surf. Sci. 2016, 360, 594−600. (377) Cai, J.; Liu, W.; Li, Z. One-Pot Self-Assembly of Cu2O/RGO Composite Aerogel for Aqueous Photocatalysis. Appl. Surf. Sci. 2015, 358, 146−151. (378) Li, J.; Fang, W.; Yu, C.; Zhou, W.; Zhu, L.; Xie, Y. Ag-Based Semiconductor Photocatalysts in Environmental Purification. Appl. Surf. Sci. 2015, 358, 46−56. (379) Liu, H.; Lv, T.; Wu, X.; Zhu, C.; Zhu, Z. Preparation and Enhanced Photocatalytic Activity of CdS@RGO Core-Shell Structural Microspheres. Appl. Surf. Sci. 2014, 305, 242−246. (380) Sun, L.; Wang, G.; Hao, R.; Han, D.; Cao, S. Solvothermal Fabrication and Enhanced Visible Light Photocatalytic Activity of Cu2O-Reduced Graphene Oxide Composite Microspheres for Photodegradation of Rhodamine B. Appl. Surf. Sci. 2015, 358, 91−99. (381) Tian, J.; Liu, R. Y.; Zhen, L.; Yu, C. L.; Liu, M. Boosting the Photocatalytic Performance of Ag2CO3 Crystals in Phenol Degradation Via Coupling with Trace N-Cqds. Chin. J. Catal. 2017, 38, 1999− 2008. (382) Radich, J. G.; Krenselewski, A. L.; Zhu, J.; Kamat, P. V. Is Graphene a Stable Platform for Photocatalysis? Mineralization of Reduced Graphene Oxide with Uv-Irradiated TiO2 Nanoparticles. Chem. Mater. 2014, 26, 4662−4668.

(383) Akhavan, O.; Abdolahad, M.; Esfandiar, A.; Mohatashamifar, M. Photodegradation of Graphene Oxide Sheets by TiO2 Nanoparticles after a Photocatalytic Reduction. J. Phys. Chem. C 2010, 114, 12955−12959. (384) Tang, Y.; Hu, X.; Liu, C. Perfect Inhibition of CdS Photocorrosion by Graphene Sheltering Engineering on TiO2 Nanotube Array for Highly Stable Photocatalytic Activity. Phys. Chem. Chem. Phys. 2014, 16, 25321−25329. (385) Zhai, J.; Yu, H.; Li, H.; Sun, L.; Zhang, K.; Yang, H. VisibleLight Photocatalytic Activity of Graphene Oxide-Wrapped Bi2WO6 Hierarchical Microspheres. Appl. Surf. Sci. 2015, 344, 101−106. (386) Amaranatha Reddy, D.; Ma, R.; Choi, M. Y.; Kim, T. K. Reduced Graphene Oxide Wrapped ZnS-Ag2S Ternary Composites Synthesized Via Hydrothermal Method: Applications in Photocatalyst Degradation of Organic Pollutants. Appl. Surf. Sci. 2015, 324, 725− 735. (387) Xu, X.; Gao, Z.; Cui, Z.; Liang, Y.; Li, Z.; Zhu, S.; Yang, X.; Ma, J. Synthesis of Cu2O Octadecahedron/TiO2 Quantum Dot Heterojunctions with High Visible Light Photocatalytic Activity and High Stability. ACS Appl. Mater. Interfaces 2016, 8, 91−101. (388) Liu, Y.; Zhang, B.; Luo, L.; Chen, X.; Wang, Z.; Wu, E.; Su, D.; Huang, W. TiO2/Cu2O Core/Ultrathin Shell Nanorods as Efficient and Stable Photocatalysts for Water Reduction. Angew. Chem., Int. Ed. 2015, 54, 15260−15265. (389) Liu, L.; Yang, W.; Sun, W.; Li, Q.; Shang, J. K. Creation of Cu2O@TiO2 Composite Photocatalysts with P-N Heterojunctions Formed on Exposed Cu2O Facets, Their Energy Band Alignment Study, and Their Enhanced Photocatalytic Activity under Illumination with Visible Light. ACS Appl. Mater. Interfaces 2015, 7, 1465−1476. (390) Liu, J.; Wen, M.; Chen, H.; Li, J.; Wu, Q.-S. Assembly of TiO2on-Cu2O Nanocubes with Narrow-Band Cu2O-Induced Visible-LightEnhanced Photocatalytic Activity. ChemPlusChem 2014, 79, 298−303. (391) Lalitha, K.; Sadanandam, G.; Kumari, V. D.; Subrahmanyam, M.; Sreedhar, B.; Hebalkar, N. Y. Highly Stabilized and Finely Dispersed Cu2O/TiO2A Promising Visible Sensitive Photocatalyst for Continuous Production of Hydrogen from Glycerol:Water Mixtures. J. Phys. Chem. C 2010, 114, 22181−22189. (392) Ahmad Beigi, A.; Fatemi, S.; Salehi, Z. Synthesis of Nanocomposite CdS/TiO2 and Investigation of Its Photocatalytic Activity for CO2 Reduction to C and CH4 under Visible Light Irradiation. J. CO2 Util. 2014, 7, 23−29. (393) Xiao, F.-X.; Miao, J.; Wang, H.-Y.; Liu, B. Self-Assembly of Hierarchically Ordered CdS Quantum Dots-TiO2 Nanotube Array Heterostructures as Efficient Visible Light Photocatalysts for Photoredox Applications. J. Mater. Chem. A 2013, 1, 12229−12238. (394) Tian, F.; Hou, D.; Hu, F.; Xie, K.; Qiao, X.; Li, D. Pouous TiO2Nanofibers Decorated CdS Nanoparticles by Silar Method for Enhanced Visible-Light-Driven Photocatalytic Activity. Appl. Surf. Sci. 2017, 391, 295−302. (395) Yang, G.; Yang, B.; Xiao, T.; Yan, Z. One-Step Solvothermal Synthesis of Hierarchically Porous Nanostructured CdS/TiO 2 Heterojunction with Higher Visible Light Photocatalytic Activity. Appl. Surf. Sci. 2013, 283, 402−410. (396) Fujishima, M.; Nakabayashi, Y.; Takayama, K.; Kobayashi, H.; Tada, H. High Coverage Formation of CdS Quantum Dots on TiO2 by the Photocatalytic Growth of Preformed Seeds. J. Phys. Chem. C 2016, 120, 17365−17371. (397) Pan, X.; Xu, Y.-J. Graphene-Templated Bottom-up Fabrication of Ultralarge Binary CdS-TiO2 Nanosheets for Photocatalytic Selective Reduction. J. Phys. Chem. C 2015, 119, 7184−7194. (398) Ma, K.; Yehezkeli, O.; Domaille, D. W.; Funke, H. H.; Cha, J. N. Enhanced Hydrogen Production from DNA-Assembled Z-Scheme TiO2-CdS Photocatalyst Systems. Angew. Chem., Int. Ed. 2015, 54, 11490−11494. (399) Wei, Y.; Jiao, J.; Zhao, Z.; Liu, J.; Li, J.; Jiang, G.; Wang, Y.; Duan, A. Fabrication of Inverse Opal TiO2-Supported Au@CdS CoreShell Nanoparticles for Efficient Photocatalytic CO2 Conversion. Appl. Catal., B 2015, 179, 422−432. FQ


Chemical Reviews

Review

(400) Wei, Y.; Jiao, J.; Zhao, Z.; Zhong, W.; Li, J.; Liu, J.; Jiang, G.; Duan, A. 3D Ordered Macroporous TiO2-Supported Pt@CdS CoreShell Nanoparticles: Design, Synthesis and Efficient Photocatalytic Conversion of CO2 with Water to Methane. J. Mater. Chem. A 2015, 3, 11074−11085. (401) Dong, W.; Pan, F.; Xu, L.; Zheng, M.; Sow, C. H.; Wu, K.; Xu, G. Q.; Chen, W. Facile Synthesis of CdS@TiO2 Core-Shell Nanorods with Controllable Shell Thickness and Enhanced Photocatalytic Activity under Visible Light Irradiation. Appl. Surf. Sci. 2015, 349, 279−286. (402) Liu, S.; Zhang, N.; Tang, Z.-R.; Xu, Y.-J. Synthesis of OneDimensional CdS@TiO2 Core-Shell Nanocomposites Photocatalyst for Selective Redox: The Dual Role of TiO2 Shell. ACS Appl. Mater. Interfaces 2012, 4, 6378−6385. (403) Butburee, T.; Bai, Y.; Pan, J.; Zong, X.; Sun, C.; Liu, G.; Wang, L. Step-Wise Controlled Growth of Metal@TiO2 Core-Shells with Plasmonic Hot Spots and Their Photocatalytic Properties. J. Mater. Chem. A 2014, 2, 12776−12784. (404) Tanaka, A.; Fuku, K.; Nishi, T.; Hashimoto, K.; Kominami, H. Functionalization of Au/TiO2 Plasmonic Photocatalysts with Pd by Formation of a Core-Shell Structure for Effective Dechlorination of Chlorobenzene under Irradiation of Visible Light. J. Phys. Chem. C 2013, 117, 16983−16989. (405) Wu, X.-F.; Song, H.-Y.; Yoon, J.-M.; Yu, Y.-T.; Chen, Y.-F. Synthesis of Core-Shell Au@TiO2 Nanoparticles with Truncated Wedge-Shaped Morphology and Their Photocatalytic Properties. Langmuir 2009, 25, 6438−6447. (406) Ji, L.; McDaniel, M. D.; Wang, S. J.; Posadas, A. B.; Li, X. H.; Huang, H. Y.; Lee, J. C.; Demkov, A. A.; Bard, A. J.; Ekerdt, J. G.; et al. A Silicon-Based Photocathode for Water Reduction with an Epitaxial SrTiO3 Protection Layer and a Nanostructured Catalyst. Nat. Nanotechnol. 2015, 10, 84−90. (407) Yu, H.; Chen, F.; Chen, F.; Wang, X. In Situ SelfTransformation Synthesis of g-C3N4-Modified CdS Heterostructure with Enhanced Photocatalytic Activity. Appl. Surf. Sci. 2015, 358, 385− 392. (408) Liu, L.; Qi, Y.; Hu, J.; Liang, Y.; Cui, W. Efficient Visible-Light Photocatalytic Hydrogen Evolution and Enhanced Photostability of Core@Shell Cu2O@ g-C3N4 Octahedra. Appl. Surf. Sci. 2015, 351, 1146−1154. (409) Zhang, J.; Wang, Y.; Jin, J.; Zhang, J.; Lin, Z.; Huang, F.; Yu, J. Efficient Visible-Light Photocatalytic Hydrogen Evolution and Enhanced Photostability of Core/Shell CdS/ g-C3N4 Nanowires. ACS Appl. Mater. Interfaces 2013, 5, 10317−10324. (410) Pijpers, J. J. H.; Winkler, M. T.; Surendranath, Y.; Buonassisi, T.; Nocera, D. G. Light-Induced Water Oxidation at Silicon Electrodes Functionalized with a Cobalt Oxygen-Evolving Catalyst. Proc. Natl. Acad. Sci. U. S. A. 2011, 108, 10056−10061. (411) Kim, J. H.; Magesh, G.; Kang, H. J.; Banu, M.; Kim, J. H.; Lee, J.; Lee, J. S. Carbonate-Coordinated Cobalt Co-Catalyzed BiVO4/ WO3 Composite Photoanode Tailored for CO2 Reduction to Fuels. Nano Energy 2015, 15, 153−163. (412) Kanan, M. W.; Nocera, D. G. In Situ Formation of an Oxygen-

(416) Le Formal, F.; Tetreault, N.; Cornuz, M.; Moehl, T.; Gratzel, M.; Sivula, K. Passivating Surface States on Water Splitting Hematite Photoanodes with Alumina Overlayers. Chem. Sci. 2011, 2, 737−743. (417) Song, G.; Xin, F.; Chen, J.; Yin, X. Photocatalytic Reduction of CO2 in Cyclohexanol on CdS-TiO2 Heterostructured Photocatalyst. Appl. Catal., A 2014, 473, 90−95. (418) Zhai, J.; Tao, X.; Pu, Y.; Zeng, X.-F.; Chen, J.-F. Core/Shell Structured ZnO/SiO2 Nanoparticles: Preparation, Characterization and Photocatalytic Property. Appl. Surf. Sci. 2010, 257, 393−397. (419) Chen, J.-J.; Wu, J. C. S.; Wu, P. C.; Tsai, D. P. Improved Photocatalytic Activity of Shell-Isolated Plasmonic Photocatalyst Au@ SiO2/TiO2 by Promoted Lspr. J. Phys. Chem. C 2012, 116, 26535− 26542. (420) Yoo, J. B.; Yoo, H. J.; Lim, B. W.; Lee, K. H.; Kim, M. H.; Kang, D.; Hur, N. H. Controlled Synthesis of Monodisperse SiO2TiO2 Microspheres with a Yolk-Shell Structure as Effective Photocatalysts. ChemSusChem 2012, 5, 2334−2340. (421) Zhang, X.; Zhu, Y.; Yang, X.; Wang, S.; Shen, J.; Lin, B.; Li, C. Enhanced Visible Light Photocatalytic Activity of Interlayer-Isolated Triplex Ag@SiO2@TiO2 Core-Shell Nanoparticles. Nanoscale 2013, 5, 3359−3366. (422) Yao, X.; Liu, X. One-Pot Synthesis of Ag/AgCl@SiO2 CoreShell Plasmonic Photocatalyst in Natural Geothermal Water for Efficient Photocatalysis under Visible Light. J. Mol. Catal. A: Chem. 2014, 393, 30−38. (423) Nadrah, P.; Gaberscek, M.; Sever Skapin, A. Selective Degradation of Model Pollutants in the Presence of Core@Shell TiO2@SiO2 Photocatalyst. Appl. Surf. Sci. 2017, 405, 389−394. (424) Lian, Z.; Xu, P.; Wang, W.; Zhang, D.; Xiao, S.; Li, X.; Li, G. C60-Decorated CdS/TiO2 Mesoporous Architectures with Enhanced Photostability and Photocatalytic Activity for H2 Evolution. ACS Appl. Mater. Interfaces 2015, 7, 4533−4540. (425) Luo, G.; Jiang, X.; Li, M.; Shen, Q.; Zhang, L.; Yu, H. Facile Fabrication and Enhanced Photocatalytic Performance of Ag/AgCl/ RGo Heterostructure Photocatalyst. ACS Appl. Mater. Interfaces 2013, 5, 2161−2168. (426) Tong, R.; Liu, C.; Xu, Z.; Kuang, Q.; Xie, Z.; Zheng, L. Efficiently Enhancing Visible Light Photocatalytic Activity of Faceted TiO2 Nanocrystals by Synergistic Effects of Core-Shell Structured Au@CdS Nanoparticles and Their Selective Deposition. ACS Appl. Mater. Interfaces 2016, 8, 21326−21333. (427) Hu, Z.; Yu, J. C. Pt3Co-Loaded CdS and TiO2 for Photocatalytic Hydrogen Evolution from Water. J. Mater. Chem. A 2013, 1, 12221−12228. (428) Liu, S.; Yang, M.-Q.; Xu, Y.-J. Surface Charge Promotes the Synthesis of Large, Flat Structured Graphene-(CdS Nanowire)-TiO2 Nanocomposites as Versatile Visible Light Photocatalysts. J. Mater. Chem. A 2014, 2, 430−440. (429) Wang, P.; Ming, T.; Wang, G.; Wang, X.; Yu, H.; Yu, J. Cocatalyst Modification and Nanonization of Ag/AgCl Photocatalyst with Enhanced Photocatalytic Performance. J. Mol. Catal. A: Chem. 2014, 381, 114−119. (430) Park, H.; Kim, Y. K.; Choi, W. Reversing CdS Preparation Order and Its Effects on Photocatalytic Hydrogen Production of CdS/ Pt-TiO2 Hybrids under Visible Light. J. Phys. Chem. C 2011, 115, 6141−6148. (431) Liu, S.; Yu, J.; Jaroniec, M. Tunable Photocatalytic Selectivity of Hollow TiO2 Microspheres Composed of Anatase Polyhedra with Exposed {001} Facets. J. Am. Chem. Soc. 2010, 132, 11914−11916. (432) Dai, Y.; Song, Y.; Tu, X.; Jiang, Y.; Yuan, Y. Sequential ShapeSelective Adsorption and Photocatalytic Transformation of Acrylonitrile Production Wastewater. Water Res. 2015, 85, 216−225. (433) Calza, P.; Pazé, C.; Pelizzetti, E.; Zecchina, A. Shape-Selective Photocatalytic Transformation of Phenols in an Aqueous Medium. Chem. Commun. 2001, 2130−2131. (434) Llabres I Xamena, F. X.; Calza, P.; Lamberti, C.; Prestipino, C.; Damin, A.; Bordiga, S.; Pelizzetti, E.; Zecchina, A. Enhancement of the Ets-10 Titanosilicate Activity in the Shape-Selective Photocatalytic

2+

Evolving Catalyst in Neutral Water Containing Phosphate and Co . Science 2008, 321, 1072−1075. (413) Chang, X.; Wang, T.; Zhang, P.; Zhang, J.; Li, A.; Gong, J. Enhanced Surface Reaction Kinetics and Charge Separation of P-N Heterojunction Co3O4/BiVO4 Photoanodes. J. Am. Chem. Soc. 2015, 137, 8356−8359. (414) Zhong, M.; Hisatomi, T.; Kuang, Y.; Zhao, J.; Liu, M.; Iwase, A.; Jia, Q.; Nishiyama, H.; Minegishi, T.; Nakabayashi, M.; et al. Surface Modification of CoOx Loaded BiVO4 Photoanodes with Ultrathin P-Type Nio Layers for Improved Solar Water Oxidation. J. Am. Chem. Soc. 2015, 137, 5053−5060. (415) Sun, K. N.; Li, Y. Y.; Zhang, Q. G.; Wang, L.; Zhang, J. L.; Zhou, X. Theoretical Insight into the Distinct Photocatalytic Activity between NiOx and CoOx Loaded Ta3N5Photocatalyst. Appl. Surf. Sci. 2017, 405, 289−297. FR


Chemical Reviews

Review

Degradation of Large Aromatic Molecules by Controlled Defect Production. J. Am. Chem. Soc. 2003, 125, 2264−2271. (435) Dong, G.; Ho, W.; Wang, C. Selective Photocatalytic N2 Fixation Dependent on g-C3N4 Induced by Nitrogen Vacancies. J. Mater. Chem. A 2015, 3, 23435−23441. (436) Shiraishi, Y.; Saito, N.; Hirai, T. Adsorption-Driven Photocatalytic Activity of Mesoporous Titanium Dioxide. J. Am. Chem. Soc. 2005, 127, 12820−12822. (437) Xiang, Q.; Yu, J.; Jaroniec, M. Tunable Photocatalytic Selectivity of TiO2 Films Consisted of Flower-Like Microspheres with Exposed {001} Facets. Chem. Commun. 2011, 47, 4532−4534. (438) Sofianou, M.-V.; Psycharis, V.; Boukos, N.; Vaimakis, T.; Yu, J.; Dillert, R.; Bahnemann, D.; Trapalis, C. Tuning the Photocatalytic Selectivity of TiO2 Anatase Nanoplates by Altering the Exposed Crystal Facets Content. Appl. Catal., B 2013, 142, 761−768. (439) Liu, S.; Liu, C.; Wang, W.; Cheng, B.; Yu, J. Unique Photocatalytic Oxidation Reactivity and Selectivity of TiO2-Graphene Nanocomposites. Nanoscale 2012, 4, 3193−3200. (440) Cropek, D.; Kemme, P. A.; Makarova, O. V.; Chen, L. X.; Rajh, T. Selective Photocatalytic Decomposition of Nitrobenzene Using Surface Modified TiO2 Nanoparticles. J. Phys. Chem. C 2008, 112, 8311−8318. (441) Yurdakal, S.; Palmisano, G.; Loddo, V.; Augugliaro, V.; Palmisano, L. Nanostructured Rutile TiO2 for Selective Photocatalytic Oxidation of Aromatic Alcohols to Aldehydes in Water. J. Am. Chem. Soc. 2008, 130, 1568−1569. (442) Yurdakal, S.; Palmisano, G.; Loddo, V.; Alagoez, O.; Augugliaro, V.; Palmisano, L. Selective Photocatalytic Oxidation of 4-Substituted Aromatic Alcohols in Water with Rutile TiO2 Prepared at Room Temperature. Green Chem. 2009, 11, 510−516. (443) Ikeda, S.; Ikoma, Y.; Kobayashi, H.; Harada, T.; Torimoto, T.; Ohtani, B.; Matsumura, M. Encapsulation of Titanium(Iv) Oxide Particles in Hollow Silica for Size-Selective Photocatalytic Reactions. Chem. Commun. 2007, 3753−3755. (444) Ikeda, S.; Kobayashi, H.; Ikoma, Y.; Harada, T.; Torimoto, T.; Ohtani, B.; Matsumura, M. Size-Selective Photocatalytic Reactions by Titanium(Iv) Oxide Coated with a Hollow Silica Shell in Aqueous Solutions. Phys. Chem. Chem. Phys. 2007, 9, 6319−6326. (445) Shen, X.; Zhu, L.; Liu, G.; Yu, H.; Tang, H. Enhanced Photocatalytic Degradation and Selective Removal of Nitrophenols by Using Surface Molecular Imprinted Titania. Environ. Sci. Technol. 2008, 42, 1687−1692. (446) Zeng, M.; Chai, Z.; Deng, X.; Li, Q.; Feng, S.; Wang, J.; Xu, D. Core-Shell CdS@ZIF-8 Structures for Improved Selectivity in Photocatalytic H2 Generation from Formic Acid. Nano Res. 2016, 9, 2729−2734. (447) Tsuji, E.; Taguchi, Y.; Aoki, Y.; Hashimoto, T.; Skeldon, P.; Thompson, G. E.; Habazaki, H. Morphological Control of Anodic Crystalline TiO2 Nanochannel Films for Use in Size-Selective Photocatalytic Decomposition of Organic Molecules. Appl. Surf. Sci. 2014, 301, 500−507. (448) Lai, C.; Wang, M.-M.; Zeng, G.-M.; Liu, Y.-G.; Huang, D.-L.; Zhang, C.; Wang, R.-Z.; Xu, P.; Cheng, M.; Huang, C.; et al. Synthesis of Surface Molecular Imprinted TiO2/Graphene Photocatalyst and Its Highly Efficient Photocatalytic Degradation of Target Pollutant under Visible Light Irradiation. Appl. Surf. Sci. 2016, 390, 368−376. (449) Lu, Z.; Zhu, Z.; Wang, D.; Ma, Z.; Shi, W.; Yan, Y.; Zhao, X.; Dong, H.; Yang, L.; Hua, Z. Specific Oriented Recognition of a New Stable ICTX@Mfa with Retrievability for Selective Photocatalytic Degrading of Ciprofloxacin. Catal. Sci. Technol. 2016, 6, 1367−1377. (450) He, M. Q.; Bao, L. L.; Sun, K. Y.; Zhao, D. X.; Li, W. B.; Xia, J. X.; Li, H. M. Synthesis of Molecularly Imprinted Polypyrrole/ Titanium Dioxide Nanocomposites and Its Selective Photocatalytic Degradation of Rhodamine B under Visible Light Irradiation. eXPRESS Polym. Lett. 2014, 8, 850−861. (451) Liu, Y.; Zhu, J.; Liu, X.; Li, H. A Convenient Approach of MIP/Co-TiO2 Nanocomposites with Highly Enhanced Photocatalytic Activity and Selectivity under Visible Light Irradiation. RSC Adv. 2016, 6, 69326−69333.

(452) Wang, Y.; Lu, Z.; Zhu, Z.; Zhao, X.; Gao, N.; Wang, D.; Hua, Z.; Yan, Y.; Huo, P.; Song, M. Enhanced Selective Photocatalytic Properties of a Novel Magnetic Retrievable Imprinted ZnFe2O4/PPy Composite with Specific Recognition Ability. RSC Adv. 2016, 6, 51877−51887. (453) Xu, S.; Lu, H.; Chen, L.; Wang, X. Molecularly Imprinted TiO2 Hybridized Magnetic Fe3O4 Nanoparticles for Selective Photocatalytic Degradation and Removal of Estrone. RSC Adv. 2014, 4, 45266− 45274. (454) Zhu, Z.; Lu, Z.; Zhao, X.; Yan, Y.; Shi, W.; Wang, D.; Yang, L.; Lin, X.; Hua, Z.; Liu, Y. Surface Imprinting of a g-C3N4 Photocatalyst for Enhanced Photocatalytic Activity and Selectivity Towards Photodegradation of 2-Mercaptobenzothiazole. RSC Adv. 2015, 5, 40726−40736. (455) Sano, T.; Kutsuna, S.; Negishi, N.; Takeuchi, K. Effect of PdPhotodeposition over TiO2 on Product Selectivity in Photocatalytic Degradation of Vinyl Chloride Monomer. J. Mol. Catal. A: Chem. 2002, 189, 263−270. (456) Zhang, F.; Pi, Y.; Cui, J.; Yang, Y.; Zhang, X.; Guan, N. Unexpected Selective Photocatalytic Reduction of Nitrite to Nitrogen on Silver-Doped Titanium Dioxide. J. Phys. Chem. C 2007, 111, 3756− 3761. (457) Yu, X.; Shi, J.; Feng, L.; Li, C.; Wang, L. A Three-Dimensional BiOBr/RGO Heterostructural Aerogel with Enhanced and Selective Photocatalytic Properties under Visible Light. Appl. Surf. Sci. 2017, 396, 1775−1782. (458) Kominami, H.; Nakaseko, T.; Shimada, Y.; Furusho, A.; Inoue, H.; Murakami, S.; Kera, Y.; Ohtani, B. Selective Photocatalytic Reduction of Nitrate to Nitrogen Molecules in an Aqueous Suspension of Metal-Loaded Titanium(Iv) Oxide Particles. Chem. Commun. 2005, 2933−2935. (459) Zhang, F. X.; Jin, R. C.; Chen, J. X.; Shao, C. Z.; Gao, W. L.; Li, L. D.; Guan, N. J. High Photocatalytic Activity and Selectivity for Nitrogen in Nitrate Reduction on Ag/TiO2 Catalyst with Fine Silver Clusters. J. Catal. 2005, 232, 424−431. (460) Ye, L.; Liu, X.; Zhao, Q.; Xie, H.; Zan, L. Dramatic Visible Light Photocatalytic Activity of MnOx-BiOI Heterogeneous Photocatalysts and the Selectivity of the Cocatalyst. J. Mater. Chem. A 2013, 1, 8978−8983. (461) Michal, R.; Dworniczek, E.; Caplovicova, M.; Monfort, O.; Lianos, P.; Caplovic, L.; Plesch, G. Photocatalytic Properties and Selective Antimicrobial Activity of TiO2(Eu)/CuO Nanocomposite. Appl. Surf. Sci. 2016, 371, 538−546. (462) Tanaka, A.; Hashimoto, K.; Kominami, H. Selective Photocatalytic Oxidation of Aromatic Alcohols to Aldehydes in an Aqueous Suspension of Gold Nanoparticles Supported on Cerium(Iv) Oxide under Irradiation of Green Light. Chem. Commun. 2011, 47, 10446− 10448. (463) Shiraishi, Y.; Sakamoto, H.; Fujiwara, K.; Ichikawa, S.; Hirai, T. Selective Photocatalytic Oxidation of Aniline to Nitrosobenzene by Pt Nanoparticles Supported on TiO2 under Visible Light Irradiation. ACS Catal. 2014, 4, 2418−2425. (464) Furukawa, S.; Tamura, A.; Shishido, T.; Teramura, K.; Tanaka, T. Solvent-Free Aerobic Alcohol Oxidation Using Cu/Nb2O5Green and Highly Selective Photocatalytic System. Appl. Catal., B 2011, 110, 216−220. (465) Bi, J.; Zhou, Z.; Chen, M.; Liang, S.; He, Y.; Zhang, Z.; Wu, L. Plasmonic Au/CdMoO4 Photocatalyst: Influence of Surface Plasmon Resonance for Selective Photocatalytic Oxidation of Benzylic Alcohol. Appl. Surf. Sci. 2015, 349, 292−298. (466) Zhao, J.; Zheng, Z.; Bottle, S.; Chou, A.; Sarina, S.; Zhu, H. Highly Efficient and Selective Photocatalytic Hydroamination of Alkynes by Supported Gold Nanoparticles Using Visible Light at Ambient Temperature. Chem. Commun. 2013, 49, 2676−2678. (467) Su, R.; Kesavan, L.; Jensen, M. M.; Tiruvalam, R.; He, Q.; Dimitratos, N.; Wendt, S.; Glasius, M.; Kiely, C. J.; Hutchings, G. J.; et al. Selective Photocatalytic Oxidation of Benzene for the Synthesis of Phenol Using Engineered Au-Pd Alloy Nanoparticles Supported on Titanium Dioxide. Chem. Commun. 2014, 50, 12612−12614. FS


Chemical Reviews

Review

(468) Feng, W.; Wu, G.; Li, L.; Guan, N. Solvent-Free Selective Photocatalytic Oxidation of Benzyl Alcohol over Modified TiO2. Green Chem. 2011, 13, 3265−3272. (469) Hao, C.-H.; Guo, X.-N.; Pan, Y.-T.; Chen, S.; Jiao, Z.-F.; Yang, H.; Guo, X.-Y. Visible-Light-Driven Selective Photocatalytic Hydrogenation of Cinnamaldehyde over Au/Sic Catalysts. J. Am. Chem. Soc. 2016, 138, 9361−9364. (470) Kraeutler, B.; Bard, A. J. Heterogeneous Photocatalytic Preparation of Supported Catalysts. Photodeposition of Platinum on Titanium Dioxide Powder and Other Substrates. J. Am. Chem. Soc. 1978, 100, 4317−4318. (471) Bard, A. J. Photoelectrochemistry and Heterogeneous PhotoCatalysis at Semiconductors. J. Photochem. 1979, 10, 59−75. (472) Bard, A. J. Photoelectrochemistry. Science 1980, 207, 139−144. (473) Wen, F.; Li, C. Hybrid Artificial Photosynthetic Systems Comprising Semiconductors as Light Harvesters and Biomimetic Complexes as Molecular Cocatalysts. Acc. Chem. Res. 2013, 46, 2355− 2364. (474) Jiang, Z.; Isaacs, M. A.; Huang, Z. W.; Shangguan, W. F.; Deng, Y. F.; Lee, A. F. Active Site Elucidation and Optimization in Pt CoCatalysts for Photocatalytic Hydrogen Production over Titania. ChemCatChem 2017, 9, 4268−4274. (475) Zhang, J. L.; Lu, Y.; Ge, L.; Han, C. C.; Li, Y. J.; Gao, Y. Q.; Li, S. S.; Xu, H. Novel Aupd Bimetallic Alloy Decorated 2D BiVO4 Nanosheets with Enhanced Photocatalytic Performance under Visible Light Irradiation. Appl. Catal., B 2017, 204, 385−393. (476) Han, C. C.; Lu, Y.; Zhang, J. L.; Ge, L.; Li, Y. J.; Chen, C. F.; Xin, Y. J.; Wu, L. E.; Fang, S. M. Novel PtCo Alloy Nanoparticle Decorated 2D g-C3N4 Nanosheets with Enhanced Photocatalytic Activity for H-2 Evolution under Visible Light Irradiation. J. Mater. Chem. A 2015, 3, 23274−23282. (477) Zhang, G. G.; Li, G. S.; Wang, X. C. Surface Modification of Carbon Nitride Polymers by Core-Shell Nickel/Nickel Oxide Cocatalysts for Hydrogen Evolution Photocatalysis. ChemCatChem 2015, 7, 2864−2870. (478) Lu, X.; Xie, J.; Liu, S.-y.; Adamski, A.; Chen, X.; Li, X. LowCost Ni3B/Ni(OH)2 as an Ecofriendly Hybrid Cocatalyst for Remarkably Boosting Photocatalytic H2 Production over g-C3N4 Nanosheets. ACS Sustainable Chem. Eng. 2018, 6, 13140−13150. (479) Bi, G.; Wen, J.; Li, X.; Liu, W.; Xie, J.; Fang, Y.; Zhang, W. Efficient Visible-Light Photocatalytic H2 Evolution over Metal-Free gC3N4 Co-Modified Via Robust Acetylene Black and Ni(OH)2 as Dual Co-Catalysts. RSC Adv. 2016, 6, 31497−31506. (480) Chang, K.; Hai, X.; Ye, J. H. Transition Metal Disulfides as Noble-Metal-Alternative Co-Catalysts for Solar Hydrogen Production. Adv. Energy Mater. 2016, 6, 1502555. (481) He, K.; Xie, J.; Li, M.; Li, X. In Situ One-Pot Fabrication of gC3N4 Nanosheets/NiS Cocatalyst Heterojunction with Intimate Interfaces for Efficient Visible Light Photocatalytic H2 Generation. Appl. Surf. Sci. 2018, 430, 208−217. (482) Wen, J.; Xie, J.; Yang, Z.; Shen, R.; Li, H.; Luo, X.; Chen, X.; Li, X. Fabricating the Robust g-C3N4 Nanosheets/Carbons/Nis Multiple Heterojunctions for Enhanced Photocatalytic H2 Generation: An Insight into the Tri-Functional Roles of Nanocarbons. ACS Sustainable Chem. Eng. 2017, 5, 2224−2236. (483) Ma, S.; Xie, J.; Wen, J.; He, K.; Li, X.; Liu, W.; Zhang, X. Constructing 2D Layered Hybrid CdS Nanosheets/MoS2 Heterojunctions for Enhanced Visible-Light Photocatalytic H2 Generation. Appl. Surf. Sci. 2017, 391, 580−591. (484) Zhao, H.; Zhang, H. Z.; Cui, G. W.; Dong, Y. M.; Wang, G. L.; Jiang, P. P.; Wu, X. M.; Zhao, N. A Photochemical Synthesis Route to Typical Transition Metal Sulfides as Highly Efficient Cocatalyst for Hydrogen Evolution: From the Case of NiS/ g-C3N4. Appl. Catal., B 2018, 225, 284−290. (485) Nguyen, Q. T.; Nguyen, P. D.; Nguyen, D. N.; Truong, Q. D.; Chi, T. T. K.; Ung, T. T. D.; Honma, I.; Liem, N. Q.; Tran, P. D. Novel Amorphous Molybdenum Selenide as an Efficient Catalyst for Hydrogen Evolution Reaction. ACS Appl. Mater. Interfaces 2018, 10, 8659−8665.

(486) Hou, Y.; Qiu, M.; Nam, G.; Kim, M. G.; Zhang, T.; Liu, K. J.; Zhuang, X. D.; Cho, J.; Yuan, C.; Feng, X. L. Integrated Hierarchical Cobalt Sulfide/Nickel Selenide Hybrid Nanosheets as an Efficient Three-Dimensional Electrode for Electrochemical and Photoelectrochemical Water Splitting. Nano Lett. 2017, 17, 4202−4209. (487) Cao, S.; Wang, C. J.; Fu, W. F.; Chen, Y. Metal Phosphides as Co-Catalysts for Photocatalytic and Photoelectrocatalytic Water Splitting. ChemSusChem 2017, 10, 4306−4323. (488) Shen, R.; Liu, W.; Ren, D.; Xie, J.; Li, X. Co1.4Ni0.6P Cocatalysts Modified Metallic Carbon Black/ g-C3N4 Nanosheet Schottky Heterojunctions for Active and Durable Photocatalytic H2Production. Appl. Surf. Sci. 2019, 466, 393−400. (489) Shen, R.; Xie, J.; Zhang, H.; Zhang, A.; Chen, X.; Li, X. Enhanced Solar Fuel H2 Generation over g-C3N4 Nanosheet Photocatalysts by the Synergetic Effect of Noble Metal-Free Co2P Cocatalyst and the Environmental Phosphorylation Strategy. ACS Sustainable Chem. Eng. 2018, 6, 816−826. (490) Shen, R.; Xie, J.; Lu, X.; Chen, X.; Li, X. Bifunctional Cu3P Decorated g-C3N4 Nanosheets as a Highly Active and Robust VisibleLight Photocatalyst for H2 Production. ACS Sustainable Chem. Eng. 2018, 6, 4026−4036. (491) Li, S. S.; Wang, L.; Liu, S.; Xu, B. R.; Xiao, N.; Gao, Y. Q.; Song, W. Y.; Ge, L.; Liu, J. In Situ Synthesis of Strongly Coupled Co2P-CdS Nanohybrids: An Effective Strategy to Regulate Photocatalytic Hydrogen Evolution Activity. ACS Sustainable Chem. Eng. 2018, 6, 9940−9950. (492) Dai, D. S.; Wang, L.; Xiao, N.; Li, S. S.; Xu, H.; Liu, S.; Xu, B. R.; Lv, D.; Gao, Y. Q.; Song, W. Y.; et al. In-Situ Synthesis of Ni2P CoCatalyst Decorated Zn0.5Cd0.5S Nanorods for High Quantum-Yield Photocatalytic Hydrogen Production under Visible Light Irradiation. Appl. Catal., B 2018, 233, 194−201. (493) Dai, D. S.; Xu, H.; Ge, L.; Han, C. C.; Gao, Y. Q.; Li, S. S.; Lu, Y. In-Situ Synthesis of CoP Co-Catalyst Decorated Zn0.5Cd0.5 s Photocatalysts with Enhanced Photocatalytic Hydrogen Production Activity under Visible Light Irradiation. Appl. Catal., B 2017, 217, 429−436. (494) Zhao, H.; Wang, J. W.; Dong, Y. M.; Jiang, P. P. Noble-MetalFree Iron Phosphide Cocatalyst Loaded Graphitic Carbon Nitride as an Efficient and Robust Photocatalyst for Hydrogen Evolution under Visible Light Irradiation. ACS Sustainable Chem. Eng. 2017, 5, 8053− 8060. (495) Dong, Y. M.; Kong, L. G.; Wang, G. L.; Jiang, P. P.; Zhao, N.; Zhang, H. Z. Photochemical Synthesis of CoxP as Cocatalyst for Boosting Photocatalytic H2 Production Via Spatial Charge Separation. Appl. Catal., B 2017, 211, 245−251. (496) Dong, Y. M.; Kong, L. G.; Jiang, P. P.; Wang, G. L.; Zhao, N.; Zhang, H. Z.; Tang, B. A General Strategy to Fabricate NixP as Highly Efficient Cocatalyst Via Photoreduction Deposition for Hydrogen Evolution. ACS Sustainable Chem. Eng. 2017, 5, 6845−6853. (497) Wu, M.; Zhang, J.; Liu, C. X.; Gong, Y. S.; Wang, R.; He, B. B.; Wang, H. W. Rational Design and Fabrication of Noble-Metal-Free NixP Cocatalyst Embedded 3D N-TiO2/g-C3N4 Heterojunctions with Enhanced Photocatalytic Hydrogen Evolution. ChemCatChem 2018, 10, 3069−3077. (498) Guo, Q.; Liang, F.; Gao, X. Y.; Gan, Q. C.; Li, X. B.; Li, J.; Lin, Z. S.; Tung, C. H.; Wu, L. Z. Metallic Co2C: A Promising Co-Catalyst to Boost Photocatalytic Hydrogen Evolution of Colloidal Quantum Dots. ACS Catal. 2018, 8, 5890−5895. (499) Chen, H. L.; Jiang, D. C.; Sun, Z. J.; Irfan, R. M.; Zhang, L.; Du, P. W. Cobalt Nitride as an Efficient Cocatalyst on CdS Nanorods for Enhanced Photocatalytic Hydrogen Production in Water. Catal. Sci. Technol. 2017, 7, 1515−1522. (500) Sun, Z. J.; Chen, H. L.; Zhang, L.; Lu, D. P.; Du, P. W. Enhanced Photocatalytic H2 Production on Cadmium Sulfide Photocatalysts Using Nickel Nitride as a Novel Cocatalyst. J. Mater. Chem. A 2016, 4, 13289−13295. (501) Chen, L.; Huang, H. J.; Zheng, Y. H.; Sun, W. H.; Zhao, Y.; Francis, P. S.; Wang, X. X. Noble-Metal-Free Ni3N/g-C3N4 PhotoFT


Chemical Reviews

Review

catalysts with Enhanced Hydrogen Production under Visible Light Irradiation. Dalton Trans. 2018, 47, 12188−12196. (502) Zhang, W.; Lai, W.; Cao, R. Energy-Related Small Molecule Activation Reactions: Oxygen Reduction and Hydrogen and Oxygen Evolution Reactions Catalyzed by Porphyrin- and Corrole-Based Systems. Chem. Rev. 2017, 117, 3717−3797. (503) Shi, Y.; Zhang, B. Recent Advances in Transition Metal Phosphide Nanomaterials: Synthesis and Applications in Hydrogen Evolution Reaction. Chem. Soc. Rev. 2016, 45, 1529−1541. (504) Zhang, W. Y.; Gao, W.; Zhang, X. Q.; Li, Z.; Lu, G. X. Surface Spintronics Enhanced Photo-Catalytic Hydrogen Evolution: Mechanisms, Strategies, Challenges and Future. Appl. Surf. Sci. 2018, 434, 643−668. (505) Li, R. Latest Progress in Hydrogen Production from Solar Water Splitting Via Photocatalysis, Photoelectrochemical, and Photovoltaic-Photoelectrochemical Solutions. Chin. J. Catal. 2017, 38, 5−12. (506) Christoforidis, K. C.; Fornasiero, P. Photocatalytic Hydrogen Production: A Rift into the Future Energy Supply. ChemCatChem 2017, 9, 1523−1544. (507) Hao, J. H.; Shi, W. D. Transition Metal (Mo, Fe, Co, and Ni)Based Catalysts for Electrochemical CO2 Reduction. Chin. J. Catal. 2018, 39, 1157−1166. (508) Duan, X. C.; Xu, J. T.; Wei, Z. X.; Ma, J. M.; Guo, S. J.; Wang, S. Y.; Liu, H. K.; Dou, S. X. Metal-Free Carbon Materials for CO2 Electrochemical Reduction. Adv. Mater. 2017, 29, 1701784. (509) Zhang, L.; Zhao, Z. J.; Gong, J. L. Nanostructured Materials for Heterogeneous Electrocatalytic CO2 Reduction and Their Related Reaction Mechanisms. Angew. Chem., Int. Ed. 2017, 56, 11326−11353. (510) Chen, X. Z.; Li, N.; Kong, Z. Z.; Ong, W. J.; Zhao, X. J. Photocatalytic Fixation of Nitrogen to Ammonia: State-of-the-Art Advancements and Future Prospects. Mater. Horiz. 2018, 5, 9−27. (511) Li, R. G. Photocatalytic Nitrogen Fixation: An Attractive Approach for Artificial Photocatalysis. Chin. J. Catal. 2018, 39, 1180− 1188. (512) Chen, J. G.; Crooks, R. M.; Seefeldt, L. C.; Bren, K. L.; Bullock, R. M.; Darensbourg, M. Y.; Holland, P. L.; Hoffman, B.; Janik, M. J.; Jones, A. K.; et al. Inorganic Chemistry Beyond Fossil Fuel-Driven Nitrogen Transformations. Science 2018, 360, No. eaar6611. (513) Kulkarni, A.; Siahrostami, S.; Patel, A.; Norskov, J. K. Understanding Catalytic Activity Trends in the Oxygen Reduction Reaction. Chem. Rev. 2018, 118, 2302−2312. (514) Kong, J. F.; Cheng, W. L. Recent Advances in the Rational Design of Electrocatalysts Towards the Oxygen Reduction Reaction. Chin. J. Catal. 2017, 38, 951−969. (515) Gewirth, A. A.; Varnell, J. A.; DiAscro, A. M. Nonprecious Metal Catalysts for Oxygen Reduction in Heterogeneous Aqueous Systems. Chem. Rev. 2018, 118, 2313−2339. (516) Wang, N.; Zheng, H. Q.; Zhang, W.; Cao, R. Mononuclear First-Row Transition-Metal Complexes as Molecular Catalysts for Water Oxidation. Chin. J. Catal. 2018, 39, 228−244. (517) Hunter, B. M.; Gray, H. B.; Muller, A. M. Earth-Abundant Heterogeneous Water Oxidation Catalysts. Chem. Rev. 2016, 116, 14120−14136. (518) Blakemore, J. D.; Crabtree, R. H.; Brudvig, G. W. Molecular Catalysts for Water Oxidation. Chem. Rev. 2015, 115, 12974−13005. (519) Peng, L. S.; Shah, S. S. A.; Wei, Z. D. Recent Developments in Metal Phosphide and Sulfide Electrocatalysts for Oxygen Evolution Reaction. Chin. J. Catal. 2018, 39, 1575−1593. (520) Li, D.; Shi, J. Y.; Li, C. Transition-Metal-Based Electrocatalysts as Cocatalysts for Photoelectrochemical Water Splitting: A Mini Review. Small 2018, 14, 1704179. (521) Shen, R.; Xie, J.; Guo, P.; Chen, L.; Chen, X.; Li, X. Bridging the g-C3N4 Nanosheets and Robust CuS Cocatalysts by Metallic Acetylene Black Interface Mediators for Active and Durable Photocatalytic H2 Production. ACS Applied Energy Materials 2018, 1, 2232− 2241. (522) Deng, D.; Novoselov, K. S.; Fu, Q.; Zheng, N.; Tian, Z.; Bao, X. Catalysis with Two-Dimensional Materials and Their Heterostructures. Nat. Nanotechnol. 2016, 11, 218−230.

(523) Hinnemann, B.; Moses, P. G.; Bonde, J.; Jørgensen, K. P.; Nielsen, J. H.; Horch, S.; Chorkendorff, I.; Nørskov, J. K. Biomimetic Hydrogen Evolution: MoS2 Nanoparticles as Catalyst for Hydrogen Evolution. J. Am. Chem. Soc. 2005, 127, 5308−5309. (524) Jaramillo, T. F.; Jørgensen, K. P.; Bonde, J.; Nielsen, J. H.; Horch, S.; Chorkendorff, I. Identification of Active Edge Sites for Electrochemical H2 Evolution from MoS2 Nanocatalysts. Science 2007, 317, 100. (525) Liu, P.; Zhu, J.; Zhang, J.; Xi, P.; Tao, K.; Gao, D.; Xue, D. P Dopants Triggered New Basal Plane Active Sites and Enlarged Interlayer Spacing in MoS2Nanosheets toward Electrocatalytic Hydrogen Evolution. ACS Energy Letters 2017, 2, 745−752. (526) Zhang, J.; Wu, J.; Guo, H.; Chen, W.; Yuan, J.; Martinez, U.; Gupta, G.; Mohite, A.; Ajayan, P. M.; Lou, J. Unveiling Active Sites for the Hydrogen Evolution Reaction on Monolayer MoS2. Adv. Mater. 2017, 29, 1701955. (527) Anjum, M. A. R.; Jeong, H. Y.; Lee, M. H.; Shin, H. S.; Lee, J. S. Efficient Hydrogen Evolution Reaction Catalysis in Alkaline Media by All-in-One MoS2 with Multifunctional Active Sites. Adv. Mater. 2018, 30, 1707105. (528) Pham, V. P.; Yeom, G. Y. Recent Advances in Doping of Molybdenum Disulfide: Industrial Applications and Future Prospects. Adv. Mater. 2016, 28, 9024−9059. (529) Ahn, H. S.; Bard, A. J. Surface Interrogation Scanning Electrochemical Microscopy of Ni1−xFexOOH (0< x< 0.27) Oxygen Evolving Catalyst: Kinetics of the “Fast” Iron Sites. J. Am. Chem. Soc. 2016, 138, 313−318. (530) Liang, Z. X.; Ahn, H. S.; Bard, A. J. A Study of the Mechanism of the Hydrogen Evolution Reaction on Nickel by Surface Interrogation Scanning Electrochemical Microscopy. J. Am. Chem. Soc. 2017, 139, 4854−4858. (531) Hu, C. Y.; Ma, Q. Y.; Hung, S. F.; Chen, Z. N.; Ou, D. H.; Ren, B.; Chen, H. M.; Fu, G.; Zheng, N. F. In Situ Electrochemical Production of Ultrathin Nickel Nanosheets for Hydrogen Evolution Electrocatalysis. Chem. 2017, 3, 122−133. (532) Ma, Q. Y.; Hu, C. Y.; Liu, K. L.; Hung, S. F.; Ou, D. H.; Chen, H. M.; Fu, G.; Zheng, N. F. Identifying the Electrocatalytic Sites of Nickel Disulfide in Alkaline Hydrogen Evolution Reaction. Nano Energy 2017, 41, 148−153. (533) Bolton, J. R. Solar Fuels. Science 1978, 202, 705−711. (534) Wang, W.-H.; Himeda, Y.; Muckerman, J. T.; Manbeck, G. F.; Fujita, E. CO2 Hydrogenation to Formate and Methanol as an Alternative to Photo- and Electrochemical CO2 Reduction. Chem. Rev. 2015, 115, 12936−12973. (535) Cheng, D.; Negreiros, F. R.; Aprà, E.; Fortunelli, A. Computational Approaches to the Chemical Conversion of Carbon Dioxide. ChemSusChem 2013, 6, 944−965. (536) Tahir, M.; Tahir, B.; Amin, N. A. S. Synergistic Effect in Plasmonic Au/Ag Alloy NPs Co-Coated TiO2 Nws toward VisibleLight Enhanced CO2 Photoreduction to Fuels. Appl. Catal., B 2017, 204, 548−560. (537) Tahir, M.; Tahir, B. Dynamic Photocatalytic Reduction of CO2 to CO2 in a Honeycomb Monolith Reactor Loaded with Cu and N Doped TiO2 Nanocatalysts. Appl. Surf. Sci. 2016, 377, 244−252. (538) Tahir, B.; Tahir, M.; Amin, N. S. Gold-Indium Modified TiO2 Nanocatalysts for Photocatalytic CO2 Reduction with H2 as Reductant in a Monolith Photoreactor. Appl. Surf. Sci. 2015, 338, 1−14. (539) Tahir, M.; Tahir, B.; Amin, N. A. S. Gold-NanoparticleModified TiO2Nanowires for Plasmon-Enhanced Photocatalytic TiO2 Reduction with H2 under Visible Light Irradiation. Appl. Surf. Sci. 2015, 356, 1289−1299. (540) Tahir, M.; Tahir, B.; Saidina Amin, N. A.; Alias, H. Selective Photocatalytic Reduction of CO2 by H2O/H2 to CH4 and CH3OH over Cu-Promoted In2O3/TiO2 Nanocatalyst. Appl. Surf. Sci. 2016, 389, 46−55. (541) Kanemoto, M.; Shiragami, T.; Pac, C.; Yanagida, S. Semiconductor Photocatalysis. 13. Effective Photoreduction of Carbon Dioxide Catalyzed by Zinc Sulfide Quantum Crystallites with Low Density of Surface Defects. J. Phys. Chem. 1992, 96, 3521−3526. FU


Chemical Reviews

Review

(542) Fujishima, A.; Honda, K. Electrochemical Photolysis of Water at a Semiconductor Electrode. Nature 1972, 238, 37−38. (543) Nakata, K.; Fujishima, A. TiO2 Photocatalysis: Design and Applications. J. Photochem. Photobiol., C 2012, 13, 169−189. (544) Linsebigler, A.; Lu, G.; Yates, J., Jr Photocatalysis on TiO2 Surfaces: Principles, Mechanisms, and Selected Results. Chem. Rev. 1995, 95, 735−758. (545) Fujita, E. Photochemical Carbon Dioxide Reduction with Metal Complexes. Coord. Chem. Rev. 1999, 185, 373−384. (546) Lehn, J.-M.; Ziessel, R. Photochemical Generation of Carbon Monoxide and Hydrogen by Reduction of Carbon Dioxide and Water under Visible Light Irradiation. Proc. Natl. Acad. Sci. U. S. A. 1982, 79, 701−704. (547) Yahaya, A. H.; Gondal, M. A.; Hameed, A. Selective Laser Enhanced Photocatalytic Conversion of CO2 into Methanol. Chem. Phys. Lett. 2004, 400, 206−212. (548) Willner, I.; Maidan, R.; Mandler, D.; Duerr, H.; Doerr, G.; Zengerle, K. Photosensitized Reduction of Carbon Dioxide to Methane and Hydrogen Evolution in the Presence of Ruthenium and Osmium Colloids: Strategies to Design Selectivity of Products Distribution. J. Am. Chem. Soc. 1987, 109, 6080−6086. (549) Hori, Y.: Electrochemical CO2 Reduction on Metal Electrodes. In Modern Aspects of Electrochemistry; Vayenas, C., White, R., GamboaAldeco, M., Eds.; Springer: New York, 2008; Vol. 42, pp 89−189. (550) Schneider, J.; Jia, H. F.; Muckerman, J. T.; Fujita, E. Thermodynamics and Kinetics of CO2CO, and H+ Binding to the Metal Centre of CO2 Reduction Catalysts. Chem. Soc. Rev. 2012, 41, 2036−2051. (551) Wang, Z.; Teramura, K.; Huang, Z.; Hosokawa, S.; Sakata, Y.; Tanaka, T. Tuning the Selectivity toward CO Evolution in the Photocatalytic Conversion of CO2 with H2O through the Modification of Ag-Loaded Ga2O3 with a ZnGa2O4 Layer. Catal. Sci. Technol. 2016, 6, 1025−1032. (552) Teramura, K.; Wang, Z.; Hosokawa, S.; Sakata, Y.; Tanaka, T. A Doping Technique That Suppresses Undesirable H2 Evolution Derived from Overall Water Splitting in the Highly Selective Photocatalytic Conversion of CO2 in and by Water. Chem. - Eur. J. 2014, 20, 9906−9909. (553) Chen, X. Y.; Zhou, Y.; Liu, Q.; Li, Z. D.; Liu, J. G.; Zou, Z. G. Ultrathin, Single-Crystal WO3 Nanosheets by Two-Dimensional Oriented Attachment toward Enhanced Photocatalystic Reduction of CO2 into Hydrocarbon Fuels under Visible Light. ACS Appl. Mater. Interfaces 2012, 4, 3372−3377. (554) Wang, P. Q.; Bai, Y.; Luo, P. Y.; Liu, J. Y. Graphene-WO3 Nanobelt Composite: Elevated Conduction Band toward Photocatalytic Reduction of CO2 into Hydrocarbon Fuels. Catal. Commun. 2013, 38, 82−85. (555) Ohno, T.; Murakami, N.; Koyanagi, T.; Yang, Y. Photocatalytic Reduction of CO2 over a Hybrid Photocatalyst Composed of WO3 and Graphitic Carbon Nitride (g-C3N4) under Visible Light. J. CO2 Util. 2014, 6, 17−25. (556) Wang, L.; Wang, Y.; Cheng, Y.; Liu, Z.; Guo, Q.; Ha, M. N.; Zhao, Z. Hydrogen-Treated Mesoporous WO3 as a Reducing Agent of CO2 to Fuels (CH4 and CH3OH) with Enhanced Photothermal Catalytic Performance. J. Mater. Chem. A 2016, 4, 5314−5322. (557) Cheng, H.; Huang, B.; Liu, Y.; Wang, Z.; Qin, X.; Zhang, X.; Dai, Y. An Anion Exchange Approach to Bi2WO6 Hollow Microspheres with Efficient Visible Light Photocatalytic Reduction of CO2 to Methanol. Chem. Commun. 2012, 48, 9729−9731. (558) Sun, Z.; Yang, Z.; Liu, H.; Wang, H.; Wu, Z. Visible-Light CO2 Photocatalytic Reduction Performance of Ball-Flower-Like Bi2WO6 Synthesized without Organic Precursor: Effect of Post-Calcination and Water Vapor. Appl. Surf. Sci. 2014, 315, 360−367. (559) Dai, W.; Xu, H.; Yu, J.; Hu, X.; Luo, X.; Tu, X.; Yang, L. Photocatalytic Reduction of CO2 into Methanol and Ethanol over Conducting Polymers Modified Bi2WO6 Microspheres under Visible Light. Appl. Surf. Sci. 2015, 356, 173−180.

(560) Murcia-Lopez, S.; Vaiano, V.; Hidalgo, M. C.; Navio, J. A.; Sannino, D. Photocatalytic Reduction of CO2 over Platinised Bi2WO6Based Materials. Photoch. Photobio. Sci. 2015, 14, 678−685. (561) Mao, J.; Peng, T. Y.; Zhang, X. H.; Li, K.; Zan, L. Selective Methanol Production from Photocatalytic Reduction of CO2 on BiVO4 under Visible Light Irradiation. Catal. Commun. 2012, 28, 38− 41. (562) Liu, Y. Y.; Huang, B. B.; Dai, Y.; Zhang, X. Y.; Qin, X. Y.; Jiang, M. H.; Whangbo, M. H. Selective Ethanol Formation from Photocatalytic Reduction of Carbon Dioxide in Water with BiVO4 Photocatalyst. Catal. Commun. 2009, 11, 210−213. (563) Tachibana, Y.; Vayssieres, L.; Durrant, J. R. Artificial Photosynthesis for Solar Water-Splitting. Nat. Photonics 2012, 6, 511−518. (564) Zhou, H.; Qu, Y.; Zeid, T.; Duan, X. Towards Highly Efficient Photocatalysts Using Semiconductor Nanoarchitectures. Energy Environ. Sci. 2012, 5, 6732−6743. (565) Bi, W.; Wu, C.; Xie, Y. Atomically Thin Two-Dimensional Solids: An Emerging Platform for CO2 Electroreduction. ACS Energy Letters 2018, 3, 624−633. (566) Liu, M.; Pang, Y.; Zhang, B.; De Luna, P.; Voznyy, O.; Xu, J.; Zheng, X.; Dinh, C. T.; Fan, F.; Cao, C.; et al. Enhanced Electrocatalytic CO2 Reduction Via Field-Induced Reagent Concentration. Nature 2016, 537, 382−386. (567) White, J. L.; Baruch, M. F.; Pander, J. E., III; Hu, Y.; Fortmeyer, I. C.; Park, J. E.; Zhang, T.; Liao, K.; Gu, J.; Yan, Y.; et al. Light-Driven Heterogeneous Reduction of Carbon Dioxide: Photocatalysts and Photoelectrodes. Chem. Rev. 2015, 115, 12888−12935. (568) Li, X. K.; Zhuang, Z. J.; Li, W.; Pan, H. Q. Photocatalytic Reduction of CO2 over Noble Metal-Loaded and Nitrogen-Doped Mesoporous TiO2. Appl. Catal., A 2012, 429, 31−38. (569) Fu, J.; Cao, S.; Yu, J.; Low, J.; Lei, Y. Enhanced Photocatalytic CO2-Reduction Activity of Electrospun Mesoporous TiO2 Nanofibers by Solvothermal Treatment. Dalton Trans. 2014, 43, 9158−9165. (570) Wang, T.; Meng, X.; Li, P.; Ouyang, S.; Chang, K.; Liu, G.; Mei, Z.; Ye, J. Photoreduction of CO2 over the Well-Crystallized Ordered Mesoporous TiO2 with the Confined Space Effect. Nano Energy 2014, 9, 50−60. (571) Ramacharyulu, P. V. R. K.; Muhammad, R.; Praveen Kumar, J.; Prasad, G. K.; Mohanty, P. Iron Phthalocyanine Modified Mesoporous Titania Nanoparticles for Photocatalytic Activity and CO2 Capture Applications. Phys. Chem. Chem. Phys. 2015, 17, 26456−26462. (572) Wang, T.; Meng, X.; Liu, G.; Chang, K.; Li, P.; Kang, Q.; Liu, L.; Li, M.; Ouyang, S.; Ye, J. In Situ Synthesis of Ordered Mesoporous Co-Doped TiO2 and Its Enhanced Photocatalytic Activity and Selectivity for the Reduction of CO2. J. Mater. Chem. A 2015, 3, 9491−9501. (573) Suzuki, T. M.; Nakamura, T.; Saeki, S.; Matsuoka, Y.; Tanaka, H.; Yano, K.; Kajino, T.; Morikawa, T. Visible Light-Sensitive Mesoporous N-Doped Ta2O5 Spheres: Synthesis and Photocatalytic Activity for Hydrogen Evolution and CO2 Reduction. J. Mater. Chem. 2012, 22, 24584−24590. (574) Yan, S.; Yu, H.; Wang, N.; Li, Z.; Zou, Z. Efficient Conversion of CO2 and H2O into Hydrocarbon Fuel over ZnAl2O4-Modified Mesoporous ZnGaNO under Visible Light Irradiation. Chem. Commun. 2012, 48, 1048−1050. (575) Zhang, N.; Ouyang, S.; Kako, T.; Ye, J. Mesoporous Zinc Germanium Oxynitride for CO2 Photoreduction under Visible Light. Chem. Commun. 2012, 48, 1269−1271. (576) Guo, J.; Ouyang, S.; Kako, T.; Ye, J. Mesoporous In(OH)3 for Photoreduction of CO2 into Renewable Hydrocarbon Fuels. Appl. Surf. Sci. 2013, 280, 418−423. (577) Wang, Y.; Wang, F.; Chen, Y.; Zhang, D.; Li, B.; Kang, S.; Li, X.; Cui, L. Enhanced Photocatalytic Performance of Ordered Mesoporous Fe-Doped CeO2 Catalysts for the Reduction of CO2 with H2O under Simulated Solar Irradiation. Appl. Catal., B 2014, 147, 602−609. (578) Kumar, P.; Kumar, A.; Joshi, C.; Singh, R.; Saran, S.; Jain, S. L. Heterostructured Nanocomposite Tin Phthalocyanine@Mesoporous FV


Chemical Reviews

Review

by Evaporation Driven Self-Assembly. Catal. Sci. Technol. 2011, 1, 593−600. (596) Kumar, P.; Chauhan, R. K.; Sain, B.; Jain, S. L. Photo-Induced Reduction of CO2 Using a Magnetically Separable Ru-CoPc@TiO2@ SiO2@Fe3O4Catalyst under Visible Light Irradiation. Dalton Trans. 2015, 44, 4546−4553. (597) Bera, S.; Lee, J. E.; Rawal, S. B.; Lee, W. I. Size-Dependent Plasmonic Effects of Au and Au@SiO2 Nanoparticles in Photocatalytic CO2 Conversion Reaction of Pt/TiO2. Appl. Catal., B 2016, 199, 55− 63. (598) Dong, C.; Xing, M.; Zhang, J. Economic Hydrophobicity Triggering of CO2 Photoreduction for Selective CH4 Generation on Noble-Metal-Free TiO2-SiO2. J. Phys. Chem. Lett. 2016, 7, 2962−2966. (599) Ikeue, K.; Yamashita, H.; Anpo, M. Photocatalytic Reduction of CO2 with H2O on Titanium Oxides Prepared within Zeolites and Mesoporous Molecular Sieves. Electrochemistry 2002, 70, 402−408. (600) Cai, W.; Hu, Y.; Yu, J.; Wang, W.; Zhou, J.; Jaroniec, M. Template-Free Synthesis of Hierarchical Gamma-Al2O3 Nanostructures and Their Adsorption Affinity toward Phenol and CO2. RSC Adv. 2015, 5, 7066−7073. (601) Yu, J.; Zhang, L.; Cheng, B.; Su, Y. Hydrothermal Preparation and Photocatalytic Activity of Hierarchically Sponge-Like Macro-/ Mesoporous Titania. J. Phys. Chem. C 2007, 111, 10582−10589. (602) Yu, J. G.; Su, Y. R.; Cheng, B. Template-Free Fabrication and Enhanced Photocatalytic Activity of Hierarchical Macro-/Mesoporous Titania. Adv. Funct. Mater. 2007, 17, 1984−1990. (603) Yu, J.; Liu, W.; Yu, H. A One-Pot Approach to Hierarchically Nanoporous Titania Hollow Microspheres with High Photocatalytic Activity. Cryst. Growth Des. 2008, 8, 930−934. (604) Chen, L.; Tang, X.; Xie, P.; Xu, J.; Chen, Z.; Cai, Z.; He, P.; Zhou, H.; Zhang, D.; Fan, T. 3D Printing of Artificial Leaf with Tunable Hierarchical Porosity for CO2 Photoreduction. Chem. Mater. 2018, 30, 799−806. (605) Xue, H.; Wang, T.; Gong, H.; Guo, H.; Fan, X.; Gao, B.; Feng, Y.; Meng, X.; Huang, X.; He, J. Constructing Ordered Three Dimensional TiO2Channels for Enhanced Visible Light Photocatalytic Performance in CO2Conversion Induced by Au Nanoparticles. Chem. Asian J. 2018, 13, 577−583. (606) Wang, F.; Zhou, Y.; Li, P.; Li, H.; Tu, W.; Yan, S.; Zou, Z. Formation of 3d Interconnectively Macro/Mesoporous TiO2 Sponges through Gelation of Lotus Root Starch toward CO2 Photoreduction into Hydrocarbon Fuels. RSC Adv. 2014, 4, 43172−43177. (607) Di, T. M.; Zhang, J. F.; Cheng, B.; Yu, J. G.; Xu, J. S. Hierarchically Nanostructured Porous TiO2(B) with Superior Photocatalytic CO2 Reduction Activity. Sci. China: Chem. 2018, 61, 344. (608) Fang, B.; Bonakdarpour, A.; Reilly, K.; Xing, Y.; Taghipour, F.; Wilkinson, D. P. Large-Scale Synthesis of TiO2 Microspheres with Hierarchical Nanostructure for Highly Efficient Photodriven Reduction of CO2 to CH4. ACS Appl. Mater. Interfaces 2014, 6, 15488− 15498. (609) Zhang, T.; Low, J. X.; Koh, K.; Yu, J. G.; Asefa, T. Mesoporous TiO2 Comprising Small, Highly Crystalline Nanoparticles for Efficient CO2 Reduction by H2O. ACS Sustainable Chem. Eng. 2018, 6, 531− 540. (610) Wang, F.; Zhou, Y.; Li, P.; Kuai, L.; Zou, Z. Synthesis of Bionic-Macro/Microporous MgO-Modified TiO2 for Enhanced CO2 Photoreduction into Hydrocarbon Fuels. Chin. J. Catal. 2016, 37, 863−868. (611) Jiao, J.; Wei, Y.; Chi, K.; Zhao, Z.; Duan, A.; Liu, J.; Jiang, G.; Wang, Y.; Wang, X.; Han, C.; et al. Platinum Nanoparticles Supported on TiO2 Photonic Crystals as Highly Active Photocatalyst for the Reduction of CO2 in the Presence of Water. Energy Technology 2017, 5, 877−883. (612) Zheng, X. Z.; Yang, Y.; Chen, S. F.; Zhang, L. W. Slow Photons for Solar Fuels. Chin. J. Catal. 2018, 39, 379−389. (613) Yang, Y.; Qiu, M.; Liu, L. TiO2 Nanorod Array@Carbon Cloth Photocatalyst for CO2 Reduction. Ceram. Int. 2016, 42, 15081−15086. (614) Tu, W.; Zhou, Y.; Liu, Q.; Yan, S.; Bao, S.; Wang, X.; Xiao, M.; Zou, Z. An in Situ Simultaneous Reduction-Hydrolysis Technique for

Ceria (SnPc@CeO2) for Photoreduction of CO2 in Visible Light. RSC Adv. 2015, 5, 42414−42421. (579) Zhang, S. G.; Fujii, Y.; Yamashita, K.; Koyano, K.; Tatsumi, T.; Anpo, M. Photocatalytic Reduction of CO2 with H2O on Ti-Mcm-41 and Ti-Mcm-48 Mesoporous Zeolites at 328 K. Chem. Lett. 1997, 26, 659−660. (580) Shioya, Y.; Ikeue, K.; Ogawa, M.; Anpo, M. Synthesis of Transparent Ti-Containing Mesoporous Silica Thin Film Materials and Their Unique Photocatalytic Activity for the Reduction of CO2 with H2O. Appl. Catal., A 2003, 254, 251−259. (581) Jo, S. W.; Kwak, B. S.; Kim, K. M.; Do, J. Y.; Park, N.-K.; Ryu, S. O.; Ryu, H.-J.; Baek, J.-I.; Kang, M. Effectively CO2 Photoreduction to CH4 by the Synergistic Effects of Ca and Ti on Ca-Loaded Tisimcm-41 Mesoporous Photocatalytic Systems. Appl. Surf. Sci. 2015, 355, 891−901. (582) Wang, Y. G.; Li, B.; Zhang, C. L.; Cui, L. F.; Kang, S. F.; Li, X.; Zhou, L. H. Ordered Mesoporous CeO2-TiO2 Composites: Highly Efficient Photocatalysts for the Reduction of CO2 with H2O under Simulated Solar Irradiation. Appl. Catal., B 2013, 130, 277−284. (583) Hwang, J. S.; Chang, J. S.; Park, S. E.; Ikeue, K.; Anpo, M. High-Performance Photocatalytic Reduction of CO2 with H2O by TiSBA-15 Mesoporous Material. In Studies in Surface Science and Catalysis; Park, S.-E., Chang, J.S., Lee, K.-W., Eds.; Elsevier, 2004; Vol. 153; pp 299−302. (584) Yang, H.-C.; Lin, H.-Y.; Chien, Y.-S.; Wu, J.; Wu, H.-H. Mesoporous TiO2/SBA-15, and Cu/TiO2/SBA-15 Composite Photocatalysts for Photoreduction of CO2 to Methanol. Catal. Lett. 2009, 131, 381−387. (585) Yang, C. C.; Vernimmen, J.; Meynen, V.; Cool, P.; Mul, G. Mechanistic Study of Hydrocarbon Formation in Photocatalytic CO2 Reduction over Ti-SBA-15. J. Catal. 2011, 284, 1−8. (586) Wang, H.; Jiang, D.; Wu, D.; Li, D.; Sun, Y. Synthesis of Supported TiO2/SBA-15 Catalysts and Their Performance on Photocatalytic Reduction of CO2. Huaxue Xuebao 2012, 70, 2412− 2418. (587) Zhao, C. Y.; Liu, L. J.; Zhang, Q. Y.; Wang, J.; Li, Y. Photocatalytic Conversion of CO2 and H2O to Fuels by Nanostructured Ce-TiO2/SBA-15 Composites. Catal. Sci. Technol. 2012, 2, 2558−2568. (588) Mei, B.; Pougin, A.; Strunk, J. Influence of Photodeposited Gold Nanoparticles on the Photocatalytic Activity of Titanate Species in the Reduction of CO2 to Hydrocarbons. J. Catal. 2013, 306, 184− 189. (589) Gao, M.; Jiang, D.; Sun, D.; Hou, B.; Li, D. Synthesis of Ag/NTiO2/SBA-15 Photocatalysts and Photocatalytic Reduction of CO2 under Visible Light Irradiation. Huaxue Xuebao 2014, 72, 1092−1098. (590) Macnaughtan, M. L.; Soo, H. S.; Frei, H. Binuclear ZrOCo Metal-to-Metal Charge-Transfer Unit in Mesoporous Silica for LightDriven CO2 Reduction to CO and Formate. J. Phys. Chem. C 2014, 118, 7874−7885. (591) Chen, R.; Cheng, X.; Zhu, X.; Liao, Q.; An, L.; Ye, D. D.; He, X. F.; Wang, Z. B. High-Performance Optofluidic Membrane Microreactor with a Mesoporous CdS/TiO2/SBA-15@Carbon Paper Composite Membrane for the CO2 Photoreduction. Chem. Eng. J. 2017, 316, 911−918. (592) Chang, F.; Wang, G.; Xie, Y.; Zhang, M.; Zhang, J.; Yang, H.-J.; Hu, X. Synthesis of TiO2 Nanoparticles on Mesoporous Aluminosilicate Al-SBA-15 in Supercritical CO2 for Photocatalytic Decolorization of Methylene Blue. Ceram. Int. 2013, 39, 3823−3829. (593) Shi, D. X.; Feng, Y. Q.; Zhong, S. H. Photocatalytic Conversion of CH4 and CO2 to Oxygenated Compounds over Cu/ CdS-TiO2/SiO2 Catalyst. Catal. Today 2004, 98, 505−509. (594) Nalepa, K.; Goralski, J.; Szynkowska, M. I.; Rynkowski, J. Studies on Physicochemical Properties of TiO2/SiO2 and 1%Pt/TiO2/ SiO2 Photocatalysts in the Reduction of CO2 in H2O to Methanol. Przem. Chem. 2010, 89, 500−504. (595) Wang, W.-N.; Park, J.; Biswas, P. Rapid Synthesis of Nanostructured Cu-TiO2-SiO2 Composites for CO2 Photoreduction FW


Chemical Reviews

Review

for CO2 Reduction: Influence of Morphology and Phase Composition on Catalytic Activity. J. CO2 Util. 2016, 15, 24−31. (631) Khan, M. S.; Ashiq, M. N.; Ehsan, M. F.; He, T.; Ijaz, S. Controlled Synthesis of Cobalt Telluride Superstructures for the Visible Light Photo-Conversion of Carbon Dioxide into Methane. Appl. Catal., A 2014, 487, 202−209. (632) Dai, W. L.; Yu, J. J.; Deng, Y. Q.; Hu, X.; Wang, T. Y.; Luo, X. B. Facile Synthesis of MoS2/Bi2WO6 Nanocomposites for Enhanced CO2 Photoreduction Activity under Visible Light Irradiation. Appl. Surf. Sci. 2017, 403, 230−239. (633) Chen, J.; Qin, S.; Song, G.; Xiang, T.; Xin, F.; Yin, X. ShapeControlled Solvothermal Synthesis of Bi2S3 for Photocatalytic Reduction of CO2 to Methyl Formate in Methanol. Dalton Trans. 2013, 42, 15133−15138. (634) Fang, B.; Xing, Y.; Bonakdarpour, A.; Zhang, S.; Wilkinson, D. P. Hierarchical CuO-TiO2 Hollow Microspheres for Highly Efficient Photodriven Reduction of CO2 to CH4. ACS Sustainable Chem. Eng. 2015, 3, 2381−2388. (635) Bafaqeer, A.; Tahir, M.; Amin, N. A. S. Synthesis of Hierarchical ZnV2O6 Nanosheets with Enhanced Activity and Stability for Visible Light Driven CO2 Reduction to Solar Fuels. Appl. Surf. Sci. 2018, 435, 953−962. (636) Zhang, Y.; Li, P.; Tang, L.-Q.; Li, Y.-Q.; Zhou, Y.; Liu, J.-M.; Zou, Z.-G. Robust, Double-Shelled ZnGa2O4 Hollow Spheres for Photocatalytic Reduction of CO2 to Methane. Dalton Trans. 2017, 46, 10564−10568. (637) Chen, S.; Yu, J.; Zhang, J. Enhanced Photocatalytic CO2Reduction Activity of MOF-Derived ZnO/NiO Porous Hollow Spheres. J. CO2 Util. 2018, 24, 548−554. (638) Pan, B.; Zhou, Y.; Su, W.; Wang, X. Self-Assembly Synthesis of LaPO4 Hierarchical Hollow Spheres with Enhanced Photocatalytic CO2-Reduction Performance. Nano Res. 2017, 10, 534−545. (639) Wang, Y.; Zhang, L. N.; Zhang, X. Y.; Zhang, Z. Z.; Tong, Y. C.; Li, F. Y.; Wu, J. C. S.; Wang, X. X. Openmouthed Beta-Sic HollowSphere with Highly Photocatalytic Activity for Reduction of CO2 with H2O. Appl. Catal., B 2017, 206, 158−167. (640) Liu, Q.; Xu, M.; Zhou, B.; Liu, R.; Tao, F.; Mao, G. Unique Zinc Germanium Oxynitride Hyperbranched Nanostructures with Enhanced Visible Light Photocatalystic Activity for CO2 Reduction. Eur. J. Inorg. Chem. 2017, 2017, 2195−2200. (641) Ong, W.-J.; Tan, L.-L.; Chai, S.-P.; Yong, S.-T. Graphene Oxide as a Structure-Directing Agent for the Two-Dimensional Interface Engineering of Sandwich-Like Graphene-g-C3N4 Hybrid Nanostructures with Enhanced Visible-Light Photoreduction of CO2 to Methane. Chem. Commun. 2015, 51, 858−861. (642) Fu, J.; Zhu, B.; Jiang, C.; Cheng, B.; You, W.; Yu, J. Hierarchical Porous O-Doped g-C3N4 with Enhanced Photocatalytic CO2 Reduction Activity. Small 2017, 13, 1603938. (643) Wang, S.; Guan, B. Y.; Lou, X. W. D. Construction of ZnIn2S4−In2O3 Hierarchical Tubular Heterostructures for Efficient CO2 Photoreduction. J. Am. Chem. Soc. 2018, 140, 5037−5040. (644) Wang, S. B.; Guan, B. Y.; Lu, Y.; Lou, X. W. Formation of Hierarchical In2S3-CdIn2S4 Heterostructured Nanotubes for Efficient and Stable Visible Light CO2 Reduction. J. Am. Chem. Soc. 2017, 139, 17305−17308. (645) Yang, G.; Chen, D. M.; Ding, H.; Feng, J. J.; Zhang, J. Z.; Zhu, Y. F.; Hamid, S.; Bahnemann, D. W. Well-Designed 3d ZnIn2S4Nanosheets/TiO2 Nanobelts as Direct Z-Scheme Photocatalysts for CO2 Photoreduction into Renewable Hydrocarbon Fuel with High Efficiency. Appl. Catal., B 2017, 219, 611−618. (646) Wang, S. B.; Guan, B. Y.; Lou, X. W. Rationally Designed Hierarchical N-Doped Carbon@NiCO2O4 Double-Shelled Nanoboxes for Enhanced Visible Light CO2 Reduction. Energy Environ. Sci. 2018, 11, 306−310. (647) Dai, W. L.; Yu, J. J.; Xu, H.; Hu, X.; Luo, X. B.; Yang, L. X.; Tu, X. M. Synthesis of Hierarchical Flower-Like Bi2MoO6 Microspheres as Efficient Photocatalyst for Photoreduction of CO2 into Solar Fuels under Visible Light. CrystEngComm 2016, 18, 3472−3480.

Fabrication of TiO2-Graphene 2D Sandwich-Like Hybrid Nanosheets: Graphene-Promoted Selectivity of Photocatalytic-Driven Hydrogenation and Coupling of CO2 into Methane and Ethane. Adv. Funct. Mater. 2013, 23, 1743−1749. (615) Wang, Y.; Chen, Y.; Zuo, Y.; Wang, F.; Yao, J.; Li, B.; Kang, S.; Li, X.; Cui, L. Hierarchically Mesostructured TiO2/Graphitic Carbon Composite as a New Efficient Photocatalyst for the Reduction of CO2 under Simulated Solar Irradiation. Catal. Sci. Technol. 2013, 3, 3286− 3291. (616) Jiang, W.; Yin, X.; Xin, F.; Bi, Y.; Liu, Y.; Li, X. Preparation of CdIn2S4 Microspheres and Application for Photocatalytic Reduction of Carbon Dioxide. Appl. Surf. Sci. 2014, 288, 138−142. (617) Liu, H.; Meng, J. C.; Zhang, J. Self-Assembled ThreeDimensional Flowerlike Mn0.8Cd0.2S Microspheres as Efficient VisibleLight-Driven Photocatalysts for H2 Evolution and CO2 Reduction. Catal. Sci. Technol. 2017, 7, 3802−3811. (618) Liu, Q.; Zhou, Y.; Tian, Z. P.; Chen, X. Y.; Gao, J.; Zou, Z. G. Zn2GeO4 Crystal Splitting toward Sheaf-Like, Hyperbranched Nanostructures and Photocatalytic Reduction of CO2 into CH4 under Visible Light after Nitridation. J. Mater. Chem. 2012, 22, 2033−2038. (619) Han, Q.; Zhou, Y.; Tang, L.; Li, P.; Tu, W.; Li, L.; Li, H.; Zou, Z. Synthesis of Single-Crystalline, Porous Taon Microspheres toward Visible-Light Photocatalytic Conversion of CO2 into Liquid Hydrocarbon Fuels. RSC Adv. 2016, 6, 90792−90796. (620) Wang, P. Q.; Yang, P.; Bai, Y.; Chen, T.; Shi, X.; Ye, L. Q.; Zhang, X. Synthesis of 3D BiOBr Microspheres for Enhanced Photocatalytic CO2 Reduction. J. Taiwan Inst. Chem. Eng. 2016, 68, 295−300. (621) Zhou, H.; Li, P.; Guo, J.; Yan, R.; Fan, T.; Zhang, D.; Ye, J. Artificial Photosynthesis on Tree Trunk Derived Alkaline Tantalates with Hierarchical Anatomy: Towards CO2 Photo-Fixation into CO and CH4. Nanoscale 2015, 7, 113−120. (622) Bai, Y.; Ye, L. Q.; Chen, T.; Wang, P. Q.; Wang, L.; Shi, X.; Wong, P. K. Synthesis of Hierarchical Bismuth-Rich Bi4O5BrxI2‑x Solid Solutions for Enhanced Photocatalytic Activities of CO2 Conversion and Cr(VI) Reduction under Visible Light. Appl. Catal., B 2017, 203, 633−640. (623) Jiao, J.; Wei, Y.; Zhao, Z.; Liu, J.; Li, J.; Duan, A.; Jiang, G. Photocatalysts of 3D Ordered Macroporous TiO2-Supported CeO2 Nano Layers: Design, Preparation, and Their Catalytic Performances for the Reduction of CO2 with H2O under Simulated Solar Irradiation. Ind. Eng. Chem. Res. 2014, 53, 17345−17354. (624) Ijaz, S.; Ehsan, M. F.; Ashiq, M. N.; Karamat, N.; He, T. Preparation of CdS@CeO2 Core/Shell Composite for Photocatalytic Reduction of CO2 under Visible-Light Irradiation. Appl. Surf. Sci. 2016, 390, 550−559. (625) Dai, W. L.; Hu, X.; Wang, T. Y.; Xiong, W. W.; Luo, X. B.; Zou, J. P. Hierarchical CeO2/Bi2MoO6 Heterostructured Nanocomposites for Photoreduction of CO2 into Hydrocarbons under Visible Light Irradiation. Appl. Surf. Sci. 2018, 434, 481−491. (626) Ijaz, S.; Ehsan, M. F.; Ashiq, M. N.; He, T. Synthesis of a Bi2S3/CeO2 Nanocatalyst and Its Visible Light-Driven Conversion of CO2 into CH3OH and CH4. Catal. Sci. Technol. 2015, 5, 5208−5215. (627) Ovcharov, M. L.; Mishura, A. M.; Shcherban, N. D.; Filonenko, S. M.; Granchak, V. M. Photocatalytic Reduction of CO2 Using Nanostructured Cu2O with Foam-Like Structure. Sol. Energy 2016, 139, 452−457. (628) Ijaz, S.; Ehsan, M. F.; Ashiq, M. N.; Karamt, N.; Najam-ul-Haq, M.; He, T. Flower-Like CdS/CdV2O6Composite for Visible-Light Photoconversion of CO2 into CH4. Mater. Des. 2016, 107, 178−186. (629) Zeng, C.; Huang, H.; Zhang, T.; Dong, F.; Zhang, Y.; Hu, Y. Fabrication of Heterogeneous-Phase Solid-Solution Promoting Band Structure and Charge Separation for Enhancing Photocatalytic CO2 Reduction: A Case of ZnxCa1−xIn2S4. ACS Appl. Mater. Interfaces 2017, 9, 27773−27783. (630) Renones, P.; Moya, A.; Fresno, F.; Collado, L.; Vilatela, J. J.; de la Pena O’Shea, V. A. Hierarchical TiO2 Nanofibres as Photocatalyst FX


Chemical Reviews

Review

(648) Zhou, H.; Guo, J. J.; Li, P.; Fan, T. X.; Zhang, D.; Ye, J. H. Leaf-Architectured 3D Hierarchical Artificial Photosynthetic System of Perovskite Titanates Towards CO2 Photoreduction into Hydrocarbon Fuels. Sci. Rep. 2013, 3, 1667. (649) Liu, Q.; Wu, D.; Zhou, Y.; Su, H.; Wang, R.; Zhang, C.; Yan, S.; Xiao, M.; Zou, Z. Single-Crystalline, Ultrathin ZnGa2O4Nanosheet Scaffolds to Promote Photocatalytic Activity in CO2 Reduction into Methane. ACS Appl. Mater. Interfaces 2014, 6, 2356−2361. (650) Ehsan, M. F.; He, T. In Situ Synthesis of Zno/ZnTe Common Cation Heterostructure and its Visible-Light Photocatalytic Reduction of CO2 into CH4. Appl. Catal., B 2015, 166, 345−352. (651) Ehsan, M. F.; Ashiq, M. N.; He, T. Hollow and Mesoporous Znte Microspheres: Synthesis and Visible-Light Photocatalytic Reduction of Carbon Dioxide into Methane. RSC Adv. 2015, 5, 6186−6194. (652) Ma, X.; Wang, X.; Song, C. “Molecular Basket” Sorbents for Separation of CO2 and H2S from Various Gas Streams. J. Am. Chem. Soc. 2009, 131, 5777−5783. (653) Huang, Q.; Yu, J.; Cao, S.; Cui, C.; Cheng, B. Efficient Photocatalytic Reduction of CO2 by Amine-Functionalized g-C3N4. Appl. Surf. Sci. 2015, 358, 350−355. (654) Liao, Y.; Hu, Z.; Gu, Q.; Xue, C. Amine-Functionalized ZnO Nanosheets for Efficient CO2 Capture and Photoreduction. Molecules 2015, 20, 18847−18855. (655) Liu, S.; Xia, J.; Yu, J. Amine-Functionalized Titanate Nanosheet-Assembled Yolk@Shell Microspheres for Efficient Cocatalyst-Free Visible-Light Photocatalytic CO2 Reduction. ACS Appl. Mater. Interfaces 2015, 7, 8166−8175. (656) Nie, Y.; Wang, W.-N.; Jiang, Y.; Fortner, J.; Biswas, P. Crumpled Reduced Graphene Oxide-Amine-Titanium Dioxide Nanocomposites for Simultaneous Carbon Dioxide Adsorption and Photoreduction. Catal. Sci. Technol. 2016, 6, 6187−6196. (657) Indrakanti, V. P.; Schobert, H. H.; Kubicki, J. D. Quantum Mechanical Modeling of CO2 Interactions with Irradiated Stoichiometric and Oxygen-Deficient Anatase TiO2 Surfaces: Implications for the Photocatalytic Reduction of CO2. Energy Fuels 2009, 23, 5247− 5256. (658) Freund, H. J.; Roberts, M. W. Surface Chemistry of Carbon Dioxide. Surf. Sci. Rep. 1996, 25, 225−273. (659) Chang, X.; Wang, T.; Gong, J. CO2 Photo-Reduction: Insights into CO2 Activation and Reaction on Surfaces of Photocatalysts. Energy Environ. Sci. 2016, 9, 2177−2196. (660) Yang, C.-T.; Wood, B. C.; Bhethanabotla, V. R.; Joseph, B. CO2 Adsorption on Anatase TiO2 (101) Surfaces in the Presence of Subnanometer Ag/Pt Clusters: Implications for CO2Photoreduction. J. Phys. Chem. C 2014, 118, 26236−26248. (661) Lee, J.; Sorescu, D. C.; Deng, X. Electron-Induced Dissociation of CO2 on TiO2 (110). J. Am. Chem. Soc. 2011, 133, 10066−10069. (662) Pipornpong, W.; Wanbayor, R.; Ruangpornvisuti, V. Adsorption CO2 on the Perfect and Oxygen Vacancy Defect Surfaces of Anatase TiO2 and Its Photocatalytic Mechanism of Conversion to Co. Appl. Surf. Sci. 2011, 257, 10322−10328. (663) Ji, Y.; Luo, Y. Theoretical Study on the Mechanism of Photoreduction of CO2 to CH4 on the Anatase TiO2 (101) Surface. ACS Catal. 2016, 6, 2018−2025. (664) Ji, Y. F.; Luo, Y. New Mechanism for Photocatalytic Reduction of CO2 on the Anatase TiO2(101) Surface: The Essential Role of Oxygen Vacancy. J. Am. Chem. Soc. 2016, 138, 15896−15902. (665) Dimitrijevic, N. M.; Vijayan, B. K.; Poluektov, O. G.; Rajh, T.; Gray, K. A.; He, H. Y.; Zapol, P. Role of Water and Carbonates in Photocatalytic Transformation of CO2 to CH4 on Titania. J. Am. Chem. Soc. 2011, 133, 3964−3971. (666) Anpo, M.; Yamashita, H.; Ichihashi, Y.; Ehara, S. Photocatalytic Reduction of CO2 with H2O on Various Titanium Oxide Catalysts. Electroanal. Chem. 1995, 396, 21−26. (667) Zhang, L.; Wang, W.; Jiang, D.; Gao, E.; Sun, S. Photoreduction of CO2 on BiOCl Nanoplates with the Assistance of Photoinduced Oxygen Vacancies. Nano Res. 2015, 8, 821−831.

(668) Jiang, D.; Wang, W.; Gao, E.; Sun, S.; Zhang, L. Highly Selective Defect-Mediated Photochemical CO2 Conversion over Fluorite Ceria under Ambient Conditions. Chem. Commun. 2014, 50, 2005−2007. (669) Xi, G.; Ouyang, S.; Li, P.; Ye, J.; Ma, Q.; Su, N.; Bai, H.; Wang, C. Ultrathin W18O49 Nanowires with Diameters Below 1 Nm: Synthesis, near-Infrared Absorption, Photoluminescence, and Photochemical Reduction of Carbon Dioxide. Angew. Chem., Int. Ed. 2012, 51, 2395−2399. (670) Zhu, S.; Liang, S.; Tong, Y.; An, X.; Long, J.; Fu, X.; Wang, X. Photocatalytic Reduction of CO2 with H2O to CH4 on Cu(I) Supported TiO2 Nanosheets with Defective {001} Facets. Phys. Chem. Chem. Phys. 2015, 17, 9761−9770. (671) Liu, Y.; Yang, Y.; Sun, Q.; Wang, Z.; Huang, B.; Dai, Y.; Qin, X.; Zhang, X. Chemical Adsorption Enhanced CO2 Capture and Photoreduction over a Copper Porphyrin Based Metal Organic Framework. ACS Appl. Mater. Interfaces 2013, 5, 7654−7658. (672) Liu, L.; Zhao, C.; Li, Y. Spontaneous Dissociation of CO2 to CO on Defective Surface of Cu(I)/TiO2−x Nanoparticles at Room Temperature. J. Phys. Chem. C 2012, 116, 7904−7912. (673) Ahmed, N.; Shibata, Y.; Taniguchi, T.; Izumi, Y. Photocatalytic Conversion of Carbon Dioxide into Methanol Using Zinc-CopperM(III) (M = Aluminum, Gallium) Layered Double Hydroxides. J. Catal. 2011, 279, 123−135. (674) Ahmed, N.; Morikawa, M.; Izumi, Y. Photocatalytic Conversion of Carbon Dioxide into Methanol Using Optimized Layered Double Hydroxide Catalysts. Catal. Today 2012, 185, 263− 269. (675) Yang, H.; He, X.-W.; Wang, F.; Kang, Y.; Zhang, J. Doping Copper into ZIF-67 for Enhancing Gas Uptake Capacity and VisibleLight-Driven Photocatalytic Degradation of Organic Dye. J. Mater. Chem. 2012, 22, 21849−21851. (676) Subrahmanyam, M.; Kaneco, S.; Alonso-Vante, N. A Screening for the Photo Reduction of Carbon Dioxide Supported on Metal Oxide Catalysts for C1-C3 Selectivity. Appl. Catal., B 1999, 23, 169− 174. (677) Centi, G.; Perathoner, S.; Wine, G.; Gangeri, M. Electrocatalytic Conversion of CO2 to Long Carbon-Chain Hydrocarbons. Green Chem. 2007, 9, 671−678. (678) Tan, S. S.; Zou, L.; Hu, E. Kinetic Modelling for Photosynthesis of Hydrogen and Methane through Catalytic Reduction of Carbon Dioxide with Water Vapour. Catal. Today 2008, 131, 125−129. (679) Shkrob, I. A.; Marin, T. W.; He, H.; Zapol, P. Photoredox Reactions and the Catalytic Cycle for Carbon Dioxide Fixation and Methanogenesis on Metal Oxides. J. Phys. Chem. C 2012, 116, 9450− 9460. (680) Dimitrijevic, N. M.; Shkrob, I. A.; Gosztola, D. J.; Rajh, T. Dynamics of Interfacial Charge Transfer to Formic Acid, Formaldehyde, and Methanol on the Surface of TiO2 Nanoparticles and Its Role in Methane Production. J. Phys. Chem. C 2012, 116, 878−885. (681) Kuhl, K. P.; Cave, E. R.; Abram, D. N.; Jaramillo, T. F. New Insights into the Electrochemical Reduction of Carbon Dioxide on Metallic Copper Surfaces. Energy Environ. Sci. 2012, 5, 7050−7059. (682) Schouten, K. J. P.; Kwon, Y.; van der Ham, C. J. M.; Qin, Z.; Koper, M. T. M. A New Mechanism for the Selectivity to C1 and C2 Species in the Electrochemical Reduction of Carbon Dioxide on Copper Electrodes. Chem. Sci. 2011, 2, 1902−1909. (683) Anpo, M.; Chiba, K. Photocatalytic Reduction of CO2 on Anchored Titanium Oxide Catalysts. J. Mol. Catal. 1992, 74, 207−212. (684) Yamashita, H.; Nishiguchi, H.; Kamada, N.; Anpo, M.; Teraoka, Y.; Hatano, H.; Ehara, S.; Kikui, K.; Palmisano, L.; Sclafani, A.; et al. Photocatalytic Reduction of CO2 with H2O on TiO2 and Cu/ TiO2 Catalysts. Res. Chem. Intermed. 1994, 20, 815−823. (685) Kohno, Y.; Tanaka, T.; Funabiki, T.; Yoshida, S. Reaction Mechanism in the Photoreduction of CO2 with CH4 over ZrO2. Phys. Chem. Chem. Phys. 2000, 2, 5302−5307. FY


Chemical Reviews

Review

Dioxide into Hydrocarbon Fuels. Energy Environ. Sci. 2010, 3, 1311− 1315. (707) Yoo, J. S.; Christensen, R.; Vegge, T.; Norskov, J. K.; Studt, F. Theoretical Insight into the Trends That Guide the Electrochemical Reduction of Carbon Dioxide to Formic Acid. ChemSusChem 2016, 9, 358−363. (708) Feaster, J. T.; Shi, C.; Cave, E. R.; Hatsukade, T.; Abram, D. N.; Kuhl, K. P.; Hahn, C.; Nørskov, J. K.; Jaramillo, T. F. Understanding Selectivity for the Electrochemical Reduction of Carbon Dioxide to Formic Acid and Carbon Monoxide on Metal Electrodes. ACS Catal. 2017, 7, 4822−4827. (709) Kuhl, K. P.; Hatsukade, T.; Cave, E. R.; Abram, D. N.; Kibsgaard, J.; Jaramillo, T. F. Electrocatalytic Conversion of Carbon Dioxide to Methane and Methanol on Transition Metal Surfaces. J. Am. Chem. Soc. 2014, 136, 14107−14113. (710) Yang, K. D.; Lee, C. W.; Jin, K.; Im, S. W.; Nam, K. T. Current Status and Bioinspired Perspective of Electrochemical Conversion of CO2 to a Long-Chain Hydrocarbon. J. Phys. Chem. Lett. 2017, 8, 538− 545. (711) Luo, W. J.; Nie, X. W.; Janik, M. J.; Asthagiri, A. Facet Dependence of CO2 Reduction Paths on Cu Electrodes. ACS Catal. 2016, 6, 219−229. (712) Baruch, M. F.; Pander, J. E.; White, J. L.; Bocarsly, A. B. Mechanistic Insights into the Reduction of CO2 on Tin Electrodes Using in Situ ATR-IR Spectroscopy. ACS Catal. 2015, 5, 3148−3156. (713) Rosen, J.; Hutchings, G. S.; Lu, Q.; Forest, R. V.; Moore, A.; Jiao, F. Electrodeposited Zn Dendrites with Enhanced CO Selectivity for Electrocatalytic CO2 Reduction. ACS Catal. 2015, 5, 4586−4591. (714) Deng, Y. L.; Yeo, B. S. Characterization of Electrocatalytic Water Splitting and CO2 Reduction Reactions Using in Situ/ Operando Raman Spectroscopy. ACS Catal. 2017, 7, 7873−7889. (715) Schmitt, K. G.; Gewirth, A. A. In Situ Surface-Enhanced Raman Spectroscopy of the Electrochemical Reduction of Carbon Dioxide on Silver with 3,5-Diamino-1,2,4-Triazole. J. Phys. Chem. C 2014, 118, 17567−17576. (716) Papasizza, M.; Cuesta, A. In Situ Monitoring Using ATR-Seiras of the Electrocatalytic Reduction of CO2 on Au in an Ionic Liquid/ Water Mixture. ACS Catal. 2018, 8, 6345−6352. (717) Yu, Y.; Mao, B. H.; Geller, A.; Chang, R.; Gaskell, K.; Liu, Z.; Eichhorn, B. W. CO2 Activation and Carbonate Intermediates: An Operando AP-XPS Study of CO2 Electrolysis Reactions on Solid Oxide Electrochemical Cells. Phys. Chem. Chem. Phys. 2014, 16, 11633−11639. (718) Kamat, P. V. Manipulation of Charge Transfer across Semiconductor Interface. A Criterion That Cannot be Ignored in Photocatalyst Design. J. Phys. Chem. Lett. 2012, 3, 663−672. (719) Tvrdy, K.; Frantsuzov, P. A.; Kamat, P. V. Photoinduced Electron Transfer from Semiconductor Quantum Dots to Metal Oxide Nanoparticles. Proc. Natl. Acad. Sci. U. S. A. 2011, 108, 29−34. (720) Harris, C.; Kamat, P. V. Photocatalytic Events of CdSe Quantum Dots in Confined Media. Electrodic Behavior of Coupled Platinum Nanoparticles. ACS Nano 2010, 4, 7321−7330. (721) Meekins, B. H.; Kamat, P. V. Role of Water Oxidation Catalyst IrO2 in Shuttling Photogenerated Holes across TiO2 Interface. J. Phys. Chem. Lett. 2011, 2, 2304−2310. (722) Wang, N.; Tachikawa, T.; Majima, T. Single-Molecule, SingleParticle Observation of Size-Dependent Photocatalytic Activity in Au/ TiO2 Nanocomposites. Chem. Sci. 2011, 2, 891−900. (723) Jin, S.; Lian, T. Electron Transfer Dynamics from Single CdSe/ ZnS Quantum Dots to TiO2 Nanoparticles. Nano Lett. 2009, 9, 2448− 2454. (724) Zhang, Z. Y.; Shao, C. L.; Li, X. H.; Sun, Y. Y.; Zhang, M. Y.; Mu, J. B.; Zhang, P.; Guo, Z. C.; Liu, Y. C. Hierarchical Assembly of Ultrathin Hexagonal SnS2 Nanosheets onto Electrospun TiO2 Nanofibers: Enhanced Photocatalytic Activity Based on Photoinduced Interfacial Charge Transfer. Nanoscale 2013, 5, 606−618. (725) Chen, R.; Pang, S.; An, H.; Zhu, J.; Ye, S.; Gao, Y.; Fan, F.; Li, C. Charge Separation via Asymmetric Illumination in Photocatalytic Cu2O Particles. Nature Energy 2018, 3, 655−663.

(686) Tan, S. S.; Zou, L.; Hu, E. Photocatalytic Reduction of Carbon Dioxide into Gaseous Hydrocarbon Using TiO2 Pellets. Catal. Today 2006, 115, 269−273. (687) Nie, X. W.; Esopi, M. R.; Janik, M. J.; Asthagiri, A. Selectivity of CO2 Reduction on Copper Electrodes: The Role of the Kinetics of Elementary Steps. Angew. Chem., Int. Ed. 2013, 52, 2459−2462. (688) Shkrob, I. A.; Dimitrijevic, N. M.; Marin, T. W.; He, H.; Zapol, P. Heteroatom-Transfer Coupled Photoreduction and Carbon Dioxide Fixation on Metal Oxides. J. Phys. Chem. C 2012, 116, 9461−9471. (689) Lee, C. W.; Cho, N. H.; Im, S. W.; Jee, M. S.; Hwang, Y. J.; Min, B. K.; Nam, K. T. New Challenges of Electrokinetic Studies in Investigating the Reaction Mechanism of Electrochemical CO2 Reduction. J. Mater. Chem. A 2018, 6, 14043−14057. (690) Takeda, H.; Cometto, C.; Ishitani, O.; Robert, M. Electrons, Photons, Protons and Earth-Abundant Metal Complexes for Molecular Catalysis of CO2 Reduction. ACS Catal. 2017, 7, 70−88. (691) Zhang, W. J.; Hu, Y.; Ma, L. B.; Zhu, G. Y.; Wang, Y. R.; Xue, X. L.; Chen, R. P.; Yang, S. Y.; Jin, Z. Progress and Perspective of Electrocatalytic CO2 Reduction for Renewable Carbonaceous Fuels and Chemicals. Advanced Science 2018, 5, No. 1700275. (692) Sun, Z. Y.; Ma, T.; Tao, H. C.; Fan, Q.; Han, B. X. Fundamentals and Challenges of Electrochemical CO2 Reduction Using Two-Dimensional Materials. Chem. 2017, 3, 560−587. (693) Costentin, C.; Robert, M.; Saveant, J. M. Catalysis of the Electrochemical Reduction of Carbon Dioxide. Chem. Soc. Rev. 2013, 42, 2423−2436. (694) Qiao, J. L.; Liu, Y. Y.; Hong, F.; Zhang, J. J. A Review of Catalysts for the Electroreduction of Carbon Dioxide to Produce LowCarbon Fuels. Chem. Soc. Rev. 2014, 43, 631−675. (695) Maina, J. W.; Pozo-Gonzalo, C.; Kong, L. X.; Schutz, J.; Hill, M.; Dumee, L. F. Metal Organic Framework Based Catalysts for CO2 Conversion. Mater. Horiz. 2017, 4, 345−361. (696) Lu, Q.; Jiao, F. Electrochemical CO2 Reduction: Electrocatalyst, Reaction Mechanism, and Process Engineering. Nano Energy 2016, 29, 439−456. (697) Zheng, Y.; Zhang, W. Q.; Li, Y. F.; Chen, J.; Yu, B.; Wang, J. C.; Zhang, L.; Zhang, J. J. Energy Related CO2 Conversion and Utilization: Advanced Materials/Nanomaterials, Reaction Mechanisms and Technologies. Nano Energy 2017, 40, 512−539. (698) Nielsen, D. U.; Hu, X. M.; Daasbjerg, K.; Skrydstrup, T. Chemically and Electrochemically Catalysed Conversion of CO2 to CO with Follow-up Utilization to Value-Added Chemicals. Nature Catalysis 2018, 1, 244−254. (699) Voiry, D.; Shin, H. S.; Loh, K. P.; Chhowalla, M. LowDimensional Catalysts for Hydrogen Evolution and CO2 Reduction. Nature Reviews Chemistry 2018, 2, 17105. (700) Trickett, C. A.; Helal, A.; Al-Maythalony, B. A.; Yamani, Z. H.; Cordova, K. E.; Yaghi, O. M. The Chemistry of Metal-Organic Frameworks for CO2 Capture, Regeneration and Conversion. Nature Reviews Materials 2017, 2, 17045. (701) Francke, R.; Schille, B.; Roemelt, M. Homogeneously Catalyzed Electroreduction of Carbon Dioxide-Methods, Mechanisms, and Catalysts. Chem. Rev. 2018, 118, 4631−4701. (702) Chen, Y.; Li, C. W.; Kanan, M. W. Aqueous CO2 Reduction at Very Low Overpotential on Oxide-Derived Au Nanoparticles. J. Am. Chem. Soc. 2012, 134, 19969−19972. (703) Peterson, A. A.; Nørskov, J. K. Activity Descriptors for CO2Electroreduction to Methane on Transition-Metal Catalysts. J. Phys. Chem. Lett. 2012, 3, 251−258. (704) Hansen, H. A.; Varley, J. B.; Peterson, A. A.; Norskov, J. K. Understanding Trends in the Electrocatalytic Activity of Metals and Enzymes for CO2Reduction to CO. J. Phys. Chem. Lett. 2013, 4, 388− 392. (705) Shi, C.; Hansen, H. A.; Lausche, A. C.; Norskov, J. K. Trends in Electrochemical CO2 Reduction Activity for Open and ClosePacked Metal Surfaces. Phys. Chem. Chem. Phys. 2014, 16, 4720−4727. (706) Peterson, A. A.; Abild-Pedersen, F.; Studt, F.; Rossmeisl, J.; Norskov, J. K. How Copper Catalyzes the Electroreduction of Carbon FZ


Chemical Reviews

Review

(726) Chen, R.; Fan, F.; Dittrich, T.; Li, C. Imaging Photogenerated Charge Carriers on Surfaces and Interfaces of Photocatalysts with Surface Photovoltage Microscopy. Chem. Soc. Rev. 2018, 47, 8238. (727) Zhu, J.; Fan, F.; Chen, R.; An, H.; Feng, Z.; Li, C. Direct Imaging of Highly Anisotropic Photogenerated Charge Separations on Different Facets of a Single BiVO4 Photocatalyst. Angew. Chem., Int. Ed. 2015, 54, 9111−9114. (728) Zhang, L. J.; Jiang, T. F.; Li, S.; Lu, Y. C.; Wang, L. L.; Zhang, X. Q.; Wang, D. J.; Xie, T. F. Enhancement of Photocatalytic H2 Evolution on Zn0.8Cd0.2S Loaded with CuS as Cocatalyst and Its Photogenerated Charge Transfer Properties. Dalton Trans. 2013, 42, 12998−13003. (729) Bi, L. L.; Meng, D. D.; Bu, Q. J.; Lin, Y. H.; Wang, D. J.; Xie, T. F. Electron Acceptor of Ni Decorated Porous Carbon Nitride Applied in Photocatalytic Hydrogen Production. Phys. Chem. Chem. Phys. 2016, 18, 31534−31541. (730) Li, S.; Hou, L. B.; Zhang, L. J.; Chen, L. P.; Lin, Y. H.; Wang, D. J.; Xie, T. F. Direct Evidence of the Efficient Hole Collection Process of the CoOx Cocatalyst for Photocatalytic Reactions: A Surface Photovoltage Study. J. Mater. Chem. A 2015, 3, 17820−17826. (731) Du, A.; Sanvito, S.; Li, Z.; Wang, D.; Jiao, Y.; Liao, T.; Sun, Q.; Ng, Y. H.; Zhu, Z.; Amal, R.; et al. Hybrid Graphene and Graphitic Carbon Nitride Nanocomposite: Gap Opening, Electron-Hole Puddle, Interfacial Charge Transfer, and Enhanced Visible Light Response. J. Am. Chem. Soc. 2012, 134, 4393−4397. (732) Huang, Q.; Tian, S.; Zeng, D.; Wang, X.; Song, W.; Li, Y.; Xiao, W.; Xie, C. Enhanced Photocatalytic Activity of Chemically Bonded TiO2/Graphene Composites Based on the Effective Interfacial Charge Transfer through the C−Ti Bond. ACS Catal. 2013, 3, 1477−1485. (733) Gillespie, P. N. O.; Martsinovich, N. Electronic Structure and Charge Transfer in the TiO2 Rutile (110)/Graphene Composite Using Hybrid DFT Calculations. J. Phys. Chem. C 2017, 121, 4158−4171. (734) Nakada, A.; Kuriki, R.; Sekizawa, K.; Nishioka, S.; Vequizo, J. J. M.; Uchiyama, T.; Kawakami, N.; Lu, D.; Yamakata, A.; Uchimoto, Y.; et al. Effects of Interfacial Electron Transfer in Metal Complex− Semiconductor Hybrid Photocatalysts on Z-Scheme CO2 Reduction under Visible Light. ACS Catal. 2018, 8, 9744−9754. (735) Wada, K.; Ranasinghe, C. S. K.; Kuriki, R.; Yamakata, A.; Ishitani, O.; Maeda, K. Interfacial Manipulation by Rutile TiO2 Nanoparticles to Boost CO2 Reduction into CO on a MetalComplex/Semiconductor Hybrid Photocatalyst. ACS Appl. Mater. Interfaces 2017, 9, 23869−23877. (736) Oshima, T.; Ichibha, T.; Qin, K. S.; Muraoka, K.; Vequizo, J. J. M.; Hibino, K.; Kuriki, R.; Yamashita, S.; Hongo, K.; Uchiyama, T.; et al. Undoped Layered Perovskite Oxynitride Li2LaTa2O6N for Photocatalytic CO2 Reduction with Visible Light. Angew. Chem., Int. Ed. 2018, 57, 8154−8158. (737) Kuriki, R.; Ranasinghe, C. S. K.; Yamazaki, Y.; Yamakata, A.; Ishitani, O.; Maeda, K. Excited-State Dynamics of Graphitic Carbon Nitride Photocatalyst and Ultrafast Electron Injection to a Ru(II) Mononuclear Complex for Carbon Dioxide Reduction. J. Phys. Chem. C 2018, 122, 16795−16802. (738) Li, S. W.; Xu, Y.; Chen, Y. F.; Li, W. Z.; Lin, L. L.; Li, M. Z.; Deng, Y. C.; Wang, X. P.; Ge, B. H.; Yang, C.; et al. Tuning the Selectivity of Catalytic Carbon Dioxide Hydrogenation over Iridium/ Cerium Oxide Catalysts with a Strong Metal-Support Interaction. Angew. Chem., Int. Ed. 2017, 56, 10761−10765. (739) Zhang, X.; Zhu, X. B.; Lin, L. L.; Yao, S. Y.; Zhang, M. T.; Liu, X.; Wang, X. P.; Li, Y. W.; Shi, C.; Ma, D. Highly Dispersed Copper over β-Mo2C as an Efficient and Stable Catalyst for the Reverse Water Gas Shift (RWGS) Reaction. ACS Catal. 2017, 7, 912−918. (740) Matsubu, J. C.; Zhang, S. Y.; DeRita, L.; Marinkovic, N. S.; Chen, J. G. G.; Graham, G. W.; Pan, X. Q.; Christopher, P. AdsorbateMediated Strong Metal-Support Interactions in Oxide-Supported Rh Catalysts. Nat. Chem. 2017, 9, 120−127. (741) Bruix, A.; Rodriguez, J. A.; Ramirez, P. J.; Senanayake, S. D.; Evans, J.; Park, J. B.; Stacchiola, D.; Liu, P.; Hrbek, J.; Illas, F. A New Type of Strong Metal-Support Interaction and the Production of H2

through the Transformation of Water on Pt/CeO2(111) and Pt/ CeOx/TiO2(110) Catalysts. J. Am. Chem. Soc. 2012, 134, 8968−8974. (742) Wang, L.; Zhang, J.; Zhu, Y. H.; Xu, S. D.; Wang, C. T.; Bian, C. Q.; Meng, X. J.; Xiao, F. S. Strong Metal-Support Interactions Achieved by Hydroxide-to-Oxide Support Transformation for Preparation of Sinter-Resistant Gold Nanoparticle Catalysts. ACS Catal. 2017, 7, 7461−7465. (743) Mao, M.; Lv, H.; Li, Y.; Yang, Y.; Zeng, M.; Li, N.; Zhao, X. Metal Support Interaction in Pt Nanoparticles Partially Confined in the Mesopores of Microsized Mesoporous CeO2 for Highly Efficient Purification of Volatile Organic Compounds. ACS Catal. 2016, 6, 418−427. (744) Tang, H.; Liu, F.; Wei, J.; Qiao, B.; Zhao, K.; Su, Y.; Jin, C.; Li, L.; Liu, J.; Wang, J.; et al. Ultrastable Hydroxyapatite/TitaniumDioxide-Supported Gold Nanocatalyst with Strong Metal-Support Interaction for Carbon Monoxide Oxidation. Angew. Chem., Int. Ed. 2016, 55, 10606−10611. (745) Ma, C.; Zhou, J.; Zhu, H.; Yang, W.; Liu, J.; Wang, Y.; Zou, Z. Constructing a High-Efficiency MoO3/Polyimide Hybrid Photocatalyst Based on Strong Interfacial Interaction. ACS Appl. Mater. Interfaces 2015, 7, 14628−14637. (746) Huang, Y.; Shang, Q.; Wang, D.; Yang, S.; Guan, H.; Lu, Q.; Tsang, S. C. Effects of Electronic Structure and Interfacial Interaction between Metal-Quinoline Complexes and TiO2 on Visible Light Photocatalytic Activity of TiO2. Appl. Catal., B 2016, 187, 59−66. (747) Wang, Y.; Zhou, J.; Hao, X.; Wang, Y.; Zou, Z. Fabricating Direct Z-Scheme PTCDA/g-C3N4 Photocatalyst Based on Interfacial Strong Interaction for Efficient Photooxidation of Benzylamine. Appl. Surf. Sci. 2018, 456, 861−870. (748) Kong, J.; Xian, F.; Wang, Y.; Ye, K.; Balogun, M.-S.; Gu, L.; Liu, X.; Rui, Z.; Ji, H. Boosting Interfacial Interaction in Hierarchical Core-Shell Nanostructure for Highly Effective Visible Photocatalytic Performance. J. Phys. Chem. C 2018, 122, 6137−6143. (749) Su, R.; Dimitratos, N.; Liu, J.; Carter, E.; Althahban, S.; Wang, X.; Shen, Y.; Wendt, S.; Wen, X.; Niemantsverdriet, J. W.; et al. Mechanistic Insight into the Interaction between a Titanium Dioxide Photocatalyst and Pd Cocatalyst for Improved Photocatalytic Performance. ACS Catal. 2016, 6, 4239−4247. (750) Colmenares, J. C.; Magdziarz, A.; Aramendia, M. A.; Marinas, A.; Marinas, J. M.; Urbano, F. J.; Navio, J. A. Influence of the Strong Metal Support Interaction Effect (SMSI) of Pt/TiO2 and Pd/TiO2 Systems in the Photocatalytic Biohydrogen Production from Glucose Solution. Catal. Commun. 2011, 16, 1−6. (751) Wang, S. Y.; Zeng, B.; Li, C. Effects of Au Nanoparticle Size and Metal-Support Interaction on Plasmon-Induced Photocatalytic Water Oxidation. Chin. J. Catal. 2018, 39, 1219−1227. (752) Ji, H. H.; Zhang, L. L.; Hu, C. Chemical-Bond Conjugated BiO(OH)XI1‑X-AgI Heterojunction with High Visible Light Activity and Stability in Degradation of Pollutants. Appl. Catal., B 2017, 218, 443−451. (753) Kisch, H.; Weiss, H. Tuning Photoelectrochemical and Photocatalytic Properties through Electronic Semiconductor-Support Interaction. Adv. Funct. Mater. 2002, 12, 483−488. (754) Yein, W. T.; Wang, Q.; Feng, X.; Li, Y.; Wu, X. Enhancement of Photocatalytic Performance in Sonochemical Synthesized ZnORGO Nanocomposites Owing to Effective Interfacial Interaction. Environ. Chem. Lett. 2018, 16, 251−264. (755) Zou, W.; Deng, B.; Hu, X.; Zhou, Y.; Pu, Y.; Yu, S.; Ma, K.; Sun, J.; Wan, H.; Dong, L. Crystal-Plane-Dependent Metal OxideSupport Interaction in CeO2/g-C3N4 for Photocatalytic Hydrogen Evolution. Appl. Catal., B 2018, 238, 111−118. (756) Wu, H. Y.; Yang, K.; Si, Y.; Huang, W. Q.; Hu, W. Y.; Peng, P.; Huang, G. F. Interfacial Interaction between Boron Cluster and Metal Oxide Surface and Its Effects: A Case Study of B20/Ag3PO4 Van Der Waals Heterostructure. J. Phys. Chem. C 2018, 122, 6151−6158. (757) Zhou, Y.; Zhang, X.; Zhang, Q.; Dong, F.; Wang, F.; Xiong, Z. Role of Graphene on the Band Structure and Interfacial Interaction of Bi2WO6/Graphene Composites with Enhanced Photocatalytic Oxidation of No. J. Mater. Chem. A 2014, 2, 16623−16631. GA


Chemical Reviews

Review

Electrochemical Reduction of CO2. Conversion and Management 2011, 51, 30−32. (777) D’Arienzo, M.; Carbajo, J.; Bahamonde, A.; Crippa, M.; Polizzi, S.; Scotti, R.; Wahba, L.; Morazzoni, F. Photogenerated Defects in Shape-Controlled TiO2 Anatase Nanocrystals: A Probe to Evaluate the Role of Crystal Facets in Photocatalytic Processes. J. Am. Chem. Soc. 2011, 133, 17652−17661. (778) Zhang, G.; Lan, Z.-A.; Wang, X. Merging Surface Organometallic Chemistry with Graphitic Carbon Nitride Photocatalysis for CO2 Photofixation. ChemCatChem 2015, 7, 1422−1423. (779) Indrakanti, V. P.; Kubicki, J. D.; Schobert, H. H. Quantum Chemical Modeling of Ground States of CO2 Chemisorbed on Anatase (001), (101), and (010) TiO2 Surfaces. Energy Fuels 2008, 22, 2611−2618. (780) Li, K.; Peng, T.; Ying, Z.; Song, S.; Zhang, J. Ag-Loading on Brookite TiO2 Quasi Nanocubes with Exposed {210} and {001} Facets: Activity and Selectivity of CO2 Photoreduction to CO/CH4. Appl. Catal., B 2016, 180, 130−138. (781) Liu, L.; Jiang, Y.; Zhao, H.; Chen, J.; Cheng, J.; Yang, K.; Li, Y. Engineering Coexposed {001} and {101} Facets in Oxygen-Deficient TiO2 Nanocrystals for Enhanced CO2 Photoreduction under Visible Light. ACS Catal. 2016, 6, 1097−1108. (782) Xiong, Z.; Luo, Y.; Zhao, Y.; Zhang, J.; Zheng, C.; Wu, J. C. S. Synthesis, Characterization and Enhanced Photocatalytic CO 2 Reduction Activity of Graphene Supported TiO2 Nanocrystals with Coexposed {001} and {101} Facets. Phys. Chem. Chem. Phys. 2016, 18, 13186−13195. (783) Akple, M. S.; Low, J.; Qin, Z.; Wageh, S.; Al-Ghamdi, A. A.; Yu, J.; Liu, S. Nitrogen-Doped TiO2 Microsheets with Enhanced Visible Light Photocatalytic Activity for CO2 Reduction. Chin. J. Catal. 2015, 36, 2127−2134. (784) Cao, Y.; Li, Q.; Li, C.; Li, J.; Yang, J. Surface Heterojunction between (001) and (101) Facets of Ultrafine Anatase TiO 2 Nanocrystals for Highly Efficient Photoreduction CO2 to CH4. Appl. Catal., B 2016, 198, 378−388. (785) Xiong, Z.; Lei, Z.; Chen, X. X.; Gong, B. G.; Zhao, Y. C.; Zhang, J. Y.; Zheng, C. G.; Wu, J. C. S. CO2 Photocatalytic Reduction over Pt Deposited TiO2 Nanocrystals with Coexposed {101} and {001} Facets: Effect of Deposition Method and Pt Precursors. Catal. Commun. 2017, 96, 1−5. (786) Truong, Q. D.; Hoa, H. T.; Vo, D. V. N.; Le, T. S. Controlling the Shape of Anatase Nanocrystals for Enhanced Photocatalytic Reduction of CO2 to Methanol. New J. Chem. 2017, 41, 5660−5668. (787) Zhao, Y. L.; Wei, Y. C.; Wu, X. X.; Zheng, H. L.; Zhao, Z.; Liu, J.; Li, J. M. Graphene-Wrapped Pt/TiO2 Photocatalysts with Enhanced Photogenerated Charges Separation and Reactant Adsorption for High Selective Photoreduction of CO2 to CH4. Appl. Catal., B 2018, 226, 360−372. (788) Jin, J.; Luo, J.; Zan, L.; Peng, T. One-Pot Synthesis of CuNanocluster-Decorated Brookite TiO2 quasi-Nanocubes for Enhanced Activity and Selectivity of CO2 Photoreduction to CH4. ChemPhysChem 2017, 18, 3230−3239. (789) Wang, C. J.; Thompson, R. L.; Ohodnicki, P.; Baltrus, J.; Matranga, C. Size-Dependent Photocatalytic Reduction of CO2 with PbS Quantum Dot Sensitized TiO2 Heterostructured Photocatalysts. J. Mater. Chem. 2011, 21, 13452−13457. (790) Xu, H.; Chen, X.; Ouyang, S.; Kako, T.; Ye, J. Size-Dependent Mie’s Scattering Effect on TiO2 Spheres for the Superior Photoactivity of H2 Evolution. J. Phys. Chem. C 2012, 116, 3833−3839. (791) Jiang, Z. Y.; Liang, X. Z.; Zheng, H. L.; Liu, Y. Y.; Wang, Z. Y.; Wang, P.; Zhang, X. Y.; Qin, X. Y.; Dai, Y.; Whangbo, M. H.; et al. Photocatalytic Reduction of CO2 to Methanol by Three-Dimensional Hollow Structures of Bi2WO6 Quantum Dots. Appl. Catal., B 2017, 219, 209−215. (792) Sarkar, A.; Gracia-Espino, E.; Wagberg, T.; Shchukarev, A.; Mohl, M.; Rautio, A.-R.; Pitkanen, O.; Sharifi, T.; Kordas, K.; Mikkola, J.-P. Photocatalytic Reduction of CO2 with H2O over Modified TiO2 Nanofibers: Understanding the Reduction Pathway. Nano Res. 2016, 9, 1956−1968.

(758) Xu, L.; Huang, W.-Q.; Wang, L.-L.; Huang, G.-F. Interfacial Interactions of Semiconductor with Graphene and Reduced Graphene Oxide: CeO2 as a Case Study. ACS Appl. Mater. Interfaces 2014, 6, 20350−20357. (759) Fujiwara, K.; Okuyama, K.; Pratsinis, S. E. Metal-Support Interactions in Catalysts for Environmental Remediation. Environ. Sci.: Nano 2017, 4, 2076−2092. (760) Jaafar, N. F.; Jalil, A. A.; Triwahyono, S. Visible-Light Photoactivity of Plasmonic Silver Supported on Mesoporous TiO2 Nanoparticles (Ag-MTN) for Enhanced Degradation of 2-Chlorophenol: Limitation of Ag-Ti Interaction. Appl. Surf. Sci. 2017, 392, 1068− 1077. (761) Anpo, M.; Thomas, J. M. Single-Site Photocatalytic Solids for the Decomposition of Undesirable Molecules. Chem. Commun. 2006, 42, 3273−3278. (762) Xu, Q.; Yu, J.; Zhang, J.; Zhang, J.; Liu, G. Cubic Anatase TiO2 Nanocrystals with Enhanced Photocatalytic CO2 Reduction Activity. Chem. Commun. 2015, 51, 7950−7953. (763) Liu, Q.; Zhou, Y.; Ma, Y.; Zou, Z. G. Synthesis of Highly Crystalline In2Ge2O7(En) Hybrid Sub-Nanowires with Ultraviolet Photoluminescence Emissions and Their Selective Photocatalytic Reduction of CO2 into Renewable Fuel. RSC Adv. 2012, 2, 3247− 3250. (764) Wang, W.-N.; Wu, F.; Myung, Y.; Niedzwiedzki, D. M.; Im, H. S.; Park, J.; Banerjee, P.; Biswas, P. Surface Engineered CuO Nanowires with ZnO Islands for CO2 Photoreduction. ACS Appl. Mater. Interfaces 2015, 7, 5685−5692. (765) Zhu, S.; Liang, S.; Bi, J.; Liu, M.; Zhou, L.; Wu, L.; Wang, X. Photocatalytic Reduction of CO2 with H2O to CH4 over Ultrathin SnNb2O6 2D Nanosheets under Visible Light Irradiation. Green Chem. 2016, 18, 1355−1363. (766) Tang, L.; Kuai, L.; Li, Y.; Li, H.; Zhou, Y.; Zou, Z. ZnXCd1−XS Tunable Band Structure-Directing Photocatalytic Activity and Selectivity of Visible-Light Reduction of CO2 into Liquid Solar Fuels. Nanotechnology 2018, 29, 064003. (767) Qamar, S.; Lei, F.; Liang, L.; Gao, S.; Liu, K.; Sun, Y.; Ni, W.; Xie, Y. Ultrathin TiO2 Flakes Optimizing Solar Light Driven CO2Reduction. Nano Energy 2016, 26, 692−698. (768) Zhang, L.; Zhao, Z. J.; Wang, T.; Gong, J. L. Nano-Designed Semiconductors for Electro- and Photoelectro-Catalytic Conversion of Carbon Dioxide. Chem. Soc. Rev. 2018, 47, 5423−5443. (769) Ye, L.; Jin, X.; Ji, X.; Liu, C.; Su, Y.; Xie, H.; Liu, C. FacetDependent Photocatalytic Reduction of CO2 on BiOI Nanosheets. Chem. Eng. J. 2016, 291, 39−46. (770) Sajan, C. P.; Wageh, S.; Al-Ghamdi, A. A.; Yu, J.; Cao, S. TiO2 Nanosheets with Exposed {001} Facets for Photocatalytic Applications. Nano Res. 2016, 9, 3−27. (771) He, Z.; Wen, L.; Wang, D.; Xue, Y.; Lu, Q.; Wu, C.; Chen, J.; Song, S. Photocatalytic Reduction of CO2 in Aqueous Solution on Surface-Fluorinated Anatase TiO2 Nanosheets with Exposed {001} Facets. Energy Fuels 2014, 28, 3982−3993. (772) Xu, H.; Ouyang, S. X.; Li, P.; Kako, T.; Ye, J. H. High-Active Anatase TiO2 Nanosheets Exposed with 95% {100} Facets toward Efficient H2 Evolution and CO2Photoreduction. ACS Appl. Mater. Interfaces 2013, 5, 1348−1354. (773) Wang, W.; Lu, C. H.; Ni, Y. R.; Song, J. B.; Su, M. X.; Xu, Z. Z. Enhanced Visible-Light Photoactivity of {001} Facets Dominated TiO2 Nanosheets with Even Distributed Bulk Oxygen Vacancy and Ti3+. Catal. Commun. 2012, 22, 19−23. (774) Ferus, M.; Kavan, L.; Zukalova, M.; Zukal, A.; Klementova, M.; Civis, S. Spontaneous and Photoinduced Conversion of CO2 on TiO2 Anatase (001)/(101) Surfaces. J. Phys. Chem. C 2014, 118, 26845− 26850. (775) Truong, Q. D.; Hoa, H. T.; Le, T. S. Rutile TiO2 Nanocrystals with Exposed {331) Facets for Enhanced Photocatalytic CO2 Reduction Activity. J. Colloid Interface Sci. 2017, 504, 223−229. (776) Fernandes, T. R. C.; Machado, A. S. R.; Rangel, C.; Condeco, J.; Pardal, T. Scale-up of a System for Hydrocarbon Production by GB


Chemical Reviews

Review

(812) Niu, P.; Yang, Y.; Yu, J. C.; Liu, G.; Cheng, H.-M. Switching the Selectivity of the Photoreduction Reaction of Carbon Dioxide by Controlling the Band Structure of a g-C3N4 Photocatalyst. Chem. Commun. 2014, 50, 10837−10840. (813) Ong, W.-J.; Tan, L.-L.; Chai, S.-P.; Yong, S.-T.; Mohamed, A. R. Surface Charge Modification Via Protonation of Graphitic Carbon Nitride (g-C3N4) for Electrostatic Self-Assembly Construction of 2D/ 2D Reduced Graphene Oxide (RGO)/g-C3N4 Nanostructures toward Enhanced Photocatalytic Reduction of Carbon Dioxide to Methane. Nano Energy 2015, 13, 757−770. (814) Gao, G.; Jiao, Y.; Waclawik, E. R.; Du, A. Single Atom (Pd/Pt) Supported on Graphitic Carbon Nitride as an Efficient Photocatalyst for Visible-Light Reduction of Carbon Dioxide. J. Am. Chem. Soc. 2016, 138, 6292−6297. (815) Zhou, Y.; Tian, Z.; Zhao, Z.; Liu, Q.; Kou, J.; Chen, X.; Gao, J.; Yan, S.; Zou, Z. High-Yield Synthesis of Ultrathin and Uniform Bi2WO6 Square Nanoplates Benefitting from Photocatalytic Reduction of CO2 into Renewable Hydrocarbon Fuel under Visible Light. ACS Appl. Mater. Interfaces 2011, 3, 3594−3601. (816) Jin, J.; Wang, Y.; He, T. Preparation of Thickness-Tunable BiOCl Nanosheets with High Photocatalytic Activity for Photoreduction of CO2. RSC Adv. 2015, 5, 100244−100250. (817) Ma, Z. Y.; Li, P. H.; Ye, L. Q.; Zhou, Y.; Su, F. Y.; Ding, C. H.; Xie, H. Q.; Bai, Y.; Wong, P. K. Oxygen Vacancies Induced Exciton Dissociation of Flexible BiOCl Nanosheets for Effective Photocatalytic CO2 Conversion. J. Mater. Chem. A 2017, 5, 24995−25004. (818) Wu, D.; Ye, L. Q.; Yip, H. Y.; Wong, P. K. Organic-Free Synthesis of {001} Facet Dominated BiOBr Nanosheets for Selective Photoreduction of CO2 to CO. Catal. Sci. Technol. 2017, 7, 265−271. (819) Li, L.; Han, Q. T.; Tang, L. Q.; Zhang, Y.; Li, P.; Zhou, Y.; Zou, Z. G. Flux Synthesis of Regular Bi4TaO8Cl Square Nanoplates Exhibiting Dominant Exposure Surfaces of {001} Crystal Facets for Photocatalytic Reduction of CO2 to Methane. Nanoscale 2018, 10, 1905−1911. (820) Yin, G.; Nishikawa, M.; Nosaka, Y.; Srinivasan, N.; Atarashi, D.; Sakai, E.; Miyauchi, M. Photocatalytic Carbon Dioxide Reduction by Copper Oxide Nanocluster-Grafted Niobate Nanosheets. ACS Nano 2015, 9, 2111−2119. (821) Zhou, P.; Wang, X.; Yan, S.; Zou, Z. Solid Solution Photocatalyst with Spontaneous Polarization Exhibiting Low Recombination toward Efficient CO2 Photoreduction. ChemSusChem 2016, 9, 2064−2068. (822) Li, K.; Handoko, A. D.; Khraisheh, M.; Tang, J. Photocatalytic Reduction of CO2 and Protons Using Water as an Electron Donor over Potassium Tantalate Nanoflakes. Nanoscale 2014, 6, 9767−9773. (823) Ye, L.; Wang, H.; Jin, X.; Su, Y.; Wang, D.; Xie, H.; Liu, X.; Liu, X. Synthesis of Olive-Green Few-Layered BiOI for Efficient Photoreduction of CO2 into Solar Fuels under Visible/near-Infrared Light. Sol. Energy Mater. Sol. Cells 2016, 144, 732−739. (824) Guan, M.; Xiao, C.; Zhang, J.; Fan, S.; An, R.; Cheng, Q.; Xie, J.; Zhou, M.; Ye, B.; Xie, Y. Vacancy Associates Promoting SolarDriven Photocatalytic Activity of Ultrathin Bismuth Oxychloride Nanosheets. J. Am. Chem. Soc. 2013, 135, 10411−10417. (825) Wei, W.; Dai, Y.; Huang, B. First-Principles Characterization of Bi-Based Photocatalysts: Bi12TiO20Bi2Ti2O7 and Bi4Ti3O12. J. Phys. Chem. C 2009, 113, 5658−5663. (826) Shang, J.; Hao, W.; Lv, X.; Wang, T.; Wang, X.; Du, Y.; Dou, S.; Xie, T.; Wang, D.; Wang, J. Bismuth Oxybromide with Reasonable Photocatalytic Reduction Activity under Visible Light. ACS Catal. 2014, 4, 954−961. (827) Ye, L.; Jin, X.; Liu, C.; Ding, C.; Xie, H.; Chu, K. H.; Wong, P. K. Thickness-Ultrathin and Bismuth-Rich Strategies for BiOBr to Enhance Photoreduction of CO2 into Solar Fuels. Appl. Catal., B 2016, 187, 281−290. (828) Zhang, G.; Su, A.; Qu, J.; Xu, Y. Synthesis of BiOI Flowerlike Hierarchical Structures toward Photocatalytic Reduction of CO2 to CH4. Mater. Res. Bull. 2014, 55, 43−47. (829) Guo, Q.; Zhang, Q.; Wang, H.; Liu, Z.; Zhao, Z. Core-Shell Structured Zno@Cu-Zn-Al Layered Double Hydroxides with

(793) Zhou, P.; Gao, H. L.; Yan, S. C.; Zou, Z. G. The Kirkendall Effect Towards Oxynitride Nanotubes with Improved Visible Light Driven Conversion of CO2 into CH4. Dalton Trans. 2016, 45, 3480− 3485. (794) Jin, J. R.; He, T. Facile Synthesis of Bi2S3 Nanoribbons for Photocatalytic Reduction of CO2 into CH3OH. Appl. Surf. Sci. 2017, 394, 364−370. (795) Li, P.; Zhou, Y.; Tu, W.; Wang, R.; Zhang, C.; Liu, Q.; Li, H.; Li, Z.; Dai, H.; Wang, J.; et al. Synthesis of Bi6Mo2O15 Sub-Microwires Via a Molten Salt Method and Enhancing the Photocatalytic Reduction of CO2 into Solar Fuel through Tuning the Surface Oxide Vacancies by Simple Post-Heating Treatment. CrystEngComm 2013, 15, 9855−9858. (796) Yang, Z.; Wang, H.; Song, W.; Wei, W.; Mu, Q.; Kong, B.; Li, P.; Yin, H. One Dimensional SnO2 NrS/Fe2O NTs with Dual Synergistic Effects for Photoelectrocatalytic Reduction CO2 into Methanol. J. Colloid Interface Sci. 2017, 486, 232−240. (797) Pan, Y.-X.; You, Y.; Xin, S.; Li, Y.; Fu, G.; Cui, Z.; Men, Y.-L.; Cao, F.-F.; Yu, S.-H.; Goodenough, J. B. Photocatalytic CO2 Reduction by Carbon-Coated Indium-Oxide Nanobelts. J. Am. Chem. Soc. 2017, 139, 4123−4129. (798) Feng, S.; Chen, X.; Zhou, Y.; Tu, W.; Li, P.; Li, H.; Zou, Z. Na2V6O16XH2O Nanoribbons: Large-Scale Synthesis and Visible-Light Photocatalytic Activity of CO2 into Solar Fuels. Nanoscale 2014, 6, 1896−1900. (799) Zheng, Y.; Lin, L. H.; Ye, X. J.; Guo, F. S.; Wang, X. C. Helical Graphitic Carbon Nitrides with Photocatalytic and Optical Activities. Angew. Chem., Int. Ed. 2014, 53, 11926−11930. (800) Pan, B.; Luo, S.; Su, W.; Wang, X. Photocatalytic CO2 Reduction with H2O over LaPO4 Nanorods Deposited with Pt Cocatalyst. Appl. Catal., B 2015, 168, 458−464. (801) Pang, R.; Teramura, K.; Asakura, H.; Hosokawa, S.; Tanaka, T. Highly Selective Photocatalytic Conversion of CO2 by Water over AgLoaded SrNb2O6Nanorods. Appl. Catal., B 2017, 218, 770−778. (802) Xie, S.; Wang, Y.; Zhang, Q.; Deng, W.; Wang, Y. SrNb2O6 Nanoplates as Efficient Photocatalysts for the Preferential Reduction of CO2 in the Presence of H2O. Chem. Commun. 2015, 51, 3430− 3433. (803) Chen, J.; Xin, F.; Yin, X.; Xiang, T.; Wang, Y. Synthesis of Hexagonal and Cubic ZnIn2S4 Nanosheets for the Photocatalytic Reduction of CO2 with Methanol. RSC Adv. 2015, 5, 3833−3839. (804) Chen, Y.; Jia, G.; Hu, Y. F.; Fan, G. Z.; Tsang, Y. H.; Li, Z. S.; Zou, Z. G. Two-Dimensional Nanomaterials for Photocatalytic CO2 Reduction to Solar Fuels. Sustainable Energy & Fuels 2017, 1, 1875− 1898. (805) Tan, C.; Cao, X.; Wu, X.-J.; He, Q.; Yang, J.; Zhang, X.; Chen, J.; Zhao, W.; Han, S.; Nam, G.-H.; et al. Recent Advances in Ultrathin Two-Dimensional Nanomaterials. Chem. Rev. 2017, 117, 6225−6331. (806) Sun, Z. Y.; Talreja, N.; Tao, H. C.; Texter, J.; Muhler, M.; Strunk, J.; Chen, J. F. Catalysis of Carbon Dioxide Photoreduction on Nanosheets: Fundamentals and Challenges. Angew. Chem., Int. Ed. 2018, 57, 7610−7627. (807) Xin, X.; Xu, T.; Wang, L.; Wang, C. Ti3+-Self Doped Brookite TiO2 Single-Crystalline Nanosheets with High Solar Absorption and Excellent Photocatalytic CO2 Reduction. Sci. Rep. 2016, 6, 23684. (808) Wang, M.; Han, Q.; Zhou, Y.; Li, P.; Tu, W.; Tang, L.; Zou, Z. TiO2 Nanosheet-Anchoring Au Nanoplates: High-Energy Facet and Wide Spectra Surface Plasmon-Promoting Photocatalytic Efficiency and Selectivity for CO2 Reduction. RSC Adv. 2016, 6, 81510−81516. (809) Zhang, S. F.; Yin, X. H.; Zheng, Y. A. Enhanced Photocatalytic Reduction of CO2 to Methanol by ZnO Nanoparticles Deposited on ZnSe Nanosheet. Chem. Phys. Lett. 2018, 693, 170−175. (810) Jiao, X. C.; Li, X. D.; Jin, X. Y.; Sun, Y. F.; Xu, J. Q.; Liang, L.; Ju, H. X.; Zhu, J. F.; Pan, Y.; Yan, W. S.; et al. Partially Oxidized SnS2 Atomic Layers Achieving Efficient Visible-Light-Driven CO2 Reduction. J. Am. Chem. Soc. 2017, 139, 18044−18051. (811) Huang, Y.; Wang, Y.; Bi, Y.; Jin, J.; Ehsan, M. F.; Fu, M.; He, T. Preparation of 2D Hydroxyl-Rich Carbon Nitride Nanosheets for Photocatalytic Reduction of CO2. RSC Adv. 2015, 5, 33254−33261. GC


Chemical Reviews

Review

Enhanced Photocatalytic Efficiency for CO2 Reduction. Catal. Commun. 2016, 77, 118−122. (830) Liu, B.; Ye, L. Q.; Wang, R.; Yang, J. F.; Zhang, Y. X.; Guan, R.; Tian, L. H.; Chen, X. B. Phosphorus-Doped Graphitic Carbon Nitride Nanotubes with Amino-Rich Surface for Efficient CO2 Capture, Enhanced Photocatalytic Activity, and Product Selectivity. ACS Appl. Mater. Interfaces 2018, 10, 4001−4009. (831) Zhao, Z. K.; Ge, G. F.; Zhang, D. Heteroatom-Doped Carbonaceous Photocatalysts for Solar Fuel Production and Environmental Remediation. ChemCatChem 2018, 10, 62−123. (832) Wang, P.; Yin, G. H.; Bi, Q. Y.; Huang, X. Y.; Du, X. L.; Zhao, W.; Huang, F. Q. Efficient Photocatalytic Reduction of CO2 Using Carbon-Doped Amorphous Titanium Oxide. ChemCatChem 2018, 10, 3854−3861. (833) Huang, Y. Q.; Yan, Q.; Yan, H. J.; Tang, Y. Q.; Chen, S.; Yu, Z. Y.; Tian, C. G.; Jiang, B. J. Layer Stacked Iodine and Phosphorus CoDoped C3N4 for Enhanced Visible-Light Photocatalytic Hydrogen Evolution. ChemCatChem 2017, 9, 4083−4089. (834) Huang, Z. Y.; Gao, Z. G.; Gao, S. M.; Wang, Q. Y.; Wang, Z. Y.; Huang, B. B.; Dai, Y. Facile Synthesis of S-Doped Reduced TiO2‑X with Enhanced Visible-Light Photocatalytic Performance. Chin. J. Catal. 2017, 38, 821−830. (835) Deng, L.; Xie, Y.; Zhang, G. Synthesis of C-Cl-Codoped Titania/Attapulgite Composites with Enhanced Visible-Light Photocatalytic Activity. Chin. J. Catal. 2017, 38, 379−388. (836) Fan, Q. J.; Liu, J. J.; Yu, Y. C.; Zuo, S. L.; Li, B. S. A Simple Fabrication for Sulfur Doped Graphitic Carbon Nitride Porous Rods with Excellent Photocatalytic Activity Degrading Rhb Dye. Appl. Surf. Sci. 2017, 391, 360−368. (837) Chai, B.; Yan, J.; Wang, C.; Ren, Z.; Zhu, Y. Enhanced Visible Light Photocatalytic Degradation of Rhodamine B over Phosphorus Doped Graphitic Carbon Nitride. Appl. Surf. Sci. 2017, 391, 376−383. (838) Bao, N.; Hu, X. D.; Zhang, Q. Z.; Miao, X. H.; Jie, X. Y.; Zhou, S. Synthesis of Porous Carbon-Doped g-C3N4 Nanosheets with Enhanced Visible-Light Photocatalytic Activity. Appl. Surf. Sci. 2017, 403, 682−690. (839) He, D.; Li, Y.; Wang, I.; Wu, J.; Yang, Y.; An, Q. Carbon Wrapped and Doped TiO2 Mesoporous Nanostructure with Efficient Visible-Light Photocatalysis for NO Removal. Appl. Surf. Sci. 2017, 391, 318−325. (840) Peng, Y.-P.; Yeh, Y.-T.; Shah, S. I.; Huang, C. P. Concurrent Photoelectrochemical Reduction of CO2 and Oxidation of Methyl Orange Using Nitrogen-Doped TiO2. Appl. Catal., B 2012, 123, 414− 423. (841) Ong, W.-J.; Tan, L.-L.; Chai, S.-P.; Yong, S.-T.; Mohamed, A. R. Self-Assembly of Nitrogen-Doped TiO2 with Exposed {001} Facets on a Graphene Scaffold as Photo-Active Hybrid Nanostructures for Reduction of Carbon Dioxide to Methane. Nano Res. 2014, 7, 1528− 1547. (842) Zhao, Z. H.; Fan, J. M.; Wang, J. Y.; Li, R. F. Effect of Heating Temperature on Photocatalytic Reduction of CO2 by N-TiO2 Nanotube Catalyst. Catal. Commun. 2012, 21, 32−37. (843) Li, F.; Zhang, L.; Chen, X.; Liu, Y. L.; Xu, S. G.; Cao, S. K. Synergistically Enhanced Photocatalytic Reduction of CO2 on N-Fe Codoped BiVO4 under Visible Light Irradiation. Phys. Chem. Chem. Phys. 2017, 19, 21862−21868. (844) Tsai, C.-W.; Chen, H. M.; Liu, R.-S.; Asakura, K.; Chan, T.-S. Ni@NiO Core−Shell Structure-Modified Nitrogen-Doped InTaO4 for Solar-Driven Highly Efficient CO2 Reduction to Methanol. J. Phys. Chem. C 2011, 115, 10180−10186. (845) Akimov, A. V.; Asahi, R.; Jinnouchi, R.; Prezhdo, O. V. What Makes the Photocatalytic CO2 Reduction on N-Doped Ta2O5 Efficient: Insights from Nonadiabatic Molecular Dynamics. J. Am. Chem. Soc. 2015, 137, 11517−11525. (846) Tan, L.-L.; Ong, W.-J.; Chai, S.-P.; Mohamed, A. R. Band Gap Engineered, Oxygen-Rich TiO2 for Visible Light Induced Photocatalytic Reduction of CO2. Chem. Commun. 2014, 50, 6923−6926. (847) Tan, L.-L.; Ong, W.-J.; Chai, S.-P.; Mohamed, A. R. VisibleLight-Activated Oxygen-Rich TiO2 as Next Generation Photocatalyst:

Importance of Annealing Temperature on the Photoactivity toward Reduction of Carbon Dioxide. Chem. Eng. J. 2016, 283, 1254−1263. (848) Tan, L. L.; Ong, W. J.; Chai, S. P.; Mohamed, A. R. Photocatalytic Reduction of CO2 with H2O over Graphene Oxide Supported Oxygen-Rich TiO2 Hybrid Photocatalyst under Visible Light Irradiation: Process and Kinetic Studies. Chem. Eng. J. 2017, 308, 248−255. (849) Yoshitomi, F.; Sekizawa, K.; Maeda, K.; Ishitani, O. Selective Formic Acid Production via CO2 Reduction with Visible Light Using a Hybrid of a Perovskite Tantalum Oxynitride and a Binuclear Ruthenium(II) Complex. ACS Appl. Mater. Interfaces 2015, 7, 13092−13097. (850) Hafez, A. M.; Zedan, A. F.; AlQaradawi, S. Y.; Salem, N. M.; Allam, N. K. Computational Study on Oxynitride Perovskites for CO2 Photoreduction. Energy Convers. Manage. 2016, 122, 207−214. (851) Zhang, Z.; Huang, Z.; Cheng, X.; Wang, Q.; Chen, Y.; Dong, P.; Zhang, X. Product Selectivity of Visible-Light Photocatalytic Reduction of Carbon Dioxide Using Titanium Dioxide Doped by Different Nitrogen-Sources. Appl. Surf. Sci. 2015, 355, 45−51. (852) Lee, D. K.; Choi, J. I.; Lee, G. H.; Kim, Y.-H.; Kang, J. K. Energy States of a Core-Shell Metal Oxide Photocatalyst Enabling Visible Light Absorption and Utilization in Solar-to-Fuel Conversion of Carbon Dioxide. Adv. Energy Mater. 2016, 6, 1600583. (853) Sun, Z.; Wang, S.; Li, Q.; Lyu, M.; Butburee, T.; Luo, B.; Wang, H.; Fischer, J. M. T. A.; Zhang, C.; Wu, Z.; et al. Enriching CO2 Activation Sites on Graphitic Carbon Nitride with Simultaneous Introduction of Electron-Transfer Promoters for Superior Photocatalytic CO2-to-Fuel Conversion. Advanced Sustainable Systems 2017, 1, 1700003. (854) Yu, H.; Yan, S. C.; Zhou, P.; Zou, Z. G. CO2 Photoreduction on Hydroxyl-Group-Rich Mesoporous Single Crystal TiO2. Appl. Surf. Sci. 2018, 427, 603−607. (855) Wang, Y.; Huang, N. Y.; Shen, J. Q.; Liao, P. Q.; Chen, X. M.; Zhang, J. P. Hydroxide Ligands Cooperate with Catalytic Centers in Metal-Organic Frameworks for Efficient Photocatalytic CO2 Reduction. J. Am. Chem. Soc. 2018, 140, 38−41. (856) He, Z.; Tang, J.; Shen, J.; Chen, J.; Song, S. Enhancement of Photocatalytic Reduction of CO2 to CH4 over TiO2 Nanosheets by Modifying with Sulfuric Acid. Appl. Surf. Sci. 2016, 364, 416−427. (857) Liu, G.; Wang, T.; Zhang, H.; Meng, X.; Hao, D.; Chang, K.; Li, P.; Kako, T.; Ye, J. Nature-Inspired Environmental “Phosphorylation” Boosts Photocatalytic H2 Production over Carbon Nitride Nanosheets under Visible-Light Irradiation. Angew. Chem. 2015, 127, 13765−13769. (858) Ye, L.; Wu, D.; Chu, K. H.; Wang, B.; Xie, H.; Yip, H. Y.; Wong, P. K. Phosphorylation of g-C3N4 for Enhanced Photocatalytic CO2 Reduction. Chem. Eng. J. 2016, 304, 376−383. (859) Iguchi, S.; Teramura, K.; Hosokawa, S.; Tanaka, T. Photocatalytic Conversion of CO2 in Water Using Fluorinated Layered Double Hydroxides as Photocatalysts. Appl. Catal., A 2016, 521, 160−167. (860) Zhang, Q. Y.; Li, Y.; Ackerman, E. A.; Gajdardziska-Josifovska, M.; Li, H. L. Visible Light Responsive Iodine-Doped TiO2 for Photocatalytic Reduction of CO2 to Fuels. Appl. Catal., A 2011, 400, 195−202. (861) He, Z.; Yu, Y.; Wang, D.; Tang, J.; Chen, J.; Song, S. Photocatalytic Reduction of Carbon Dioxide Using Iodine-Doped Titanium Dioxide with High Exposed {001} Facets under Visible Light. RSC Adv. 2016, 6, 23134−23140. (862) Zhu, B.; Zhang, J.; Jiang, C.; Cheng, B.; Yu, J. First Principle Investigation of Halogen-Doped Monolayer g-C3N4 Photocatalyst. Appl. Catal., B 2017, 207, 27−34. (863) Navaee, A.; Salimi, A. Specific Anion Effects on Copper Surface through Electrochemical Treatment: Enhanced Photoelectrochemical CO2 Reduction Activity of Derived Nanostructures Induced by Chaotropic Anions. Appl. Surf. Sci. 2018, 440, 897−906. (864) Shevlin, S. A.; Guo, Z. X. Anionic Dopants for Improved Optical Absorption and Enhanced Photocatalytic Hydrogen Production in Graphitic Carbon Nitride. Chem. Mater. 2016, 28, 7250−7256. GD


Chemical Reviews

Review

(865) Yamashita, H.; Ikeue, K.; Takewaki, T.; Anpo, M. In Situ XAFS Studies on the Effects of the Hydrophobic-Hydrophilic Properties of Ti-BeTa Zeolites in the Photocatalytic Reduction of CO2 with H2O. Top. Catal. 2002, 18, 95−100. (866) Ikeue, K.; Yamashita, H.; Takewaki, T.; Davis, M. E.; Anpo, M. Characterization of Ti-Beta Zeolites and Their Reactivity for the Photocatalytic Reduction of CO2 with H2O. J. Synchrotron Radiat. 2001, 8, 602−604. (867) Lv, K.; Cheng, B.; Yu, J.; Liu, G. Fluorine Ions-Mediated Morphology Control of Anatase TiO2 with Enhanced Photocatalytic Activity. Phys. Chem. Chem. Phys. 2012, 14, 5349−5362. (868) Park, H.; Park, Y.; Kim, W.; Choi, W. Surface Modification of TiO2 Photocatalyst for Environmental Applications. J. Photochem. Photobiol., C 2013, 15, 1−20. (869) Dozzi, M. V.; D’Andrea, C.; Ohtani, B.; Valentini, G.; Selli, E. Fluorine-Doped TiO2 Materials: Photocatalytic Activity vs TimeResolved Photoluminescence. J. Phys. Chem. C 2013, 117, 25586− 25595. (870) Wu, Y.; Xing, M.; Tian, B.; Zhang, J.; Chen, F. Preparation of Nitrogen and Fluorine Co-Doped Mesoporous TiO2 Microsphere and Photodegradation of Acid Orange 7 under Visible Light. Chem. Eng. J. 2010, 162, 710−717. (871) Yu, C.; Fan, Q.; Xie, Y.; Chen, J.; Shu, Q.; Yu, J. C. Sonochemical Fabrication of Novel Square-Shaped F Doped TiO2 Nanocrystals with Enhanced Performance in Photocatalytic Degradation of Phenol. J. Hazard. Mater. 2012, 237, 38−45. (872) Yu, C.; Zhou, W.; Yang, K.; Rong, G. Hydrothermal Synthesis of Hemisphere-Like F-Doped Anatase TiO2 with Visible Light Photocatalytic Activity. J. Mater. Sci. 2010, 45, 5756−5761. (873) Ho, W.; Yu, J. C.; Lee, S. Synthesis of Hierarchical Nanoporous F-Doped TiO2 Spheres with Visible Light Photocatalytic Activity. Chem. Commun. 2006, 1115−1117. (874) Lamiel-Garcia, O.; Tosoni, S.; Illas, F. Relative Stability of FCovered TiO2 Anatase (101) and (001) Surfaces from Periodic DFT Calculations and Ab Initio Atomistic Thermodynamics. J. Phys. Chem. C 2014, 118, 13667−13673. (875) Tosoni, S.; Lamiel-Garcia, O.; Fernandez Hevia, D.; Doña, J. M.; Illas, F. Electronic Structure of F-Doped Bulk Rutile, Anatase, and Brookite Polymorphs of TiO2. J. Phys. Chem. C 2012, 116, 12738− 12746. (876) Yu, J. C.; Yu, J. G.; Ho, W. K.; Jiang, Z. T.; Zhang, L. Z. Effects of F- Doping on the Photocatalytic Activity and Microstructures of Nanocrystalline TiO2 Powders. Chem. Mater. 2002, 14, 3808−3816. (877) Yu, J. C.; Ho, W. K.; Yu, J. G.; Hark, S. K.; Iu, K. Effects of Trifluoroacetic Acid Modification on the Surface Microstructures and Photocatalytic Activity of Mesoporous TiO2 Thin Films. Langmuir 2003, 19, 3889−3896. (878) Yu, C.; Yu, J. C.; Chan, M. Sonochemical Fabrication of Fluorinated Mesoporous Titanium Dioxide Microspheres. J. Solid State Chem. 2009, 182, 1061−1069. (879) Yu, J.; Xiang, Q.; Ran, J.; Mann, S. One-Step Hydrothermal Fabrication and Photocatalytic Activity of Surface-Fluorinated TiO2 Hollow Microspheres and Tabular Anatase Single Micro-Crystals with High-Energy Facets. CrystEngComm 2010, 12, 872−879. (880) Yu, J.; Wang, W.; Cheng, B.; Su, B.-L. Enhancement of Photocatalytic Activity of Mesporous TiO2 Powders by Hydrothermal Surface Fluorination Treatment. J. Phys. Chem. C 2009, 113, 6743− 6750. (881) Yu, J.; Shi, L. One-Pot Hydrothermal Synthesis and Enhanced Photocatalytic Activity of Trifluoroacetic Acid Modified TiO2 Hollow Microspheres. J. Mol. Catal. A: Chem. 2010, 326, 8−14. (882) Wang, X. F.; Yu, R.; Wang, P.; Chen, F.; Yu, H. G. CoModification of F- and Fe(III) Ions as a Facile Strategy Towards Effective Separation of Photogenerated Electrons and Holes. Appl. Surf. Sci. 2015, 351, 66−73. (883) Cheng, J.; Chen, J.; Lin, W.; Liu, Y.; Kong, Y. Improved Visible Light Photocatalytic Activity of Fluorine and Nitrogen Co-Doped TiO2 with Tunable Nanoparticle Size. Appl. Surf. Sci. 2015, 332, 573− 580.

(884) Ikeue, K.; Yamashita, H.; Anpo, M.; Takewaki, T. Photocatalytic Reduction of CO2 with H2O on Ti-Beta Zeolite Photocatalysts: Effect of the Hydrophobic and Hydrophilic Properties. J. Phys. Chem. B 2001, 105, 8350−8355. (885) Yuan, L.; Han, C.; Pagliaro, M.; Xu, Y.-J. Origin of Enhancing the Photocatalytic Performance of TiO2 for Artificial Photoreduction of CO2 through a SiO2 Coating Strategy. J. Phys. Chem. C 2016, 120, 265−273. (886) Wu, D.; Ye, L.; Yue, S.; Wang, B.; Wang, W.; Yip, H. Y.; Wong, P. K. Alkali-Induced in Situ Fabrication of Bi2O4-Decorated BiOBr Nanosheets with Excellent Photocatalytic Performance. J. Phys. Chem. C 2016, 120, 7715−7727. (887) Zhao, H. L.; Chen, J. T.; Rao, G. Y.; Deng, W.; Li, Y. Enhancing Photocatalytic CO2 Reduction by Coating an Ultrathin Al2O3 Layer on Oxygen Deficient TiO2 Nanorods through Atomic Layer Deposition. Appl. Surf. Sci. 2017, 404, 49−56. (888) Zhao, H. L.; Zheng, X. Y.; Feng, X. H.; Li, Y. CO2 Reduction by Plasmonic Au Nanoparticle-Decorated TiO2 Photocatalyst with an Ultrathin Al2O3 Interlayer. J. Phys. Chem. C 2018, 122, 18949−18956. (889) Feng, X.; Pan, F. P.; Zhao, H. L.; Deng, W.; Zhang, P.; Zhou, H. C.; Li, Y. Atomic Layer Deposition Enabled MgO Surface Coating on Porous TiO2 for Improved CO2 Photoreduction. Appl. Catal., B 2018, 238, 274−283. (890) Fang, W. Z.; Khrouz, L.; Zhou, Y.; Shen, B.; Dong, C. Y.; Xing, M. Y.; Mishra, S.; Daniele, S.; Zhang, J. L. Reduced {001}-TiO2-X Photocatalysts: Noble-Metal-Free CO2 Photoreduction for Selective CH4Evolution. Phys. Chem. Chem. Phys. 2017, 19, 13875−13881. (891) Chen, X. B.; Liu, L.; Yu, P. Y.; Mao, S. S. Increasing Solar Absorption for Photocatalysis with Black Hydrogenated Titanium Dioxide Nanocrystals. Science 2011, 331, 746−750. (892) Liu, L.; Chen, X. B. Titanium Dioxide Nanomaterials: SelfStructural Modifications. Chem. Rev. 2014, 114, 9890−9918. (893) Long, M. C.; Zheng, L. H. Engineering Vacancies for Solar Photocatalytic Applications. Chin. J. Catal. 2017, 38, 617−624. (894) Li, H.; Li, J.; Ai, Z. H.; Jia, F. L.; Zhang, L. Z. Oxygen VacancyMediated Photocatalysis of Biocl: Reactivity, Selectivity, and Perspectives. Angew. Chem., Int. Ed. 2018, 57, 122−138. (895) Pan, X.; Yang, M.-Q.; Fu, X.; Zhang, N.; Xu, Y.-J. Defective TiO2 with Oxygen Vacancies: Synthesis, Properties and Photocatalytic Applications. Nanoscale 2013, 5, 3601−3614. (896) Li, X. H.; Zhang, J.; Zhou, F.; Zhang, H. L.; Bai, J.; Wang, Y. J.; Wang, H. Y. Preparation of N-Vacancy-Doped g-C3N4 with Outstanding Photocatalytic H2O2Production Ability by Dielectric Barrier Discharge Plasma Treatment. Chin. J. Catal. 2018, 39, 1090−1098. (897) Liu, L. J.; Gao, F.; Zhao, H. L.; Li, Y. Tailoring Cu Valence and Oxygen Vacancy in Cu/TiO2 Catalysts for Enhanced CO2 Photoreduction Efficiency. Appl. Catal., B 2013, 134, 349−358. (898) Fujiwara, H.; Hosokawa, H.; Murakoshi, K.; Wada, Y.; Yanagida, S.; Okada, T.; Kobayashi, H. Effect of Surface Structures on Photocatalytic CO2 Reduction Using Quantized CdS Nanocrystallites. J. Phys. Chem. B 1997, 101, 8270−8278. (899) Fujiwara, H.; Hosokawa, H.; Murakoshi, K.; Wada, Y.; Yanagida, S. Surface Characteristics of ZnS Nanocrystallites Relating to Their Photocatalysis for CO2 Reduction1. Langmuir 1998, 14, 5154−5159. (900) Li, J. L.; Zhang, M.; Guan, Z. J.; Li, Q. Y.; He, C. Q.; Yang, J. J. Synergistic Effect of Surface and Bulk Single-Electron-Trapped Oxygen Vacancy of TiO2 in the Photocatalytic Reduction of CO2. Appl. Catal., B 2017, 206, 300−307. (901) Kong, X. Y.; Lee, W. P. C.; Ong, W. J.; Chai, S. P.; Mohamed, A. R. Oxygen-Deficient BiOBr as a Highly Stable Photocatalyst for Efficient CO2 Reduction into Renewable Carbon-Neutral Fuels. ChemCatChem 2016, 8, 3074−3081. (902) Tu, W.; Xu, Y.; Wang, J.; Zhang, B.; Zhou, T.; Yin, S.; Wu, S.; Li, C.; Huang, Y.; Zhou, Y.; et al. Investigating the Role of Tunable Nitrogen Vacancies in Graphitic Carbon Nitride Nanosheets for Efficient Visible-Light-Driven H2 Evolution and CO2 Reduction. ACS Sustainable Chem. Eng. 2017, 5, 7260−7268. GE


Chemical Reviews

Review

(922) Sui, D. D.; Yin, X. H.; Dong, H. Z.; Qin, S. Y.; Chen, J. S.; Jiang, W. L. Photocatalytically Reducing CO2 to Methyl Formate in Methanol over Ag Loaded SrTiO3 Nanocrystal Catalysts. Catal. Lett. 2012, 142, 1202−1210. (923) Yang, X. X.; Xin, W. Y.; Yin, X. H.; Shao, X. Enhancement of Photocatalytic Activity in Reducing CO2 over CdS/g-C3N4 Composite Catalysts under Uv Light Irradiation. Chem. Phys. Lett. 2016, 651, 127−132. (924) Guo, L.-J.; Wang, Y.-J.; He, T. Photocatalytic Reduction of CO2 over Heterostructure Semiconductors into Value-Added Chemicals. Chemical record (New York, N.Y.) 2016, 16, 1918−1933. (925) Cheng, N.; Banis, M. N.; Liu, J.; Riese, A.; Li, X.; Li, R.; Ye, S.; Knights, S.; Sun, X. Extremely Stable Platinum Nanoparticles Encapsulated in a Zirconia Nanocage by Area-Selective Atomic Layer Deposition for the Oxygen Reduction Reaction. Adv. Mater. 2015, 27, 277−281. (926) Ma, Y.; Wang, X.; Li, C. Charge Separation Promoted by Phase Junctions in Photocatalysts. Chin. J. Catal. 2015, 36, 1519−1527. (927) Low, J.; Jiang, C.; Cheng, B.; Wageh, S.; Al-Ghamdi, A. A.; Yu, J. A Review of Direct Z-Scheme Photocatalysts. Small Methods 2017, 1, 1700080. (928) Li, X.; Liu, H. L.; Luo, D. L.; Li, J. T.; Huang, Y.; Li, H. L.; Fang, Y. P.; Xu, Y. H.; Zhu, L. Adsorption of CO2 on Heterostructure CdS(Bi2S3)/TiO2 Nanotube Photocatalysts and Their Photocatalytic Activities in the Reduction of CO2 to Methanol under Visible Light Irradiation. Chem. Eng. J. 2012, 180, 151−158. (929) Zhao, H. L.; Liu, L. J.; Andino, J. M.; Li, Y. Bicrystalline TiO2 with Controllable Anatase-Brookite Phase Content for Enhanced CO2 Photoreduction to Fuels. J. Mater. Chem. A 2013, 1, 8209−8216. (930) Wang, P. Q.; Bai, Y.; Liu, J. Y.; Fan, Z.; Hu, Y. Q. One-Pot Synthesis of Rutile TiO2 Nanoparticle Modified Anatase TiO2 Nanorods toward Enhanced Photocatalytic Reduction of CO2 into Hydrocarbon Fuels. Catal. Commun. 2012, 29, 185−188. (931) Chen, L.; Graham, M. E.; Li, G. H.; Gentner, D. R.; Dimitrijevic, N. M.; Gray, K. A. Photoreduction of CO2 by TiO2 Nanocomposites Synthesized through Reactive Direct Current Magnetron Sputter Deposition. Thin Solid Films 2009, 517, 5641− 5645. (932) Truong, Q. D.; Le, T. H.; Liu, J. Y.; Chung, C. C.; Ling, Y. C. Synthesis of TiO2 Nanoparticles Using Novel Titanium Oxalate Complex Towards Visible Light-Driven Photocatalytic Reduction of CO2 to CH3OH. Appl. Catal., A 2012, 437, 28−35. (933) Li, G.; Ciston, S.; Saponjic, Z. V.; Chen, L.; Dimitrijevic, N. M.; Rajh, T.; Gray, K. A. Synthesizing Mixed-Phase TiO2 Nanocomposites Using a Hydrothermal Method for Photo-Oxidation and Photoreduction Applications. J. Catal. 2008, 253, 105−110. (934) Kim, K.; Razzaq, A.; Sorcar, S.; Grimes, C.; In, S.-I.; Park, Y. Hybrid Mesoporous Cu2ZnSnS4 (CZTS)-TiO2 Photocatalyst for Efficient Photocatalytic Conversion of CO2 into CH4 under Solar Irradiation. RSC Adv. 2016, 6, 38964−38971. (935) Yuan, Y. J.; Yu, Z. T.; Zhang, J. Y.; Zou, Z. G. A Copper(I) Dye-Sensitised TiO2-Based System for Efficient Light Harvesting and Photoconversion of CO2 into Hydrocarbon Fuel. Dalton Trans. 2012, 41, 9594−9597. (936) Zhao, Z.; Fan, J.; Liu, S.; Wang, Z. Optimal Design and Preparation of Titania-Supported CoPc Using Sol-Gel for the PhotoReduction of CO2. Chem. Eng. J. 2009, 151, 134−140. (937) Zhao, Z. H.; Fan, J. M.; Wang, Z. Z. Photo-Catalytic CO2 Reduction Using Sol-Gel Derived Titania-Supported Zinc-Phthalocyanine. J. Cleaner Prod. 2007, 15, 1894−1897. (938) Zhao, Z. H.; Fan, J. M.; Xie, M. M.; Wang, Z. Z. PhotoCatalytic Reduction of Carbon Dioxide with in-Situ Synthesized CoPc/TiO2 under Visible Light Irradiation. J. Cleaner Prod. 2009, 17, 1025−1029. (939) Nguyen, T. V.; Wu, J. C. S.; Chiou, C. H. Photoreduction of CO2 over Ruthenium Dye-Sensitized TiO2-Based Catalysts under Concentrated Natural Sunlight. Catal. Commun. 2008, 9, 2073−2076.

(903) Xin, C. Y.; Hu, M. C.; Wang, K.; Wang, X. T. Significant Enhancement of Photocatalytic Reduction of CO2 with H2O over ZnO by the Formation of Basic Zinc Carbonate. Langmuir 2017, 33, 6667−6676. (904) Yin, G. H.; Bi, Q. Y.; Zhao, W.; Xu, J. J.; Lin, T. Q.; Huang, F. Q. Efficient Conversion of CO2 to Methane Photocatalyzed by Conductive Black Titania. ChemCatChem 2017, 9, 4389−4396. (905) Kong, X. Y.; Choo, Y. Y.; Chai, S. P.; Soh, A. K.; Mohamed, A. R. Oxygen Vacancy Induced Bi2WO6 for the Realization of Photocatalytic CO2 Reduction over the Full Solar Spectrum: From the Uv to the Nir Region. Chem. Commun. 2016, 52, 14242−14245. (906) Pan, Y. X.; Sun, Z. Q.; Cong, H. P.; Men, Y. L.; Xin, S.; Song, J.; Yu, S. H. Photocatalytic CO2 Reduction Highly Enhanced by Oxygen Vacancies on Pt-Nanoparticle-Dispersed Gallium Oxide. Nano Res. 2016, 9, 1689−1700. (907) Lu, L.; Wang, B.; Wang, S.; Shi, Z.; Yan, S.; Zou, Z. La2O3Modified LaTiO2N Photocatalyst with Spatially Separated Active Sites Achieving Enhanced CO2 Reduction. Adv. Funct. Mater. 2017, 27, 1702447. (908) Hou, J. G.; Cao, S. Y.; Wu, Y. Z.; Liang, F.; Sun, Y. F.; Lin, Z. S.; Sun, L. C. Simultaneously Efficient Light Absorption and Charge Transport of Phosphate and Oxygen-Vacancy Confined in Bismuth Tungstate Atomic Layers Triggering Robust Solar CO2 Reduction. Nano Energy 2017, 32, 359−366. (909) Hoch, L. B.; Wood, T. E.; O’Brien, P. G.; Liao, K.; Reyes, L. M.; Mims, C. A.; Ozin, G. A. The Rational Design of a SingleComponent Photocatalyst for Gas-Phase CO2 Reduction Using Both Uv and Visible Light. Advanced Science 2014, 1, 1400013. (910) Ozin, G. A. Throwing New Light on the Reduction of CO2. Adv. Mater. 2015, 27, 1957−1963. (911) Ghuman, K. K.; Hoch, L. B.; Szymanski, P.; Loh, J. Y. Y.; Kherani, N. P.; El-Sayed, M. A.; Ozin, G. A.; Singh, C. V. Photoexcited Surface Frustrated Lewis Pairs for Heterogeneous Photocatalytic CO2 Reduction. J. Am. Chem. Soc. 2016, 138, 1206−1214. (912) Wang, B.; Wang, X. H.; Lu, L.; Zhou, C. G.; Xin, Z. Y.; Wang, J. J.; Ke, X. K.; Sheng, G. D.; Yan, S. C.; Zou, Z. G. Oxygen-VacancyActivated CO2 Splitting over Amorphous Oxide Semiconductor Photocatalyst. ACS Catal. 2018, 8, 516−525. (913) Ye, C.; Li, J.-X.; Li, Z.-J.; Li, X.-B.; Fan, X.-B.; Zhang, L.-P.; Chen, B.; Tung, C.-H.; Wu, L.-Z. Enhanced Driving Force and Charge Separation Efficiency of Protonated g-C3N4 for Photocatalytic O2 Evolution. ACS Catal. 2015, 5, 6973−6979. (914) Yu, L. J.; Zhang, X. H.; Zhuang, C. S.; Lin, L.; Li, R. J.; Peng, T. Y. Syntheses of Asymmetric Zinc Phthalocyanines as Sensitizer of PtLoaded Graphitic Carbon Nitride for Efficient Visible/near-Ir-LightDriven H2 Production. Phys. Chem. Chem. Phys. 2014, 16, 4106−4114. (915) Yamashita, H.; Shiga, A.; Kawasaki, S.-i.; Ichihashi, Y.; Ehara, S.; Anpo, M. Photocatalytic Synthesis of CH4 and CH3OH from CO2 and H2O on Highly Dispersed Active Titanium Oxide Catalysts. Energy Convers. Manage. 1995, 36, 617−620. (916) Liu, B.-J.; Torimoto, T.; Matsumoto, H.; Yoneyama, H. Effect of Solvents on Photocatalytic Reduction of Carbon Dioxide Using TiO2 Nanocrystal Photocatalyst Embedded in SiO2 Matrices. J. Photochem. Photobiol., A 1997, 108, 187−192. (917) Kaneco, S.; Kurimoto, H.; Shimizu, Y.; Ohta, K.; Mizuno, T. Photocatalytic Reduction of CO2 Using TiO2 Powders in Supercritical Fluid CO2. Energy 1999, 24, 21−30. (918) Kaneco, S.; Kurimoto, H.; Ohta, K.; Mizuno, T.; Saji, A. Photocatalytic Reduction of CO2 Using TiO2 Powders in Liquid CO2 Medium. J. Photochem. Photobiol., A 1997, 109, 59−63. (919) Dodds, W. S.; Stutzman, L. F.; Sollami, B. J. Carbon Dioxide Solubility in Water. Chem. Eng. Data Ser. 1956, 1, 92−95. (920) Chen, J.; Xin, F.; Qin, S.; Yin, X. Photocatalytically Reducing CO2 to Methyl Formate in Methanol over ZnS and Ni-Doped ZnS Photocatalysts. Chem. Eng. J. 2013, 230, 506−512. (921) Qin, S. Y.; Xin, F.; Liu, Y. D.; Yin, X. H.; Ma, W. Photocatalytic Reduction of CO2 in Methanol to Methyl Formate over CuO-TiO2 Composite Catalysts. J. Colloid Interface Sci. 2011, 356, 257−261. GF


Chemical Reviews

Review

CO2 under Simulated Sunlight Irradiation. Appl. Surf. Sci. 2017, 402, 198−207. (958) Raziq, F.; Qu, Y.; Zhang, X.; Humayun, M.; Wu, J.; Zada, A.; Yu, H.; Sun, X.; Jing, L. Enhanced Cocatalyst-Free Visible-Light Activities for Photocatalytic Fuel Production of g-C3N4 by Trapping Holes and Transferring Electrons. J. Phys. Chem. C 2016, 120, 98−107. (959) Gondal, M. A.; Dastageer, M. A.; Oloore, L. E.; Baig, U. Laser Induced Selective Photo-Catalytic Reduction of CO2 into Methanol Using In2O3-WO3 Nano-Composite. J. Photochem. Photobiol., A 2017, 343, 40−50. (960) Zhang, X.; Wang, L.; Du, Q.; Wang, Z.; Ma, S.; Yu, M. Photocatalytic CO2 Reduction over B4C/C3N4 with Internal Electric Field under Visible Light Irradiation. J. Colloid Interface Sci. 2016, 464, 89−95. (961) Ou, M.; Tu, W.; Yin, S.; Xing, W.; Wu, S.; Wang, H.; Wan, S.; Zhong, Q.; Xu, R. Amino-Assisted Anchoring of CsPbBr3 Perovskite Quantum Dots on Porous g-C3N4 for Enhanced Photocatalytic CO2 Reduction. Angew. Chem., Int. Ed. 2018, 57, 13570−13574. (962) He, Y.; Wang, Y.; Zhang, L.; Teng, B.; Fan, M. High-Efficiency Conversion of CO2 to Fuel over ZnO/g-C3N4 Photocatalyst. Appl. Catal., B 2015, 168-169, 1−8. (963) Yuan, Y.-P.; Cao, S.-W.; Liao, Y.-S.; Yin, L.-S.; Xue, C. Red Phosphor/ g-C3N4 Heterojunction with Enhanced Photocatalytic Activities for Solar Fuels Production. Appl. Catal., B 2013, 140, 164− 168. (964) Li, M.; Zhang, L.; Wu, M.; Du, Y.; Fan, X.; Wang, M.; Zhang, L.; Kong, Q.; Shi, J. Mesostructured CeO2/g-C3N4 Nanocomposites: Remarkably Enhanced Photocatalytic Activity for CO2 Reduction by Mutual Component Activations. Nano Energy 2016, 19, 145−155. (965) Shi, L.; Wang, T.; Zhang, H.; Chang, K.; Ye, J. Electrostatic Self-Assembly of Nanosized Carbon Nitride Nanosheet onto a Zirconium Metal-Organic Framework for Enhanced Photocatalytic CO2 Reduction. Adv. Funct. Mater. 2015, 25, 5360−5367. (966) Zhou, J.; Chen, W.; Sun, C.; Han, L.; Qin, C.; Chen, M.; Wang, X.; Wang, E.; Su, Z. Oxidative Polyoxometalates Modified Graphitic Carbon Nitride for Visible-Light CO2 Reduction. ACS Appl. Mater. Interfaces 2017, 9, 11689−11695. (967) Liu, H.; Zhang, Z.; Meng, J. C.; Zhang, J. Novel Visible-LightDriven CdIn2S4/Mesoporous g-C3N4 Hybrids for Efficient Photocatalytic Reduction of CO2 to Methanol. Molecular Catalysis 2017, 430, 9−19. (968) Wang, N. Y.; Yan, S. C.; Zou, Z. G. Photoreduction of CO2 into Hydrocarbons Catalysed by ZnGa2O4/Ga2O3 Heterojunction. Curr. Org. Chem. 2013, 17, 2454−2458. (969) Ong, W.-J.; Putri, L. K.; Tan, L.-L.; Chai, S.-P.; Yong, S.-T. Heterostructured AgX/g-C3N4 (X = Cl and Br) Nanocomposites via a Sonication-Assisted Deposition-Precipitation Approach: Emerging Role of Halide Ions in the Synergistic Photocatalytic Reduction of Carbon Dioxide. Appl. Catal., B 2016, 180, 530−543. (970) Cao, S.-W.; Liu, X.-F.; Yuan, Y.-P.; Zhang, Z.-Y.; Liao, Y.-S.; Fang, J.; Loo, S. C. J.; Sum, T. C.; Xue, C. Solar-to-Fuels Conversion over In2O3/g-C3N4 Hybrid Photocatalysts. Appl. Catal., B 2014, 147, 940−946. (971) Shi, H.; Chen, G.; Zhang, C.; Zou, Z. Polymeric g-C3N4 Coupled with NaNbO3 Nanowires toward Enhanced Photocatalytic Reduction of CO2 into Renewable Fuel. ACS Catal. 2014, 4, 3637− 3643. (972) Lu, L.; Wang, S. M.; Zhou, C. G.; Shi, Z.; Zhu, H.; Xin, Z. Y.; Wang, X. H.; Yan, S. C.; Zou, Z. G. Surface Chemistry Imposes Selective Reduction of CO2 to CO over Ta3N5/LaTiO2N Photocatalyst. J. Mater. Chem. A 2018, 6, 14838−14846. (973) Li, P.; Xu, H.; Liu, L. Q.; Kako, T.; Umezawa, N.; Abe, H.; Ye, J. H. Constructing Cubic-Orthorhombic Surface-Phase Junctions of NaNbO3 Towards Significant Enhancement of CO2 Photoreduction. J. Mater. Chem. A 2014, 2, 5606−5609. (974) Yu, J.; Wang, S.; Low, J.; Xiao, W. Enhanced Photocatalytic Performance of Direct Z-Scheme g-C3N4-TiO2 Photocatalysts for the Decomposition of Formaldehyde in Air. Phys. Chem. Chem. Phys. 2013, 15, 16883−16890.

(940) Xu, H.; Ouyang, S. X.; Liu, L. Q.; Wang, D. F.; Kako, T.; Ye, J. H. Porous-Structured Cu2O/TiO2 Nanojunction Material toward Efficient CO2 Photoreduction. Nanotechnology 2014, 25, 165402. (941) Wang, J.; Ji, G.; Liu, Y.; Gondal, M. A.; Chang, X. Cu2O/TiO2 Heterostructure Nanotube Arrays Prepared by an Electrodeposition Method Exhibiting Enhanced Photocatalytic Activity for CO 2 Reduction to Methanol. Catal. Commun. 2014, 46, 17−21. (942) Zhao, J.; Wang, Y.; Li, Y. X.; Yue, X.; Wang, C. Y. PhaseDependent Enhancement for CO2 Photocatalytic Reduction over CeO2/TiO2 Catalysts. Catal. Sci. Technol. 2016, 6, 7967−7975. (943) Yan, Y.; Yu, Y.; Wu, D.; Yang, Y.; Cao, Y. TiO2/Vanadate (Sr10V6O25Ni3V2O8Zn2V2O7) Heterostructured Photocatalysts with Enhanced Photocatalytic Activity for Photoreduction of CO2 into CH4. Nanoscale 2016, 8, 949−958. (944) Xi, G. C.; Ouyang, S. X.; Ye, J. H. General Synthesis of Hybrid TiO2 Mesoporous ″French Fries″ toward Improved Photocatalytic Conversion of CO2 into Hydrocarbon Fuel: A Case of TiO2/ZnO. Chem. - Eur. J. 2011, 17, 9057−9061. (945) Lee, J. H.; Kim, S. I.; Park, S. M.; Kang, M. A P-N Heterojunction NiS-Sensitized TiO2Photocatalytic System for Efficient Photoreduction of Carbon Dioxide to Methane. Ceram. Int. 2017, 43, 1768−1774. (946) Crake, A.; Christoforidis, K. C.; Kafizas, A.; Zafeiratos, S.; Petit, C. CO2 Capture and Photocatalytic Reduction Using Bifunctional TiO2/MOF Nanocomposites under Uv-Vis Irradiation. Appl. Catal., B 2017, 210, 131−140. (947) Kim, H. R.; Razzaq, A.; Grimes, C. A.; In, S. I. Heterojunction P-N-P Cu2O/S-TiO2/CuO: Synthesis and Application to Photocatalytic Conversion of CO2 to Methane. J. CO2 Util. 2017, 20, 91− 96. (948) Zhou, M.; Wang, S. B.; Yang, P. J.; Huang, C. J.; Wang, X. C. Boron Carbon Nitride Semiconductors Decorated with CdS Nanoparticles for Photocatalytic Reduction of CO2. ACS Catal. 2018, 8, 4928−4936. (949) Raziq, F.; Qu, Y.; Humayun, M.; Zada, A.; Yu, H.; Jing, L. Synthesis of SnO2/B-P Codoped g-C3N4 Nanocomposites as Efficient Cocatalyst-Free Visible-Light Photocatalysts for CO2 Conversion and Pollutant Degradation. Appl. Catal., B 2017, 201, 486−494. (950) Su, Y.; Zhang, Z.; Liu, H.; Wang, Y. Cd0.2Zn0.8S@Uio-66-NH2 Nanocomposites as Efficient and Stable Visible-Light-Driven Photocatalyst for H2 Evolution and CO2 Reduction. Appl. Catal., B 2017, 200, 448−457. (951) Xiong, Z.; Lei, Z.; Xu, Z.; Chen, X.; Gong, B.; Zhao, Y.; Zhao, H.; Zhang, J.; Zheng, C. Flame Spray Pyrolysis Synthesized ZnO/ CeO2 Nanocomposites for Enhanced CO2 Photocatalytic Reduction under Uv−Vis Light Irradiation. J.CO2 Util. 2017, 18, 53−61. (952) Lingampalli, S. R.; Ayyub, M. M.; Magesh, G.; Rao, C. N. R. Photocatalytic Reduction of CO2 by Employing ZnO/Ag1‑XCux/CdS and Related Heterostructures. Chem. Phys. Lett. 2018, 691, 28−32. (953) Kumar, P.; Mungse, H. P.; Khatri, O. P.; Jain, S. L. NitrogenDoped Graphene-Supported Copper Complex: A Novel Photocatalyst for CO2 Reduction under Visible Light Irradiation. RSC Adv. 2015, 5, 54929−54935. (954) Kumar, P.; Kumar, A.; Sreedhar, B.; Sain, B.; Ray, S. S.; Jain, S. L. Cobalt Phthalocyanine Immobilized on Graphene Oxide: An Efficient Visible-Active Catalyst for the Photoreduction of Carbon Dioxide. Chem. - Eur. J. 2014, 20, 6154−6161. (955) Li, K.; Peng, B. S.; Jin, J. P.; Zan, L.; Peng, T. Y. Carbon Nitride Nanodots Decorated Brookite TiO2 Quasi Nanocubes for Enhanced Activity and Selectivity of Visible-Light-Driven CO2 Reduction. Appl. Catal., B 2017, 203, 910−916. (956) Reli, M.; Huo, P.; Sihor, M.; Ambrozova, N.; Troppova, I.; Matejova, L.; Lang, J.; Svoboda, L.; Kustrowski, P.; Ritz, M.; et al. Novel TiO2/C3N4 Photocatalysts for Photocatalytic Reduction of CO2 and for Photocatalytic Decomposition of N2O. J. Phys. Chem. A 2016, 120, 8564−8573. (957) Li, H. L.; Gao, Y.; Wu, X. Y.; Lee, P. H.; Shih, K. M. Fabrication of Heterostructured g-C3N4/Ag-TiO2 Hybrid Photocatalyst with Enhanced Performance in Photocatalytic Conversion of GG


Chemical Reviews

Review

(975) Xu, D.; Cheng, B.; Cao, S.; Yu, J. Enhanced Photocatalytic Activity and Stability of Z-Scheme Ag2CrO4-GO Composite Photocatalysts for Organic Pollutant Degradation. Appl. Catal., B 2015, 164, 380−388. (976) Wang, J.-C.; Yao, H.-C.; Fan, Z.-Y.; Zhang, L.; Wang, J.-S.; Zang, S.-Q.; Li, Z.-J. Indirect Z-Scheme BiOI/g-C3N4 Photocatalysts with Enhanced Photoreduction CO2 Activity under Visible Light Irradiation. ACS Appl. Mater. Interfaces 2016, 8, 3765−3775. (977) Bai, Y.; Ye, L. Q.; Wang, L.; Shi, X.; Wang, P. Q.; Bai, W.; Wong, P. K. g-C3N4/Bi4O5I2 Heterojunction with I‑3(−)/I‑ Redox Mediator for Enhanced Photocatalytic CO2 Conversion. Appl. Catal., B 2016, 194, 98−104. (978) Tada, H.; Mitsui, T.; Kiyonaga, T.; Akita, T.; Tanaka, K. AllSolid-State Z-Scheme in CdS-Au-TiO2Three-Component Nanojunction System. Nat. Mater. 2006, 5, 782−786. (979) Wu, F.; Li, X.; Liu, W.; Zhang, S. Highly Enhanced Photocatalytic Degradation of Methylene Blue over the Indirect AllSolid-State Z-Scheme g-C3N4-RGO-TiO2 Nanoheterojunctions. Appl. Surf. Sci. 2017, 405, 60−70. (980) Wang, P.; Wang, J.; Wang, X.; Yu, H.; Yu, J. Cu2O-RGO-CuO Composite: An Effective Z-Scheme Visible-Light Photocatalyst. Curr. Nanosci. 2015, 11, 462−469. (981) Li, P.; Zhou, Y.; Li, H.; Xu, Q.; Meng, X.; Wang, X.; Xiao, M.; Zou, Z. All-Solid-State Z-Scheme System Arrays of Fe2V4O13/RGO/ CdS for Visible Light-Driving Photocatalytic CO2 Reduction into Renewable Hydrocarbon Fuel. Chem. Commun. 2015, 51, 800−803. (982) Kuai, L.; Zhou, Y.; Tu, W.; Li, P.; Li, H.; Xu, Q.; Tang, L.; Wang, X.; Xiao, M.; Zou, Z. Rational Construction of a CdS/Reduced Graphene Oxide/TiO2 Core-Shell Nanostructure as an All-Solid-State Z-Scheme System for CO2 Photoreduction into Solar Fuels. RSC Adv. 2015, 5, 88409−88413. (983) Wang, M.; Han, Q. T.; Li, L.; Tang, L. Q.; Li, H. J.; Zhou, Y.; Zou, Z. G. Construction of an All-Solid-State Artificial Z-Scheme System Consisting of Bi2WO6/Au/CdS Nanostructure for Photocatalytic CO2 Reduction into Renewable Hydrocarbon Fuel. Nanotechnology 2017, 28, 274002. (984) Kim, C.; Cho, K. M.; Al-Saggaf, A.; Gereige, I.; Jung, H.-T. ZScheme Photocatalytic CO2 Conversion on Three-Dimensional BiVO4/Carbon-Coated Cu2O Nanowire Arrays under Visible Light. ACS Catal. 2018, 8, 4170−4177. (985) Zhou, C.; Wang, S.; Zhao, Z.; Shi, Z.; Yan, S.; Zou, Z. A FacetDependent Schottky-Junction Electron Shuttle in a BiVO4{010}−Au− Cu2O Z-Scheme Photocatalyst for Efficient Charge Separation. Adv. Funct. Mater. 2018, 28, 1801214. (986) Murugesan, P.; Narayanan, S.; Manickam, M. Experimental Studies on Photocatalytic Reduction of CO2 Using Agbr Decorated gC3N4 Composite in Tea Mediated System. J. CO2 Util. 2017, 22, 250− 261. (987) Wang, J. S.; Qin, C. L.; Wang, H. J.; Chu, M. N.; Zada, A.; Zhang, X. L.; Li, J. D.; Raziq, F.; Qu, Y.; Jing, L. Q. Exceptional Photocatalytic Activities for CO2Conversion on Al-O Bridged g-C3N4/ Alpha-Fe2O3 Z-Scheme Nanocomposites and Mechanism Insight with Isotopesz. Appl. Catal., B 2018, 221, 459−466. (988) Iwase, A.; Yoshino, S.; Takayama, T.; Ng, Y. H.; Amal, R.; Kudo, A. Water Splitting and CO2 Reduction under Visible Light Irradiation Using Z-Scheme Systems Consisting of Metal Sulfides, CoOx-Loaded BiVO4 and a Reduced Graphene Oxide Electron Mediator. J. Am. Chem. Soc. 2016, 138, 10260−10264. (989) Liu, J.; Cheng, B.; Yu, J. A New Understanding of the Photocatalytic Mechanism of the Direct Z-Scheme g-C3N4/TiO2 Heterostructure. Phys. Chem. Chem. Phys. 2016, 18, 31175−31183. (990) Zhu, B.; Xia, P.; Li, Y.; Ho, W.; Yu, J. Fabrication and Photocatalytic Activity Enhanced Mechanism of Direct Z-Scheme gC3N4/Ag2WO4 Photocatalyst. Appl. Surf. Sci. 2017, 391, 175−183. (991) Chen, W.; Liu, T.-Y.; Huang, T.; Liu, X.-H.; Zhu, J.-W.; Duan, G.-R.; Yang, X.-J. In Situ Fabrication of Novel Z-Scheme Bi2WO6 Quantum Dots/g-C3N4 Ultrathin Nanosheets Heterostructures with Improved Photocatalytic Activity. Appl. Surf. Sci. 2015, 355, 379−387.

(992) Lv, J.; Dai, K.; Zhang, J.; Geng, L.; Liang, C.; Liu, Q.; Zhu, G.; Chen, C. Facile Synthesis of Z-Scheme g-C3N4/Bi2MoO6 Nanocomposite for Enhanced Visible Photocatalytic Properties. Appl. Surf. Sci. 2015, 358, 377−384. (993) Cui, L. F.; Ding, X.; Wang, Y. G.; Shi, H. C.; Huang, L. H.; Zuo, Y. H.; Kang, S. F. Facile Preparation of Z-Scheme WO3/g-C3N4 Composite Photocatalyst with Enhanced Photocatalytic Performance under Visible Light. Appl. Surf. Sci. 2017, 391, 202−210. (994) Qi, K. Z.; Cheng, B.; Yu, J. G.; Ho, W. K. A Review on TiO2Based Z-Scheme Photocatalysts. Chin. J. Catal. 2017, 38, 1936−1955. (995) Liu, Y.; Ji, G.; Dastageer, M. A.; Zhu, L.; Wang, J.; Zhang, B.; Chang, X.; Gondal, M. A. Highly-Active Direct Z-Scheme Si/TiO2 Photocatalyst for Boosted CO2Reduction into Value-Added Methanol. RSC Adv. 2014, 4, 56961−56969. (996) Aguirre, M. E.; Zhou, R. X.; Eugene, A. J.; Guzman, M. I.; Grela, M. A. Cu2O/TiO2 Heterostructures for CO2Reduction through a Direct Z-Scheme: Protecting Cu2O from Photocorrosion. Appl. Catal., B 2017, 217, 485−493. (997) Bae, K. L.; Kim, J.; Lim, C. K.; Nam, K. M.; Song, H. Colloidal Zinc Oxide-Copper(I) Oxide Nanocatalysts for Selective Aqueous Photocatalytic Carbon Dioxide Conversion into Methane. Nat. Commun. 2017, 8, 1156. (998) Nie, N.; He, F.; Zhang, L. Y.; Cheng, B. Direct Z-Scheme PDA-Modified ZnO Hierarchical Microspheres with Enhanced Photocatalytic CO2 Reduction Performance. Appl. Surf. Sci. 2018, 457, 1096−1102. (999) Xu, F.; Zhang, J.; Zhu, B.; Yu, J.; Xu, J. CuInS2 Sensitized TiO2 Hybrid Nanofibers for Improved Photocatalytic CO2 Reduction. Appl. Catal., B 2018, 230, 194−202. (1000) Jiang, Z.; Wan, W.; Li, H.; Yuan, S.; Zhao, H.; Wong, P. K. A Hierarchical Z-Scheme Α-Fe2O3/g-C3N4 Hybrid for Enhanced Photocatalytic CO2 Reduction. Adv. Mater. 2018, 30, 1706108. (1001) Thanh Truc, N. T.; Hanh, N. T.; Nguyen, M. V.; Le Chi, N. T. P.; Van Noi, N.; Tran, D. T.; Ha, M. N.; Trung, D. Q.; Pham, T. D. Novel Direct Z-Scheme Cu2V2O7/g-C3N4 for Visible Light Photocatalytic Conversion of CO2 into Valuable Fuels. Appl. Surf. Sci. 2018, 457, 968−974. (1002) Kumar, A.; Prajapati, P. K.; Pal, U.; Jain, S. L. Ternary RGO/ InVO4/Fe2O3 Z-Scheme Heterostructured Photocatalyst for CO2 Reduction under Visible Light Irradiation. ACS Sustainable Chem. Eng. 2018, 6, 8201−8211. (1003) Xu, D.; Cheng, B.; Wang, W.; Jiang, C.; Yu, J. Ag2CrO4/gC3N4/Graphene Oxide Ternary Nanocomposite Z-Scheme Photocatalyst with Enhanced CO2 Reduction Activity. Appl. Catal., B 2018, 231, 368−380. (1004) Zubair, M.; Razzaq, A.; Grimes, C. A.; In, S. I. Cu2ZnSnS4 (CZTS)-ZnO: A Noble Metal-Free Hybrid Z-Scheme Photocatalyst for Enhanced Solar-Spectrum Photocatalytic Conversion of CO2 to CH4. J. CO2 Util. 2017, 20, 301−311. (1005) Wang, J.-C.; Zhang, L.; Fang, W.-X.; Ren, J.; Li, Y.-Y.; Yao, H.-C.; Wang, J.-S.; Li, Z.-J. Enhanced Photoreduction CO2 Activity over Direct Z-Scheme Alpha-Fe2O3/Cu2O Heterostructures under Visible Light Irradiation. ACS Appl. Mater. Interfaces 2015, 7, 8631− 8639. (1006) He, Y.; Zhang, L.; Fan, M.; Wang, X.; Walbridge, M. L.; Nong, Q.; Wu, Y.; Zhao, L. Z-Scheme SnO2−x/g-C3N4 Composite as an Efficient Photocatalyst for Dye Degradation and Photocatalytic CO2 Reduction. Sol. Energy Mater. Sol. Cells 2015, 137, 175−184. (1007) Wang, M.; Shen, M.; Zhang, L. X.; Tian, J. J.; Jin, X. X.; Zhou, Y. J.; Shi, J. L. 2D-2D MnO2/g-C3N4 Heterojunction Photocatalyst: In-Situ Synthesis and Enhanced CO2 Reduction Activity. Carbon 2017, 120, 23−31. (1008) Di, T. M.; Zhu, B. C.; Cheng, B.; Yu, J. G.; Xu, J. S. A Direct Z-Scheme g-C3N4/SnS2 Photocatalyst with Superior Visible-Light CO2 Reduction Performance. J. Catal. 2017, 352, 532−541. (1009) He, Y.; Zhang, L.; Teng, B.; Fan, M. New Application of ZScheme Ag3PO4/g-C3N4 Composite in Converting CO2 to Fuel. Environ. Sci. Technol. 2015, 49, 649−656. GH


Chemical Reviews

Review

(1010) Yu, W.; Xu, D.; Peng, T. Enhanced Photocatalytic Activity of g-C3N4 for Selective CO2 Reduction to CH3OH Via Facile Coupling of Zno: A Direct Z-Scheme Mechanism. J. Mater. Chem. A 2015, 3, 19936−19947. (1011) Nie, N.; Zhang, L.; Fu, J.; Cheng, B.; Yu, J. Self-Assembled Hierarchical Direct Z-Scheme g-C3N4/ZnO Microspheres with Enhanced Photocatalytic CO2 Reduction Performance. Appl. Surf. Sci. 2018, 441, 12−22. (1012) Zhu, D. D.; Liu, J. L.; Qiao, S. Z. Recent Advances in Inorganic Heterogeneous Electrocatalysts for Reduction of Carbon Dioxide. Adv. Mater. 2016, 28, 3423−3452. (1013) Mao, X.; Hatton, T. A. Recent Advances in Electrocatalytic Reduction of Carbon Dioxide Using Metal-Free Catalysts. Ind. Eng. Chem. Res. 2015, 54, 4033−4042. (1014) Sreekanth, N.; Nazrulla, M. A.; Vineesh, T. V.; Sailaja, K.; Phani, K. L. Metal-Free Boron-Doped Graphene for Selective Electroreduction of Carbon Dioxide to Formic Acid/Formate. Chem. Commun. 2015, 51, 16061−16064. (1015) Wu, J.; Ma, S.; Sun, J.; Gold, J. I.; Tiwary, C.; Kim, B.; Zhu, L.; Chopra, N.; Odeh, I. N.; Vajtai, R.; et al. A Metal-Free Electrocatalyst for Carbon Dioxide Reduction to Multi-Carbon Hydrocarbons and Oxygenates. Nat. Commun. 2016, 7, 13869. (1016) Li, W. L.; Seredych, M.; Rodriguez-Castellon, E.; Bandosz, T. J. Metal-Free Nanoporous Carbon as a Catalyst for Electrochemical Reduction of CO2 to CO and CH4. ChemSusChem 2016, 9, 606−616. (1017) Liu, Y. J.; Zhao, J. X.; Cai, Q. H. Pyrrolic-Nitrogen Doped Graphene: A Metal-Free Electrocatalyst with High Efficiency and Selectivity for the Reduction of Carbon Dioxide to Formic Acid: A Computational Study. Phys. Chem. Chem. Phys. 2016, 18, 5491−5498. (1018) Kumar, B.; Asadi, M.; Pisasale, D.; Sinha-Ray, S.; Rosen, B. A.; Haasch, R.; Abiade, J.; Yarin, A. L.; Salehi-Khojin, A. Renewable and Metal-Free Carbon Nanofibre Catalysts for Carbon Dioxide Reduction. Nat. Commun. 2013, 4, 2819. (1019) Sun, X. F.; Kang, X. C.; Zhu, Q. G.; Ma, J.; Yang, G. Y.; Liu, Z. M.; Han, B. X. Very Highly Efficient Reduction of CO2 to CH4 Using Metal-Free N-Doped Carbon Electrodes. Chem. Sci. 2016, 7, 2883−2887. (1020) Lu, X.; Tan, T. H.; Ng, Y. H.; Amal, R. Highly Selective and Stable Reduction of CO2 to CO by a Graphitic Carbon Nitride/ Carbon Nanotube Composite Electrocatalyst. Chem. - Eur. J. 2016, 22, 11991−11996. (1021) Li, P.; Wang, F.; Wei, S.; Li, X.; Zhou, Y. Mechanistic Insights into CO2 Reduction on Cu/Mo-Loaded Two-Dimensional gC3N4(001). Phys. Chem. Chem. Phys. 2017, 19, 4405−4410. (1022) Maeda, K.; Teramura, K.; Lu, D.; Takata, T.; Saito, N.; Inoue, Y.; Domen, K. Photocatalyst Releasing Hydrogen from Water. Nature 2006, 440, 295−295. (1023) Maeda, K.; Domen, K. Photocatalytic Water Splitting: Recent Progress and Future Challenges. J. Phys. Chem. Lett. 2010, 1, 2655− 2661. (1024) Osterloh, F. E.; Parkinson, B. A. Recent Developments in Solar Water-Splitting Photocatalysis. MRS Bull. 2011, 36, 17−22. (1025) Hori, Y.; Kikuchi, K.; Suzuki, S. Production of CO and CH4 in Electrochemical Reduction of CO2 at Metal Electrodes in Aqueous Hydrogencarbonate Solution. Chem. Lett. 1985, 14, 1695−1698. (1026) Gattrell, M.; Gupta, N.; Co, A. A Review of the Aqueous Electrochemical Reduction of CO2 to Hydrocarbons at Copper. Electroanal. Chem. 2006, 594, 1−19. (1027) Hori, Y.; Kikuchi, K.; Murata, A.; Suzuki, S. Production of Methane and Ethylene in Electrochemical Reduction of Carbon Dioxide at Copper Electrode in Aqueous Hydrogencarbonate Solution. Chem. Lett. 1986, 15, 897−898. (1028) Cook, R. L.; MacDuff, R. C.; Sammells, A. F. Photoelectrochemical Carbon Dioxide Reduction to Hydrocarbons at Ambient Temperature and Pressure. J. Electrochem. Soc. 1988, 135, 3069−3070. (1029) Adachi, K.; Ohta, K.; Mizuno, T. Photocatalytic Reduction of Carbon Dioxide to Hydrocarbon Using Copper-Loaded Titanium Dioxide. Sol. Energy 1994, 53, 187−190.

(1030) Ichikawa, S.; Doi, R. Hydrogen Production from Water and Conversion of Carbon Dioxide to Useful Chemicals by Room Temperature Photoelectrocatalysis. Catal. Today 1996, 27, 271−277. (1031) Hori, Y.; Murata, A.; Takahashi, R. Formation of Hydrocarbons in the Electrochemical Reduction of Carbon Dioxide at a Copper Electrode in Aqueous Solution. J. Chem. Soc., Faraday Trans. 1 1989, 85, 2309−2326. (1032) Frese, K. W. Electrochemical Reduction of CO2 at Intentionally Oxidized Copper Electrodes. J. Electrochem. Soc. 1991, 138, 3338−3344. (1033) Albo, J.; Alvarez-Guerra, M.; Castano, P.; Irabien, A. Towards the Electrochemical Conversion of Carbon Dioxide into Methanol. Green Chem. 2015, 17, 2304−2324. (1034) Le, M.; Ren, M.; Zhang, Z.; Sprunger, P. T.; Kurtz, R. L.; Flake, J. C. Electrochemical Reduction of CO2 to CH3OH at Copper Oxide Surfaces. J. Electrochem. Soc. 2011, 158, E45−E49. (1035) Schizodimou, A.; Kyriacou, G. Acceleration of the Reduction of Carbon Dioxide in the Presence of Multivalent Cations. Electrochim. Acta 2012, 78, 171−176. (1036) Aeshala, L. M.; Uppaluri, R. G.; Verma, A. Effect of Cationic and Anionic Solid Polymer Electrolyte on Direct Electrochemical Reduction of Gaseous CO2 to Fuel. J. CO2 Util. 2013, 3-4, 49−55. (1037) Lan, Y.; Gai, C.; Kenis, P. J. A.; Lu, J. Electrochemical Reduction of Carbon Dioxide on Cu/CuO Core/Shell Catalysts. ChemElectroChem 2014, 1, 1577−1582. (1038) de Brito, J. F.; da Silva, A. A.; Cavalheiro, A. J.; Boldrin Zanoni, M. V. Evaluation of the Parameters Affecting the Photoelectrocatalytic Reduction of CO2 to CH3OH at Cu/Cu2O Electrode. Int. J. Electrochem. Soc. 2014, 9, 5961−5973. (1039) Jia, F.; Yu, X.; Zhang, L. Enhanced Selectivity for the Electrochemical Reduction of CO2 to Alcohols in Aqueous Solution with Nanostructured Cu−Au Alloy as Catalyst. J. Power Sources 2014, 252, 85−89. (1040) Barton Cole, E.; Lakkaraju, P. S.; Rampulla, D. M.; Morris, A. J.; Abelev, E.; Bocarsly, A. B. Using a One-Electron Shuttle for the Multielectron Reduction of CO2 to Methanol: Kinetic, Mechanistic, and Structural Insights. J. Am. Chem. Soc. 2010, 132, 11539−11551. (1041) Pinsent, B. R. W.; Pearson, L.; Roughton, F. J. W. The Kinetics of Combination of Carbon Dioxide with Hydroxide Ions. Trans. Faraday Soc. 1956, 52, 1512−1520. (1042) Hawecker, J.; Lehn, J.-M.; Ziessel, R. Electrocatalytic Reduction of Carbon Dioxide Mediated by Re(Bipy)Co3Cl (Bipy = 2,2[Prime or Minute]-Bipyridine). J. Chem. Soc., Chem. Commun. 1984, 328−330. (1043) O’Toole, T. R.; Margerum, L. D.; Westmoreland, T. D.; Vining, W. J.; Murray, R. W.; Meyer, T. J. Electrocatalytic Reduction of CO2 at a Chemically Modified Electrode. J. Chem. Soc., Chem. Commun. 1985, 1416−1417. (1044) Noda, H.; Ikeda, S.; Oda, Y.; Imai, K.; Maeda, M.; Ito, K. Electrochemical Reduction of Carbon Dioxide at Various Metal Electrodes in Aqueous Potassium Hydrogen Carbonate Solution. Bull. Chem. Soc. Jpn. 1990, 63, 2459−2462. (1045) Nakagawa, S.; Kudo, A.; Azuma, M.; Sakata, T. Effect of Pressure on the Electrochemical Reduction of CO2 on Group Viii Metal Electrodes. J. Electroanal. Chem. Interfacial Electrochem. 1991, 308, 339−343. (1046) Schrebler, R.; Cury, P.; Herrera, F.; Gomez, H.; Cordova, R. Study of the Electrochemical Reduction of CO2 on Electrodeposited Rhenium Electrodes in Methanol Media. Electroanal. Chem. 2001, 516, 23−30. (1047) Rosen, B. A.; Salehi-Khojin, A.; Thorson, M. R.; Zhu, W.; Whipple, D. T.; Kenis, P. J. A.; Masel, R. I. Ionic Liquid−Mediated Selective Conversion of CO2 to CO at Low Overpotentials. Science 2011, 334, 643−644. (1048) Chen, Y.; Kanan, M. W. Tin Oxide Dependence of the CO2 Reduction Efficiency on Tin Electrodes and Enhanced Activity for Tin/Tin Oxide Thin-Film Catalysts. J. Am. Chem. Soc. 2012, 134, 1986−1989. GI


Chemical Reviews

Review

(1049) Zhu, W. L.; Michalsky, R.; Metin, O.; Lv, H. F.; Guo, S. J.; Wright, C. J.; Sun, X. L.; Peterson, A. A.; Sun, S. H. Monodisperse Au Nanoparticles for Selective Electrocatalytic Reduction of CO2 to CO. J. Am. Chem. Soc. 2013, 135, 16833−16836. (1050) Lu, Q.; Rosen, J.; Zhou, Y.; Hutchings, G. S.; Kimmel, Y. C.; Chen, J. G. G.; Jiao, F. A Selective and Efficient Electrocatalyst for Carbon Dioxide Reduction. Nat. Commun. 2014, 5, 3242. (1051) Zhu, W.; Zhang, Y.-J.; Zhang, H.; Lv, H.; Li, Q.; Michalsky, R.; Peterson, A. A.; Sun, S. Active and Selective Conversion of CO2 to CO on Ultrathin Au Nanowires. J. Am. Chem. Soc. 2014, 136, 16132− 16135. (1052) Asadi, M.; Kumar, B.; Behranginia, A.; Rosen, B. A.; Baskin, A.; Repnin, N.; Pisasale, D.; Phillips, P.; Zhu, W.; Haasch, R.; et al. Robust Carbon Dioxide Reduction on Molybdenum Disulphide Edges. Nat. Commun. 2014, 5, 4470. (1053) Ma, S.; Lan, Y.; Perez, G. M. J.; Moniri, S.; Kenis, P. J. A. Silver Supported on Titania as an Active Catalyst for Electrochemical Carbon Dioxide Reduction. ChemSusChem 2014, 7, 866−874. (1054) Raciti, D.; Livi, K. J.; Wang, C. Highly Dense Cu Nanowires for Low-Overpotential CO2 Reduction. Nano Lett. 2015, 15, 6829− 6835. (1055) Feng, X.; Jiang, K.; Fan, S.; Kanan, M. W. Grain-BoundaryDependent CO2 Electroreduction Activity. J. Am. Chem. Soc. 2015, 137, 4606−4609. (1056) Zhou, L. Q.; Ling, C.; Jones, M.; Jia, H. F. Selective CO2 Reduction on a Polycrystalline Ag Electrode Enhanced by Anodization Treatment. Chem. Commun. 2015, 51, 17704−17707. (1057) Wu, J.; Yadav, R. M.; Liu, M.; Sharma, P. P.; Tiwary, C. S.; Ma, L.; Zou, X.; Zhou, X.-D.; Yakobson, B. I.; Lou, J.; et al. Achieving Highly Efficient, Selective, and Stable CO2 Reduction on NitrogenDoped Carbon Nanotubes. ACS Nano 2015, 9, 5364−5371. (1058) Gao, D.; Zhou, H.; Wang, J.; Miao, S.; Yang, F.; Wang, G.; Wang, J.; Bao, X. Size-Dependent Electrocatalytic Reduction of CO2 over Pd Nanoparticles. J. Am. Chem. Soc. 2015, 137, 4288−4291. (1059) Kim, D.; Resasco, J.; Yu, Y.; Asiri, A. M.; Yang, P. Synergistic Geometric and Electronic Effects for Electrochemical Reduction of Carbon Dioxide Using Gold-Copper Bimetallic Nanoparticles. Nat. Commun. 2014, 5, 4948. (1060) Shen, J.; Kortlever, R.; Kas, R.; Birdja, Y. Y.; Diaz-Morales, O.; Kwon, Y.; Ledezma-Yanez, I.; Schouten, K. J. P.; Mul, G.; Koper, M. T. M. Electrocatalytic Reduction of Carbon Dioxide to Carbon Monoxide and Methane at an Immobilized Cobalt Protoporphyrin. Nat. Commun. 2015, 6, 8177. (1061) Rasul, S.; Anjum, D. H.; Jedidi, A.; Minenkov, Y.; Cavallo, L.; Takanabe, K. A Highly Selective Copper-Indium Bimetallic Electrocatalyst for the Electrochemical Reduction of Aqueous CO2 to CO. Angew. Chem., Int. Ed. 2015, 54, 2146−2150. (1062) Lin, S.; Diercks, C. S.; Zhang, Y.-B.; Kornienko, N.; Nichols, E. M.; Zhao, Y.; Paris, A. R.; Kim, D.; Yang, P.; Yaghi, O. M.; et al. Covalent Organic Frameworks Comprising Cobalt Porphyrins for Catalytic CO2Reduction in Water. Science 2015, 349, 1208−1213. (1063) Larrazabal, G. O.; Martin, A. J.; Krumeich, F.; Hauert, R.; Perez-Ramirez, J. Solvothermally-Prepared Cu2O Electrocatalysts for CO2 Reduction with Tunable Selectivity by the Introduction of pBlock Elements. ChemSusChem 2017, 10, 1255−1265. (1064) Choi, J.; Kim, M. J.; Ahn, S. H.; Choi, I.; Jang, J. H.; Ham, Y. S.; Kim, J. J.; Kim, S. K. Electrochemical CO2 Reduction to CO on Dendritic Ag-Cu Electrocatalysts Prepared by Electrodeposition. Chem. Eng. J. 2016, 299, 37−44. (1065) Ding, C.; Li, A.; Lu, S.-M.; Zhang, H.; Li, C. In Situ Electrodeposited Indium Nanocrystals for Efficient CO2Reduction to CO with Low Overpotential. ACS Catal. 2016, 6, 6438−6443. (1066) Huan, T. N.; Prakash, P.; Simon, P.; Rousse, G.; Xu, X.; Artero, V.; Gravel, E.; Doris, E.; Fontecave, M. CO2 Reduction to CO in Water: Carbon Nanotube-Gold Nanohybrid as a Selective and Efficient Electrocatalyst. ChemSusChem 2016, 9, 2317−2320. (1067) Jhong, H.-R. M.; Tornow, C. E.; Smid, B.; Gewirth, A. A.; Lyth, S. M.; Kenis, P. J. A. A Nitrogen-Doped Carbon Catalyst for

Electrochemical CO2 Conversion to CO with High Selectivity and Current Density. ChemSusChem 2017, 10, 1094−1099. (1068) Kim, H.; Jeon, H. S.; Jee, M. S.; Nursanto, E. B.; Singh, J. P.; Chae, K.; Hwang, Y. J.; Min, B. K. Contributors to Enhanced CO2 Electroreduction Activity and Stability in a Nanostructured Au Electrocatalyst. ChemSusChem 2016, 9, 2097−2102. (1069) Li, M.; Wang, J. J.; Li, P.; Chang, K.; Li, C. L.; Wang, T.; Jiang, B.; Zhang, H. B.; Liu, H. M.; Yamauchi, Y.; et al. Mesoporous Palladium-Copper Bimetallic Electrodes for Selective Electrocatalytic Reduction of Aqueous CO2 to CO. J. Mater. Chem. A 2016, 4, 4776− 4782. (1070) Ma, M.; Trzesniewski, B. J.; Xie, J.; Smith, W. A. Selective and Efficient Reduction of Carbon Dioxide to Carbon Monoxide on Oxide-Derived Nanostructured Silver Electrocatalysts. Angew. Chem., Int. Ed. 2016, 55, 9748−9752. (1071) Yin, Z.; Gao, D.; Yao, S.; Zhao, B.; Cai, F.; Lin, L.; Tang, P.; Zhai, P.; Wang, G.; Ma, D.; et al. Highly Selective Palladium-Copper Bimetallic Electrocatalysts for the Electrochemical Reduction of CO2 to CO. Nano Energy 2016, 27, 35−43. (1072) Min, S.; Yang, X.; Lu, A.-Y.; Tseng, C.-C.; Hedhili, M. N.; Li, L.-J.; Huang, K.-W. Low Overpotential and High Current CO2 Reduction with Surface Reconstructed Cu Foam Electrodes. Nano Energy 2016, 27, 121−129. (1073) Sarfraz, S.; Garcia-Esparza, A. T.; Jedidi, A.; Cavallo, L.; Takanabe, K. Cu-Sn Bimetallic Catalyst for Selective Aqueous Electroreduction of CO2 to CO. ACS Catal. 2016, 6, 2842−2851. (1074) Zhang, Z.; Chi, M.; Veith, G. M.; Zhang, P.; Lutterman, D. A.; Rosenthal, J.; Overbury, S. H.; Dai, S.; Zhu, H. Rational Design of Bi Nanoparticles for Efficient Electrochemical CO2 Reduction: The Elucidation of Size and Surface Condition Effects. ACS Catal. 2016, 6, 6255−6264. (1075) Su, P.; Iwase, K.; Nakanishi, S.; Hashimoto, K.; Kamiya, K. Nickel-Nitrogen-Modified Graphene: An Efficient Electrocatalyst for the Reduction of Carbon Dioxide to Carbon Monoxide. Small 2016, 12, 6083−6089. (1076) Won, D. H.; Shin, H.; Koh, J.; Chung, J.; Lee, H. S.; Kim, H.; Woo, S. I. Highly Efficient, Selective, and Stable CO2 Electroreduction on a Hexagonal Zn Catalyst. Angew. Chem., Int. Ed. 2016, 55, 9297− 9300. (1077) Yu, Q.; Meng, X.; Shi, L.; Liu, H.; Ye, J. Superfine Ag Nanoparticle Decorated Zn Nanoplates for the Active and Selective Electrocatalytic Reduction of CO2 to CO. Chem. Commun. 2016, 52, 14105−14108. (1078) Saberi Safaei, T.; Mepham, A.; Zheng, X.; Pang, Y.; Dinh, C.T.; Liu, M.; Sinton, D.; Kelley, S. O.; Sargent, E. H. High-Density Nanosharp Microstructures Enable Efficient CO2Electroreduction. Nano Lett. 2016, 16, 7224−7228. (1079) Kim, C.; Eom, T.; Jee, M. S.; Jung, H.; Kim, H.; Min, B. K.; Hwang, Y. J. Insight into Electrochemical CO2 Reduction on SurfaceMolecule Mediated Ag Nanoparticles. ACS Catal. 2017, 7, 779−785. (1080) Liu, S.; Tao, H.; Zeng, L.; Liu, Q.; Xu, Z.; Liu, Q.; Luo, J.-L. Shape-Dependent Electrocatalytic Reduction of CO2 to CO on Triangular Silver Nanoplates. J. Am. Chem. Soc. 2017, 139, 2160−2163. (1081) Rogers, C.; Perkins, W. S.; Veber, G.; Williams, T. E.; Cloke, R. R.; Fischer, F. R. Synergistic Enhancement of Electrocatalytic CO2 Reduction with Gold Nanoparticles Embedded in Functional Graphene Nanoribbon Composite Electrodes. J. Am. Chem. Soc. 2017, 139, 4052−4061. (1082) Zhang, X.; Wu, Z.; Zhang, X.; Li, L.; Li, Y.; Xu, H.; Li, X.; Yu, X.; Zhang, Z.; Liang, Y.; et al. Highly Selective and Active CO2 Reduction Electrocatalysts Based on Cobalt Phthalocyanine/Carbon Nanotube Hybrid Structures. Nat. Commun. 2017, 8, 14675−14675. (1083) Li, Q.; Fu, J.; Zhu, W.; Chen, Z.; Shen, B.; Wu, L.; Xi, Z.; Wang, T.; Lu, G.; Zhu, J.-j.; et al. Tuning Sn-Catalysis for Electrochemical Reduction of CO2 to CO Via the Core/Shell Cu/ SnO2 Structure. J. Am. Chem. Soc. 2017, 139, 4290−4293. (1084) He, J.; Dettelbach, K. E.; Salvatore, D. A.; Li, T.; Berlinguette, C. P. High-Throughput Synthesis of Mixed-Metal Electrocatalysts for CO2 Reduction. Angew. Chem., Int. Ed. 2017, 56, 6068−6072. GJ


Chemical Reviews

Review

(1085) Quan, F.; Xiong, M.; Jia, F.; Zhang, L. Efficient Electroreduction of CO2 on Bulk Silver Electrode in Aqueous Solution Via the Inhibition of Hydrogen Evolution. Appl. Surf. Sci. 2017, 399, 48− 54. (1086) Gao, D. F.; Zhang, Y.; Zhou, Z. W.; Cai, F.; Zhao, X. F.; Huang, W. G.; Li, Y. S.; Zhu, J. F.; Liu, P.; Yang, F.; et al. Enhancing CO2Electroreduction with the Metal-Oxide Interface. J. Am. Chem. Soc. 2017, 139, 5652−5655. (1087) Yang, H. B.; Hung, S. F.; Liu, S.; Yuan, K. D.; Miao, S.; Zhang, L. P.; Huang, X.; Wang, H. Y.; Cai, W. Z.; Chen, R.; et al. Atomically Dispersed Ni(I) as the Active Site for Electrochemical CO2 Reduction. Nature Energy 2018, 3, 140−147. (1088) Pan, Y.; Lin, R.; Chen, Y.; Liu, S.; Zhu, W.; Cao, X.; Chen, W.; Wu, K.; Cheong, W.-C.; Wang, Y.; et al. Design of Single-Atom Co−N5 Catalytic Site: A Robust Electrocatalyst for CO2 Reduction with Nearly 100% CO Selectivity and Remarkable Stability. J. Am. Chem. Soc. 2018, 140, 4218−4221. (1089) Zhang, C.; Yang, S.; Wu, J.; Liu, M.; Yazdi, S.; Ren, M.; Sha, J.; Zhong, J.; Nie, K.; Jalilov, A. S.; et al. Electrochemical CO2 Reduction with Atomic Iron Dispersed on Nitrogen-Doped Graphene. Adv. Energy Mater. 2018, 8, 1703487. (1090) Chen, D.; Yao, Q.; Cui, P.; Liu, H.; Xie, J.; Yang, J. Tailoring the Selectivity of Bimetallic Copper−Palladium Nanoalloys for Electrocatalytic Reduction of CO2 to CO. ACS Applied Energy Materials 2018, 1, 883−890. (1091) Jiang, K.; Siahrostami, S.; Zheng, T.; Hu, Y.; Hwang, S.; Stavitski, E.; Peng, Y.; Dynes, J.; Gangisetty, M.; Su, D.; et al. Isolated Ni Single Atoms in Graphene Nanosheets for High-Performance CO2 Reduction. Energy Environ. Sci. 2018, 11, 893−903. (1092) Hu, X. M.; Hval, H. H.; Bjerglund, E. T.; Dalgaard, K. J.; Madsen, M. R.; Pohl, M. M.; Welter, E.; Lamagni, P.; Buhl, K. B.; Bremholm, M.; et al. Selective CO2 Reduction to CO in Water Using Earth-Abundant Metal and Nitrogen-Doped Carbon Electrocatalysts. ACS Catal. 2018, 8, 6255−6264. (1093) Zhu, W.; Zhang, L.; Yang, P.; Hu, C.; Dong, H.; Zhao, Z.-J.; Mu, R.; Gong, J. Formation of Enriched Vacancies for Enhanced CO2 Electrocatalytic Reduction over AuCu Alloys. ACS Energy Letters 2018, 3, 2144−2149. (1094) Azuma, M.; Hashimoto, K.; Hiramoto, M.; Watanabe, M.; Sakata, T. Electrochemical Reduction of Carbon Dioxide on Various Metal Electrodes in Low-Temperature Aqueous KHCO3 Media. J. Electrochem. Soc. 1990, 137, 1772−1778. (1095) Kuwabata, S.; Tsuda, R.; Yoneyama, H. Electrochemical Conversion of Carbon Dioxide to Methanol with the Assistance of Formate Dehydrogenase and Methanol Dehydrogenase as Biocatalysts. J. Am. Chem. Soc. 1994, 116, 5437−5443. (1096) Hara, K.; Kudo, A.; Sakata, T. Electrochemical Reduction of High Pressure Carbon Dioxide on Fe Electrodes at Large Current Density. Electroanal. Chem. 1995, 386, 257−260. (1097) Komatsu, S.; Tanaka, M.; Okumura, A.; Kungi, A. Preparation of Cu-Solid Polymer Electrolyte Composite Electrodes and Application to Gas-Phase Electrochemical Reduction of CO2. Electrochim. Acta 1995, 40, 745−753. (1098) Leitner, W. Carbon Dioxide as a Raw Material: The Synthesis of Formic Acid and Its Derivatives from CO2. Angew. Chem., Int. Ed. Engl. 1995, 34, 2207−2221. (1099) Köleli, F.; Balun, D. Reduction of CO2 under High Pressure and High Temperature on Pb-Granule Electrodes in a Fixed-Bed Reactor in Aqueous Medium. Appl. Catal., A 2004, 274, 237−242. (1100) Qu, J.; Zhang, X.; Wang, Y.; Xie, C. Electrochemical Reduction of CO2 on RuO2/TiO2 Nanotubes Composite Modified Pt Electrode. Electrochim. Acta 2005, 50, 3576−3580. (1101) Wu, J.; Risalvato, F. G.; Ke, F.-S.; Pellechia, P. J.; Zhou, X.-D. Electrochemical Reduction of Carbon Dioxide I. Effects of the Electrolyte on the Selectivity and Activity with Sn Electrode. J. Electrochem. Soc. 2012, 159, F353−F359. (1102) Prakash, G. K. S.; Viva, F. A.; Olah, G. A. Electrochemical Reduction of CO2 over Sn-Nafion® Coated Electrode for a Fuel-CellLike Device. J. Power Sources 2013, 223, 68−73.

(1103) Zhang, S.; Kang, P.; Meyer, T. J. Nanostructured Tin Catalysts for Selective Electrochemical Reduction of Carbon Dioxide to Formate. J. Am. Chem. Soc. 2014, 136, 1734−1737. (1104) Zhang, S.; Kang, P.; Ubnoske, S.; Brennaman, M. K.; Song, N.; House, R. L.; Glass, J. T.; Meyer, T. J. Polyethylenimine-Enhanced Electrocatalytic Reduction of CO2 to Formate at Nitrogen-Doped Carbon Nanomaterials. J. Am. Chem. Soc. 2014, 136, 7845−7848. (1105) Zhang, R.; Lv, W.; Lei, L. Role of the Oxide Layer on Sn Electrode in Electrochemical Reduction of CO2 to Formate. Appl. Surf. Sci. 2015, 356, 24−29. (1106) Min, X.; Kanan, M. W. Pd-Catalyzed Electrohydrogenation of Carbon Dioxide to Formate: High Mass Activity at Low Overpotential and Identification of the Deactivation Pathway. J. Am. Chem. Soc. 2015, 137, 4701−4708. (1107) Zhao, C. C.; Yin, Z. S.; Wang, J. L. Efficient Electrochemical Conversion of CO2 to Hcooh Using Pd-Polyaniline/CNT Nanohybrids Prepared in Situ. ChemElectroChem 2015, 2, 1974−1982. (1108) Gao, S.; Jiao, X.; Sun, Z.; Zhang, W.; Sun, Y.; Wang, C.; Hu, Q.; Zu, X.; Yang, F.; Yang, S.; et al. Ultrathin Co3O4 Layers Realizing Optimized CO2 Electroreduction to Formate. Angew. Chem., Int. Ed. 2016, 55, 698−702. (1109) Wang, Y.; Zhou, J.; Lv, W.; Fang, H.; Wang, W. Electrochemical Reduction of CO2 to Formate Catalyzed by Electroplated Tin Coating on Copper Foam. Appl. Surf. Sci. 2016, 362, 394−398. (1110) Zhang, T.; Zhong, H.; Qiu, Y.; Li, X.; Zhang, H. Zn Electrode with a Layer of Nanoparticles for Selective Electroreduction of CO2 to Formate in Aqueous Solutions. J. Mater. Chem. A 2016, 4, 16670− 16676. (1111) Zhong, H.; Qiu, Y.; Zhang, T.; Li, X.; Zhang, H.; Chen, X. Bismuth Nanodendrites as a High Performance Electrocatalyst for Selective Conversion of CO2 to Formate. J. Mater. Chem. A 2016, 4, 13746−13753. (1112) Choi, S. Y.; Jeong, S. K.; Kim, H. J.; Baek, I. H.; Park, K. T. Electrochemical Reduction of Carbon Dioxide to Formate on TinLead Alloys. ACS Sustainable Chem. Eng. 2016, 4, 1311−1318. (1113) Chung, J.; Won, D. H.; Koh, J.; Kim, E. H.; Woo, S. I. Hierarchical Cu Pillar Electrodes for Electrochemical CO2 Reduction to Formic Acid with Low Overpotential. Phys. Chem. Chem. Phys. 2016, 18, 6252−6258. (1114) Fu, Y.; Li, Y.; Zhang, X.; Liu, Y.; Qiao, J.; Zhang, J.; Wilkinson, D. P. Novel Hierarchical SnO2 Microsphere Catalyst Coated on Gas Diffusion Electrode for Enhancing Energy Efficiency of CO2 Reduction to Formate Fuel. Appl. Energy 2016, 175, 536−544. (1115) Gupta, K.; Bersani, M.; Darr, J. A. Highly Efficient ElectroReduction of CO2 to Formic Acid by Nano-Copper. J. Mater. Chem. A 2016, 4, 13786−13794. (1116) Humphrey, J. J. L.; Plana, D.; Celorrio, V.; Sadasivan, S.; Tooze, R. P.; Rodriguez, P.; Fermin, D. J. Electrochemical Reduction of Carbon Dioxide at Gold-Palladium Core-Shell Nanoparticles: Product Distribution Versus Shell Thickness. ChemCatChem 2016, 8, 952−960. (1117) Zhao, C. C.; Wang, J. L. Electrochemical Reduction of CO2 to Formate in Aqueous Solution Using Electro-Deposited Sn Catalysts. Chem. Eng. J. 2016, 293, 161−170. (1118) Zhu, Q.; Ma, J.; Kang, X.; Sun, X.; Liu, H.; Hu, J.; Liu, Z.; Han, B. Efficient Reduction of CO2 into Formic Acid on a Lead or Tin Electrode Using an Ionic Liquid Catholyte Mixture. Angew. Chem., Int. Ed. 2016, 55, 9012−9016. (1119) Wang, H. X.; Chen, Y. B.; Hou, X. L.; Ma, C. Y.; Tan, T. W. Nitrogen-Doped Graphenes as Efficient Electrocatalysts for the Selective Reduction of Carbon Dioxide to Formate in Aqueous Solution. Green Chem. 2016, 18, 3250−3256. (1120) Liu, L.; Tian, N.; Huang, L.; Hong, Y.-H.; Xie, A.-Y.; Zhang, F.-Y.; Xiao, C.; Zhou, Z.-Y.; Sun, S.-G. Influence of Transition Metal Modification of Oxide-Derived Cu Electrodes in Electroreduction of CO2. Chin. J. Catal. 2016, 37, 1070−1075. (1121) Fu, Y.; Li, Y.; Zhang, X.; Liu, Y.; Zhou, X.; Qiao, J. Electrochemical CO2 Reduction to Formic Acid on Crystalline SnO2 GK


Chemical Reviews

Review

Nanosphere Catalyst with High Selectivity and Stability. Chin. J. Catal. 2016, 37, 1081−1088. (1122) Huan, T. N.; Simon, P.; Rousse, G.; Genois, I.; Artero, V.; Fontecave, M. Porous Dendritic Copper: An Electrocatalyst for Highly Selective CO2 Reduction to Formate in Water/Ionic Liquid Electrolyte. Chem. Sci. 2017, 8, 742−747. (1123) Li, F.; Chen, L.; Knowles, G. P.; MacFarlane, D. R.; Zhang, J. Hierarchical Mesoporous SnO+ Nanosheets on Carbon Cloth: A Robust and Flexible Electrocatalyst for CO2 Reduction with High Efficiency and Selectivity. Angew. Chem., Int. Ed. 2017, 56, 505−509. (1124) Cai, F.; Gao, D.; Zhou, H.; Wang, G.; He, T.; Gong, H.; Miao, S.; Yang, F.; Wang, J.; Bao, X. Electrochemical Promotion of Catalysis over Pd Nanoparticles for CO2 Reduction. Chem. Sci. 2017, 8, 2569−2573. (1125) Luc, W.; Collins, C.; Wang, S.; Xin, H.; He, K.; Kang, Y.; Jiao, F. Ag−Sn Bimetallic Catalyst with a Core−Shell Structure for CO2 Reduction. J. Am. Chem. Soc. 2017, 139, 1885−1893. (1126) Lv, W.; Zhou, J.; Bei, J.; Zhang, R.; Wang, L.; Xu, Q.; Wang, W. Electrodeposition of Nano-Sized Bismuth on Copper Foil as Electrocatalyst for Reduction of CO2 to Formate. Appl. Surf. Sci. 2017, 393, 191−196. (1127) Guo, S.; Zhao, S.; Gao, J.; Zhu, C.; Wu, X.; Fu, Y.; Huang, H.; Liu, Y.; Kang, Z. Cu-Cdots Nanocorals as Electrocatalyst for Highly Efficient CO2 Reduction to Formate. Nanoscale 2017, 9, 298−304. (1128) Shinagawa, T.; Larrazábal, G. O.; Martín, A. J.; Krumeich, F.; Pérez-Ramírez, J. Sulfur-Modified Copper Catalysts for the Electrochemical Reduction of Carbon Dioxide to Formate. ACS Catal. 2018, 8, 837−844. (1129) Deng, Y.; Huang, Y.; Ren, D.; Handoko, A. D.; Seh, Z. W.; Hirunsit, P.; Yeo, B. S. On the Role of Sulfur for the Selective Electrochemical Reduction of CO2 to Formate on CuSx Catalysts. ACS Appl. Mater. Interfaces 2018, 10, 28572−28581. (1130) Nakata, K.; Ozaki, T.; Terashima, C.; Fujishima, A.; Einaga, Y. High-Yield Electrochemical Production of Formaldehyde from CO2 and Seawater. Angew. Chem., Int. Ed. 2014, 53, 871−874. (1131) Parkinson, B. A.; Weaver, P. F. Photoelectrochemical Pumping of Enzymatic CO2 Reduction. Nature 1984, 309, 148−149. (1132) Summers, D. P.; Leach, S.; Frese, K. W. The Electrochemical Reduction of Aqueous Carbon Dioxide to Methanol at Molybdenum Electrodes with Low Overpotentials. J. Electroanal. Chem. Interfacial Electrochem. 1986, 205, 219−232. (1133) Popić, J.; Avramov-Ivić, M.; Vuković, N. Reduction of Carbon Dioxide on Ruthenium Oxide and Modified Ruthenium Oxide Electrodes in 0.5 M NaHCO3. Electroanal. Chem. 1997, 421, 105−110. (1134) Sun, X.; Zhu, Q.; Kang, X.; Liu, H.; Qian, Q.; Zhang, Z.; Han, B. Molybdenum-Bismuth Bimetallic Chalcogenide Nanosheets for Highly Efficient Electrocatalytic Reduction of Carbon Dioxide to Methanol. Angew. Chem., Int. Ed. 2016, 55, 6771−6775. (1135) Irfan Malik, M.; Malaibari, Z. O.; Atieh, M.; Abussaud, B. Electrochemical Reduction of CO2 to Methanol over Mwcnts Impregnated with Cu2O. Chem. Eng. Sci. 2016, 152, 468−477. (1136) Manthiram, K.; Beberwyck, B. J.; Alivisatos, A. P. Enhanced Electrochemical Methanation of Carbon Dioxide with a Dispersible Nanoscale Copper Catalyst. J. Am. Chem. Soc. 2014, 136, 13319− 13325. (1137) Guo, X.; Zhang, Y.; Deng, C.; Li, X.; Xue, Y.; Yan, Y.-M.; Sun, K. Composition Dependent Activity of Cu-Pt Nanocrystals for Electrochemical Reduction of CO2. Chem. Commun. 2015, 51, 1345−1348. (1138) Li, Y.; Cui, F.; Ross, M. B.; Kim, D.; Sun, Y.; Yang, P. Structure-Sensitive CO2 Electroreduction to Hydrocarbons on Ultrathin 5-Fold Twinned Copper Nanowires. Nano Lett. 2017, 17, 1312− 1317. (1139) Singh, S.; Gautam, R. K.; Malik, K.; Verma, A. Ag-Co Bimetallic Catalyst for Electrochemical Reduction of CO2 to Value Added Products. J. CO2 Util. 2017, 18, 139−146. (1140) Wang, Y. F.; Chen, Z.; Han, P.; Du, Y. H.; Gu, Z. X.; Xu, X.; Zheng, G. F. Single-Atomic Cu with Multiple Oxygen Vacancies on

Ceria for Electrocatalytic CO2Reduction to CH4. ACS Catal. 2018, 8, 7113−7119. (1141) Hori, Y.; Murata, A.; Takahashi, R.; Suzuki, S. Enhanced Formation of Ethylene and Alcohols at Ambient Temperature and Pressure in Electrochemical Reduction of Carbon Dioxide at a Copper Electrode. J. Chem. Soc., Chem. Commun. 1988, 17−19. (1142) Kaneco, S.; Iiba, K.; Hiei, N.; Ohta, K.; Mizuno, T.; Suzuki, T. Electrochemical Reduction of Carbon Dioxide to Ethylene with High Faradaic Efficiency at a Cu Electrode in CsOH/Methanol. Electrochim. Acta 1999, 44, 4701−4706. (1143) Li, P.; Hu, H.; Xu, J.; Jing, H.; Peng, H.; Lu, J.; Wu, C.; Ai, S. New Insights into the Photo-Enhanced Electrocatalytic Reduction of Carbon Dioxide on MoS2-Rods/TiO2 Nts with Unmatched Energy Band. Appl. Catal., B 2014, 147, 912−919. (1144) Ma, S.; Sadakiyo, M.; Luo, R.; Heima, M.; Yamauchi, M.; Kenis, P. J. A. One-Step Electrosynthesis of Ethylene and Ethanol from CO2 in an Alkaline Electrolyzer. J. Power Sources 2016, 301, 219−228. (1145) Handoko, A. D.; Ong, C. W.; Huang, Y.; Lee, Z. G.; Lin, L.; Panetti, G. B.; Yeo, B. S. Mechanistic Insights into the Selective Electroreduction of Carbon Dioxide to Ethylene on Cu2O-Derived Copper Catalysts. J. Phys. Chem. C 2016, 120, 20058−20067. (1146) Li, Q.; Zhu, W. L.; Fu, J. J.; Zhang, H. Y.; Wu, G.; Sun, S. H. Controlled Assembly of Cu Nanoparticles on Pyridinic-N Rich Graphene for Electrochemical Reduction of CO2 to Ethylene. Nano Energy 2016, 24, 1−9. (1147) Ma, M.; Djanashvili, K.; Smith, W. A. Controllable Hydrocarbon Formation from the Electrochemical Reduction of CO2 over Cu Nanowire Arrays. Angew. Chem., Int. Ed. 2016, 55, 6680−6684. (1148) Padilla, M.; Baturina, O.; Gordon, J. P.; Artyushkova, K.; Atanassov, P.; Serov, A. Selective CO2 Electroreduction to C2H4 on Porous Cu Films Synthesized by Sacrificial Support Method. J. CO2 Util. 2017, 19, 137−145. (1149) Lee, S. Y.; Jung, H.; Kim, N. K.; Oh, H. S.; Min, B. K.; Hwang, Y. J. Mixed Copper States in Anodized Cu Electrocatalyst for Stable and Selective Ethylene Production from CO2 Reduction. J. Am. Chem. Soc. 2018, 140, 8681−8689. (1150) Woan, K.; Pyrgiotakis, G.; Sigmund, W. Photocatalytic Carbon-Nanotube−TiO2 Composites. Adv. Mater. 2009, 21, 2233− 2239. (1151) Yu, Y.; Yu, J. C.; Chan, C. Y.; Che, Y. K.; Zhao, J. C.; Ding, L.; Ge, W. K.; Wong, P. K. Enhancement of Adsorption and Photocatalytic Activity of TiO2 by Using Carbon Nanotubes for the Treatment of Azo Dye. Appl. Catal., B 2005, 61, 1−11. (1152) Yu, J.; Ma, T.; Liu, S. Enhanced Photocatalytic Activity of Mesoporous TiO2 Aggregates by Embedding Carbon Nanotubes as Electron-Transfer Channel. Phys. Chem. Chem. Phys. 2011, 13, 3491− 3501. (1153) Yu, J.; Yang, B.; Cheng, B. Noble-Metal-Free Carbon Nanotube-Cd0.1Zn0.9S Composites for High Visible-Light Photocatalytic H2-Production Performance. Nanoscale 2012, 4, 2670−2677. (1154) Lukowski, M. A.; Daniel, A. S.; Meng, F.; Forticaux, A.; Li, L.; Jin, S. Enhanced Hydrogen Evolution Catalysis from Chemically Exfoliated Metallic MoS2 Nanosheets. J. Am. Chem. Soc. 2013, 135, 10274−10277. (1155) Voiry, D.; Yamaguchi, H.; Li, J.; Silva, R.; Alves, D. C. B.; Fujita, T.; Chen, M.; Asefa, T.; Shenoy, V. B.; Eda, G.; et al. Enhanced Catalytic Activity in Strained Chemically Exfoliated WS2 Nanosheets for Hydrogen Evolution. Nat. Mater. 2013, 12, 850−855. (1156) Lukowski, M. A.; Daniel, A. S.; English, C. R.; Meng, F.; Forticaux, A.; Hamers, R. J.; Jin, S. Highly Active Hydrogen Evolution Catalysis from Metallic WS2 Nanosheets. Energy Environ. Sci. 2014, 7, 2608−2613. (1157) Sharma, B. L.: Fabrication and Characterization of MetalSemiconductor Schottky Barrier Junctions. In Metal-Semiconductor Schottky Barrier Junctions and Their Applications; Sharma, B. L., Ed.; Springer US: Boston, MA, 1984; pp 113−159. (1158) Yan, F.; Wang, Y.; Zhang, J.; Lin, Z.; Zheng, J.; Huang, F. Schottky or Ohmic Metal−Semiconductor Contact: Influence on GL


Chemical Reviews

Review

(1177) Teramura, K.; Hori, K.; Terao, Y.; Huang, Z.; Iguchi, S.; Wang, Z.; Asakura, H.; Hosokawa, S.; Tanaka, T. Which Is an Intermediate Species for Photocatalytic Conversion of CO2 by H2O as the Electron Donor: CO2 Molecule, Carbonic Acid, Bicarbonate, or Carbonate Ions? J. Phys. Chem. C 2017, 121, 8711−8721. (1178) Mutch, G. A.; Shulda, S.; McCue, A. J.; Menart, M. J.; Ciobanu, C. V.; Ngo, C.; Anderson, J. A.; Richards, R. M.; Vega-Maza, D. Carbon Capture by Metal Oxides: Unleashing the Potential of the (111) Facet. J. Am. Chem. Soc. 2018, 140, 4736−4742. (1179) Slamet; Nasution, H. W.; Purnama, E.; Kosela, S.; Gunlazuardi, J. Photocatalytic Reduction of CO2 on Copper-Doped Titania Catalysts Prepared by Improved-Impregnation Method. Catal. Commun. 2005, 6, 313−319. (1180) An, X.; Li, K.; Tang, J. Cu2O/Reduced Graphene Oxide Composites for the Photocatalytic Conversion of CO2. ChemSusChem 2014, 7, 1086−1093. (1181) Pastor, E.; Pesci, F. M.; Reynal, A.; Handoko, A. D.; Guo, M.; An, X.; Cowan, A. J.; Klug, D. R.; Durrant, J. R.; Tang, J. Interfacial Charge Separation in Cu2O/RuOx as a Visible Light Driven CO2 Reduction Catalyst. Phys. Chem. Chem. Phys. 2014, 16, 5922−5926. (1182) Liu, S.; Weng, B.; Tang, Z.-R.; Xu, Y.-J. Constructing OneDimensional Silver Nanowire-Doped Reduced Graphene Oxide Integrated with CdS Nanowire Network Hybrid Structures toward Artificial Photosynthesis. Nanoscale 2015, 7, 861−866. (1183) Abou Asi, M.; Zhu, L.; He, C.; Sharma, V. K.; Shu, D.; Li, S.; Yang, J.; Xiong, Y. Visible-Light-Harvesting Reduction of CO2 to Chemical Fuels with Plasmonic Ag@AgBr/CNT Nanocomposites. Catal. Today 2013, 216, 268−275. (1184) Li, H.; Gan, S.; Wang, H.; Han, D.; Niu, L. Intercorrelated Superhybrid of AgBr Supported on Graphitic-C3N4-Decorated Nitrogen-Doped Graphene: High Engineering Photocatalytic Activities for Water Purification and CO2 Reduction. Adv. Mater. 2015, 27, 6906− 6913. (1185) Genovese, C.; Ampelli, C.; Perathoner, S.; Centi, G. Electrocatalytic Conversion of CO2 on Carbon Nanotube-Based Electrodes for Producing Solar Fuels. J. Catal. 2013, 308, 237−249. (1186) Xiong, Z.; Lei, Z.; Kuang, C. C.; Chen, X. X.; Gong, B. G.; Zhao, Y. C.; Zhang, J. Y.; Zheng, C. G.; Wu, J. C. S. Selective Photocatalytic Reduction of CO2 into CH4 over Pt-Cu2O TiO2 Nanocrystals: The Interaction between Pt and Cu2O Cocatalysts. Appl. Catal., B 2017, 202, 695−703. (1187) Wang, D.; Li, R.; Zhu, J.; Shi, J.; Han, J.; Zong, X.; Li, C. Photocatalytic Water Oxidation on BiVO4 with the Electrocatalyst as an Oxidation Cocatalyst: Essential Relations between Electrocatalyst and Photocatalyst. J. Phys. Chem. C 2012, 116, 5082−5089. (1188) Yang, Y.; Gu, J.; Young, J. L.; Miller, E. M.; Turner, J. A.; Neale, N. R.; Beard, M. C. Semiconductor Interfacial Carrier Dynamics Via Photoinduced Electric Fields. Science 2015, 350, 1061−1065. (1189) Li, L.; Salvador, P. A.; Rohrer, G. S. Photocatalysts with Internal Electric Fields. Nanoscale 2014, 6, 24−42. (1190) Asadi, M.; Kim, K.; Liu, C.; Addepalli, A. V.; Abbasi, P.; Yasaei, P.; Phillips, P.; Behranginia, A.; Cerrato, J. M.; Haasch, R.; et al. Nanostructured Transition Metal Dichalcogenide Electrocatalysts for CO2 Reduction in Ionic Liquid. Science 2016, 353, 467−470. (1191) Lang, D.; Cheng, F.; Xiang, Q. Enhancement of Photocatalytic H2 Production Activity of CdS Nanorods by Cobalt-Based Cocatalyst Modification. Catal. Sci. Technol. 2016, 6, 6207−6216. (1192) Yuan, J.; Wen, J.; Gao, Q.; Chen, S.; Li, J.; Li, X.; Fang, Y. Amorphous Co3O4 Modified CdS Nanorods with Enhanced VisibleLight Photocatalytic H2-Production Activity. Dalton Trans. 2015, 44, 1680−1689. (1193) Bi, W.; Zhang, L.; Sun, Z.; Li, X.; Jin, T.; Wu, X.; Zhang, Q.; Luo, Y.; Wu, C.; Xie, Y. Insight into Electrocatalysts as Co-Catalysts in Efficient Photocatalytic Hydrogen Evolution. ACS Catal. 2016, 6, 4253−4257. (1194) Michaelson, H. B. The Work Function of the Elements and Its Periodicity. J. Appl. Phys. 1977, 48, 4729−4733.

Photocatalytic Efficiency of Ag/ZnO and Pt/ZnO Model Systems. ChemSusChem 2014, 7, 101−104. (1159) Jeong, S.; Kim, W. D.; Lee, S.; Lee, K.; Lee, S.; Lee, D.; Lee, D. C. Bi2O3 as a Promoter for Cu/TiO2 Photocatalysts for the Selective Conversion of Carbon Dioxide into Methane. ChemCatChem 2016, 8, 1641−1645. (1160) Xie, S.; Wang, Y.; Zhang, Q.; Deng, W.; Wang, Y. MgO- and Pt-Promoted TiO2 as an Efficient Photocatalyst for the Preferential Reduction of Carbon Dioxide in the Presence of Water. ACS Catal. 2014, 4, 3644−3653. (1161) Li, Q.; Zong, L.; Li, C.; Yang, J. Photocatalytic Reduction of CO2 on MgO/TiO2 Nanotube Films. Appl. Surf. Sci. 2014, 314, 458− 463. (1162) Liu, L.; Zhao, C.; Pitts, D.; Zhao, H.; Li, Y. CO2 Photoreduction with H2O Vapor by Porous MgO-TiO2 Microspheres: Effects of Surface MgO Dispersion and CO2 Adsorption-Desorption Dynamics. Catal. Sci. Technol. 2014, 4, 1539−1546. (1163) Liu, L.; Zhao, C.; Zhao, H.; Pitts, D.; Li, Y. Porous Microspheres of MgO-Patched TiO2 for CO2 Photoreduction with H2O Vapor: Temperature-Dependent Activity and Stability. Chem. Commun. 2013, 49, 3664−3666. (1164) Meng, X.; Ouyang, S.; Kako, T.; Li, P.; Yu, Q.; Wang, T.; Ye, J. Photocatalytic CO2 Conversion over Alkali Modified TiO2 without Loading Noble Metal Cocatalyst. Chem. Commun. 2014, 50, 11517− 11519. (1165) Sun, Z. X.; Fischer, J.; Li, Q. A.; Hu, J.; Tang, Q. J.; Wang, H. Q.; Wu, Z. B.; Hankel, M.; Searles, D. J.; Wang, L. Z. Enhanced CO2 Photocatalytic Reduction on Alkali-Decorated Graphitic Carbon Nitride. Appl. Catal., B 2017, 216, 146−155. (1166) Teramura, K.; Tsuneoka, H.; Shishido, T.; Tanaka, T. Effect of H2 Gas as a Reductant on Photoreduction of CO2 over a Ga2O3 Photocatalyst. Chem. Phys. Lett. 2008, 467, 191−194. (1167) Yamamoto, M.; Yoshida, T.; Yamamoto, N.; Nomoto, T.; Yamamoto, Y.; Yagi, S.; Yoshida, H. Photocatalytic Reduction of CO2 with Water Promoted by Ag Clusters in Ag/Ga2O3 Photocatalysts. J. Mater. Chem. A 2015, 3, 16810−16816. (1168) Tsuneoka, H.; Teramura, K.; Shishido, T.; Tanaka, T. Adsorbed Species of CO2 and H2 on Ga2O3 for the Photocatalytic Reduction of CO2. J. Phys. Chem. C 2010, 114, 8892−8898. (1169) Kwon, S.; Liao, P.; Stair, P. C.; Snurr, R. Q. Alkaline-Earth Metal-Oxide Overlayers on TiO2Application toward CO2 Photoreduction. Catal. Sci. Technol. 2016, 6, 7885−7895. (1170) Matsumoto, Y.; Obata, M.; Hombo, J. Photocatalytic Reduction of Carbon Dioxide on P-Type CaFe2O4 Powder. J. Phys. Chem. 1994, 98, 2950−2951. (1171) Wang, S.; Lin, J.; Wang, X. Semiconductor-Redox Catalysis Promoted by Metal-Organic Frameworks for CO2 Reduction. Phys. Chem. Chem. Phys. 2014, 16, 14656−14660. (1172) Wang, S.; Wang, X. Photocatalytic CO2 Reduction by CdS Promoted with a Zeolitic Imidazolate Framework. Appl. Catal., B 2015, 162, 494−500. (1173) Zhao, H.; Wang, X. S.; Feng, J. F.; Chen, Y. N.; Yang, X.; Gao, S. Y.; Cao, R. Synthesis and Characterization of Zn2GeO4/Mg-MOF74 Composites with Enhanced Photocatalytic Activity for CO2 Reduction. Catal. Sci. Technol. 2018, 8, 1288−1295. (1174) Hong, J.; Zhang, W.; Wang, Y.; Zhou, T.; Xu, R. Photocatalytic Reduction of Carbon Dioxide over Self-Assembled Carbon Nitride and Layered Double Hydroxide: The Role of Carbon Dioxide Enrichment. ChemCatChem 2014, 6, 2315−2321. (1175) Kim, K. H.; Kim, S.; Moon, B. C.; Choi, J. W.; Jeong, H. M.; Kwon, Y.; Kwon, S.; Choi, H. S.; Kang, J. K. Quadruple Metal-Based Layered Structure as the Photocatalyst for Conversion of Carbon Dioxide into a Value Added Carbon Monoxide with High Selectivity and Efficiency. J. Mater. Chem. A 2017, 5, 8274−8279. (1176) Liu, G.; Xie, S.; Zhang, Q.; Tian, Z.; Wang, Y. Carbon Dioxide-Enhanced Photosynthesis of Methane and Hydrogen from Carbon Dioxide and Water over Pt-Promoted Polyaniline-TiO2 Nanocomposites. Chem. Commun. 2015, 51, 13654−13657. GM


Chemical Reviews

Review

(1195) Hölzl, J.; Schulte, F. K.: Work Function of Metals. In Solid Surface Physics; Hölzl, J., Schulte, F. K., Wagner, H., Eds.; Springer: Berlin, Heidelberg, 1979; pp 1−150. (1196) Skriver, H. L.; Rosengaard, N. M. Surface Energy and Work Function of Elemental Metals. Phys. Rev. B: Condens. Matter Mater. Phys. 1992, 46, 7157−7168. (1197) Shiraishi, M.; Ata, M. Work Function of Carbon Nanotubes. Carbon 2001, 39, 1913−1917. (1198) Liu, P.; Sun, Q.; Zhu, F.; Liu, K.; Jiang, K.; Liu, L.; Li, Q.; Fan, S. Measuring the Work Function of Carbon Nanotubes with Thermionic Method. Nano Lett. 2008, 8, 647−651. (1199) Shi, Y.; Kim, K. K.; Reina, A.; Hofmann, M.; Li, L.-J.; Kong, J. Work Function Engineering of Graphene Electrode Via Chemical Doping. ACS Nano 2010, 4, 2689−2694. (1200) Wen, J.; Xie, J.; Zhang, H.; Zhang, A.; Liu, Y.; Chen, X.; Li, X. Constructing Multi-Functional Metallic Ni Interface Layers in the gC3N4 Nanosheets/Amorphous Nis Heterojunctions for Efficient Photocatalytic H2 Generation. ACS Appl. Mater. Interfaces 2017, 9, 14031−14042. (1201) Matsubu, J. C.; Lin, E. T.; Gunther, K. L.; Bozhilov, K. N.; Jiang, Y.; Christopher, P. Critical Role of Interfacial Effects on the Reactivity of Semiconductor-Cocatalyst Junctions for Photocatalytic Oxygen Evolution from Water. Catal. Sci. Technol. 2016, 6, 6836− 6844. (1202) Bai, S.; Wang, L.; Chen, X.; Du, J.; Xiong, Y. Chemically Exfoliated Metallic MoS2Nanosheets: A Promising Supporting CoCatalyst for Enhancing the Photocatalytic Performance of TiO2 Nanocrystals. Nano Res. 2015, 8, 175−183. (1203) Qi, Y. H.; Xu, Q.; Wang, Y.; Yan, B.; Ren, Y. M.; Chen, Z. M. CO2-Induced Phase Engineering: Protocol for Enhanced Photoelectrocatalytic Performance of 2D MoS2 Nanosheets. ACS Nano 2016, 10, 2903−2909. (1204) Liu, Q.; Li, X.; He, Q.; Khalil, A.; Liu, D.; Xiang, T.; Wu, X.; Song, L. Gram-Scale Aqueous Synthesis of Stable Few-Layered 1TMoS2Applications for Visible-Light-Driven Photocatalytic Hydrogen Evolution. Small 2015, 11, 5556−5564. (1205) Liu, Q.; Shang, Q.; Khalil, A.; Fang, Q.; Chen, S.; He, Q.; Xiang, T.; Liu, D.; Zhang, Q.; Luo, Y.; et al. In Situ Integration of a Metallic 1T-MoS2/CdS Heterostructure as a Means to Promote Visible-Light-Driven Photocatalytic Hydrogen Evolution. ChemCatChem 2016, 8, 2614−2619. (1206) Peng, R.; Liang, L.; Hood, Z. D.; Boulesbaa, A.; Puretzky, A.; Ievlev, A. V.; Come, J.; Ovchinnikova, O. S.; Wang, H.; Ma, C.; et al. In-Plane Heterojunctions Enable Multiphasic Two-Dimensional (2D) MoS2 Nanosheets as Efficient Photocatalysts for Hydrogen Evolution from Water Reduction. ACS Catal. 2016, 6, 6723−6729. (1207) Du, H.; Guo, H.-L.; Liu, Y.-N.; Xie, X.; Liang, K.; Zhou, X.; Wang, X.; Xu, A.-W. Metallic 1T-LixMoS2 Cocatalyst Significantly Enhanced the Photocatalytic H2Evolution over Cd0.5Zn0.5S Nanocrystals under Visible Light Irradiation. ACS Appl. Mater. Interfaces 2016, 8, 4023−4030. (1208) Wang, L.; Liu, X.; Luo, J.; Duan, X.; Crittenden, J.; Liu, C.; Zhang, S.; Pei, Y.; Zeng, Y.; Duan, X. Active Site Self-Optimization by Irreversible Phase Transition of 1T-MoS2 in Photocatalytic Hydrogen Evolution. Angew. Chem., Int. Ed. 2017, 56, 7610−7614. (1209) Tang, Q.; Jiang, D.-e. Mechanism of Hydrogen Evolution Reaction on 1T-MoS2 from First Principles. ACS Catal. 2016, 6, 4953−4961. (1210) Ambrosi, A.; Sofer, Z.; Pumera, M. 2H→1T Phase Transition and Hydrogen Evolution Activity of MoS2MoSe2WS2 and WSe2 Strongly Depends on the MX2 Composition. Chem. Commun. 2015, 51, 8450−8453. (1211) Yang, J.; Wang, K.; Zhu, J. X.; Zhang, C.; Liu, T. X. SelfTemplated Growth of Vertically Aligned 2H-1T MoS2 for Efficient Electrocatalytic Hydrogen Evolution. ACS Appl. Mater. Interfaces 2016, 8, 31702−31708. (1212) Wang, D.; Zhang, X.; Bao, S.; Zhang, Z.; Fei, H.; Wu, Z. Phase Engineering of a Multiphasic 1T/2H MoS2 Catalyst for Highly Efficient Hydrogen Evolution. J. Mater. Chem. A 2017, 5, 2681−2688.

(1213) Chang, K.; Hai, X.; Pang, H.; Zhang, H.; Shi, L.; Liu, G.; Liu, H.; Zhao, G.; Li, M.; Ye, J. Targeted Synthesis of 2H- and 1T-Phase MoS2 Monolayers for Catalytic Hydrogen Evolution. Adv. Mater. 2016, 28, 10033−10041. (1214) Zhang, H.; Li, Y.; Xu, T.; Wang, J.; Huo, Z.; Wan, P.; Sun, X. Amorphous Co-Doped MoS2 Nanosheet Coated Metallic CoS2 Nanocubes as an Excellent Electrocatalyst for Hydrogen Evolution. J. Mater. Chem. A 2015, 3, 15020−15023. (1215) Mahler, B.; Hoepfner, V.; Liao, K.; Ozin, G. A. Colloidal Synthesis of 1T-WS2 and 2H-WS2 Nanosheets: Applications for Photocatalytic Hydrogen Evolution. J. Am. Chem. Soc. 2014, 136, 14121−14127. (1216) Feng, L.-L.; Fan, M.; Wu, Y.; Liu, Y.; Li, G.-D.; Chen, H.; Chen, W.; Wang, D.; Zou, X. Metallic Co9S8 Nanosheets Grown on Carbon Cloth as Efficient Binder-Free Electrocatalysts for the Hydrogen Evolution Reaction in Neutral Media. J. Mater. Chem. A 2016, 4, 6860−6867. (1217) Long, X.; Li, G.; Wang, Z.; Zhu, H.; Zhang, T.; Xiao, S.; Guo, W.; Yang, S. Metallic Iron-Nickel Sulfide Ultrathin Nanosheets as a Highly Active Electrocatalyst for Hydrogen Evolution Reaction in Acidic Media. J. Am. Chem. Soc. 2015, 137, 11900−11903. (1218) Yang, L.; Zhou, W.; Hou, D.; Zhou, K.; Li, G.; Tang, Z.; Li, L.; Chen, S. Porous Metallic MoO2-Supported MoS2 Nanosheets for Enhanced Electrocatalytic Activity in the Hydrogen Evolution Reaction. Nanoscale 2015, 7, 5203−5208. (1219) Ma, Y.; Liu, B.; Zhang, A.; Chen, L.; Fathi, M.; Shen, C.; Abbas, A. N.; Ge, M.; Mecklenburg, M.; Zhou, C. Reversible Semiconducting-to-Metallic Phase Transition in Chemical Vapor Deposition Grown Mono Layer WSe2 and Applications for Devices. ACS Nano 2015, 9, 7383−7391. (1220) Chen, Y.; Ge, H.; Wei, L.; Li, Z.; Yuan, R.; Liu, P.; Fu, X. Reduction Degree of Reduced Graphene Oxide (RGO) Dependence of Photocatalytic Hydrogen Evolution Performance over RGO/ ZnIn2S4 Nanocomposites. Catal. Sci. Technol. 2013, 3, 1712−1717. (1221) Zhang, N.; Yang, M.-Q.; Tang, Z.-R.; Xu, Y.-J. CdS− Graphene Nanocomposites as Visible Light Photocatalyst for Redox Reactions in Water: A Green Route for Selective Transformation and Environmental Remediation. J. Catal. 2013, 303, 60−69. (1222) Yang, M.-Q.; Zhang, N.; Pagliaro, M.; Xu, Y.-J. Artificial Photosynthesis over Graphene-Semiconductor Composites. Are We Getting Better? Chem. Soc. Rev. 2014, 43, 8240−8254. (1223) Zhang, N.; Xu, Y.-J. The Endeavour to Advance GrapheneSemiconductor Composite-Based Photocatalysis. CrystEngComm 2016, 18, 24−37. (1224) Zhang, N.; Yang, M.-Q.; Liu, S.; Sun, Y.; Xu, Y.-J. Waltzing with the Versatile Platform of Graphene to Synthesize Composite Photocatalysts. Chem. Rev. 2015, 115, 10307−10377. (1225) Yuan, L.; Yu, Q.; Zhang, Y.; Xu, Y.-J. Graphene-TiO2 Nanocomposite Photocatalysts for Selective Organic Synthesis in Water under Simulated Solar Light Irradiation. RSC Adv. 2014, 4, 15264−15270. (1226) Zhang, Y.; Zhang, N.; Tang, Z.-R.; Xu, Y.-J. Improving the Photocatalytic Performance of Graphene-TiO2 Nanocomposites Via a Combined Strategy of Decreasing Defects of Graphene and Increasing Interfacial Contact. Phys. Chem. Chem. Phys. 2012, 14, 9167−9175. (1227) Trapalis, A.; Todorova, N.; Giannakopoulou, T.; Boukos, N.; Speliotis, T.; Dimotikali, D.; Yu, J. TiO2/Graphene Composite Photocatalysts for NOx Removal: A Comparison of SurfactantStabilized Graphene and Reduced Graphene Oxide. Appl. Catal., B 2016, 180, 637−647. (1228) Weng, B.; Xu, Y.-J. What If the Electrical Conductivity of Graphene Is Significantly Deteriorated for the Graphene−Semiconductor Composite-Based Photocatalysis? ACS Appl. Mater. Interfaces 2015, 7, 27948−27958. (1229) Liang, L.; Lei, F. C.; Gao, S.; Sun, Y. F.; Jiao, X. C.; Wu, J.; Qamar, S.; Xie, Y. Single Unit Cell Bismuth Tungstate Layers Realizing Robust Solar CO2 Reduction to Methanol. Angew. Chem., Int. Ed. 2015, 54, 13971−13974. GN


Chemical Reviews

Review

(1230) Zhao, S. L.; Wang, Y.; Dong, J. C.; He, C. T.; Yin, H. J.; An, P. F.; Zhao, K.; Zhang, X. F.; Gao, C.; Zhang, L. J.; et al. Ultrathin MetalOrganic Framework Nanosheets for Electrocatalytic Oxygen Evolution. Nature Energy 2016, 1, 16184. (1231) Song, F.; Hu, X. L. Exfoliation of Layered Double Hydroxides for Enhanced Oxygen Evolution Catalysis. Nat. Commun. 2014, 5, 4477. (1232) Liang, H. F.; Meng, F.; Caban-Acevedo, M.; Li, L. S.; Forticaux, A.; Xiu, L. C.; Wang, Z. C.; Jin, S. Hydrothermal Continuous Flow Synthesis and Exfoliation of NiCo Layered Double Hydroxide Nanosheets for Enhanced Oxygen Evolution Catalysis. Nano Lett. 2015, 15, 1421−1427. (1233) Zhang, N.; Yang, M. Q.; Tang, Z. R.; Xu, Y. J. Toward Improving the Graphene-Semiconductor Composite Photoactivity Via the Addition of Metal Ions as Generic Interfacial Mediator. ACS Nano 2014, 8, 623−633. (1234) Wu, J.; Lu, H.; Zhang, X.; Raziq, F.; Qu, Y.; Jing, L. Enhanced Charge Separation of Rutile TiO2 Nanorods by Trapping Holes and Transferring Electrons for Efficient Cocatalyst-Free Photocatalytic Conversion of CO2 to Fuels. Chem. Commun. 2016, 52, 5027−5029. (1235) Han, C.; Yang, M.-Q.; Zhang, N.; Xu, Y.-J. Enhancing the Visible Light Photocatalytic Performance of Ternary CdS-(GraphenePd) Nanocomposites Via a Facile Interfacial Mediator and Co-Catalyst Strategy. J. Mater. Chem. A 2014, 2, 19156−19166. (1236) Tang, Z.-R.; Yu, Q.; Xu, Y.-J. Toward Improving the Photocatalytic Activity of BiVO4-Graphene 2D-2D Composites under Visible Light by the Addition of Mediator. RSC Adv. 2014, 4, 58448− 58452. (1237) Bai, S.; Ge, J.; Wang, L.; Gong, M.; Deng, M.; Kong, Q.; Song, L.; Jiang, J.; Zhang, Q.; Luo, Y.; et al. A Unique SemiconductorMetal-Graphene Stack Design to Harness Charge Flow for Photocatalysis. Adv. Mater. 2014, 26, 5689−5695. (1238) Zhong, Y.; Yuan, J.; Wen, J.; Li, X.; Xu, Y.; Liu, W.; Zhang, S.; Fang, Y. Earth-Abundant NiS Co-Catalyst Modified Metal-Free mpgC3N4/CNT Nanocomposites for Highly Efficient Visible-Light Photocatalytic H2 Evolution. Dalton Trans. 2015, 44, 18260−18269. (1239) Zhang, X.; Shao, C.; Li, X.; Lu, N.; Wang, K.; Miao, F.; Liu, Y. In2A3/Carbon Nanofibers/Au Ternary Synergetic System: Hierarchical Assembly and Enhanced Visible-Light Photocatalytic Activity. J. Hazard. Mater. 2015, 283, 599−607. (1240) Wen, J.; Li, X.; Li, H.; Ma, S.; He, K.; Xu, Y.; Fang, Y.; Liu, W.; Gao, Q. Enhanced Visible-Light H 2 Evolution of g-C3N4 Photocatalysts Via the Synergetic Effect of Amorphous NiS and Cheap Metal-Free Carbon Black Nanoparticles as Co-Catalysts. Appl. Surf. Sci. 2015, 358, 204−212. (1241) Yuan, J.; Wen, J.; Zhong, Y.; Li, X.; Fang, Y.; Zhang, S.; Liu, W. Enhanced Photocatalytic H2 Evolution over Noble-Metal-Free NiS Cocatalyst Modified CdS Nanorods/g-C3N4 Heterojunctions. J. Mater. Chem. A 2015, 3, 18244−18255. (1242) Zada, A.; Humayun, M.; Raziq, F.; Zhang, X.; Qu, Y.; Bai, L.; Qin, C.; Jing, L.; Fu, H. Exceptional Visible-Light-Driven CocatalystFree Photocatalytic Activity of g-C3N4 by Well Designed Nanocomposites with Plasmonic Au and SnO2. Adv. Energy Mater. 2016, 6, 1601190. (1243) Zhang, L.; Liu, Q.; Aoki, T.; Crozier, P. A. Structural Evolution During Photocorrosion of Ni/NiO Core/Shell Cocatalyst on TiO2. J. Phys. Chem. C 2015, 119, 7207−7214. (1244) Zhang, J.; Wang, J.; Chen, P.; Sun, Y.; Wu, S.; Jia, Z.; Lu, X.; Yu, H.; Chen, W.; Zhu, J.; et al. Observation of Strong Interlayer Coupling in MoS2/WS2Heterostructures. Adv. Mater. 2016, 28, 1950− 1956. (1245) Luo, C.-Y.; Huang, W.-Q.; Hu, W.; Peng, P.; Huang, G.-F. Non-Covalent Functionalization of WS2 Monolayer with Small Fullerenes: Tuning Electronic Properties and Photoactivity. Dalton Trans. 2016, 45, 13383−13391. (1246) Zhang, X.; Meng, Z.; Rao, D.; Wang, Y.; Shi, Q.; Liu, Y.; Wu, H.; Deng, K.; Liu, H.; Lu, R. Efficient Band Structure Tuning, Charge Separation, and Visible-Light Response in ZrS2-Based Van Der Waals Heterostructures. Energy Environ. Sci. 2016, 9, 841−849.

(1247) Fu, C.-F.; Luo, Q.; Li, X.; Yang, J. Two-Dimensional Van Der Waals Nanocomposites as Z-Scheme Type Photocatalysts for Hydrogen Production from Overall Water Splitting. J. Mater. Chem. A 2016, 4, 18892−18898. (1248) Liao, J.; Sa, B.; Zhou, J.; Ahuja, R.; Sun, Z. Design of HighEfficiency Visible-Light Photocatalysts for Water Splitting: MoS2/ Aln(GaN) Heterostructures. J. Phys. Chem. C 2014, 118, 17594− 17599. (1249) Liu, J. Origin of High Photocatalytic Efficiency in Monolayer g-C3N4/CdS Heterostructure: A Hybrid DFT Study. J. Phys. Chem. C 2015, 119, 28417−28423. (1250) Jin, H.; Dai, Y.; Ma, X.-C.; Yu, L.; Wei, W.; Huang, B.-B. Enhancement of Photocatalytic Activity of a Two-Dimensional GeH/ Graphene Heterobilayer under Visible Light. RSC Adv. 2015, 5, 52264−52268. (1251) Luo, C.-Y.; Huang, W.-Q.; Xu, L.; Yang, Y.-C.; Li, X.; Hu, W.; Peng, P.; Huang, G.-F. Electronic Properties and Photoactivity of Monolayer MoS2/Fullerene Van Der Waals Heterostructures. RSC Adv. 2016, 6, 43228−43236. (1252) Meng, R.; Jiang, J.; Liang, Q.; Yang, Q.; Tan, C.; Sun, X.; Chen, X. Design of Graphene-Like Gallium Nitride and WS2/WSe2 Nanocomposites for Photocatalyst Applications. Science ChinaMaterials 2016, 59, 1027−1036. (1253) Peng, Q.; Wang, Z.; Sa, B.; Wu, B.; Sun, Z. Electronic Structures and Enhanced Optical Properties of Blue Phosphorene/ Transition Metal Dichalcogenides Van Der Waals Heterostructures. Sci. Rep. 2016, 6, 31994. (1254) Shi, J.; Tong, R.; Zhou, X.; Gong, Y.; Zhang, Z.; Ji, Q.; Zhang, Y.; Fang, Q.; Gu, L.; Wang, X.; et al. Temperature-Mediated Selective Growth of MoS2 /WS2 and WS2/MoS2 Vertical Stacks on Au Foils for Direct Photocatalytic Applications. Adv. Mater. 2016, 28, 10664− 10672. (1255) Li, J.; Zhan, G.; Yu, Y.; Zhang, L. Superior Visible Light Hydrogen Evolution of Janus Bilayer Junctions Via Atomic-Level Charge Flow Steering. Nat. Commun. 2016, 7, 11480. (1256) Lee, E.; Hong, J.-Y.; Kang, H.; Jang, J. Synthesis of TiO2 Nanorod-Decorated Graphene Sheets and Their Highly Efficient Photocatalytic Activities under Visible-Light Irradiation. J. Hazard. Mater. 2012, 219, 13−18. (1257) Li, Y.; Zhang, H.; Liu, P.; Wang, D.; Li, Y.; Zhao, H. CrossLinked g-C3N4/RGO Nanocomposites with Tunable Band Structure and Enhanced Visible Light Photocatalytic Activity. Small 2013, 9, 3336−3344. (1258) Zhou, X.; Shi, T.; Wu, J.; Zhou, H. (001) Facet-Exposed Anatase-Phase TiO2 Nanotube Hybrid Reduced Graphene Oxide Composite: Synthesis, Characterization and Application in Photocatalytic Degradation. Appl. Surf. Sci. 2013, 287, 359−368. (1259) Mao, L.; Zhu, S.; Ma, J.; Shi, D.; Chen, Y.; Chen, Z.; Yin, C.; Li, Y.; Zhang, D. Superior H2 Production by Hydrophilic Ultrafine Ta2O5 Engineered Covalently on Graphene. Nanotechnology 2014, 25, 215401. (1260) Qiu, B.; Xing, M.; Zhang, J. Mesoporous TiO2 Nanocrystals Grown in Situ on Graphene Aerogels for High Photocatalysis and Lithium-Ion Batteries. J. Am. Chem. Soc. 2014, 136, 5852−5855. (1261) Wang, C.; Bai, S.; Xiong, Y. Recent Advances in Surface and Interface Engineering for Electrocatalysis. Chin. J. Catal. 2015, 36, 1476−1493. (1262) Bai, S.; Wang, L. L.; Li, Z. Q.; Xiong, Y. J. Facet-Engineered Surface and Interface Design of Photocatalytic Materials. Advanced Science 2017, 4, 1600216. (1263) Cao, S.; Tao, F.; Tang, Y.; Li, Y.; Yu, J. Size- and ShapeDependent Catalytic Performances of Oxidation and Reduction Reactions on Nanocatalysts. Chem. Soc. Rev. 2016, 45, 4747−4765. (1264) Bai, S.; Yin, W.; Wang, L.; Li, Z.; Xiong, Y. Surface and Interface Design in Cocatalysts for Photocatalytic Water Splitting and CO2 Reduction. RSC Adv. 2016, 6, 57446−57463. (1265) Sharma, P. P.; Wu, J.; Yadav, R. M.; Liu, M.; Wright, C. J.; Tiwary, C. S.; Yakobson, B. I.; Lou, J.; Ajayan, P. M.; Zhou, X.-D. Nitrogen-Doped Carbon Nanotube Arrays for High-Efficiency GO


Chemical Reviews

Review

Electrochemical Reduction of CO2On the Understanding of Defects, Defect Density, and Selectivity. Angew. Chem., Int. Ed. 2015, 54, 13701−13705. (1266) Wu, J. J.; Liu, M. J.; Sharma, P. P.; Yadav, R. M.; Ma, L. L.; Yang, Y. C.; Zou, X. L.; Zhou, X. D.; Vajtai, R.; Yakobson, B. I.; et al. Incorporation of Nitrogen Defects for Efficient Reduction of CO2 Via Two-Electron Pathway on Three-Dimensional Graphene Foam. Nano Lett. 2016, 16, 466−470. (1267) Gao, S.; Sun, Z.; Liu, W.; Jiao, X.; Zu, X.; Hu, Q.; Sun, Y.; Yao, T.; Zhang, W.; Wei, S.; et al. Atomic Layer Confined Vacancies for Atomic-Level Insights into Carbon Dioxide Electroreduction. Nat. Commun. 2017, 8, 14503. (1268) Lim, D.-H.; Jo, J. H.; Shin, D. Y.; Wilcox, J.; Ham, H. C.; Nam, S. W. Carbon Dioxide Conversion into Hydrocarbon Fuels on Defective Graphene-Supported Cu Nanoparticles from First Principles. Nanoscale 2014, 6, 5087−5092. (1269) Lin, T.; Chen, I. W.; Liu, F.; Yang, C.; Bi, H.; Xu, F.; Huang, F. Nitrogen-Doped Mesoporous Carbon of Extraordinary Capacitance for Electrochemical Energy Storage. Science 2015, 350, 1508−1513. (1270) Guo, D.; Shibuya, R.; Akiba, C.; Saji, S.; Kondo, T.; Nakamura, J. Active Sites of Nitrogen-Doped Carbon Materials for Oxygen Reduction Reaction Clarified Using Model Catalysts. Science 2016, 351, 361−365. (1271) Gong, K. P.; Du, F.; Xia, Z. H.; Durstock, M.; Dai, L. M. Nitrogen-Doped Carbon Nanotube Arrays with High Electrocatalytic Activity for Oxygen Reduction. Science 2009, 323, 760−764. (1272) Yang, H.-P.; Qin, S.; Yue, Y.-N.; Liu, L.; Wang, H.; Lu, J.-X. Entrapment of a Pyridine Derivative within a Copper-Palladium Alloy: A Bifunctional Catalyst for Electrochemical Reduction of CO2 to Alcohols with Excellent Selectivity and Reusability. Catal. Sci. Technol. 2016, 6, 6490−6494. (1273) Jupally, V. R.; Dharmaratne, A. C.; Crasto, D.; Huckaba, A. J.; Kumara, C.; Nimmala, P. R.; Kothalawala, N.; Delcamp, J. H.; Dass, A. Au137(SR)56 Nanomolecules: Composition, Optical Spectroscopy, Electrochemistry and Electrocatalytic Reduction of CO2. Chem. Commun. 2014, 50, 9895−9898. (1274) Jovanov, Z. P.; Hansen, H. A.; Varela, A. S.; Malacrida, P.; Peterson, A. A.; Norskov, J. K.; Stephens, I. E. L.; Chorkendorff, I. Opportunities and Challenges in the Electrocatalysis of CO2 and CO Reduction Using Bifunctional Surfaces: A Theoretical and Experimental Study of Au-Cd Alloys. J. Catal. 2016, 343, 215−231. (1275) Hahn, C.; Abram, D. N.; Hansen, H. A.; Hatsukade, T.; Jackson, A.; Johnson, N. C.; Hellstern, T. R.; Kuhl, K. P.; Cave, E. R.; Feaster, J. T.; et al. Synthesis of Thin Film Aupd Alloys and Their Investigation for Electrocatalytic CO2 Reduction. J. Mater. Chem. A 2015, 3, 20185−20194. (1276) Jedidi, A.; Rasul, S.; Masih, D.; Cavallo, L.; Takanabe, K. Generation of Cu-in Alloy Surfaces from CuInI2 as Selective Catalytic Sites for CO2 Electroreduction. J. Mater. Chem. A 2015, 3, 19085− 19092. (1277) Zhao, X.; Luo, B.; Long, R.; Wang, C.; Xiong, Y. Composition-Dependent Activity of Cu-Pt Alloy Nanocubes for Electrocatalytic CO2 Reduction. J. Mater. Chem. A 2015, 3, 4134− 4138. (1278) Lee, S.; Jeong, S.; Kim, W. D.; Lee, S.; Lee, K.; Bae, W. K.; Moon, J. H.; Lee, S.; Lee, D. C. Low-Coordinated Surface Atoms of Cupt Alloy Cocatalysts on TiO2 for Enhanced Photocatalytic Conversion of CO2. Nanoscale 2016, 8, 10043−10048. (1279) Cheng, M.-J.; Clark, E. L.; Pham, H. H.; Bell, A. T.; HeadGordon, M. Quantum Mechanical Screening of Single-Atom Bimetallic Alloys for the Selective Reduction of CO 2 to C 1 Hydrocarbons. ACS Catal. 2016, 6, 7769−7777. (1280) Klinkova, A.; De Luna, P.; Dinh, C.-T.; Voznyy, O.; Larin, E. M.; Kumacheva, E.; Sargent, E. H. Rational Design of Efficient Palladium Catalysts for Electroreduction of Carbon Dioxide to Formate. ACS Catal. 2016, 6, 8115−8120. (1281) Lee, H.-E.; Yang, K. D.; Yoon, S. M.; Ahn, H.-Y.; Lee, Y. Y.; Chang, H.; Jeong, D. H.; Lee, Y.-S.; Kim, M. Y.; Nam, K. T. Concave

Rhombic Dodecahedral Au Nanocatalyst with Multiple High-Index Facets for CO2 Reduction. ACS Nano 2015, 9, 8384−8393. (1282) Wang, Z.-L.; Li, C.; Yamauchi, Y. Nanostructured Nonprecious Metal Catalysts for Electrochemical Reduction of Carbon Dioxide. Nano Today 2016, 11, 373−391. (1283) Bai, S.; Wang, X.; Hu, C.; Xie, M.; Jiang, J.; Xiong, Y. TwoDimensional g-C3N4 an Ideal Platform for Examining Facet Selectivity of Metal Co-Catalysts in Photocatalysis. Chem. Commun. 2014, 50, 6094−6097. (1284) Wenderich, K.; Mul, G. Methods, Mechanism, and Applications of Photodeposition in Photocatalysis: A Review. Chem. Rev. 2016, 116, 14587−14619. (1285) Zhu, Z.; Qin, J.; Jiang, M.; Ding, Z.; Hou, Y. Enhanced Selective Photocatalytic CO2 Reduction into CO over Ag/CdS Nanocomposites under Visible Light. Appl. Surf. Sci. 2017, 391, 572−579. (1286) Kim, W.; Frei, H. Directed Assembly of Cuprous Oxide Nanocatalyst for CO2 Reduction Coupled to Heterobinuclear ZrOCoII Light Absorber in Mesoporous Silica. ACS Catal. 2015, 5, 5627−5635. (1287) Wang, Y.; Lai, Q.; Zhang, F.; Shen, X.; Fan, M.; He, Y.; Ren, S. High Efficiency Photocatalytic Conversion of CO2 with H2O over Pt/TiO2 Nanoparticles. RSC Adv. 2014, 4, 44442−44451. (1288) Yang, F.; Chen, Y.; Cheng, G.; Chen, S.; Luo, W. Ultrathin Nitrogen-Doped Carbon Coated with Cop for Efficient Hydrogen Evolution. ACS Catal. 2017, 7, 3824−3831. (1289) Wang, J.; Xu, F.; Jin, H.; Chen, Y.; Wang, Y. Non-Noble Metal-Based Carbon Composites in Hydrogen Evolution Reaction: Fundamentals to Applications. Adv. Mater. 2017, 29, 1605838. (1290) Shi, Z.; Wang, Y.; Lin, H.; Zhang, H.; Shen, M.; Xie, S.; Zhang, Y.; Gao, Q.; Tang, Y. Porous Nanomoc@Graphite Shell Derived from a MOFs-Directed Strategy: An Efficient Electrocatalyst for the Hydrogen Evolution Reaction. J. Mater. Chem. A 2016, 4, 6006−6013. (1291) Yan, G.; Wu, C.; Tan, H.; Feng, X.; Yan, L.; Zang, H.; Li, Y. N-Carbon Coated P-W2C Composite as Efficient Electrocatalyst for Hydrogen Evolution Reactions over the Whole Ph Range. J. Mater. Chem. A 2017, 5, 765−772. (1292) Yang, J.; Ouyang, Y.; Zhang, H.; Xu, H.; Zhang, Y.; Wang, Y. Novel Fe2P/Graphitized Carbon Yolk/Shell Octahedra for HighEfficiency Hydrogen Production and Lithium Storage. J. Mater. Chem. A 2016, 4, 9923−9930. (1293) Zhu, X.; Liu, M.; Liu, Y.; Chen, R.; Nie, Z.; Li, J.; Yao, S. Carbon-Coated Hollow Mesoporous FeP Microcubes: An Efficient and Stable Electrocatalyst for Hydrogen Evolution. J. Mater. Chem. A 2016, 4, 8974−8977. (1294) Chung, D. Y.; Jun, S. W.; Yoon, G.; Kim, H.; Yoo, J. M.; Lee, K.-S.; Kim, T.; Shin, H.; Sinha, A. K.; Kwon, S. G.; et al. Large-Scale Synthesis of Carbon-Shell-Coated FeP Nanoparticles for Robust Hydrogen Evolution Reaction Electrocatalyst. J. Am. Chem. Soc. 2017, 139, 6669−6674. (1295) Fan, L.; Liu, P. F.; Yan, X.; Gu, L.; Yang, Z. Z.; Yang, H. G.; Qiu, S.; Yao, X. Atomically Isolated Nickel Species Anchored on Graphitized Carbon for Efficient Hydrogen Evolution Electrocatalysis. Nat. Commun. 2016, 7, 10667. (1296) Liu, J. Y.; Zhuang, C. S.; Li, K.; Peng, T. Y. Preparation of [email protected] Nanocomposites with Highly Efficient and Stable Photocatalytic Hydrogen Production Activity. Phys. Chem. Chem. Phys. 2015, 17, 10944−10952. (1297) Liu, S.; Wang, J.; Yu, J. ZIF-8 Derived Bimodal Carbon Modified ZnO Photocatalysts with Enhanced Photocatalytic CO2 Reduction Performance. RSC Adv. 2016, 6, 59998−60006. (1298) Yu, L.; Li, G.; Zhang, X.; Ba, X.; Shi, G.; Li, Y.; Wong, P. K.; Yu, J. C.; Yu, Y. Enhanced Activity and Stability of Carbon-Decorated Cuprous Oxide Mesoporous Nanorods for CO2 Reduction in Artificial Photosynthesis. ACS Catal. 2016, 6, 6444−6454. (1299) Hori, Y.; Wakebe, H.; Tsukamoto, T.; Koga, O. Electrocatalytic Process of CO Selectivity in Electrochemical Reduction of CO2 at Metal Electrodes in Aqueous Media. Electrochim. Acta 1994, 39, 1833−1839. GP


Chemical Reviews

Review

with Controllable Facets Enabling Highly Efficient Visible-Light Photocatalytic Reduction of CO2. Adv. Mater. 2016, 28, 6485−6490. (1321) Yin, P.; Yao, T.; Wu, Y.; Zheng, L.; Lin, Y.; Liu, W.; Ju, H.; Zhu, J.; Hong, X.; Deng, Z.; et al. Single Cobalt Atoms with Precise NCoordination as Superior Oxygen Reduction Reaction Catalysts. Angew. Chem., Int. Ed. 2016, 55, 10800−10805. (1322) Jones, J.; Xiong, H.; DeLaRiva, A. T.; Peterson, E. J.; Hien, P.; Challa, S. R.; Qi, G.; Oh, S.; Wiebenga, M. H.; Hernandez, X. I. P.; et al. Thermally Stable Single-Atom Platinum-on-Ceria Catalysts Via Atom Trapping. Science 2016, 353, 150−154. (1323) Pei, G. X.; Liu, X. Y.; Wang, A.; Lee, A. F.; Isaacs, M. A.; Li, L.; Pan, X.; Yang, X.; Wang, X.; Tai, Z.; et al. Ag Alloyed Pd SingleAtom Catalysts for Efficient Selective Hydrogenation of Acetylene to Ethylene in Excess Ethylene. ACS Catal. 2015, 5, 3717−3725. (1324) Li, F.; Li, Y.; Zeng, X. C.; Chen, Z. Exploration of HighPerformance Single-Atom Catalysts on Support M1/FeOx for CO Oxidation Via Computational Study. ACS Catal. 2015, 5, 544−552. (1325) Du, C.; Lin, H.; Lin, B.; Ma, Z.; Hou, T.; Tang, J.; Li, Y. MoS2 Supported Single Platinum Atoms and Their Superior Catalytic Activity for CO Oxidation: A Density Functional Theory Study. J. Mater. Chem. A 2015, 3, 23113−23119. (1326) Yang, X.-F.; Wang, A.; Qiao, B.; Li, J.; Liu, J.; Zhang, T. Single-Atom Catalysts: A New Frontier in Heterogeneous Catalysis. Acc. Chem. Res. 2013, 46, 1740−1748. (1327) Liu, P.; Zhao, Y.; Qin, R.; Mo, S.; Chen, G.; Gu, L.; Chevrier, D. M.; Zhang, P.; Guo, Q.; Zang, D.; et al. Photochemical Route for Synthesizing Atomically Dispersed Palladium Catalysts. Science 2016, 352, 797−801. (1328) Bruix, A.; Lykhach, Y.; Matolinova, I.; Neitzel, A.; Skala, T.; Tsud, N.; Vorokhta, M.; Stetsovych, V.; Sevcikova, K.; Myslivecek, J.; et al. Maximum Noble-Metal Efficiency in Catalytic Materials: Atomically Dispersed Surface Platinum. Angew. Chem., Int. Ed. 2014, 53, 10525−10530. (1329) Zhang, H.; Liu, G.; Shi, L.; Ye, J. Single Atom Catalysts: Emerging Multifunctional Materials in Heterogeneous Catalysis. Adv. Energy Mater. 2018, 8, 1701343. (1330) Back, S.; Jung, Y. S. TiC- and TiN-Supported Single-Atom Catalysts for Dramatic Improvements in CO2 Electrochemical Reduction to CH4. ACS Energy Letters 2017, 2, 969−975. (1331) He, H. Y.; Jagvaral, Y. Electrochemical Reduction of CO2 on Graphene Supported Transition Metals-Towards Single Atom Catalysts. Phys. Chem. Chem. Phys. 2017, 19, 11436−11446. (1332) Jiang, K.; Siahrostami, S.; Akey, A. J.; Li, Y. B.; Lu, Z. Y.; Lattimer, J.; Hu, Y. F.; Stokes, C.; Gangishetty, M.; Chen, G. X.; et al. Transition-Metal Single Atoms in a Graphene Shell as Active Centers for Highly Efficient Artificial Photosynthesis. Chem. 2017, 3, 950−960. (1333) Tong, T.; Zhu, B.; Jiang, C.; Cheng, B.; Yu, J. Mechanistic Insight into the Enhanced Photocatalytic Activity of Single-Atom Pt, Pd or Au-Embedded g-C3N4. Appl. Surf. Sci. 2018, 433, 1175−1183. (1334) Li, X.; Bi, W.; Zhang, L.; Tao, S.; Chu, W.; Zhang, Q.; Luo, Y.; Wu, C.; Xie, Y. Single-Atom Pt as Co-Catalyst for Enhanced Photocatalytic H2 Evolution. Adv. Mater. 2016, 28, 2427−2431. (1335) Mavrikakis, M.; Hammer, B.; Nørskov, J. K. Effect of Strain on the Reactivity of Metal Surfaces. Phys. Rev. Lett. 1998, 81, 2819− 2822. (1336) Kibler, L. A.; El-Aziz, A. M.; Hoyer, R.; Kolb, D. M. Tuning Reaction Rates by Lateral Strain in a Palladium Monolayer. Angew. Chem., Int. Ed. 2005, 44, 2080−2084. (1337) Esposito, D. V.; Hunt, S. T.; Stottlemyer, A. L.; Dobson, K. D.; McCandless, B. E.; Birkmire, R. W.; Chen, J. G. G. Low-Cost Hydrogen-Evolution Catalysts Based on Monolayer Platinum on Tungsten Monocarbide Substrates. Angew. Chem., Int. Ed. 2010, 49, 9859−9862. (1338) Bligaard, T.; Norskov, J. K. Ligand Effects in Heterogeneous Catalysis and Electrochemistry. Electrochim. Acta 2007, 52, 5512− 5516. (1339) Reske, R.; Duca, M.; Oezaslan, M.; Schouten, K. J. P.; Koper, M. T. M.; Strasser, P. Controlling Catalytic Selectivities During CO2

(1300) Cao, S.; Li, Y.; Zhu, B.; Jaroniec, M.; Yu, J. Facet Effect of Pd Cocatalyst on Photocatalytic CO2 Reduction over g-C3N4. J. Catal. 2017, 349, 208−217. (1301) Hamdy, M. S.; Amrollahi, R.; Sinev, I.; Mei, B.; Mul, G. Strategies to Design Efficient Silica-Supported Photocatalysts for Reduction of CO2. J. Am. Chem. Soc. 2014, 136, 594−597. (1302) Li, X.; Li, Z.; Xia, Q.; Xi, H.; Zhao, Z. Effects of Textural Properties and Surface Oxygen Content of Activated Carbons on the Desorption Activation Energy of Water. Adsorpt. Sci. Technol. 2006, 24, 363−374. (1303) Li, X.; Li, Z.; Xia, Q.; Xi, H. Effects of Pore Sizes of Porous Silica Gels on Desorption Activation Energy of Water Vapour. Appl. Therm. Eng. 2007, 27, 869−876. (1304) Li, X.; Chen, X.; Li, Z. Adsorption Equilibrium and Desorption Activation Energy of Water Vapor on Activated Carbon Modified by an Oxidation and Reduction Treatment. J. Chem. Eng. Data 2010, 55, 3164−3169. (1305) Li, X.; Li, Z. Equilibrium and Do−Do Model Fitting of Water Adsorption on Four Commercial Activated Carbons with Different Surface Chemistry and Pore Structure. J. Chem. Eng. Data 2010, 55, 5729−5732. (1306) Li, X.; Li, Z. Adsorption of Water Vapor onto and Its Electrothermal Desorption from Activated Carbons with Different Electric Conductivities. Sep. Purif. Technol. 2012, 85, 77−82. (1307) Seh, Z. W.; Kibsgaard, J.; Dickens, C. F.; Chorkendorff, I. B.; Norskov, J. K.; Jaramillo, T. F. Combining Theory and Experiment in Electrocatalysis: Insights into Materials Design. Science 2017, 355, No. eaad4998. (1308) Li, W.; Liu, J.; Zhao, D. Y. Mesoporous Materials for Energy Conversion and Storage Devices. Nature Reviews Materials 2016, 1, 16023. (1309) Luo, M. C.; Guo, S. J. Strain-Controlled Electrocatalysis on Multimetallic Nanomaterials. Nature Reviews Materials 2017, 2, 17059. (1310) Montoya, J. H.; Seitz, L. C.; Chakthranont, P.; Vojvodic, A.; Jaramillo, T. F.; Norskov, J. K. Materials for Solar Fuels and Chemicals. Nat. Mater. 2017, 16, 70−81. (1311) Mistry, H.; Varela, A. S.; Kuhl, S.; Strasser, P.; Cuenya, B. R. Nanostructured Electrocatalysts with Tunable Activity and Selectivity. Nature Reviews Materials 2016, 1, 16009. (1312) Zhang, L.; Wang, Z. Y.; Mehio, N. D.; Jin, X. B.; Dai, S. Thickness- and Particle-Size-Dependent Electrochemical Reduction of Carbon Dioxide on Thin-Layer Porous Silver Electrodes. ChemSusChem 2016, 9, 428−432. (1313) Mistry, H.; Reske, R.; Zeng, Z.; Zhao, Z.-J.; Greeley, J.; Strasser, P.; Cuenya, B. R. Exceptional Size-Dependent Activity Enhancement in the Electroreduction of CO2 over Au Nanoparticles. J. Am. Chem. Soc. 2014, 136, 16473−16476. (1314) Dong, C.; Lian, C.; Hu, S.; Deng, Z.; Gong, J.; Li, M.; Liu, H.; Xing, M.; Zhang, J. Size-Dependent Activity and Selectivity of Carbon Dioxide Photocatalytic Reduction over Platinum Nanoparticles. Nat. Commun. 2018, 9, 1252. (1315) Dong, C.; Xing, M.; Zhang, J. Double-Cocatalysts Promote Charge Separation Efficiency in CO2 Photoreduction: Spatial Location Matters. Mater. Horiz. 2016, 3, 608−612. (1316) Roberts, F. S.; Kuhl, K. P.; Nilsson, A. High Selectivity for Ethylene from Carbon Dioxide Reduction over Copper Nanocube Electrocatalysts. Angew. Chem., Int. Ed. 2015, 54, 5179−5182. (1317) Guo, Y. Q.; Xu, K.; Wu, C. Z.; Zhao, J. Y.; Xie, Y. Surface Chemical-Modification for Engineering the Intrinsic Physical Properties of Inorganic Two-Dimensional Nanomaterials. Chem. Soc. Rev. 2015, 44, 637−646. (1318) Sun, Y. F.; Gao, S.; Lei, F. C.; Xiao, C.; Xie, Y. Ultrathin TwoDimensional Inorganic Materials: New Opportunities for Solid State Nanochemistry. Acc. Chem. Res. 2015, 48, 3−12. (1319) Gao, S.; Lin, Y.; Jiao, X.; Sun, Y.; Luo, Q.; Zhang, W.; Li, D.; Yang, J.; Xie, Y. Partially Oxidized Atomic Cobalt Layers for Carbon Dioxide Electroreduction to Liquid Fuel. Nature 2016, 529, 68−71. (1320) Gao, C.; Meng, Q.; Zhao, K.; Yin, H.; Wang, D.; Guo, J.; Zhao, S.; Chang, L.; He, M.; Li, Q.; et al. Co3O4 Hexagonal Platelets GQ


Chemical Reviews

Review

Electroreduction on Thin Cu Metal Overlayers. J. Phys. Chem. Lett. 2013, 4, 2410−2413. (1340) Varela, A. S.; Schlaup, C.; Jovanov, Z. P.; Malacrida, P.; Horch, S.; Stephens, I. E. L.; Chorkendorff, I. CO2 Electroreduction on Well-Defined Bimetallic Surfaces: Cu over Layers on Pt(111) and Pt(211). J. Phys. Chem. C 2013, 117, 20500−20508. (1341) Friebel, D.; Mbuga, F.; Rajasekaran, S.; Miller, D. J.; Ogasawara, H.; Alonso-Mori, R.; Sokaras, D.; Nordlund, D.; Weng, T. C.; Nilsson, A. Structure, Redox Chemistry, and Interfacial Alloy Formation in Monolayer and Multilayer Cu/Au(111) Model Catalysts for CO2 Electroreduction. J. Phys. Chem. C 2014, 118, 7954−7961. (1342) Zhao, W. G.; Yang, L. N.; Yin, Y. D.; Jin, M. S. Thermodynamic Controlled Synthesis of Intermetallic Au3Cu Alloy Nanocrystals from Cu Microparticles. J. Mater. Chem. A 2014, 2, 902− 906. (1343) Christophe, J.; Doneux, T.; Buess-Herman, C. Electroreduction of Carbon Dioxide on Copper-Based Electrodes: Activity of Copper Single Crystals and Copper-Gold Alloys. Electrocatalysis 2012, 3, 139−146. (1344) Hirunsit, P. Electroreduction of Carbon Dioxide to Methane on Copper, Copper-Silver, and Copper-Gold Catalysts: A Dft Study. J. Phys. Chem. C 2013, 117, 8262−8268. (1345) Li, C. W.; Kanan, M. W. CO2 Reduction at Low Overpotential on Cu Electrodes Resulting from the Reduction of Thick Cu2O Films. J. Am. Chem. Soc. 2012, 134, 7231−7234. (1346) Kim, D.; Lee, S.; Ocon, J. D.; Jeong, B.; Lee, J. K.; Lee, J. Insights into an Autonomously Formed Oxygen-Evacuated Cu2O Electrode for the Selective Production of C2H4 from CO2. Phys. Chem. Chem. Phys. 2015, 17, 824−830. (1347) Rahaman, M.; Dutta, A.; Zanetti, A.; Broekmann, P. Electrochemical Reduction of CO2 into Multicarbon Alcohols on Activated Cu Mesh Catalysts: An Identical Location (Il) Study. ACS Catal. 2017, 7, 7946−7956. (1348) Kas, R.; Kortlever, R.; Milbrat, A.; Koper, M. T. M.; Mul, G.; Baltrusaitis, J. Electrochemical CO2 Reduction on Cu2O-Derived Copper Nanoparticles: Controlling the Catalytic Selectivity of Hydrocarbons. Phys. Chem. Chem. Phys. 2014, 16, 12194−12201. (1349) Ren, D.; Deng, Y.; Handoko, A. D.; Chen, C. S.; Malkhandi, S.; Yeo, B. S. Selective Electrochemical Reduction of Carbon Dioxide to Ethylene and Ethanol on Copper(I) Oxide Catalysts. ACS Catal. 2015, 5, 2814−2821. (1350) Guan, G. Q.; Kida, T.; Harada, T.; Isayama, M.; Yoshida, A. Photoreduction of Carbon Dioxide with Water over K2Ti6O13 Photocatalyst Combined with Cu/ZnO Catalyst under Concentrated Sunlight. Appl. Catal., A 2003, 249, 11−18. (1351) Zhang, Z.; Wang, Z.; Cao, S.-W.; Xue, C. Au/Pt Nanoparticle-Decorated TiO2 Nanofibers with Plasmon-Enhanced Photocatalytic Activities for Solar-to-Fuel Conversion. J. Phys. Chem. C 2013, 117, 25939−25947. (1352) Kang, Q.; Wang, T.; Li, P.; Liu, L.; Chang, K.; Li, M.; Ye, J. Photocatalytic Reduction of Carbon Dioxide by Hydrous Hydrazine over Au-Cu Alloy Nanoparticles Supported on SrTiO3/TiO2 Coaxial Nanotube Arrays. Angew. Chem., Int. Ed. 2015, 54, 841−845. (1353) Yin, G.; Abe, H.; Kodiyath, R.; Ueda, S.; Srinivasan, N.; Yamaguchi, A.; Miyauchi, M. Selective Electro- or Photo-Reduction of Carbon Dioxide to Formic Acid Using a Cu-Zn Alloy Catalyst. J. Mater. Chem. A 2017, 5, 12113−12119. (1354) Yin, G.; Sako, H.; Gubbala, R. V.; Ueda, S.; Yamaguchi, A.; Abe, H.; Miyauchi, M. A Cu-Zn Nanoparticle Promoter for Selective Carbon Dioxide Reduction and Its Application in Visible-Light-Active Z-Scheme Systems Using Water as an Electron Donor. Chem. Commun. 2018, 54, 3947−3950. (1355) Long, R.; Li, Y.; Liu, Y.; Chen, S. M.; Zheng, X. S.; Gao, C.; He, C. H.; Chen, N. S.; Qi, Z. M.; Song, L.; et al. Isolation of Cu Atoms in Pd Lattice: Forming Highly Selective Sites for Photocatalytic Conversion of CO2 to CH4. J. Am. Chem. Soc. 2017, 139, 4486−4492. (1356) Ni, B.; Wang, X. Face the Edges: Catalytic Active Sites of Nanomaterials. Advanced Science 2015, 2, 1500085.

(1357) Zhu, Y.; Xu, Z.; Lang, Q.; Jiang, W.; Yin, Q.; Zhong, S.; Bai, S. Grain Boundary Engineered Metal Nanowire Cocatalysts for Enhanced Photocatalytic Reduction of Carbon Dioxide. Appl. Catal., B 2017, 206, 282−292. (1358) Kim, K.-S.; Kim, W. J.; Lim, H.-K.; Lee, E. K.; Kim, H. Tuned Chemical Bonding Ability of Au at Grain Boundaries for Enhanced Electrochemical CO2 Reduction. ACS Catal. 2016, 6, 4443−4448. (1359) Hori, Y.; Takahashi, I.; Koga, O.; Hoshi, N. Selective Formation of C2 Compounds from Electrochemical Reduction of CO2 at a Series of Copper Single Crystal Electrodes. J. Phys. Chem. B 2002, 106, 15−17. (1360) Montoya, J. H.; Shi, C.; Chan, K.; Norskov, J. K. Theoretical Insights into a CO Dimerization Mechanism in CO2 Electroreduction. J. Phys. Chem. Lett. 2015, 6, 2032−2037. (1361) Schouten, K. J. P.; Qin, Z.; Pérez Gallent, E.; Koper, M. T. M. Two Pathways for the Formation of Ethylene in CO Reduction on Single-Crystal Copper Electrodes. J. Am. Chem. Soc. 2012, 134, 9864− 9867. (1362) Durand, W. J.; Peterson, A. A.; Studt, F.; Abild-Pedersen, F.; Norskov, J. K. Structure Effects on the Energetics of the Electrochemical Reduction of CO2 by Copper Surfaces. Surf. Sci. 2011, 605, 1354−1359. (1363) Lang, Q. Q.; Hu, W. L.; Zhou, P. H.; Huang, T. L.; Zhong, S. X.; Yang, L. N.; Chen, J. R.; Bai, S. Twin Defects Engineered Pd Cocatalyst on C3N4 Nanosheets for Enhanced Photocatalytic Performance in CO2 Reduction Reaction. Nanotechnology 2017, 28, 484003. (1364) Lang, Q.; Yang, Y.; Zhu, Y.; Hu, W.; Jiang, W.; Zhong, S.; Gong, P.; Teng, B.; Zhao, L.; Bai, S. High-Index Facet Engineering on PtCu Cocatalyst for Superior Photocatalytic Reduction of CO2 to CH4. J. Mater. Chem. A 2017, 5, 6686−6694. (1365) Kim, C.; Jeon, H. S.; Eom, T.; Jee, M. S.; Kim, H.; Friend, C. M.; Min, B. K.; Hwang, Y. J. Achieving Selective and Efficient Electrocatalytic Activity for CO2 Reduction Using Immobilized Silver Nanoparticles. J. Am. Chem. Soc. 2015, 137, 13844−13850. (1366) Low, J.; Cao, S.; Yu, J.; Wageh, S. Two-Dimensional Layered Composite Photocatalysts. Chem. Commun. 2014, 50, 10768−10777. (1367) Hou, Y.; Laursen, A. B.; Zhang, J.; Zhang, G.; Zhu, Y.; Wang, X.; Dahl, S.; Chorkendorff, I. Layered Nanojunctions for HydrogenEvolution Catalysis. Angew. Chem., Int. Ed. 2013, 52, 3621−3625. (1368) Kaneco, S.; Iiba, K.; Ohta, K.; Mizuno, T.; Saji, A. Electrochemical Reduction of CO2 on Au in KOH+methanol at Low Temperature. Electroanal. Chem. 1998, 441, 215−220. (1369) Xiang, Q.; Yu, J.; Jaroniec, M. Enhanced Photocatalytic H2Production Activity of Graphene-Modified Titania Nanosheets. Nanoscale 2011, 3, 3670−3678. (1370) Xiang, Q.; Yu, J.; Jaroniec, M. Synergetic Effect of MoS2 and Graphene as Cocatalysts for Enhanced Photocatalytic H2 Production Activity of TiO2 Nanoparticles. J. Am. Chem. Soc. 2012, 134, 6575− 6578. (1371) Akple, M. S.; Low, J.; Wageh, S.; Al-Ghamdi, A. A.; Yu, J.; Zhang, J. Enhanced Visible Light Photocatalytic H2-Production of gC3N4/WS2 Composite Heterostructures. Appl. Surf. Sci. 2015, 358, 196−203. (1372) Tian, Y.; Ge, L.; Wang, K.; Chai, Y. Synthesis of Novel MoS2/ g-C3N4 Heterojunction Photocatalysts with Enhanced Hydrogen Evolution Activity. Mater. Charact. 2014, 87, 70−73. (1373) Liang, Y. T.; Vijayan, B. K.; Lyandres, O.; Gray, K. A.; Hersam, M. C. Effect of Dimensionality on the Photocatalytic Behavior of Carbon−Titania Nanosheet Composites: Charge Transfer at Nanomaterial Interfaces. J. Phys. Chem. Lett. 2012, 3, 1760−1765. (1374) Bafaqeer, A.; Tahir, M.; Amin, N. A. S. Synergistic Effects of 2D/2D ZnV2O6/RGO Nanosheets Heterojunction for Stable and High Performance Photo-Induced CO2 Reduction to Solar Fuels. Chem. Eng. J. 2018, 334, 2142−2153. (1375) Xiang, Q.; Yu, J.; Jaroniec, M. Preparation and Enhanced Visible-Light Photocatalytic H2-Production Activity of Graphene/ C3N4 Composites. J. Phys. Chem. C 2011, 115, 7355−7363. GR


Chemical Reviews

Review

(1376) Cao, S.; Shen, B.; Tong, T.; Fu, J.; Yu, J. 2D/2D Heterojunction of Ultrathin Mxene/Bi2WO6 Nanosheets for Improved Photocatalytic CO2 Reduction. Adv. Funct. Mater. 2018, 28, 1800136. (1377) Tonda, S.; Kumar, S.; Bhardwaj, M.; Yadav, P.; Ogale, S. gC3N4/NiAl-LDH 2D/2D Hybrid Heterojunction for High-Performance Photocatalytic Reduction of CO2 into Renewable Fuels. ACS Appl. Mater. Interfaces 2018, 10, 2667−2678. (1378) Zhu, X.; Zhang, T.; Sun, Z.; Chen, H.; Guan, J.; Chen, X.; Ji, H.; Du, P.; Yang, S. Black Phosphorus Revisited: A Missing Metal-Free Elemental Photocatalyst for Visible Light Hydrogen Evolution. Adv. Mater. 2017, 29, 1605776. (1379) Hu, Z. F.; Shen, Z. R.; Yu, J. C. Phosphorus Containing Materials for Photocatalytic Hydrogen Evolution. Green Chem. 2017, 19, 588−613. (1380) Zhu, M. S.; Cai, X. Y.; Fujitsuka, M.; Zhang, J. Y.; Majima, T. Au/La2Ti2O7 Nanostructures Sensitized with Black Phosphorus for Plasmon-Enhanced Photocatalytic Hydrogen Production in Visible and near-Infrared Light. Angew. Chem., Int. Ed. 2017, 56, 2064−2068. (1381) Hu, Z. F.; Yuan, L. Y.; Liu, Z. F.; Shen, Z. R.; Yu, J. C. An Elemental Phosphorus Photocatalyst with a Record High Hydrogen Evolution Efficiency. Angew. Chem., Int. Ed. 2016, 55, 9580−9585. (1382) Ye, L. Q.; Su, Y. R.; Jin, X. L.; Xie, H. Q.; Zhang, C. Recent Advances in BiOX (X = Cl, Br and I) Photocatalysts: Synthesis, Modification, Facet Effects and Mechanisms. Environ. Sci.: Nano 2014, 1, 90−112. (1383) Li, J.; Li, H.; Zhan, G. M.; Zhang, L. Z. Solar Water Splitting and Nitrogen Fixation with Layered Bismuth Oxyhalides. Acc. Chem. Res. 2017, 50, 112−121. (1384) Cheng, H. F.; Huang, B. B.; Dai, Y. Engineering BiOX(X = Cl, Br, I) Nanostructures for Highly Efficient Photocatalytic Applications. Nanoscale 2014, 6, 2009−2026. (1385) Seh, Z. W.; Fredrickson, K. D.; Anasori, B.; Kibsgaard, J.; Strickler, A. L.; Lukatskaya, M. R.; Gogotsi, Y.; Jaramillo, T. F.; Vojvodic, A. Two-Dimensional Molybdenum Carbide (Mxene) as an Efficient Electrocatalyst for Hydrogen Evolution. ACS Energy Letters 2016, 1, 589−594. (1386) Ran, J.; Gao, G.; Li, F.-T.; Ma, T.-Y.; Du, A.; Qiao, S.-Z. Ti3C2 Mxene Co-Catalyst on Metal Sulfide Photo-Absorbers for Enhanced Visible-Light Photocatalytic Hydrogen Production. Nat. Commun. 2017, 8, 13907. (1387) Wu, X.; Wang, Z.; Yu, M.; Xiu, L.; Qiu, J. Stabilizing the Mxenes by Carbon Nanoplating for Developing Hierarchical Nanohybrids with Efficient Lithium Storage and Hydrogen Evolution Capability. Adv. Mater. 2017, 29, 1607017. (1388) Ling, C.; Shi, L.; Ouyang, Y.; Wang, J. Searching for Highly Active Catalysts for Hydrogen Evolution Reaction Based on OTerminated Mxenes through a Simple Descriptor. Chem. Mater. 2016, 28, 9026−9032. (1389) Guo, Z.; Zhou, J.; Zhu, L.; Sun, Z. Mxene: A Promising Photocatalyst for Water Splitting. J. Mater. Chem. A 2016, 4, 11446− 11452. (1390) Gao, G.; O’Mullane, A. P.; Du, A. 2D Mxenes: A New Family of Promising Catalysts for the Hydrogen Evolution Reaction. ACS Catal. 2017, 7, 494−500. (1391) Harvey, A.; Backes, C.; Gholamvand, Z.; Hanlon, D.; McAteer, D.; Nerl, H. C.; McGuire, E.; Seral-Ascaso, A.; Ramasse, Q. M.; McEvoy, N.; et al. Preparation of Gallium Sulfide Nanosheets by Liquid Exfoliation and Their Application as Hydrogen Evolution Catalysts. Chem. Mater. 2015, 27, 3483−3493. (1392) Voiry, D.; Yang, J.; Chhowalla, M. Recent Strategies for Improving the Catalytic Activity of 2D TMD Nanosheets toward the Hydrogen Evolution Reaction. Adv. Mater. 2016, 28, 6197−6206. (1393) Voiry, D.; Fullon, R.; Yang, J. E.; de Carvalho Castro e Silva, C.; Kappera, R.; Bozkurt, I.; Kaplan, D.; Lagos, M. J.; Batson, P. E.; Gupta, G.; et al. The Role of Electronic Coupling between Substrate and 2D MoS2 Nanosheets in Electrocatalytic Production of Hydrogen. Nat. Mater. 2016, 15, 1003−1009. (1394) Shifa, T. A.; Wang, F. M.; Liu, K. L.; Xu, K.; Wang, Z. X.; Zhan, X. Y.; Jiang, C.; He, J. Engineering the Electronic Structure of

2D WS2 Nanosheets Using Co Incorporation as CoxW1‑xS2 for Conspicuously Enhanced Hydrogen Generation. Small 2016, 12, 3802−3809. (1395) Lu, Q. P.; Yu, Y. F.; Ma, Q. L.; Chen, B.; Zhang, H. 2D Transition-Metal-Dichalcogenide-Nanosheet-Based Composites for Photocatalytic and Electrocatalytic Hydrogen Evolution Reactions. Adv. Mater. 2016, 28, 1917−1933. (1396) Xie, T.-f.; Wang, D.-j.; Zhu, L.-j.; Li, T.-j.; Xu, Y.-j. Application of Surface Photovoltage Technique in Photocatalysis Studies on Modified TiO2 Photo-Catalysts for Photo-Reduction of CO2. Mater. Chem. Phys. 2001, 70, 103−106. (1397) Bai, Y.; Ye, L.; Wang, L.; Shi, X.; Wang, P.; Bai, W. A DualCocatalyst-Loaded Au/BiOI/MnOx System for Enhanced Photocatalytic Greenhouse Gas Conversion into Solar Fuels. Environ. Sci.: Nano 2016, 3, 902−909. (1398) Jiang, Z.; Ding, D.; Wang, L. J.; Zhang, Y. X.; Zan, L. Interfacial Effects of MnOx-Loaded TiO2 with Exposed {001} Facets and Its Catalytic Activity for the Photoreduction of CO2. Catal. Sci. Technol. 2017, 7, 3065−3072. (1399) Meng, A.; Zhang, L.; Cheng, B.; Yu, J. TiO2−MnOx−Pt Hybrid Multiheterojunction Film Photocatalyst with Enhanced Photocatalytic CO2-Reduction Activity. ACS Appl. Mater. Interfaces 2018, DOI: 10.1021/acsami.8b02552. (1400) Dong, C. Y.; Hu, S. C.; Xing, M. Y.; Zhang, J. L. Enhanced Photocatalytic CO2 Reduction to CH4 over Separated Dual CoCatalysts Au and RuO2. Nanotechnology 2018, 29, 154005. (1401) Feng, S. C.; Chen, X. Y.; Zhou, Y.; Tu, W. G.; Li, P.; Li, H. J.; Zou, Z. G. Na2V6O16•XH2O Nanoribbons: Large-Scale Synthesis and Visible-Light Photocatalytic Activity of CO2 into Solar Fuels. Nanoscale 2014, 6, 1896−1900. (1402) Li, Z.; Zhou, Y.; Zhang, J.; Tu, W.; Liu, Q.; Yu, T.; Zou, Z. Hexagonal Nanoplate-Textured Micro-Octahedron Zn2SnO4Combined Effects toward Enhanced Efficiencies of DyeSensitized Solar Cell and Photoreduction of CO2 into Hydrocarbon Fuels. Cryst. Growth Des. 2012, 12, 1476−1481. (1403) Shoji, S.; Yamaguchi, A.; Sakai, E.; Miyauchi, M. Strontium Titanate Based Artificial Leaf Loaded with Reduction and Oxidation Cocatalysts for Selective CO2 Reduction Using Water as an Electron Donor. ACS Appl. Mater. Interfaces 2017, 9, 20613−20619. (1404) Kuwabata, S.; Nishida, K.; Tsuda, R.; Inoue, H.; Yoneyama, H. Photochemical Reduction of Carbon Dioxide to Methanol Using Zns Microcrystallite as a Photocatalyst in the Presence of Methanol Dehydrogenase. J. Electrochem. Soc. 1994, 141, 1498−1503. (1405) Bian, Z.-Y.; Sumi, K.; Furue, M.; Sato, S.; Koike, K.; Ishitani, O. A Novel Tripodal Ligand, Tris (4’-Methyl-2,2’-Bipyridyl-4-Yl)Methyl Carbinol and its Trinuclear Ru-II/Re-I Mixed-Metal Complexes: Synthesis, Emission Properties, and Photocatalytic CO2 Reduction. Inorg. Chem. 2008, 47, 10801−10803. (1406) Bian, Z. Y.; Sumi, K.; Furue, M.; Sato, S.; Koike, K.; Ishitani, O. Synthesis and Properties of a Novel Tripodal Bipyridyl Ligand TbCarbinol and Its Ru(II)-Re(I) Trimetallic Complexes: Investigation of Multimetallic Artificial Systems for Photocatalytic CO2 Reduction. Dalton Trans. 2009, 983−993. (1407) Koike, K.; Naito, S.; Sato, S.; Tamaki, Y.; Ishitani, O. Architecture of Supramolecular Metal Complexes for Photocatalytic CO2 Reduction: III: Effects of Length of Alkyl Chain Connecting Photosensitizer to Catalyst. J. Photochem. Photobiol., A 2009, 207, 109−114. (1408) Takeda, H.; Koike, K.; Inoue, H.; Ishitani, O. Development of an Efficient Photocatalytic System for CO2 Reduction Using Rhenium(L) Complexes Based on Mechanistic Studies. J. Am. Chem. Soc. 2008, 130, 2023−2031. (1409) Kumar, B.; Smieja, J. M.; Kubiak, C. P. Photoreduction of CO2 on P-Type Silicon Using Re(Bipy-Bu’)Co3Cl: Photovoltages Exceeding 600 mV for the Selective Reduction of CO2 to CO. J. Phys. Chem. C 2010, 114, 14220−14223. (1410) Suzuki, T. M.; Tanaka, H.; Morikawa, T.; Iwaki, M.; Sato, S.; Saeki, S.; Inoue, M.; Kajino, T.; Motohiro, T. Direct Assembly Synthesis of Metal Complex-Semiconductor Hybrid Photocatalysts GS


Chemical Reviews

Review

Anchored by Phosphonate for Highly Efficient CO2Reduction. Chem. Commun. 2011, 47, 8673−8675. (1411) Arai, T.; Tajima, S.; Sato, S.; Uemura, K.; Morikawa, T.; Kajino, T. Selective CO2 Conversion to Formate in Water Using a CZTS Photocathode Modified with a Ruthenium Complex Polymer. Chem. Commun. 2011, 47, 12664−12666. (1412) Yokoi, N.; Miura, Y.; Huang, C.-Y.; Takatani, N.; Inaba, H.; Koshiyama, T.; Kanamaru, S.; Arisaka, F.; Watanabe, Y.; Kitagawa, S.; et al. Dual Modification of a Triple-Stranded Beta-Helix Nanotube with Ru and Re Metal Complexes to Promote Photocatalytic Reduction of CO2. Chem. Commun. 2011, 47, 2074−2076. (1413) Wang, C.; Ma, X.-X.; Li, J.; Xu, L.; Zhang, F.-x. Reduction of CO2 Aqueous Solution by Using Photosensitized-TiO2 Nanotube Catalysts Modified by Supramolecular Metalloporphyrins-Ruthenium(II) Polypyridyl Complexes. J. Mol. Catal. A: Chem. 2012, 363, 108− 114. (1414) Tamaki, Y.; Morimoto, T.; Koike, K.; Ishitani, O. Photocatalytic CO2 Reduction with High Turnover Frequency and Selectivity of Formic Acid Formation Using Ru(II) Multinuclear Complexes. Proc. Natl. Acad. Sci. U. S. A. 2012, 109, 15673−15678. (1415) Arai, T.; Sato, S.; Kajino, T.; Morikawa, T. Solar CO2 Reduction Using H2O by a Semiconductor/Metal-Complex Hybrid Photocatalyst: Enhanced Efficiency and Demonstration of a Wireless System Using SrTiO3 Photoanodes. Energy Environ. Sci. 2013, 6, 1274−1282. (1416) Morikawa, T.; Sato, S.; Arai, T.; Uemura, K.; Yamanaka, K. I.; Suzuki, T. M.; Kajino, T.; Motohiro, T.: Selective CO2 Reduction Conjugated with H2O Oxidation Utilizing Semiconductor/MetalComplex Hybrid Photocatalysts. In Solar Chemical Energy Storage; Sugiyama, M., Fujii, K., Nakamura, S., Eds.; AIP Conference Proceedings, 2013; Vol. 1568, pp 11−15. (1417) Maeda, K.; Sekizawa, K.; Ishitani, O. A Polymeric-Semiconductor-Metal-Complex Hybrid Photocatalyst for Visible-Light CO2 Reduction. Chem. Commun. 2013, 49, 10127−10129. (1418) Takeda, H.; Koizumi, H.; Okamoto, K.; Ishitani, O. Photocatalytic CO2 Reduction Using a Mn Complex as a Catalyst. Chem. Commun. 2014, 50, 1491−1493. (1419) Maeda, K.; Kuriki, R.; Zhang, M.; Wang, X.; Ishitani, O. The Effect of the Pore-Wall Structure of Carbon Nitride on Photocatalytic CO2 Reduction under Visible Light. J. Mater. Chem. A 2014, 2, 15146−15151. (1420) He, H.; Liu, C.; Louis, M. E.; Li, G. Infrared Studies of a Hybrid CO2-Reduction Photocatalyst Consisting of a Molecular Re(I) Complex Grafted on Kaolin. J. Mol. Catal. A: Chem. 2014, 395, 145− 150. (1421) Kuriki, R.; Sekizawa, K.; Ishitani, O.; Maeda, K. Visible-LightDriven CO2 Reduction with Carbon Nitride: Enhancing the Activity of Ruthenium Catalysts. Angew. Chem., Int. Ed. 2015, 54, 2406−2409. (1422) Won, D.-I.; Lee, J.-S.; Ji, J.-M.; Jung, W.-J.; Son, H.-J.; Pac, C.; Kang, S. O. Highly Robust Hybrid Photocatalyst for Carbon Dioxide Reduction: Tuning and Optimization of Catalytic Activities of Dye/ TiO2/Re(I) Organic-Inorganic Ternary Systems. J. Am. Chem. Soc. 2015, 137, 13679−13690. (1423) Sun, D.; Gao, Y.; Fu, J.; Zeng, X.; Chen, Z.; Li, Z. Construction of a Supported Ru Complex on Bifunctional MOF-253 for Photocatalytic CO2 Reduction under Visible Light. Chem. Commun. 2015, 51, 2645−2648. (1424) Kuriki, R.; Ishitani, O.; Maeda, K. Unique Solvent Effects on Visible-Light CO2 Reduction over Ruthenium(II)-Complex/Carbon Nitride Hybrid Photocatalysts. ACS Appl. Mater. Interfaces 2016, 8, 6011−6018. (1425) Maeda, K.; Kuriki, R.; Ishitani, O. Photocatalytic Activity of Carbon Nitride Modified with a Ruthenium(II) Complex Having Carboxylic- or Phosphonic Acid Anchoring Groups for Visible-Light CO2 Reduction. Chem. Lett. 2016, 45, 182−184. (1426) Muraoka, K.; Kumagai, H.; Eguchi, M.; Ishitani, O.; Maeda, K. A Z-Scheme Photocatalyst Constructed with an Yttrium-Tantalum Oxynitride and a Binuclear Ru(II) Complex for Visible-Light CO2 Reduction. Chem. Commun. 2016, 52, 7886−7889.

(1427) Huang, H.; Lin, J.; Zhu, G.; Weng, Y.; Wang, X.; Fu, X.; Long, J. A Long-Lived Mononuclear Cyclopentadienyl Ruthenium Complex Grafted onto Anatase TiO2 for Efficient CO2 Photoreduction. Angew. Chem., Int. Ed. 2016, 55, 8314−8318. (1428) Nakada, A.; Nakashima, T.; Sekizawa, K.; Maeda, K.; Ishitani, O. Visible-Light-Driven CO2 Reduction on a Hybrid Photocatalyst Consisting of a Ru(II) Binuclear Complex and a Ag-Loaded Taon in Aqueous Solutions. Chem. Sci. 2016, 7, 4364−4371. (1429) Kuriki, R.; Matsunaga, H.; Nakashima, T.; Wada, K.; Yamakata, A.; Ishitani, O.; Maeda, K. Nature-Inspired, Highly Durable CO2 Reduction System Consisting of a Binuclear Ruthenium(II) Complex and an Organic Semiconductor Using Visible Light. J. Am. Chem. Soc. 2016, 138, 5159−5170. (1430) Guo, Z.; Cheng, S.; Cometto, C.; Anxolabehere-Mallart, E.; Ng, S.-M.; Ko, C.-C.; Liu, G.; Chen, L.; Robert, M.; Lau, T.-C. Highly Efficient and Selective Photocatalytic CO2Reduction by Iron and Cobalt Quaterpyridine Complexes. J. Am. Chem. Soc. 2016, 138, 9413−9416. (1431) Kuriki, R.; Maeda, K. Development of Hybrid Photocatalysts Constructed with a Metal Complex and Graphitic Carbon Nitride for Visible-Light-Driven CO2 Reduction. Phys. Chem. Chem. Phys. 2017, 19, 4938−4950. (1432) Kuramochi, Y.; Sekine, M.; Kitamura, K.; Maegawa, Y.; Goto, Y.; Shirai, S.; Inagaki, S.; Ishida, H. Photocatalytic CO2 Reduction by Periodic Mesoporous Organosilica (PMO) Containing Two Different Ruthenium Complexes as Photosensitizing and Catalytic Sites. Chem. Eur. J. 2017, 23, 10301−10309. (1433) Hong, D.; Tsukakoshi, Y.; Kotani, H.; Ishizuka, T.; Kojima, T. Visible-Light-Driven Photocatalytic CO2 Reduction by a Ni(II) Complex Bearing a Bioinspired Tetradentate Ligand for Selective CO Production. J. Am. Chem. Soc. 2017, 139, 6538−6541. (1434) Do, J. Y.; Tamilavan, V.; Agneeswari, R.; Hyun, M. H.; Kang, M. Synthesis and Optical Properties of TDQD and Effective CO2 Reduction Using a TDQD -Photosensitized TiO2 Film. J. Photochem. Photobiol., A 2016, 330, 30−36. (1435) Kuramochi, Y.; Ishitani, O. Iridium(III) 1-Phenylisoquinoline Complexes as a Photosensitizer for Photocatalytic CO2 Reduction: A Mixed System with a Re(I) Catalyst and a Supramolecular Photocatalyst. Inorg. Chem. 2016, 55, 5702−5709. (1436) Takeda, H.; Ohashi, K.; Sekine, A.; Ishitani, O. Photocatalytic CO2 Reduction Using Cu(I) Photosensitizers with a Fe(II) Catalyst. J. Am. Chem. Soc. 2016, 138, 4354−4357. (1437) Liu, S.-Q.; Zhou, S.-S.; Chen, Z.-G.; Liu, C.-B.; Chen, F.; Wu, Z.-Y. An Artificial Photosynthesis System Based on CeO2 as Light Harvester and N-Doped Graphene Cu(II) Complex as Artificial Metalloenzyme for CO2 Reduction to Methanol Fuel. Catal. Commun. 2016, 73, 7−11. (1438) Jin, T.; Liu, C.; Li, G. Photocatalytic CO2 Reduction Using a Molecular Cobalt Complex Deposited on TiO2 Nanoparticles. Chem. Commun. 2014, 50, 6221−6224. (1439) Jin, T.; Liu, C.; Li, G. Heterogenization of a Macrocyclic Cobalt Complex for Photocatalytic CO2 Reduction. J. Coord. Chem. 2016, 69, 1748−1758. (1440) Jeyalakshmi, V.; Tamilmani, S.; Mahalakshmy, R.; Bhyrappa, P.; Krishnamurthy, K. R.; Viswanathan, B. Sensitization of La Modified NaTaO3 with Cobalt Tetra Phenyl Porphyrin for Photo Catalytic Reduction of CO2 by Water with Uv-Visible Light. J. Mol. Catal. A: Chem. 2016, 420, 200−207. (1441) Zhao, G.; Pang, H.; Liu, G.; Li, P.; Liu, H.; Zhang, H.; Shi, L.; Ye, J. Co-Porphyrin/Carbon Nitride Hybrids for Improved Photocatalytic CO2 Reduction under Visible Light. Appl. Catal., B 2017, 200, 141−149. (1442) Wang, X.; Goudy, V.; Genesio, G.; Maynadie, J.; Meyer, D.; Fontecave, M. Ruthenium-Cobalt Dinuclear Complexes as Photocatalysts for CO2 Reduction. Chem. Commun. 2017, 53, 5040−5043. (1443) Liu, J. B.; Shi, H. J.; Shen, Q.; Guo, C. Y.; Zhao, G. H. A Biomimetic Photoelectrocatalyst of Co-Porphyrin Combined with a gC3N4 Nanosheet Based on π-π Supramolecular Interaction for HighGT


Chemical Reviews

Review

Efficiency CO2 Reduction in Water Medium. Green Chem. 2017, 19, 5900−5910. (1444) Cometto, C.; Kuriki, R.; Chen, L. J.; Maeda, K.; Lau, T. C.; Ishitani, O.; Robert, M. A Carbon Nitride/Fe Quaterpyridine Catalytic System for Photostimulated CO2-to-CO Conversion with Visible Light. J. Am. Chem. Soc. 2018, 140, 7437−7440. (1445) Boston, D. J.; Pachon, Y. M. F.; Lezna, R. O.; de Tacconi, N. R.; MacDonnell, F. M. Electrocatalytic and Photocatalytic Conversion of CO2 to Methanol Using Ruthenium Complexes with Internal Pyridyl Cocatalysts. Inorg. Chem. 2014, 53, 6544−6553. (1446) Gholamkhass, B.; Mametsuka, H.; Koike, K.; Tanabe, T.; Furue, M.; Ishitani, O. Architecture of Supramolecular Metal Complexes for Photocatalytic CO2Reduction: Ruthenium-Rhenium Bi- and Tetranuclear Complexes. Inorg. Chem. 2005, 44, 2326−2336. (1447) Lee, C.-W.; Antoniou Kourounioti, R.; Wu, J. C. S.; Murchie, E.; Maroto-Valer, M.; Jensen, O. E.; Huang, C.-W.; Ruban, A. Photocatalytic Conversion of CO2 to Hydrocarbons by LightHarvesting Complex Assisted Rh-Doped TiO2 Photocatalyst. J. CO2 Util. 2014, 5, 33−40. (1448) Nakada, A.; Koike, K.; Nakashima, T.; Morimoto, T.; Ishitani, O. Photocatalytic CO2 Reduction to Formic Acid Using a Ru(II)Re(I) Supramolecular Complex in an Aqueous Solution. Inorg. Chem. 2015, 54, 1800−1807. (1449) Ohkubo, K.; Yamazaki, Y.; Nakashima, T.; Tamaki, Y.; Koike, K.; Ishitani, O. Photocatalyses of Ru(II)-Re(I) Binuclear Complexes Connected through Two Ethylene Chains for CO2 Reduction. J. Catal. 2016, 343, 278−289. (1450) Choi, K. M.; Kim, D.; Rungtaweevoranit, B.; Trickett, C. A.; Barmanbek, J. T. D.; Alshammari, A. S.; Yang, P.; Yaghi, O. M. Plasmon-Enhanced Photocatalytic CO2 Conversion within Metal− Organic Frameworks under Visible Light. J. Am. Chem. Soc. 2017, 139, 356−362. (1451) Tamaki, Y.; Koike, K.; Morimoto, T.; Yamazaki, Y.; Ishitani, O. Red-Light-Driven Photocatalytic Reduction of CO2 Using Os(II)Re(I) Supramolecular Complexes. Inorg. Chem. 2013, 52, 11902− 11909. (1452) Ishitani, O.; Inoue, C.; Suzuki, Y.; Ibusuki, T. Photocatalytic Reduction of Carbon Dioxide to Methane and Acetic Acid by an Aqueous Suspension of Metal-Deposited TiO2. J. Photochem. Photobiol., A 1993, 72, 269−271. (1453) Yui, T.; Kan, A.; Saitoh, C.; Koike, K.; Ibusuki, T.; Ishitani, O. Photochemical Reduction of CO2 Using TiO2Effects of Organic Adsorbates on TiO2 and Deposition of Pd onto TiO2. ACS Appl. Mater. Interfaces 2011, 3, 2594−2600. (1454) Kim, W.; Seok, T.; Choi, W. Nafion Layer-Enhanced Photosynthetic Conversion of CO2 into Hydrocarbons on TiO2 Nanoparticles. Energy Environ. Sci. 2012, 5, 6066−6070. (1455) Liu, H.; Li, M.; Dao, T. D.; Liu, Y.; Zhou, W.; Liu, L.; Meng, X.; Nagao, T.; Ye, J. Design of PdAu Alloy Plasmonic Nanoparticles for Improved Catalytic Performance in CO2 Reduction with Visible Light Irradiation. Nano Energy 2016, 26, 398−404. (1456) Camarillo, R.; Tostón, S.; Martínez, F.; Jiménez, C.; Rincón, J. Enhancing the Photocatalytic Reduction of CO2 through Engineering of Catalysts with High Pressure Technology: Pd/TiO2 Photocatalysts. J. Supercrit. Fluids 2017, 123, 18−27. (1457) Xu, Y.-F.; Yang, M.-Z.; Chen, H.-Y.; Liao, J.-F.; Wang, X.-D.; Kuang, D.-B. Enhanced Solar-Driven Gaseous CO2 Conversion by CsPbBr3 Nanocrystal/Pd Nanosheet Schottky-Junction Photocatalyst. ACS Applied Energy Materials 2018, 1, 5083−5089. (1458) Zhang, Q. H.; Han, W. D.; Hong, Y. J.; Yu, J. G. Photocatalytic Reduction of CO2 with H2O on Pt-Loaded TiO2 Catalyst. Catal. Today 2009, 148, 335−340. (1459) Shi, H. F.; Wang, T. Z.; Chen, J.; Zhu, C.; Ye, J. H.; Zou, Z. G. Photoreduction of Carbon Dioxide over NaNbO3 Nanostructured Photocatalysts. Catal. Lett. 2011, 141, 525−530. (1460) Feng, X. J.; Sloppy, J. D.; LaTempa, T. J.; Paulose, M.; Komarneni, S.; Bao, N. Z.; Grimes, C. A. Synthesis and Deposition of Ultrafine Pt Nanoparticles within High Aspect Ratio TiO2 Nanotube

Arrays: Application to the Photocatalytic Reduction of Carbon Dioxide. J. Mater. Chem. 2011, 21, 13429−13433. (1461) Xie, K.; Umezawa, N.; Zhang, N.; Reunchan, P.; Zhang, Y.; Ye, J. Self-Doped SrTiO3-Delta Photocatalyst with Enhanced Activity for Artificial Photosynthesis under Visible Light. Energy Environ. Sci. 2011, 4, 4211−4219. (1462) Zhang, N.; Ouyang, S. X.; Li, P.; Zhang, Y. J.; Xi, G. C.; Kako, T.; Ye, J. H. Ion-Exchange Synthesis of a Micro/Mesoporous Zn2GeO4 Photocatalyst at Room Temperature for Photoreduction of CO2. Chem. Commun. 2011, 47, 2041−2043. (1463) Pan, J.; Wu, X.; Wang, L. Z.; Liu, G.; Lu, G. Q.; Cheng, H. M. Synthesis of Anatase TiO2Rods with Dominant Reactive {010} Facets for the Photoreduction of CO2 to CH4 and Use in Dye-Sensitized Solar Cells. Chem. Commun. 2011, 47, 8361−8363. (1464) Kamegawa, T.; Matsuoka, M.; Anpo, M. Photocatalytic Selective Oxidation of CO with O2 in the Presence of H2 over Highly Dispersed Chromium Oxide on Silica under Visible or Solar Light Irradiation. Res. Chem. Intermed. 2008, 34, 427−434. (1465) Li, X.; Li, W.; Zhuang, Z.; Zhong, Y.; Li, Q.; Wang, L. Photocatalytic Reduction of Carbon Dioxide to Methane over SiO2Pillared HnB3O8. J. Phys. Chem. C 2012, 116, 16047−16053. (1466) Li, P.; Ouyang, S.; Zhang, Y.; Kako, T.; Ye, J. SurfaceCoordination-Induced Selective Synthesis of Cubic and Orthorhombic NaNbO3 and Their Photocatalytic Properties. J. Mater. Chem. A 2013, 1, 1185−1191. (1467) Liu, Q.; Low, Z.-X.; Li, L.; Razmjou, A.; Wang, K.; Yao, J.; Wang, H. ZIF-8/Zn2GeO4 Nanorods with an Enhanced CO2 Adsorption Property in an Aqueous Medium for Photocatalytic Synthesis of Liquid Fuel. J. Mater. Chem. A 2013, 1, 11563−11569. (1468) Li, P.; Zhou, Y.; Tu, W. G.; Liu, Q.; Yan, S. C.; Zou, Z. G. Direct Growth of Fe2V4O13 Nanoribbons on a Stainless-Steel Mesh for Visible-Light Photoreduction of CO2 into Renewable Hydrocarbon Fuel and Degradation of Gaseous Isopropyl Alcohol. ChemPlusChem 2013, 78, 274−278. (1469) Li, Q.; Zong, L.; Li, C.; Yang, J. Photocatalytic Reduction of CO2 on MgO/TiO2 Nanotube Films. Appl. Surf. Sci. 2014, 319, 16− 20. (1470) Yu, J.; Wang, K.; Xiao, W.; Cheng, B. Photocatalytic Reduction of CO2 into Hydrocarbon Solar Fuels over g-C3N4-Pt Nanocomposite Photocatalysts. Phys. Chem. Chem. Phys. 2014, 16, 11492−11501. (1471) Ong, W.-J.; Tan, L.-L.; Chai, S.-P.; Yong, S.-T. Heterojunction Engineering of Graphitic Carbon Nitride (g-C3N4) Via Pt Loading with Improved Daylight-Induced Photocatalytic Reduction of Carbon Dioxide to Methane. Dalton Trans. 2015, 44, 1249−1257. (1472) Manzi, A.; Simon, T.; Sonnleitner, C.; Doeblinger, M.; Wyrwich, R.; Stern, O.; Stolarczyk, J. K.; Feldmann, J. Light-Induced Cation Exchange for Copper Sulfide Based CO2 Reduction. J. Am. Chem. Soc. 2015, 137, 14007−14010. (1473) AlOtaibi, B.; Fan, S.; Wang, D.; Ye, J.; Mi, Z. Wafer-Level Artificial Photosynthesis for CO2 Reduction into CH4 and CO Using GaN Nanowires. ACS Catal. 2015, 5, 5342−5348. (1474) Sorcar, S.; Hwang, Y. J.; Grimes, C. A.; In, S. I. Highly Enhanced and Stable Activity of Defect-Induced Titania Nanoparticles for Solar Light-Driven CO2 Reduction into CH4. Mater. Today 2017, 20, 507−515. (1475) Razzaq, A.; Sinhamahapatra, A.; Kang, T. H.; Grimes, C. A.; Yu, J. S.; In, S. I. Efficient Solar Light Photoreduction of CO2 to Hydrocarbon Fuels Via Magnesiothermally Reduced TiO2 Photocatalyst. Appl. Catal., B 2017, 215, 28−35. (1476) Wang, Y.; Lai, Q.; He, Y.; Fan, M. Selective Photocatalytic Carbon Dioxide Conversion with Pt@Ag-TiO2 Nanoparticles. Catal. Commun. 2018, 108, 98−102. (1477) Wang, C.; Ranasingha, O.; Natesakhawat, S.; Ohodnicki, P. R., Jr.; Andio, M.; Lewis, J. P.; Matranga, C. Visible Light Plasmonic Heating of Au-ZnO for the Catalytic Reduction of CO2. Nanoscale 2013, 5, 6968−6974. (1478) Jiao, J.; Wei, Y.; Zhao, Z.; Zhong, W.; Liu, J.; Li, J.; Duan, A.; Jiang, G. Synthesis of 3D Ordered Macroporous TiO2-Supported Au GU


Chemical Reviews

Review

Nanoparticle Photocatalysts and Their Photocatalytic Performances for the Reduction of CO2 to Methane. Catal. Today 2015, 258, 319− 326. (1479) Tu, W.; Zhou, Y.; Li, H.; Li, P.; Zou, Z. Au@TiO2 Yolk-Shell Hollow Spheres for Plasmon-Induced Photocatalytic Reduction of CO2 to Solar Fuel Via a Local Electromagnetic Field. Nanoscale 2015, 7, 14232−14236. (1480) Bai, Y.; Chen, T.; Wang, P.; Wang, L.; Ye, L.; Shi, X.; Bai, W. Size-Dependent Role of Gold in g-C3N4/BiOBr/Au System for Photocatalytic CO2 Reduction and Dye Degradation. Sol. Energy Mater. Sol. Cells 2016, 157, 406−414. (1481) Zhou, H.; Li, P.; Liu, J.; Chen, Z.; Liu, L.; Dontsova, D.; Yan, R.; Fan, T.; Zhang, D.; Ye, J. Biomimetic Polymeric Semiconductor Based Hybrid Nanosystems for Artificial Photosynthesis Towards Solar Fuels Generation Via CO2 Reduction. Nano Energy 2016, 25, 128−135. (1482) Kar, P.; Farsinezhad, S.; Mahdi, N.; Zhang, Y.; Obuekwe, U.; Sharma, H.; Shen, J.; Semagina, N.; Shankar, K. Enhanced CH4 Yield by Photocatalytic CO2 Reduction Using TiO2 Nanotube Arrays Grafted with Au, Ru, and Znpd Nanoparticles. Nano Res. 2016, 9, 3478−3493. (1483) Tahir, B.; Tahir, M.; Amin, N. A. S. Photocatalytic CO2 Conversion over Au/TiO2 Nanostructures for Dynamic Production of Clean Fuels in a Monolith Photoreactor. Clean Technol. Environ. Policy 2016, 18, 2147−2160. (1484) Chen, S.; Pan, B.; Zeng, L.; Luo, S.; Wang, X.; Su, W. La2Sn2O7 Enhanced Photocatalytic CO2Reduction with H2O by Deposition of Au Co-Catalyst. RSC Adv. 2017, 7, 14186−14191. (1485) Tahir, M. Synergistic Effect in MMT-Dispersed Au/TiO2 Monolithic Nanocatalyst for Plasmon-Absorption and Metallic Interband Transitions Dynamic CO2 Photo-Reduction to CO. Appl. Catal., B 2017, 219, 329−343. (1486) Li, H. L.; Gao, Y.; Xiong, Z.; Liao, C.; Shih, K. Enhanced Selective Photocatalytic Reduction of CO2 to CH4 over Plasmonic Au Modified g-C3N4 Photocatalyst under Uv-Vis Light Irradiation. Appl. Surf. Sci. 2018, 439, 552−559. (1487) An, C.; Wang, J.; Jiang, W.; Zhang, M.; Ming, X.; Wang, S.; Zhang, Q. Strongly Visible-Light Responsive Plasmonic Shaped AgX:Ag (X = Cl, Br) Nanoparticles for Reduction of CO2 to Methanol. Nanoscale 2012, 4, 5646−5650. (1488) Liu, E.; Kang, L.; Wu, F.; Sun, T.; Hu, X.; Yang, Y.; Liu, H.; Fan, J. Photocatalytic Reduction of CO2 into Methanol over Ag/TiO2 Nanocomposites Enhanced by Surface Plasmon Resonance. Plasmonics 2014, 9, 61−70. (1489) Kong, D.; Tan, J. Z. Y.; Yang, F.; Zeng, J.; Zhang, X. Electrodeposited Ag Nanoparticles on TiO2 Nanorods for Enhanced UV Visible Light Photoreduction CO2 to CH4. Appl. Surf. Sci. 2013, 277, 105−110. (1490) Collado, L.; Jana, P.; Sierra, B.; Coronado, J. M.; Pizarro, P.; Serrano, D. P.; de la Peña O’Shea, V. A. Enhancement of Hydrocarbon Production Via Artificial Photosynthesis Due to Synergetic Effect of Ag Supported on TiO2 and ZnO Semiconductors. Chem. Eng. J. 2013, 224, 128−135. (1491) He, Z. Q.; Wang, D.; Fang, H. Y.; Chen, J. M.; Song, S. Highly Efficient and Stable Ag/AgIO3 Particles for Photocatalytic Reduction of CO2 under Visible Light. Nanoscale 2014, 6, 10540− 10544. (1492) Kawamura, S.; Puscasu, M. C.; Yoshida, Y.; Izumi, Y.; Carja, G. Tailoring Assemblies of Plasmonic Silver/Gold and Zinc-Gallium Layered Double Hydroxides for Photocatalytic Conversion of Carbon Dioxide Using Uv-Visible Light. Appl. Catal., A 2015, 504, 238−247. (1493) Wang, Z.; Teramura, K.; Hosokawa, S.; Tanaka, T. Photocatalytic Conversion of CO2 in Water over Ag-Modified La2Ti2O7. Appl. Catal., B 2015, 163, 241−247. (1494) Wang, Z.; Teramura, K.; Hosokawa, S.; Tanaka, T. Highly Efficient Photocatalytic Conversion of CO2 into Solid CO Using H2O as a Reductant over Ag-Modified ZnGa2O4. J. Mater. Chem. A 2015, 3, 11313−11319.

(1495) Feng, S.; Wang, M.; Zhou, Y.; Li, P.; Tu, W.; Zou, Z. DoubleShelled Plasmonic Ag-TiO2 Hollow Spheres toward Visible LightActive Photocatalytic Conversion of CO2 into Solar Fuel. APL Mater. 2015, 3, 104416. (1496) Wang, J.; Huang, C.; Chen, X.; Zhang, H.; Li, Z.; Zou, Z. Photocatalytic CO2 Reduction of BaCeO3 with 4f Configuration Electrons. Appl. Surf. Sci. 2015, 358, 463−467. (1497) Wang, D.; Yu, Y.; Zhang, Z.; Fang, H.; Chen, J.; He, Z.; Song, S. Ag/Ag2SO3 Plasmonic Catalysts with High Activity and Stability for CO2 Reduction with Water Vapor under Visible Light. Environ. Sci. Pollut. R. 2016, 1−10. (1498) Li, H. L.; Wu, X. Y.; Wang, J.; Gao, Y.; Li, L. Q.; Shih, K. M. Enhanced Activity of Ag-MgO-TiO2 Catalyst for Photocatalytic Conversion of CO2 and H2O into CH4. Int. J. Hydrogen Energy 2016, 41, 8479−8488. (1499) Xu, F.; Meng, K.; Cheng, B.; Yu, J.; Ho, W. Enhanced Photocatalytic Activity and Selectivity for CO2 Reduction over a TiO2 Nanofibre Mat Using Ag and MgO as Bi-Cocatalyst. ChemCatChem 2019, 11, 465−472. (1500) Iguchi, S.; Teramura, K.; Hosokawa, S.; Tanaka, T. A ZnTa2O6 Photocatalyst Synthesized via Solid State Reaction for Conversion of CO2 into CO in Water. Catal. Sci. Technol. 2016, 6, 4978−4985. (1501) Yu, B.; Zhou, Y.; Li, P.; Tu, W.; Li, P.; Tang, L.; Ye, J.; Zou, Z. Photocatalytic Reduction of CO2 over Ag/TiO2 Nanocomposites Prepared with a Simple and Rapid Silver Mirror Method. Nanoscale 2016, 8, 11870−11874. (1502) Tahir, M.; Tahir, B.; Amin, N. A. S.; Zakaria, Z. Y. PhotoInduced Reduction of CO2 to CO with Hydrogen over Plasmonic AgNPs/TiO2 NWs Core/Shell Hetero-Junction under Uv and Visible Light. J. CO2 Util. 2017, 18, 250−260. (1503) Pham, T. D.; Lee, B. K. Novel Capture and Photocatalytic Conversion of CO2 into Solar Fuels by Metals co-Doped TiO2 Deposited on PU under Visible Light. Appl. Catal., A 2017, 529, 40−48. (1504) Cheng, X. D.; Dong, P. M.; Huang, Z. F.; Zhang, Y. Z.; Chen, Y.; Nie, X. X.; Zhang, X. W. Green Synthesis of Plasmonic Ag Nanoparticles Anchored TiO2 Nanorod Arrays Using Cold Plasma for Visible-Light-Driven Photocatalytic Reduction of CO2. J. CO2 Util. 2017, 20, 200−207. (1505) Dilla, M.; Pougin, A.; Strunk, J. Evaluation of the Plasmonic Effect of Au and Ag on Ti-Based Photocatalysts in the Reduction of CO2 to CH4. J. Energy Chem. 2017, 26, 277−283. (1506) Choi, K. M.; Kim, D.; Rungtaweevoranit, B.; Trickett, C. A.; Barmanbek, J. T. D.; Alshammari, A. S.; Yang, P. D.; Yaghi, O. M. Plasmon-Enhanced Photocatalytic CO2 Conversion within Metal Organic Frameworks under Visible Light. J. Am. Chem. Soc. 2017, 139, 356−362. (1507) Zhu, Z.; Han, Y.; Chen, C.; Ding, Z.; Long, J.; Hou, Y. Reduced Graphene Oxide-Cadmium Sulfide Nanorods Decorated with Silver Nanoparticles for Efficient Photocatalytic Reduction Carbon Dioxide under Visible Light. ChemCatChem 2018, 10, 1627−1634. (1508) Shao, K. J.; Wang, Y. J.; Iqbal, M.; Lin, L.; Wang, K.; Zhang, X. H.; He, M.; He, T. Modification of Ag Nanoparticles on the Surface of SrTiO3 Particles and Resultant Influence on Photoreduction of CO2. Appl. Surf. Sci. 2018, 434, 717−724. (1509) Tan, D. X.; Zhang, J. L.; Shi, J. B.; Li, S. P.; Zhang, B. X.; Tan, X. N.; Zhang, F. Y.; Liu, L. F.; Shao, D.; Han, B. X. Photocatalytic CO2 Transformation to CH4 by Ag/Pd Bimetals Supported on N-Doped TiO2 Nanosheet. ACS Appl. Mater. Interfaces 2018, 10, 24516−24522. (1510) Yan, S. C.; Wan, L. J.; Li, Z. S.; Zou, Z. G. Facile Temperature-Controlled Synthesis of Hexagonal Zn2GeO4 Nanorods with Different Aspect Ratios toward Improved Photocatalytic Activity for Overall Water Splitting and Photoreduction of CO2. Chem. Commun. 2011, 47, 5632−5634. (1511) Liu, J.-Y.; Garg, B.; Ling, Y.-C. Cuxagyinzznksm Solid Solutions Customized with RuO2 or Rh1.32Cr0.66O3 Co-Catalyst Display Visible Light-Driven Catalytic Activity for CO2 Reduction to CH3OH. Green Chem. 2011, 13, 2029−2031. GV


Chemical Reviews

Review

Photoreduction of CO2 into CH4. CrystEngComm 2016, 18, 2956− 2964. (1530) Adekoya, D. O.; Tahir, M.; Amin, N. A. S. g-C3N4/(Cu/ TiO2) Nanocomposite for Enhanced Photoreduction of CO2 to CH3OH and HCOOH under Uv/Visible Light. J. CO2 Util. 2017, 18, 261−274. (1531) Zhang, T.; Low, J. X.; Huang, X. X.; Al-Sharab, J. F.; Yu, J. G.; Asefa, T. Copper-Decorated Microsized Nanoporous Titanium Dioxide Photocatalysts for Carbon Dioxide Reduction by Water. ChemCatChem 2017, 9, 3054−3062. (1532) Wu, J. C. S.; Lin, H. M.; Lai, C. L. Photo Reduction of CO2 to Methanol Using Optical-Fiber Photoreactor. Appl. Catal., A 2005, 296, 194−200. (1533) Li, H. L.; Lei, Y. G.; Huang, Y.; Fang, Y. P.; Xu, Y. H.; Zhu, L.; Li, X. Photocatalytic Reduction of Carbon Dioxide to Methanol by Cu2O/SiC Nanocrystallite under Visible Light Irradiation. J. Nat. Gas Chem. 2011, 20, 145−150. (1534) Ba, X.; Yan, L.-L.; Huang, S.; Yu, J.; Xia, X.-J.; Yu, Y. New Way for CO2 Reduction under Visible Light by a Combination of a Cu Electrode and Semiconductor Thin Film: Cu2O Conduction Type and Morphology Effect. J. Phys. Chem. C 2014, 118, 24467−24478. (1535) Li, Y.; Zhang, W.; Shen, X.; Peng, P.; Xiong, L.; Yu, Y. Octahedral Cu2O-Modified TiO2 Nanotube Arrays for Efficient Photocatalytic Reduction of CO2. Chin. J. Catal. 2015, 36, 2229−2236. (1536) Alves Melo, M. A., Jr.; Morais, A.; Nogueira, A. F. Boosting the Solar-Light-Driven Methanol Production through CO2 Photoreduction by Loading Cu2O on TiO2-Pillared K2Ti4O9. Microporous Mesoporous Mater. 2016, 234, 1−11. (1537) Xiang, T. Y.; Xin, F.; Chen, J. S.; Wang, Y. W.; Yin, X. H.; Shao, X. Selective Photocatalytic Reduction of CO2 to Methanol in CuO-Loaded NaTaO3 Nanocubes in Isopropanol. Beilstein J. Nanotechnol. 2016, 7, 776−783. (1538) Pastrana-Martinez, L. M.; Silva, A. M. T.; Fonseca, N. N. C.; Vaz, J. R.; Figueiredo, J. L.; Faria, J. L. Photocatalytic Reduction of CO2 with Water into Methanol and Ethanol Using Graphene Derivative-TiO2 Composites: Effect of Ph and Copper(I) Oxide. Top. Catal. 2016, 59, 1279−1291. (1539) Pan, P. W.; Chen, Y. W. Photocatalytic Reduction of Carbon Dioxide on NiO/InTaO4 under Visible Light Irradiation. Catal. Commun. 2007, 8, 1546−1549. (1540) Wang, Z. Y.; Chou, H. C.; Wu, J. C. S.; Tsai, D. P.; Mul, G. CO2 Photoreduction Using NiO/InTaO4 in Optical-Fiber Reactor for Renewable Energy. Appl. Catal., A 2010, 380, 172−177. (1541) Lee, D. S.; Chen, H. J.; Chen, Y. W. Photocatalytic Reduction of Carbon Dioxide with Water Using InNbO4 Catalyst with NiO and Co3O4 Cocatalysts. J. Phys. Chem. Solids 2012, 73, 661−669. (1542) Albero, J.; Garcia, H.; Corma, A. Temperature Dependence of Solar Light Assisted CO2 Reduction on Ni Based Photocatalyst. Top. Catal. 2016, 59, 787−791. (1543) Liu, H. M.; Meng, X. G.; Dao, T. D.; Liu, L. Q.; Li, P.; Zhao, G. X.; Nagao, T.; Yang, L. Q.; Ye, J. H. Light Assisted CO2 Reduction with Methane over SiO2 Encapsulated Ni Nanocatalysts for Boosted Activity and Stability. J. Mater. Chem. A 2017, 5, 10567−10573. (1544) Singhal, N.; Goyal, R.; Kumar, U. Visible-Light-Assisted Photocatalytic CO2 Reduction over InTaO4Selective Methanol Formation. Energy Fuels 2017, 31, 12434−12438. (1545) Billo, T.; Fu, F. Y.; Raghunath, P.; Shown, I.; Chen, W. F.; Lien, H. T.; Shen, T. H.; Lee, J. F.; Chan, T. S.; Huang, K. Y.; et al. NiNanocluster Modified Black TiO2 with Dual Active Sites for Selective Photocatalytic CO2 Reduction. Small 2018, 14, 1702928. (1546) Meng, A.; Wu, S.; Cheng, B.; Yu, J.; Xu, J. Hierarchical TiO2/ Ni(OH)2 Composite Fibers with Enhanced Photocatalytic CO2 Reduction Performance. J. Mater. Chem. A 2018, 6, 4729−4736. (1547) Tahir, M.; Tahir, B.; Amin, N. A. S.; Muhammad, A. Photocatalytic CO2Methanation over NiO/In2O3 Promoted TiO2 Nanocatalysts Using H2O and/or H2 Reductants. Energy Convers. Manage. 2016, 119, 368−378. (1548) Shao, X.; Yin, X. H.; Wang, J. Z. Nanoheterostructures of Potassium Tantalate and Nickel Oxide for Photocatalytic Reduction of

(1512) Jiao, W.; Wang, L.; Liu, G.; Lu, G. Q.; Cheng, H.-M. Hollow Anatase TiO2 Single Crystals and Mesocrystals with Dominant {101} Facets for Improved Photocatalysis Activity and Tuned Reaction Preference. ACS Catal. 2012, 2, 1854−1859. (1513) Yan, S.; Wang, J.; Gao, H.; Wang, N.; Yu, H.; Li, Z.; Zhou, Y.; Zou, Z. An Ion-Exchange Phase Transformation to ZnGa 2O4 Nanocube Towards Efficient Solar Fuel Synthesis. Adv. Funct. Mater. 2013, 23, 758−763. (1514) Liu, Q.; Zhou, Y.; Tu, W.; Yan, S.; Zou, Z. Solution-Chemical Route to Generalized Synthesis of Metal Germanate Nanowires with Room-Temperature, Light-Driven Hydrogenation Activity of CO2 into Renewable Hydrocarbon Fuels. Inorg. Chem. 2014, 53, 359−364. (1515) Jeyalakshmi, V.; Mahalakshmy, R.; Krishnamurthy, K. R.; Viswanathan, B. Photocatalytic Reduction of Carbon Dioxide in Alkaline Medium on La Modified Sodium Tantalate with Different Co-Catalysts under Uv-Visible Radiation. Catal. Today 2016, 266, 160−167. (1516) Baran, T.; Wojtyla, S.; Dibenedetto, A.; Aresta, M.; Macyk, W. Zinc Sulfide Functionalized with Ruthenium Nanoparticles for Photocatalytic Reduction of CO2. Appl. Catal., B 2015, 178, 170−176. (1517) Wang, K.; Yu, J.; Liu, L.; Hou, L.; Jin, F. Hierarchical PDoped TiO2 Nanotubes Array@Ti Plate: Towards Advanced CO2 Photocatalytic Reduction Catalysts. Ceram. Int. 2016, 42, 16405− 16411. (1518) Wang, S. M.; Guan, Y.; Lu, L.; Shi, Z.; Yan, S. C.; Zou, Z. G. Effective Separation and Transfer of Carriers into the Redox Sites on Ta3N5/Bi Photocatalyst for Promoting Conversion of CO2 into CH4. Appl. Catal., B 2018, 224, 10−16. (1519) Bai, Y.; Yang, P.; Wang, P.; Xie, H.; Dang, H.; Ye, L. Semimetal Bismuth Mediated Uv−Vis-Ir Driven Photo-Thermocatalysis of Bi4O5I2 for Carbon Dioxide to Chemical Energy. J. CO2 Util. 2018, 23, 51−60. (1520) Tang, J.-y.; Zhou, W.-g.; Guo, R.-t.; Huang, C.-y.; Pan, W.-g. Enhancement of Photocatalytic Performance in CO2 Reduction over Mg/g-C3N4Catalysts under Visible Light Irradiation. Catal. Commun. 2018, 107, 92−95. (1521) Inoue, H.; Moriwaki, H.; Maeda, K.; Yoneyama, H. Photoreduction of Carbon Dioxide Using Chalcogenide Semiconductor Microcrystals. J. Photochem. Photobiol., A 1995, 86, 191− 196. (1522) Hirano, K.; Inoue, K.; Yatsu, T. Photocatalysed Reduction of CO2 in Aqueous TiO2 Suspension Mixed with Copper Powder. J. Photochem. Photobiol., A 1992, 64, 255−258. (1523) Li, H.; He, X.; Kang, Z.; Huang, H.; Liu, Y.; Liu, J.; Lian, S.; Tsang, C. H. A.; Yang, X.; Lee, S. T. Water Soluble Fluorescent Carbon Quantum Dots and Photocatalyst Design. Angew. Chem., Int. Ed. 2010, 49, 4430−4434. (1524) Ambrozova, N.; Reli, M.; Sihor, M.; Kustrowski, P.; Wu, J. C. S.; Koci, K. Copper and Platinum Doped Titania for Photocatalytic Reduction of Carbon Dioxide. Appl. Surf. Sci. 2018, 430, 475−487. (1525) Tan, J. Z. Y.; Fernandez, Y.; Liu, D.; Maroto-Valer, M.; Bian, J. C.; Zhang, X. W. Photoreduction of CO2 Using Copper-Decorated TiO2 Nanorod Films with Localized Surface Plasmon Behavior. Chem. Phys. Lett. 2012, 531, 149−154. (1526) Rani, S.; Bao, N. Z.; Roy, S. C. Solar Spectrum Photocatalytic Conversion of CO2 and Water Vapor into Hydrocarbons Using TiO2 Nanoparticle Membranes. Appl. Surf. Sci. 2014, 289, 203−208. (1527) Singhal, N.; Ali, A.; Vorontsov, A.; Pendem, C.; Kumar, U. Efficient Approach for Simultaneous CO and H2 Production Via Photoreduction of CO2 with Water over Copper Nanoparticles Loaded TiO2. Appl. Catal., A 2016, 523, 107−117. (1528) Liu, E.; Qi, L.; Bian, J.; Chen, Y.; Hu, X.; Fan, J.; Liu, H.; Zhu, C.; Wang, Q. A Facile Strategy to Fabricate Plasmonic Cu Modified TiO2 Nano-Flower Films for Photocatalytic Reduction of CO2 to Methanol. Mater. Res. Bull. 2015, 68, 203−209. (1529) Yan, Y. B.; Yu, Y. L.; Cao, C.; Huang, S. L.; Yang, Y. J.; Yang, X. D.; Cao, Y. Enhanced Photocatalytic Activity of TiO2-Cu/C with Regulation and Matching of Energy Levels by Carbon and Copper for GW


Chemical Reviews

Review

Carbon Dioxide to Methanol in Isopropanol. J. Colloid Interface Sci. 2018, 512, 466−473. (1549) Iguchi, S.; Hasegawa, Y.; Teramura, K.; Kidera, S.; Kikkawa, S.; Hosokawa, S.; Asakura, H.; Tanaka, T. Drastic Improvement in the Photocatalytic Activity of Ga2O3 Modified with Mg-Al Layered Double Hydroxide for the Conversion of CO2 in Water. Sustainable Energy & Fuels 2017, 1, 1740−1747. (1550) Yan, S. S.; Ouyang, S. X.; Xu, H.; Zhao, M.; Zhang, X. L.; Ye, J. H. Co-ZIF-9/TiO2 Nanostructure for Superior CO2 Photoreduction Activity. J. Mater. Chem. A 2016, 4, 15126−15133. (1551) Qin, J.; Wang, S.; Wang, X. Visible-Light Reduction CO2 with Dodecahedral Zeolitic Imidazolate Framework ZIF-67 as an Efficient Co-Catalyst. Appl. Catal., B 2017, 209, 476−482. (1552) Xu, G.; Zhang, H.; Wei, J.; Zhang, H.-X.; Wu, X.; Li, Y.; Li, C.; Zhang, J.; Ye, J. Integrating the g-C3N4 Nanosheet with B−H Bonding Decorated Metal−Organic Framework for CO2 Activation and Photoreduction. ACS Nano 2018, 12, 5333−5340. (1553) Zhu, W.; Zhang, C. F.; Li, Q.; Xiong, L. K.; Chen, R. X.; Wan, X. B.; Wang, Z.; Chen, W.; Deng, Z.; Peng, Y. Selective Reduction of CO2 by Conductive MOF Nanosheets as an Efficient Co-Catalyst under Visible Light Illumination. Appl. Catal., B 2018, 238, 339−345. (1554) Pan, B.; Zhou, Y.; Su, W.; Wang, X. Enhanced Photocatalytic CO2 Conversion over LaPO4 by Introduction of CoCl2 as a Hole Mediator. RSC Adv. 2016, 6, 34744−34747. (1555) Jiang, M.; Gao, Y.; Wang, Z.; Ding, Z. Photocatalytic CO2 Reduction Promoted by a CuCo2O4 Cocatalyst with Homogeneous and Heterogeneous Light Harvesters. Appl. Catal., B 2016, 198, 180− 188. (1556) Zhao, K.; Zhao, S.; Gao, C.; Qi, J.; Yin, H.; Wei, D.; Mideksa, M. F.; Wang, X.; Gao, Y.; Tang, Z.; et al. Metallic Cobalt−Carbon Composite as Recyclable and Robust Magnetic Photocatalyst for Efficient CO2 Reduction. Small 2018, 14, 1800762. (1557) Lee, H.; Kwak, B. S.; Park, N. K.; Baek, J. I.; Ryu, H. J.; Kang, M. Assembly of a Check-Patterned CuSx-TiO2 Film with an ElectronRich Pool and its Application for the Photoreduction of Carbon Dioxide to Methane. Appl. Surf. Sci. 2017, 393, 385−396. (1558) Wang, L.; Ha, M. N.; Liu, Z.; Zhao, Z. Mesoporous WO3 Modified by Mo for Enhancing Reduction of CO2 to Solar Fuels under Visible Light and Thermal Conditions. Integr. Ferroelectr. 2016, 172, 97−108. (1559) Men, Y.-L.; You, Y.; Pan, Y.-X.; Gao, H.; Xia, Y.; Cheng, D.G.; Song, J.; Cui, D.-X.; Wu, N.; Li, Y.; et al. Selective Co Evolution from Photoreduction of CO2 on a Metal-Carbide-Based Composite Catalyst. J. Am. Chem. Soc. 2018, 140, 13071−13077. (1560) Peng, H.; Lu, J.; Wu, C.; Yang, Z.; Chen, H.; Song, W.; Li, P.; Yin, H. Co-Doped MoS2 NPs with Matched Energy Band and Low Overpotential High Efficiently Convert CO2 to Methanol. Appl. Surf. Sci. 2015, 353, 1003−1012. (1561) Gui, M. M.; Chai, S.-P.; Mohamed, A. R. Modification of MWCNT@TiO2 Core-Shell Nanocomposites with Transition Metal Oxide Dopants for Photoreduction of Carbon Dioxide into Methane. Appl. Surf. Sci. 2014, 319, 37−43. (1562) Wang, Y.; Zhao, J.; Wang, T. F.; Li, Y. X.; Li, X. Y.; Yin, J.; Wang, C. Y. CO2 Photoreduction with H2O Vapor on Highly Dispersed CeO2/TiO2 Catalysts: Surface Species and Their Reactivity. J. Catal. 2016, 337, 293−302. (1563) Zhang, J.-X.; Hu, C.-Y.; Wang, W.; Wang, H.; Bian, Z.-Y. Visible Light Driven Reduction of CO2 Catalyzed by an Abundant Manganese Catalyst with Zinc Porphyrin Photosensitizer. Appl. Catal., A 2016, 522, 145−151. (1564) Kwak, B. S.; Kim, K. M.; Park, S.-M.; Kang, M. Synthesis of Basalt Fiber@Zn1‑xMgxO Core/Shell Nanostructures for Selective Photoreduction of CO2 to CO. Appl. Surf. Sci. 2017, 407, 109−116. (1565) Matejova, L.; Koci, K.; Reli, M.; Capek, L.; Matejka, V.; Solcova, O.; Obalova, L. On Sol-Gel Derived Au-Enriched TiO2 and TiO2-ZrO2 Photocatalysts and Their Investigation in Photocatalytic Reduction of Carbon Dioxide. Appl. Surf. Sci. 2013, 285, 688−696. (1566) Putri, L. K.; Ong, W.-J.; Chang, W. S.; Chai, S.-P. Enhancement in the Photocatalytic Activity of Carbon Nitride through

Hybridization with Light-Sensitive AgCl for Carbon Dioxide Reduction to Methane. Catal. Sci. Technol. 2016, 6, 744−754. (1567) Ye, M.; Wang, X.; Liu, E.; Ye, J.; Wang, D. Boosting the Photocatalytic Activity of P25 for Carbon Dioxide Reduction Using a Surface-Alkalinized Titanium Carbide Mxene as Co-Catalyst. ChemSusChem 2018, 11, 1606−1611. (1568) Low, J.; Zhang, L.; Tong, T.; Shen, B.; Yu, J. TiO2/Mxene Ti3C2 Composite with Excellent Photocatalytic CO2 Reduction Activity. J. Catal. 2018, 361, 255−266. (1569) Wang, S.; Hou, Y.; Wang, X. Development of a Stable MnCo2O4 Cocatalyst for Photocatalytic CO2 Reduction with Visible Light. ACS Appl. Mater. Interfaces 2015, 7, 4327−4335. (1570) Bi, Y.; Zong, L.; Li, C.; Li, Q.; Yang, J. Photoreduction of CO2 on TiO2/SrTiO3 Heterojunction Network Film. Nanoscale Res. Lett. 2015, 10, 345. (1571) Obert, R.; Dave, B. C. Enzymatic Conversion of Carbon Dioxide to Methanol: Enhanced Methanol Production in Silica Sol-Gel Matrices. J. Am. Chem. Soc. 1999, 121, 12192−12193. (1572) Sun, Q.; Jiang, Y.; Jiang, Z.; Zhang, L.; Sun, X.; Li, J. Green and Efficient Conversion of CO2 to Methanol by Biomimetic Coimmobilization of Three Dehydrogenases in Protamine-Templated Titania. Ind. Eng. Chem. Res. 2009, 48, 4210−4215. (1573) Xu, S.-w.; Lu, Y.; Li, J.; Jiang, Z.-y.; Wu, H. Efficient Conversion of CO2 to Methanol Catalyzed by Three Dehydrogenases Co-Encapsulated in an Alginate−Silica (ALG−SiO2) Hybrid Gel. Ind. Eng. Chem. Res. 2006, 45, 4567−4573. (1574) El-Zahab, B.; Donnelly, D.; Wang, P. Particle-Tethered NADH for Production of Methanol from CO2 Catalyzed by Coimmobilized Enzymes. Biotechnol. Bioeng. 2008, 99, 508−514. (1575) Lu, Y.; Jiang, Z.-y.; Xu, S.-w.; Wu, H. Efficient Conversion of CO2 to Formic Acid by Formate Dehydrogenase Immobilized in a Novel Alginate−Silica Hybrid Gel. Catal. Today 2006, 115, 263−268. (1576) Reda, T.; Plugge, C. M.; Abram, N. J.; Hirst, J. Reversible Interconversion of Carbon Dioxide and Formate by an Electroactive Enzyme. Proc. Natl. Acad. Sci. U. S. A. 2008, 105, 10654−10658. (1577) Rajendran, V.; König, A.; Rabe, K. S.; Niemeyer, C. M. Photocatalytic Activity of Protein-Conjugated CdS Nanoparticles. Small 2010, 6, 2035−2040. (1578) Choudhury, S.; Baeg, J. O.; Park, N. J.; Yadav, R. K. A Photocatalyst/Enzyme Couple That Uses Solar Energy in the Asymmetric Reduction of Acetophenones. Angew. Chem., Int. Ed. 2012, 51, 11624−11628. (1579) Woolerton, T. W.; Sheard, S.; Pierce, E.; Ragsdale, S. W.; Armstrong, F. A. CO2 Photoreduction at Enzyme-Modified Metal Oxide Nanoparticles. Energy Environ. Sci. 2011, 4, 2393−2399. (1580) Yadav, R. K.; Baeg, J. O.; Oh, G. H.; Park, N. J.; Kong, K. J.; Kim, J.; Hwang, D. W.; Biswas, S. K. A Photocatalyst-Enzyme Coupled Artificial Photosynthesis System for Solar Energy in Production of Formic Acid from CO2. J. Am. Chem. Soc. 2012, 134, 11455−11461. (1581) Yadav, R. K.; Oh, G. H.; Park, N.-J.; Kumar, A.; Kong, K.-j.; Baeg, J.-O. Highly Selective Solar-Driven Methanol from CO2 by a Photocatalyst/Biocatalyst Integrated System. J. Am. Chem. Soc. 2014, 136, 16728−16731. (1582) Noji, T.; Jin, T.; Nango, M.; Kamiya, N.; Amao, Y. CO2 Photoreduction by Formate Dehydrogenase and a Ru-Complex in a Nanoporous Glass Reactor. ACS Appl. Mater. Interfaces 2017, 9, 3260− 3265. (1583) Sakimoto, K. K.; Wong, A. B.; Yang, P. Self-Photosensitization of Nonphotosynthetic Bacteria for Solar-to-Chemical Production. Science 2016, 351, 74−77. (1584) Liu, C.; Colon, B. C.; Ziesack, M.; Silver, P. A.; Nocera, D. G. Water Splitting-Biosynthetic System with CO2 Reduction Efficiencies Exceeding Photosynthesis. Science 2016, 352, 1210−1213. (1585) Ji, X.; Su, Z.; Wang, P.; Ma, G.; Zhang, S. Integration of Artificial Photosynthesis System for Enhanced Electronic EnergyTransfer Efficacy: A Case Study for Solar-Energy Driven Bioconversion of Carbon Dioxide to Methanol. Small 2016, 12, 4753−4762. GX


Chemical Reviews

Review

(1586) Finn, C.; Schnittger, S.; Yellowlees, L. J.; Love, J. B. Molecular Approaches to the Electrochemical Reduction of Carbon Dioxide. Chem. Commun. 2012, 48, 1392−1399. (1587) Heyduk, A. F.; Nocera, D. G. Hydrogen Produced from Hydrohalic Acid Solutions by a Two-Electron Mixed-Valence Photocatalyst. Science 2001, 293, 1639−1641. (1588) Ettedgui, J.; Diskin-Posner, Y.; Weiner, L.; Neumann, R. Photoreduction of Carbon Dioxide to Carbon Monoxide with Hydrogen Catalyzed by a Rhenium(I) Phenanthroline-Polyoxometalate Hybrid Complex. J. Am. Chem. Soc. 2011, 133, 188−190. (1589) Tran, P. D.; Artero, V.; Fontecave, M. Water Electrolysis and Photoelectrolysis on Electrodes Engineered Using Biological and BioInspired Molecular Systems. Energy Environ. Sci. 2010, 3, 727−747. (1590) Genoni, A.; Chirdon, D. N.; Boniolo, M.; Sartorel, A.; Bernhard, S.; Bonchio, M. Tuning Iridium Photocatalysts and Light Irradiation for Enhanced CO2 Reduction. ACS Catal. 2017, 7, 154− 160. (1591) Jin, T.; He, D.; Li, W.; Stanton, C. J.; Pantovich, S. A.; Majetich, G. F.; Schaefer, H. F.; Agarwal, J.; Wang, D. W.; Li, G. H. CO2 Reduction with Re(I)-Nhc Compounds: Driving Selective Catalysis with a Silicon Nanowire Photoelectrode. Chem. Commun. 2016, 52, 14258−14261. (1592) Neri, G.; Forster, M.; Walsh, J. J.; Robertson, C. M.; Whittles, T. J.; Farras, P.; Cowan, A. J. Photochemical CO2 Reduction in Water Using a Co-Immobilised Nickel Catalyst and a Visible Light Sensitiser. Chem. Commun. 2016, 52, 14200−14203. (1593) Sahara, G.; Ishitani, O. Efficient Photocatalysts for CO2 Reduction. Inorg. Chem. 2015, 54, 5096−5104. (1594) Dubois, K. D.; He, H.; Liu, C.; Vorushilov, A. S.; Li, G. Covalent Attachment of a Molecular CO2-Reduction Photocatalyst to Mesoporous Silica. J. Mol. Catal. A: Chem. 2012, 363−364, 208−213. (1595) Takeda, H.; Ohashi, M.; Tani, T.; Ishitani, O.; Inagaki, S. Enhanced Photocatalysis of Rhenium(I) Complex by Light-Harvesting Periodic Mesoporous Organosilica. Inorg. Chem. 2010, 49, 4554−4559. (1596) Ueda, Y.; Takeda, H.; Yui, T.; Koike, K.; Goto, Y.; Inagaki, S.; Ishitani, O. A Visible-Light Harvesting System for CO2 Reduction Using a Ru-II-Re-I Photocatalyst Adsorbed in Mesoporous Organosilica. ChemSusChem 2015, 8, 439−442. (1597) Windle, C. D.; Pastor, E.; Reynal, A.; Whitwood, A. C.; Vaynzof, Y.; Durrant, J. R.; Perutz, R. N.; Reisner, E. Improving the Photocatalytic Reduction of CO2 to CO through Immobilisation of a Molecular Re Catalyst on TiO2. Chem. - Eur. J. 2015, 21, 3746−3754. (1598) Suzuki, T. M.; Takayama, T.; Sato, S.; Iwase, A.; Kudo, A.; Morikawa, T. Enhancement of CO2 Reduction Activity under Visible Light Irradiation over Zn-Based Metal Sulfides by Combination with Ru-Complex Catalysts. Appl. Catal., B 2018, 224, 572−578. (1599) Kuehnel, M. F.; Orchard, K. L.; Dalle, K. E.; Reisner, E. Selective Photocatalytic CO2 Reduction in Water through Anchoring of a Molecular Ni Catalyst on CdS Nanocrystals. J. Am. Chem. Soc. 2017, 139, 7217−7223. (1600) Schreier, M.; Luo, J.; Gao, P.; Moehl, T.; Mayer, M. T.; Gratzel, M. Covalent Immobilization of a Molecular Catalyst on Cu2O Photocathodes for CO2 Reduction. J. Am. Chem. Soc. 2016, 138, 1938−1946. (1601) Kumar, P.; Bansiwal, A.; Labhsetwar, N.; Jain, S. L. Visible Light Assisted Photocatalytic Reduction of CO2 Using a Graphene Oxide Supported Heteroleptic Ruthenium Complex. Green Chem. 2015, 17, 1605−1609. (1602) Kumar, P.; Sain, B.; Jain, S. L. Photocatalytic Reduction of Carbon Dioxide to Methanol Using a Ruthenium Trinuclear Polyazine Complex Immobilized on Graphene Oxide under Visible Light Irradiation. J. Mater. Chem. A 2014, 2, 11246−11253. (1603) Sahara, G.; Kumagai, H.; Maeda, K.; Kaeffer, N.; Artero, V.; Higashi, M.; Abe, R.; Ishitani, O. Photoelectrochemical Reduction of CO2 Coupled to Water Oxidation Using a Photocathode with a Ru(II)−Re(I) Complex Photocatalyst and a CoOx/TaON Photoanode. J. Am. Chem. Soc. 2016, 138, 14152−14158. (1604) Shirai, S.; Sato, S.; Suzuki, T. M.; Jinnouchi, R.; Ohba, N.; Asahi, R.; Morikawa, T. Effects of Ta2O5 Surface Modification by NH3

on the Electronic Structure of a Ru-Complex/N-Ta2O5 Hybrid Photocatalyst for Selective CO2 Reduction. J. Phys. Chem. C 2018, 122, 1921−1929. (1605) Sekizawa, K.; Sato, S.; Arai, T.; Morikawa, T. Solar-Driven Photocatalytic CO2 Reduction in Water Utilizing a Ruthenium Complex Catalyst on P-Type Fe2O3 with a Multiheterojunction. ACS Catal. 2018, 8, 1405−1416. (1606) Liu, X.; Inagaki, S.; Gong, J. Heterogeneous Molecular Systems for Photocatalytic CO2 Reduction with Water Oxidation. Angew. Chem., Int. Ed. 2016, 55, 14924. (1607) Sayama, K.; Mukasa, K.; Abe, R.; Abe, Y.; Arakawa, H. A New Photocatalytic Water Splitting System under Visible Light Irradiation Mimicking a Z-Scheme Mechanism in Photosynthesis. J. Photochem. Photobiol., A 2002, 148, 71−77. (1608) Abe, R.; Sayama, K.; Domen, K.; Arakawa, H. A New Type of Water Splitting System Composed of Two Different TiO2 Photocatalysts (Anatase, Rutile) and a IO3−/I− Shuttle Redox Mediator. Chem. Phys. Lett. 2001, 344, 339−344. (1609) Kuriki, R.; Yamamoto, M.; Higuchi, K.; Yamamoto, Y.; Akatsuka, M.; Lu, D.; Yagi, S.; Yoshida, T.; Ishitani, O.; Maeda, K. Robust Binding between Carbon Nitride Nanosheets and a Binuclear Ruthenium(II) Complex Enabling Durable, Selective CO2 Reduction under Visible Light in Aqueous Solution. Angew. Chem., Int. Ed. 2017, 56, 4867−4871. (1610) Walter, M. G.; Warren, E. L.; McKone, J. R.; Boettcher, S. W.; Mi, Q.; Santori, E. A.; Lewis, N. S. Solar Water Splitting Cells. Chem. Rev. 2010, 110, 6446−6473. (1611) Maeda, K. Z-Scheme Water Splitting Using Two Different Semiconductor Photocatalysts. ACS Catal. 2013, 3, 1486−1503. (1612) Sampson, M. D.; Nguyen, A. D.; Grice, K. A.; Moore, C. E.; Rheingold, A. L.; Kubiak, C. P. Manganese Catalysts with Bulky Bipyridine Ligands for the Electrocatalytic Reduction of Carbon Dioxide: Eliminating Dimerization and Altering Catalysis. J. Am. Chem. Soc. 2014, 136, 5460−5471. (1613) Fei, H.; Sampson, M. D.; Lee, Y.; Kubiak, C. P.; Cohen, S. M. Photocatalytic CO2 Reduction to Formate Using a Mn(I) Molecular Catalyst in a Robust Metal-Organic Framework. Inorg. Chem. 2015, 54, 6821−6828. (1614) Ngo, K. T.; McKinnon, M.; Mahanti, B.; Narayanan, R.; Grills, D. C.; Ertem, M. Z.; Rochford, J. Turning on the ProtonationFirst Pathway for Electrocatalytic CO2 Reduction by Manganese Bipyridyl Tricarbonyl Complexes. J. Am. Chem. Soc. 2017, 139, 2604− 2618. (1615) Torralba-Penalver, E.; Luo, Y.; Compain, J.-D.; ChardonNoblat, S.; Fabre, B. Selective Catalytic Electroreduction of CO2 at Silicon Nanowires (SiNWs) Photocathodes Using Non-Noble MetalBased Manganese Carbonyl Bipyridyl Molecular Catalysts in Solution and Grafted onto Sinws. ACS Catal. 2015, 5, 6138−6147. (1616) Bourrez, M.; Molton, F.; Chardon-Noblat, S.; Deronzier, A. Mn(Bipyridyl)Co3Br: An Abundant Metal Carbonyl Complex as Efficient Electrocatalyst for CO2 Reduction. Angew. Chem., Int. Ed. 2011, 50, 9903−9906. (1617) Angamuthu, R.; Byers, P.; Lutz, M.; Spek, A. L.; Bouwman, E. Electrocatalytic CO2 Conversion to Oxalate by a Copper Complex. Science 2010, 327, 313−315. (1618) Brown, N. J.; Garcia-Trenco, A.; Weiner, J.; White, E. R.; Allinson, M.; Chen, Y.; Wells, P. P.; Gibson, E. K.; Hellgardt, K.; Shaffer, M. S. P.; et al. From Organometallic Zinc and Copper Complexes to Highly Active Colloidal Catalysts for the Conversion of CO2 to Methanol. ACS Catal. 2015, 5, 2895−2902. (1619) Weng, Z.; Jiang, J.; Wu, Y.; Wu, Z.; Guo, X.; Materna, K. L.; Liu, W.; Batista, V. S.; Brudvig, G. W.; Wang, H. Electrochemical CO2 Reduction to Hydrocarbons on a Heterogeneous Molecular Cu Catalyst in Aqueous Solution. J. Am. Chem. Soc. 2016, 138, 8076− 8079. (1620) Thoi, V. S.; Kornienko, N.; Margarit, C. G.; Yang, P. D.; Chang, C. J. Visible-Light Photoredox Catalysis: Selective Reduction of Carbon Dioxide to Carbon Monoxide by a Nickel N-Heterocyclic GY


Chemical Reviews

Review

Carbene-Isoquinoline Complex. J. Am. Chem. Soc. 2013, 135, 14413− 14424. (1621) Burks, D. B.; Davis, S.; Lamb, R. W.; Liu, X.; Rodrigues, R. R.; Liyanage, N. P.; Sun, Y.; Webster, C. E.; Delcamp, J. H.; Papish, E. T. Nickel(II) Pincer Complexes Demonstrate That the Remote Substituent Controls Catalytic Carbon Dioxide Reduction. Chem. Commun. 2018, 54, 3819−3822. (1622) Rios, P.; Rodriguez, A.; Lopez-Serrano, J. Mechanistic Studies on the Selective Reduction of CO2 to the Aldehyde Level by a BiS(Phosphino)Boryl (PBP)-Supported Nickel Complex. ACS Catal. 2016, 6, 5715−5723. (1623) Medina-Ramos, J.; DiMeglio, J. L.; Rosenthal, J. Efficient Reduction of CO2 to CO with High Current Density Using in Situ or Ex Situ Prepared Bi-Based Materials. J. Am. Chem. Soc. 2014, 136, 8361−8367. (1624) Yao, S. A.; Ruther, R. E.; Zhang, L.; Franking, R. A.; Hamers, R. J.; Berry, J. F. Covalent Attachment of Catalyst Molecules to Conductive Diamond: CO2 Reduction Using “Smart” Electrodes. J. Am. Chem. Soc. 2012, 134, 15632−15635. (1625) Zhao, G. X.; Zhou, W.; Sun, Y. B.; Wang, X. K.; Liu, H. M.; Meng, X. G.; Chang, K.; Ye, J. H. Efficient Photocatalytic CO2 Reduction over Co(II) Species Modified CdS in Aqueous Solution. Appl. Catal., B 2018, 226, 252−257. (1626) Chen, L.; Guo, Z.; Wei, X.-G.; Gallenkamp, C.; Bonin, J.; Anxolabehere-Mallart, E.; Lau, K.-C.; Lau, T.-C.; Robert, M. Molecular Catalysis of the Electrochemical and Photochemical Reduction of CO2 with Earth-Abundant Metal Complexes. Selective Production of CO vs HCOOH by Switching of the Metal Center. J. Am. Chem. Soc. 2015, 137, 10918−10921. (1627) Bonin, J.; Maurin, A.; Robert, M. Molecular Catalysis of the Electrochemical and Photochemical Reduction of CO2 with Fe and Co Metal Based Complexes. Recent Advances. Coord. Chem. Rev. 2017, 334, 184−198. (1628) Roy, S.; Sharma, B.; Pecaut, J.; Simon, P.; Fontecave, M.; Tran, P. D.; Derat, E.; Artero, V. Molecular Cobalt Complexes with Pendant Amines for Selective Electrocatalytic Reduction of Carbon Dioxide to Formic Acid. J. Am. Chem. Soc. 2017, 139, 3685−3696. (1629) Elgrishi, N.; Chambers, M. B.; Artero, V.; Fontecave, M. Terpyridine Complexes of First Row Transition Metals and Electrochemical Reduction of CO2 to CO. Phys. Chem. Chem. Phys. 2014, 16, 13635−13644. (1630) Costentin, C.; Drouet, S.; Robert, M.; Savéant, J.-M. A Local Proton Source Enhances CO2 Electroreduction to CO by a Molecular Fe Catalyst. Science 2012, 338, 90−94. (1631) Lian, S. C.; Kodaimati, M. S.; Weiss, E. A. Photocatalytically Active Superstructures of Quantum Dots and Iron Porphyrins for Reduction of CO2 to CO in Water. ACS Nano 2018, 12, 568−575. (1632) Lin, L.; Hou, C. C.; Zhang, X. H.; Wang, Y. J.; Chen, Y.; He, T. Highly Efficient Visible-Light Driven Photocatalytic Reduction of CO2 over g-C3N4 Nanosheets/Tetra(4-Carboxyphenyl)Porphyrin Iron(III) Chloride Heterogeneous Catalysts. Appl. Catal., B 2018, 221, 312−319. (1633) Rao, H.; Schmidt, L. C.; Bonin, J.; Robert, M. Visible-LightDriven Methane Formation from CO2 with a Molecular Iron Catalyst. Nature 2017, 548, 74−77. (1634) Maurin, A.; Robert, M. Noncovalent Immobilization of a Molecular Iron-Based Electrocatalyst on Carbon Electrodes for Selective, Efficient CO2-to-CO Conversion in Water. J. Am. Chem. Soc. 2016, 138, 2492−2495. (1635) Wuttig, A.; Surendranath, Y. Impurity Ion Complexation Enhances Carbon Dioxide Reduction Catalysis. ACS Catal. 2015, 5, 4479−4484. (1636) Elgrishi, N.; Chambers, M. B.; Wang, X.; Fontecave, M. Molecular Polypyridine-Based Metal Complexes as Catalysts for the Reduction of CO2. Chem. Soc. Rev. 2017, 46, 761−796. (1637) Rakowski Dubois, M.; Dubois, D. L. Development of Molecular Electrocatalysts for CO2 Reduction and H2 Production/ Oxidation. Acc. Chem. Res. 2009, 42, 1974−1982.

(1638) Yamazaki, Y.; Takeda, H.; Ishitani, O. Photocatalytic Reduction of CO2 Using Metal Complexes. J. Photochem. Photobiol., C 2015, 25, 106−137. (1639) Diercks, C. S.; Lin, S.; Kornienko, N.; Kapustin, E. A.; Nichols, E. M.; Zhu, C.; Zhao, Y.; Chang, C. J.; Yaghi, O. M. Reticular Electronic Tuning of Porphyrin Active Sites in Covalent Organic Frameworks for Electrocatalytic Carbon Dioxide Reduction. J. Am. Chem. Soc. 2018, 140, 1116−1122. (1640) Bard, A. J.; Fox, M. A. Artificial Photosynthesis: Solar Splitting of Water to Hydrogen and Oxygen. Acc. Chem. Res. 1995, 28, 141−145. (1641) Xiong, Z.; Wang, H.; Xu, N.; Li, H.; Fang, B.; Zhao, Y.; Zhang, J.; Zheng, C. Photocatalytic Reduction of CO2 on Pt2+-Pt0/ TiO2 Nanoparticles under Uv/Vis Light Irradiation: A Combination of Pt2+ Doping and Pt Nanoparticles Deposition. Int. J. Hydrogen Energy 2015, 40, 10049−10062. (1642) Nakanishi, H.; Iizuka, K.; Takayama, T.; Iwase, A.; Kudo, A. Highly Active NaTaO3-Based Photocatalysts for CO2 Reduction to Form CO Using Water as the Electron Donor. ChemSusChem 2017, 10, 112−118. (1643) Takayama, T.; Tanabe, K.; Saito, K.; Iwase, A.; Kudo, A. The KCaSrTa5O15 Photocatalyst with Tungsten Bronze Structure for Water Splitting and CO2 Reduction. Phys. Chem. Chem. Phys. 2014, 16, 24417−24422. (1644) Tahir, M.; Amin, N. A. S. Photo-Induced CO2 Reduction by Hydrogen for Selective CO Evolution in a Dynamic Monolith Photoreactor Loaded with Ag-Modified TiO2 Nanocatalyst. Int. J. Hydrogen Energy 2017, 42, 15507−15522. (1645) Zhao, C. Y.; Krall, A.; Zhao, H. L.; Zhang, Q. Y.; Li, Y. Ultrasonic Spray Pyrolysis Synthesis of Ag/TiO2 Nanocomposite Photocatalysts for Simultaneous H2 Production and CO2 Reduction. Int. J. Hydrogen Energy 2012, 37, 9967−9976. (1646) Tseng, I. H.; Wu, J. C. S. Chemical States of Metal-Loaded Titania in the Photoreduction of CO2. Catal. Today 2004, 97, 113− 119. (1647) Pathak, P.; Meziani, M. J.; Castillo, L.; Sun, Y. P. MetalCoated Nanoscale TiO2 Catalysts for Enhanced CO2 Photoreduction. Green Chem. 2005, 7, 667−670. (1648) Jiao, J. Q.; Wei, Y. C.; Zhao, Y. L.; Zhao, Z.; Duan, A. J.; Liu, J.; Pang, Y. Y.; Li, J. M.; Jiang, G. Y.; Wang, Y. J. AuPd/3DOM-TiO2 Catalysts for Photocatalytic Reduction of CO2 High Efficient Separation of Photogenerated Charge Carriers. Appl. Catal., B 2017, 209, 228−239. (1649) Ovcharov, M. L.; Shvalagin, V. V.; Granchak, V. M. Photocatalytic Reduction of Carbon Dioxide by Water Vapor on Mesoporous Titania Modified by Bimetallic Au/Cu Nanostructures. Theor. Exp. Chem. 2014, 50, 53−58. (1650) Mankidy, B. D.; Joseph, B.; Gupta, V. K. Photo-Conversion of CO2 Using Titanium Dioxide: Enhancements by Plasmonic and CoCatalytic Nanoparticles. Nanotechnology 2013, 24, 405402. (1651) Handoko, A. D.; Tang, J. Controllable Proton and CO2 Photoreduction over Cu2O with Various Morphologies. Int. J. Hydrogen Energy 2013, 38, 13017−13022. (1652) Uzunova, E. L.; Seriani, N.; Mikosch, H. CO2 Conversion to Methanol on Cu(I) Oxide Nanolayers and Clusters: An Electronic Structure Insight into the Reaction Mechanism. Phys. Chem. Chem. Phys. 2015, 17, 11088−11094. (1653) Cheng, M.; Yang, S.; Chen, R.; Zhu, X.; Liao, Q.; Huang, Y. Copper-Decorated TiO2 Nanorod Thin Films in Optofluidic Planar Reactors for Efficient Photocatalytic Reduction of CO2. Int. J. Hydrogen Energy 2017, 42, 9722−9732. (1654) Ola, O.; Mercedes Maroto-Valer, M. Copper Based TiO2 Honeycomb Monoliths for CO2 Photoreduction. Catal. Sci. Technol. 2014, 4, 1631−1637. (1655) Kumar, P.; Naumov, N. G.; Boukherroub, R.; Jain, S. L. Octahedral Rhenium K-4 Re6S8CN6 and Cu(OH)2 Cluster Modified TiO2 for the Photoreduction of CO2 under Visible Light Irradiation. Appl. Catal., A 2015, 499, 32−38. GZ


Chemical Reviews

Review

(1656) Liu, L. J.; Zhao, C. Y.; Miller, J. T.; Li, Y. Mechanistic Study of CO2 Photoreduction with H2O on Cu/TiO2 Nanocomposites by in Situ X-Ray Absorption and Infrared Spectroscopies. J. Phys. Chem. C 2017, 121, 490−499. (1657) Zhang, Q. Y.; Gao, T. T.; Andino, J. M.; Li, Y. Copper and Iodine Co-Modified TiO2 Nanoparticles for Improved Activity of CO2 Photoreduction with Water Vapor. Appl. Catal., B 2012, 123, 257− 264. (1658) Gonell, F.; Puga, A. V.; Julián-López, B.; García, H.; Corma, A. Copper-Doped Titania Photocatalysts for Simultaneous Reduction of CO2 and Production of H2 from Aqueous Sulfide. Appl. Catal., B 2016, 180, 263−270. (1659) In, S. I.; Vaughn, D. D.; Schaak, R. E. Hybrid CuO-TiO2−xNx Hollow Nanocubes for Photocatalytic Conversion of CO2 into Methane under Solar Irradiation. Angew. Chem., Int. Ed. 2012, 51, 3915−3918. (1660) Park, H.; Ou, H.-H.; Colussi, A. J.; Hoffmann, M. R. Artificial Photosynthesis of C1-C3 Hydrocarbons from Water and CO2 on Titanate Nanotubes Decorated with Nanoparticle Elemental Copper and CdS Quantum Dots. J. Phys. Chem. A 2015, 119, 4658−4666. (1661) Asefa, T.; Zhang, T.; Low, J.; Huang, X.; Al-Sharab, J. F.; Yu, J. Copper-Decorated Microsized Nanoporous TiO2 Photocatalysts for CO2 Reduction by H2O. ChemCatChem 2017, 9, 3054−3062. (1662) Shown, I.; Hsu, H.-C.; Chang, Y.-C.; Lin, C.-H.; Roy, P. K.; Ganguly, A.; Wang, C.-H.; Chang, J.-K.; Wu, C.-I.; Chen, L.-C.; et al. Highly Efficient Visible Light Photocatalytic Reduction of CO2 to Hydrocarbon Fuels by Cu-Nanoparticle Decorated Graphene Oxide. Nano Lett. 2014, 14, 6097−6103. (1663) Shi, G.; Yang, L.; Liu, Z.; Chen, X.; Zhou, J.; Yu, Y. Photocatalytic Reduction of CO2 to CO over Copper Decorated gC3N4 Nanosheets with Enhanced Yield and Selectivity. Appl. Surf. Sci. 2018, 427, 1165−1173. (1664) Sen, S.; Liu, D.; Palmore, G. T. R. Electrochemical Reduction of CO2 at Copper Nanofoams. ACS Catal. 2014, 4, 3091−3095. (1665) Tang, W.; Peterson, A. A.; Varela, A. S.; Jovanov, Z. P.; Bech, L.; Durand, W. J.; Dahl, S.; Norskov, J. K.; Chorkendorff, I. The Importance of Surface Morphology in Controlling the Selectivity of Polycrystalline Copper for CO2 Electroreduction. Phys. Chem. Chem. Phys. 2012, 14, 76−81. (1666) Reske, R.; Mistry, H.; Behafarid, F.; Roldan Cuenya, B.; Strasser, P. Particle Size Effects in the Catalytic Electroreduction of CO2 on Cu Nanoparticles. J. Am. Chem. Soc. 2014, 136, 6978−6986. (1667) Xiao, J. P.; Kuc, A.; Frauenheim, T.; Heine, T. CO2 Reduction at Low Overpotential on Cu Electrodes in the Presence of Impurities at the Subsurface. J. Mater. Chem. A 2014, 2, 4885−4889. (1668) Tran, P. D.; Wong, L. H.; Barber, J.; Loo, J. S. C. Recent Advances in Hybrid Photocatalysts for Solar Fuel Production. Energy Environ. Sci. 2012, 5, 5902−5918. (1669) Zhang, Z.; Dua, R.; Zhang, L.; Zhu, H.; Zhang, H.; Wang, P. Carbon Layer Protected Cuprous Oxide Nanowire Arrays for Efficient Water Reduction. ACS Nano 2013, 7, 1709−1717. (1670) Tilley, S. D.; Schreier, M.; Azevedo, J.; Stefik, M.; Graetzel, M. Ruthenium Oxide Hydrogen Evolution Catalysis on Composite Cuprous Oxide Water-Splitting Photocathodes. Adv. Funct. Mater. 2014, 24, 303−311. (1671) Tran, P. D.; Batabyal, S. K.; Pramana, S. S.; Barber, J.; Wong, L. H.; Loo, S. C. J. A Cuprous Oxide-Reduced Graphene Oxide (Cu2O-RGO) Composite Photocatalyst for Hydrogen Generation: Employing RGO as an Electron Acceptor to Enhance the Photocatalytic Activity and Stability of Cu2O. Nanoscale 2012, 4, 3875− 3878. (1672) Hu, C.-C.; Teng, H. Structural Features of P-Type Semiconducting NiO as a Co-Catalyst for Photocatalytic Water Splitting. J. Catal. 2010, 272, 1−8. (1673) Domen, K.; Kudo, A.; Onishi, T. Mechanism of Photocatalytic Decomposition of Water into H2 and O2 over NiO-SrTiO3. J. Catal. 1986, 102, 92−98. (1674) Domen, K.; Kudo, A.; Onishi, T.; Kosugi, N.; Kuroda, H. Photocatalytic Decomposition of Water into Hydrogen and Oxygen

over Nickel(II) Oxide-Strontium Titanate (SrTiO3) Powder. 1. Structure of the Catalysts. J. Phys. Chem. 1986, 90, 292−295. (1675) Lee, D.-S.; Chen, Y.-W. Photocatalytic Reduction of Carbon Dioxide with Water on InVO4 with NiO Cocatalysts. J. CO2 Util. 2015, 10, 1−6. (1676) Maeda, K.; Teramura, K.; Lu, D. L.; Saito, N.; Inoue, Y.; Domen, K. Noble-Metal/Cr2O3 Core/Shell Nanoparticles as a Cocatalyst for Photocatalytic Overall Water Splitting. Angew. Chem., Int. Ed. 2006, 45, 7806−7809. (1677) Maeda, K.; Teramura, K.; Lu, D. L.; Takata, T.; Saito, N.; Inoue, Y.; Domen, K. Photocatalyst Releasing Hydrogen from WaterEnhancing Catalytic Performance Holds Promise for Hydrogen Production by Water Splitting in Sunlight. Nature 2006, 440, 295− 295. (1678) Maeda, K.; Teramura, K.; Lu, D. L.; Saito, N.; Inoue, Y.; Domen, K. Roles of Rh/Cr2O3 (Core/Shell) Nanoparticles Photodeposited on Visible-Light-Responsive (Ga1−xZnx)(N1−xOx) Solid Solutions in Photocatalytic Overall Water Splitting. J. Phys. Chem. C 2007, 111, 7554−7560. (1679) Yoshida, M.; Takanabe, K.; Maeda, K.; Ishikawa, A.; Kubota, J.; Sakata, Y.; Ikezawa, Y.; Domen, K. Role and Function of NobleMetal/Cr-Layer Core/Shell Structure Cocatalysts for Photocatalytic Overall Water Splitting Studied by Model Electrodes. J. Phys. Chem. C 2009, 113, 10151−10157. (1680) Lin, J.; Pan, Z.; Wang, X. Photochemical Reduction of CO2 by Graphitic Carbon Nitride Polymers. ACS Sustainable Chem. Eng. 2014, 2, 353−358. (1681) Wang, T.; Shi, L.; Tang, J.; Malgras, V.; Asahina, S.; Liu, G.; Zhang, H.; Meng, X.; Chang, K.; He, J.; et al. A Co3O4-Embedded Porous ZnO Rhombic Dodecahedron Prepared Using Zeolitic Imidazolate Frameworks as Precursors for CO2 Photoreduction. Nanoscale 2016, 8, 6712−6720. (1682) Wang, S.; Ding, Z.; Wang, X. A Stable ZnCo2O4 Cocatalyst for Photocatalytic CO2 Reduction. Chem. Commun. 2015, 51, 1517− 1519. (1683) Nguyen, T. V.; Wu, J. C. S. Photoreduction of CO2 in an Optical-Fiber Photoreactor: Effects of Metals Addition and Catalyst Carrier. Appl. Catal., A 2008, 335, 112−120. (1684) Luo, D. M.; Bi, Y.; Kan, W.; Zhang, N.; Hong, S. G. Copper and Cerium Co-Doped Titanium Dioxide on Catalytic Photo Reduction of Carbon Dioxide with Water: Experimental and Theoretical Studies. J. Mol. Struct. 2011, 994, 325−331. (1685) Pham, T. D.; Lee, B. K. Novel Photocatalytic Activity of Cu@ V Co-Doped TiO2/Pu for CO2 Reduction with H2O Vapor to Produce Solar Fuels under Visible Light. J. Catal. 2017, 345, 87−95. (1686) Yan, Y. B.; Yu, Y. L.; Huang, S. L.; Yang, Y. J.; Yang, X. D.; Yin, S. G.; Cao, Y. A. Adjustment and Matching of Energy Band of TiO2-Based Photocatalysts by Metal Ions (Pd, Cu, Mn) for Photoreduction of CO2 into CH4. J. Phys. Chem. C 2017, 121, 1089−1098. (1687) Cao, C.; Yan, Y. B.; Yu, Y. L.; Yang, X. D.; Liu, W. S.; Cao, Y. A. Modification of Pd and Mn on the Surface of TiO2 with Enhanced Photocatalytic Activity for Photoreduction of CO2 into CH4. J. Phys. Chem. C 2017, 121, 270−277. (1688) Kornienko, N.; Resasco, J.; Becknell, N.; Jiang, C.-M.; Liu, Y.S.; Nie, K.; Sun, X.; Guo, J.; Leone, S. R.; Yang, P. Operando Spectroscopic Analysis of an Amorphous Cobalt Sulfide Hydrogen Evolution Electrocatalyst. J. Am. Chem. Soc. 2015, 137, 7448−7455. (1689) Faber, M. S.; Lukowski, M. A.; Ding, Q.; Kaiser, N. S.; Jin, S. Earth-Abundant Metal Pyrites (FeS2CoS2NiS2 and Their Alloys) for Highly Efficient Hydrogen Evolution and Polysulfide Reduction Electrocatalysis. J. Phys. Chem. C 2014, 118, 21347−21356. (1690) Faber, M. S.; Dziedzic, R.; Lukowski, M. A.; Kaiser, N. S.; Ding, Q.; Jin, S. High-Performance Electrocatalysis Using Metallic Cobalt Pyrite (CoS2) Micro- and Nanostructures. J. Am. Chem. Soc. 2014, 136, 10053−10061. (1691) Staszak-Jirkovsky, J.; Malliakas, C. D.; Lopes, P. P.; Danilovic, N.; Kota, S. S.; Chang, K.-C.; Genorio, B.; Strmcnik, D.; Stamenkovic, V. R.; Kanatzidis, M. G.; et al. Design of Active and Stable Co-Mo-Sx HA


Chemical Reviews

Review

Chalcogels as Ph-Universal Catalysts for the Hydrogen Evolution Reaction. Nat. Mater. 2016, 15, 197−203. (1692) Kar, P.; Farsinezhad, S.; Zhang, X.; Shankar, K. Anodic Cu2S and CuS Nanorod and Nanowall Arrays: Preparation, Properties and Application in CO2 Photoreduction. Nanoscale 2014, 6, 14305−14318. (1693) Jung, H.; Cho, K. M.; Kim, K. H.; Yoo, H. W.; Al-Saggaf, A.; Gereige, I.; Jung, H. T. Highly Efficient and Stable CO2 Reduction Photocatalyst with a Hierarchical Structure of Mesoporous TiO2 on 3D Graphene with Few-Layered MoS2. ACS Sustainable Chem. Eng. 2018, 6, 5718−5724. (1694) Chan, K.; Tsai, C.; Hansen, H. A.; Nørskov, J. K. Molybdenum Sulfides and Selenides as Possible Electrocatalysts for CO2 Reduction. ChemCatChem 2014, 6, 1899−1905. (1695) Hong, X.; Chan, K.; Tsai, C.; Norskov, J. K. How Doped MoS2 Breaks Transition-Metal Scaling Relations for CO2 Electrochemical Reduction. ACS Catal. 2016, 6, 4428−4437. (1696) Tu, W. G.; Li, Y. C.; Kuai, L. B.; Zhou, Y.; Xu, Q. F.; Li, H. J.; Wang, X. Y.; Xiao, M.; Zou, Z. G. Construction of Unique TwoDimensional MoS2-TiO2 Hybrid Nanojunctions:MoS2 as a Promising Cost-Effective Cocatalyst toward Improved Photocatalytic Reduction of CO2 to Methanol. Nanoscale 2017, 9, 9065−9070. (1697) Zhou, B. W.; Song, J. L.; Xie, C.; Chen, C. J.; Qian, Q. L.; Han, B. X. Mo-Bi-Cd Ternary Metal Chalcogenides: Highly Efficient Photocatalyst for CO2 Reduction to Formic Acid under Visible Light. ACS Sustainable Chem. Eng. 2018, 6, 5754−5759. (1698) Porosoff, M. D.; Yang, X.; Boscoboinik, J. A.; Chen, J. G. Molybdenum Carbide as Alternative Catalysts to Precious Metals for Highly Selective Reduction of CO2 to CO. Angew. Chem., Int. Ed. 2014, 53, 6705−6709. (1699) Gao, J.; Wu, Y.; Jia, C.; Zhong, Z.; Gao, F.; Yang, Y.; Liu, B. Controllable Synthesis of Alpha-MoC1‑x and Beta-Mo2C Nanowires for Highly Selective CO2 Reduction to CO. Catal. Commun. 2016, 84, 147−150. (1700) Porosoff, M. D.; Kattel, S.; Li, W.; Liu, P.; Chen, J. G. Identifying Trends and Descriptors for Selective CO2 Conversion to CO over Transition Metal Carbides. Chem. Commun. 2015, 51, 6988− 6991. (1701) Porosoff, M. D.; Yan, B.; Chen, J. G. Catalytic Reduction of CO2 by H2 for Synthesis of CO, Methanol and Hydrocarbons: Challenges and Opportunities. Energy Environ. Sci. 2016, 9, 62−73. (1702) Naguib, M.; Kurtoglu, M.; Presser, V.; Lu, J.; Niu, J. J.; Heon, M.; Hultman, L.; Gogotsi, Y.; Barsoum, M. W. Two-Dimensional Nanocrystals Produced by Exfoliation of Ti3AlC2. Adv. Mater. 2011, 23, 4248−4253. (1703) Wang, H.; Peng, R.; Hood, Z. D.; Naguib, M.; Adhikari, S. P.; Wu, Z. L. Titania Composites with 2D Transition Metal Carbides as Photocatalysts for Hydrogen Production under Visible-Light Irradiation. ChemSusChem 2016, 9, 1490−1497. (1704) Su, T. M.; Peng, R.; Hood, Z. D.; Naguib, M.; Ivanov, I. N.; Keum, J. K.; Qin, Z. Z.; Guo, Z. H.; Wu, Z. L. One-Step Synthesis of Nb2O5/C/Nb2C (Mxene) Composites and Their Use as Photocatalysts for Hydrogen Evolution. ChemSusChem 2018, 11, 688−699. (1705) Shao, M. M.; Shao, Y. F.; Chai, J. W.; Qu, Y. J.; Yang, M. Y.; Wang, Z. L.; Yang, M.; Ip, W. F.; Kwok, C. T.; Shi, X. Q.; et al. Synergistic Effect of 2D Ti2C and g-C3N4 for Efficient Photocatalytic Hydrogen Production. J. Mater. Chem. A 2017, 5, 16748−16756. (1706) Zhang, H.; Yang, G.; Zuo, X.; Tang, H.; Yang, Q.; Li, G. Computational Studies on the Structural, Electronic and Optical Properties of Graphene-Like Mxenes (M2CT2M = Ti, Zr, Hf; T = O, F, OH) and Their Potential Applications as Visible-Light Driven Photocatalysts. J. Mater. Chem. A 2016, 4, 12913−12920. (1707) Liu, Y.; Xiao, H.; Goddard, W. A., III Schottky-Barrier-Free Contacts with Two-Dimensional Semiconductors by Surface-Engineered Mxenes. J. Am. Chem. Soc. 2016, 138, 15853−15856. (1708) Li, S.; Wang, H.; Li, D.; Zhang, X.; Wang, Y.; Xie, J.; Wang, J.; Tian, Y.; Ni, W.; Xie, Y. Siloxene Nanosheets: A Metal-Free Semiconductor for Water Splitting. J. Mater. Chem. A 2016, 4, 15841−15844.

(1709) Li, N.; Chen, X. Z.; Ong, W. J.; MacFarlane, D. R.; Zhao, X. J.; Cheetham, A. K.; Sun, C. H. Understanding of Electrochemical Mechanisms for CO2 Capture and Conversion into Hydrocarbon Fuels in Transition-Metal Carbides (MXenes). ACS Nano 2017, 11, 10825−10833. (1710) Zhang, R.; Wang, X.; Yu, S.; Wen, T.; Zhu, X.; Yang, F.; Sun, X.; Wang, X.; Hu, W. Ternary NiCo2PX Nanowires as Ph-Universal Electrocatalysts for Highly Efficient Hydrogen Evolution Reaction. Adv. Mater. 2017, 29, 1605502. (1711) Popczun, E. J.; McKone, J. R.; Read, C. G.; Biacchi, A. J.; Wiltrout, A. M.; Lewis, N. S.; Schaak, R. E. Nanostructured Nickel Phosphide as an Electrocatalyst for the Hydrogen Evolution Reaction. J. Am. Chem. Soc. 2013, 135, 9267−9270. (1712) Weng, B.; Wei, W.; Yiliguma; Wu, H.; Alenizi, A. M.; Zheng, G. Bifunctional CoP and CoN Porous Nanocatalysts Derived from ZIF-67 in Situ Grown on Nanowire Photoelectrodes for Efficient Photoelectrochemical Water Splitting and CO2 Reduction. J. Mater. Chem. A 2016, 4, 15353−15360. (1713) Pan, Y.; Chen, Y.; Lin, Y.; Cui, P.; Sun, K.; Liu, Y.; Liu, C. Cobalt Nickel Phosphide Nanoparticles Decorated Carbon Nanotubes as Advanced Hybrid Catalysts for Hydrogen Evolution. J. Mater. Chem. A 2016, 4, 14675−14686. (1714) Anantharaj, S.; Ede, S. R.; Sakthikumar, K.; Karthick, K.; Mishra, S.; Kundu, S. Recent Trends and Perspectives in Electrochemical Water Splitting with an Emphasis on Sulfide, Selenide, and Phosphide Catalysts of Fe, Co, and Ni: A Review. ACS Catal. 2016, 6, 8069−8097. (1715) Hao, J.; Yang, W.; Huang, Z.; Zhang, C. Superhydrophilic and Superaerophobic Copper Phosphide Microsheets for Efficient Electrocatalytic Hydrogen and Oxygen Evolution. Adv. Mater. Interfaces 2016, 3, 1600236. (1716) Park, H.; Encinas, A.; Scheifers, J. P.; Zhang, Y.; Fokwa, B. P. T. Boron-Dependency of Molybdenum Boride Electrocatalysts for the Hydrogen Evolution Reaction. Angew. Chem., Int. Ed. 2017, 56, 5575− 5578. (1717) Benson, E. E.; Kubiak, C. P.; Sathrum, A. J.; Smieja, J. M. Electrocatalytic and Homogeneous Approaches to Conversion of CO2 to Liquid Fuels. Chem. Soc. Rev. 2009, 38, 89−99. (1718) Yan, Y.; Zeitler, E. L.; Gu, J.; Hu, Y.; Bocarsly, A. B. Electrochemistry of Aqueous Pyridinium: Exploration of a Key Aspect of Electrocatalytic Reduction of CO2 to Methanol. J. Am. Chem. Soc. 2013, 135, 14020−14023. (1719) Oh, Y.; Hu, X. Organic Molecules as Mediators and Catalysts for Photocatalytic and Electrocatalytic CO2 Reduction. Chem. Soc. Rev. 2013, 42, 2253−2261. (1720) Keith, J. A.; Carter, E. A. Theoretical Insights into Pyridinium-Based Photoelectrocatalytic Reduction of CO2. J. Am. Chem. Soc. 2012, 134, 7580−7583. (1721) Xiang, Q.; Yu, J. Graphene-Based Photocatalysts for Hydrogen Generation. J. Phys. Chem. Lett. 2013, 4, 753−759. (1722) Xiang, Q. J.; Yu, J. G.; Jaroniec, M. Graphene-Based Semiconductor Photocatalysts. Chem. Soc. Rev. 2012, 41, 782−796. (1723) Zhou, X.; Gao, Q.; Li, X.; Liu, Y.; Zhang, S.; Fang, Y.; Li, J. Ultra-Thin SiC Layer Covered Graphene Nanosheets as Advanced Photocatalysts for Hydrogen Evolution. J. Mater. Chem. A 2015, 3, 10999−11005. (1724) Sun, H. Q.; Wang, S. B. Research Advances in the Synthesis of Nanocarbon-Based Photocatalysts and Their Applications for Photocatalytic Conversion of Carbon Dioxide to Hydrocarbon Fuels. Energy Fuels 2014, 28, 22−36. (1725) Gui, M. M.; Chai, S.-P.; Xu, B.-Q.; Mohamed, A. R. Enhanced Visible Light Responsive MWCNT/TiO2 Core−Shell Nanocomposites as the Potential Photocatalyst for Reduction of CO2 into Methane. Sol. Energy Mater. Sol. Cells 2014, 122, 183−189. (1726) Ding, J.; Bu, Y. F.; Ou, M.; Yu, Y.; Zhong, Q.; Fan, M. H. Facile Decoration of Carbon Fibers with Ag Nanoparticles for Adsorption and Photocatalytic Reduction of CO2. Appl. Catal., B 2017, 202, 314−325. HB


Chemical Reviews

Review

(1727) Liu, L. J. Controllable ZnO Nanorod Arrays@Carbon Fibers Composites: Towards Advanced CO2 Photocatalytic Reduction Catalysts. Ceram. Int. 2016, 42, 12516−12520. (1728) Aoi, S.; Mase, K.; Ohkubo, K.; Fukuzumi, S. Photocatalytic Reduction of CO2 and H2O to CO and H2 with a Cobalt Chlorin Complex Adsorbed on Multi-Walled Carbon Nanotubes. Catal. Sci. Technol. 2016, 6, 4077−4080. (1729) Wang, Y.; Cai, Q.; Yao, M.; Kang, S.; Ge, Z.; Li, X. Easy Synthesis of Ordered Mesoporous Carbon−Carbon Nanotube Nanocomposite as a Promising Support for CO2 Photoreduction. ACS Sustainable Chem. Eng. 2018, 6, 2529−2534. (1730) Wadas, A.; Rutkowska, I. A.; Gorczynski, A.; Kubicki, M.; Patroniak, V.; Kulesza, P. J. Fabrication of Nanostructured Palladium within Tridentate Schiff-Base-Ligand Coordination Architecture: Enhancement of Electrocatalytic Activity toward CO2 Electroreduction. Electrocatalysis 2014, 5, 229−234. (1731) Sim, L. C.; Leong, K. H.; Saravanan, P.; Ibrahim, S. Rapid Thermal Reduced Graphene Oxide/Pt-TiO2 Nanotube Arrays for Enhanced Visible-Light-Driven Photocatalytic Reduction of CO2. Appl. Surf. Sci. 2015, 358, 122−129. (1732) Tan, L.-L.; Ong, W.-J.; Chai, S.-P.; Mohamed, A. R. Noble Metal Modified Reduced Graphene Oxide/TiO2 Ternary Nanostructures for Efficient Visible-Light-Driven Photoreduction of Carbon Dioxide into Methane. Appl. Catal., B 2015, 166, 251−259. (1733) Liu, H.; Zhang, H.; Shen, P.; Chen, F.; Zhang, S. Synergistic Effects in Nanoengineered HnB3O8/Graphene Hybrids with Improved Photocatalytic Conversion Ability of CO2 into Renewable Fuels. Langmuir 2016, 32, 254−264. (1734) Xing, M. Y.; Shen, F.; Qiu, B. C.; Zhang, J. L. HighlyDispersed Boron-Doped Graphene Nanosheets Loaded with TiO2 Nanoparticles for Enhancing CO2Photoreduction. Sci. Rep. 2015, 4, 6341. (1735) Wang, A. L.; Li, X. S.; Zhao, Y. B.; Wu, W.; Chen, J. F.; Meng, H. Preparation and Characterizations of Cu2O/Reduced Graphene Oxide Nanocomposites with High Photo-Catalytic Performances. Powder Technol. 2014, 261, 42−48. (1736) Hou, J.; Cheng, H.; Takeda, O.; Zhu, H. Three-Dimensional Bimetal-Graphene-Semiconductor Coaxial Nanowire Arrays to Harness Charge Flow for the Photochemical Reduction of Carbon Dioxide. Angew. Chem., Int. Ed. 2015, 54, 8480−8484. (1737) Lv, X. J.; Fu, W. F.; Hu, C. Y.; Chen, Y.; Zhou, W. B. Photocatalytic Reduction of CO2 with H2O over a Graphene-Modified NiOx-Ta2O5 Composite Photocatalyst: Coupling Yields of Methanol and Hydrogen. RSC Adv. 2013, 3, 1753−1757. (1738) Li, X. S.; Wang, Q. A.; Zhao, Y. B.; Wu, W.; Chen, J. F.; Meng, H. Green Synthesis and Photo-Catalytic Performances for ZnO-Reduced Graphene Oxide Nanocomposites. J. Colloid Interface Sci. 2013, 411, 69−75. (1739) Yadav, R. K.; Baeg, J.-O.; Kumar, A.; Kong, K.-j.; Oh, G. H.; Park, N.-J. Graphene-BODIPY as a Photocatalyst in the Photocatalytic-Biocatalytic Coupled System for Solar Fuel Production from CO2. J. Mater. Chem. A 2014, 2, 5068−5076. (1740) Cui, S.-C.; Sun, X.-Z.; Liu, J.-G. Photo-Reduction of CO2 Using a Rhenium Complex Covalently Supported on a Graphene/ TiO2 Composite. ChemSusChem 2016, 9, 1698−1703. (1741) Li, F.; Zhang, L.; Tong, J.; Liu, Y.; Xu, S.; Cao, Y.; Cao, S. Photocatalytic CO2 Conversion to Methanol by Cu2O/Graphene/ TNA Heterostructure Catalyst in a Visible-Light-Driven DualChamber Reactor. Nano Energy 2016, 27, 320−329. (1742) Kumar, P.; Joshi, C.; Barras, A.; Sieber, B.; Addad, A.; Boussekey, L.; Szunerits, S.; Boukherroub, R.; Jain, S. L. Core−Shell Structured Reduced Graphene Oxide Wrapped Magnetically Separable RGO@CuZnO@Fe3O4 Microspheres as Superior Photocatalyst for CO2Reduction under Visible Light. Appl. Catal., B 2017, 205, 654− 665. (1743) Lin, L.-Y.; Nie, Y.; Kavadiya, S.; Soundappan, T.; Biswas, P. N-Doped Reduced Graphene Oxide Promoted Nano TiO2 as a Bifunctional Adsorbent/Photocatalyst for CO2Photoreduction: Effect of N Species. Chem. Eng. J. 2017, 316, 449−460.

(1744) Liu, J.; Niu, Y.; He, X.; Qi, J.; Li, X. Photocatalytic Reduction of CO2 Using TiO2-Graphene Nanocomposites. J. Nanomater. 2016, 2016, 6012896. (1745) Liu, L. J.; Jin, F. Y. Hybrid Zno Nanorod Arrays@Graphene through a Facile Room-Temperature Bipolar Solution Route Towards Advanced CO2 Photocatalytic Reduction Properties. Ceram. Int. 2017, 43, 860−865. (1746) Zhang, Q.; Lin, C.-F.; Chen, B.-Y.; Ouyang, T.; Chang, C.-T. Deciphering Visible Light Photoreductive Conversion of CO2 to Formic Acid and Methanol Using Waste Prepared Material. Environ. Sci. Technol. 2015, 49, 2405−2417. (1747) Baeissa, E. S. Green Synthesis of Methanol by Photocatalytic Reduction of CO2 under Visible Light Using a Graphene and Tourmaline Co-Doped Titania Nanocomposites. Ceram. Int. 2014, 40, 12431−12438. (1748) Gusain, R.; Kumar, P.; Sharma, O. P.; Jain, S. L.; Khatri, O. P. Reduced Graphene Oxide−CuO Nanocomposites for Photocatalytic Conversion of CO2 into Methanol under Visible Light Irradiation. Appl. Catal., B 2016, 181, 352−362. (1749) Kumar, P.; Mungse, H. P.; Cordier, S.; Boukherroub, R.; Khatri, O. P.; Jain, S. L. Hexamolybdenum Clusters Supported on Graphene Oxide: Visible-Light Induced Photocatalytic Reduction of Carbon Dioxide into Methanol. Carbon 2015, 94, 91−100. (1750) Piao, M.; Liu, N.; Wang, Y.; Feng, C. Efficiently Converting CO2 into C2H4 Using a Porphyrin-Graphene Composite Photocatalyst. Aust. J. Chem. 2016, 69, 27−32. (1751) Tan, L. L.; Ong, W. J.; Chai, S. P.; Mohamed, A. R. Reduced Graphene Oxide-TiO2 Nanocomposite as a Promising Visible-LightActive Photocatalyst for the Conversion of Carbon Dioxide. Nanoscale Res. Lett. 2013, 8, 465. (1752) Tan, L.-L.; Ong, W.-J.; Chai, S.-P.; Goh, B. T.; Mohamed, A. R. Visible-Light-Active Oxygen-Rich TiO2 Decorated 2D Graphene Oxide with Enhanced Photocatalytic Activity toward Carbon Dioxide Reduction. Appl. Catal., B 2015, 179, 160−170. (1753) Wang, H.; Raziq, F.; Qu, Y.; Qin, C.; Wang, J.; Jing, L. Role of Quaternary N in N-Doped Graphene-Fe2O3 Nanocomposites as Efficient Photocatalysts for CO2 Reduction and Acetaldehyde Degradation. RSC Adv. 2015, 5, 85061−85064. (1754) Wang, W.-N.; Jiang, Y.; Fortner, J. D.; Biswas, P. Nanostructured Graphene-Titanium Dioxide Composites Synthesized by a Single-Step Aerosol Process for Photoreduction of Carbon Dioxide. Environ. Eng. Sci. 2014, 31, 428−434. (1755) Yang, K. D.; Ha, Y.; Sim, U.; An, J.; Lee, C. W.; Jin, K.; Kim, Y.; Park, J.; Hong, J. S.; Lee, J. H.; et al. Graphene Quantum Sheet Catalyzed Silicon Photocathode for Selective CO2 Conversion to CO. Adv. Funct. Mater. 2016, 26, 233−242. (1756) Zhang, L.; Li, N.; Jiu, H.; Qi, G.; Huang, Y. Zno-Reduced Graphene Oxide Nanocomposites as Efficient Photocatalysts for Photocatalytic Reduction of CO2. Ceram. Int. 2015, 41, 6256−6262. (1757) Yan, Y.; Chen, J.; Li, N.; Tian, J.; Li, K.; Jiang, J.; Liu, J.; Tian, Q.; Chen, P. Systematic Bandgap Engineering of Graphene Quantum Dots and Applications for Photocatalytic Water Splitting and CO2 Reduction. ACS Nano 2018, 12, 3523−3532. (1758) Cho, K. M.; Kim, K. H.; Park, K.; Kim, C.; Kim, S.; Al-Saggaf, A.; Gereige, I.; Jung, H. T. Amine-Functionalized Graphene/CdS Composite for Photocatalytic Reduction of CO2. ACS Catal. 2017, 7, 7064−7069. (1759) Qiao, X.; Li, Q.; Schaugaard, R. N.; Noffke, B. W.; Liu, Y.; Li, D.; Liu, L.; Raghavachari, K.; Li, L.-s. Well-Defined Nanographene− Rhenium Complex as an Efficient Electrocatalyst and Photocatalyst for Selective CO2 Reduction. J. Am. Chem. Soc. 2017, 139, 3934−3937. (1760) Hasan, M. R.; Hamid, S. B. A.; Basirun, W. J. Charge Transfer Behavior of Graphene-Titania Photoanode in CO2 Photoelectrocatalysis Process. Appl. Surf. Sci. 2015, 339, 22−27. (1761) Sahu, S.; Liu, Y.; Wang, P.; Bunker, C. E.; Fernando, K. A. S.; Lewis, W. K.; Guliants, E. A.; Yang, F.; Wang, J.; Sun, Y.-P. VisibleLight Photoconversion of Carbon Dioxide into Organic Acids in an Aqueous Solution of Carbon Dots. Langmuir 2014, 30, 8631−8636. HC


Chemical Reviews

Review

(1762) Kong, X. Y.; Tan, W. L.; Ng, B.-J.; Chai, S.-P.; Mohamed, A. R. Harnessing Vis−Nir Broad Spectrum for Photocatalytic CO2 Reduction over Carbon Quantum Dots-Decorated Ultrathin Bi2WO6 Nanosheets. Nano Res. 2017, 10, 1720−1731. (1763) Li, H.; Zhang, X.; MacFarlane, D. R. Carbon Quantum Dots/ Cu2O Heterostructures for Solar-Light-Driven Conversion of CO2 to Methanol. Adv. Energy Mater. 2015, 5, 1401077. (1764) Ong, W.-J.; Putri, L. K.; Tan, Y.-C.; Tan, L.-L.; Li, N.; Ng, Y. H.; Wen, X.; Chai, S.-P. Unravelling Charge Carrier Dynamics in Protonated g-C3N4 Interfaced with Carbon Nanodots as Co-Catalysts toward Enhanced Photocatalytic CO2 Reduction: A Combined Experimental and First-Principles Dft Study. Nano Res. 2017, 10, 1673−1696. (1765) Wang, Y.; Bai, X.; Qin, H.; Wang, F.; Li, Y.; Li, X.; Kang, S.; Zuo, Y.; Cui, L. Facile One-Step Synthesis of Hybrid Graphitic Carbon Nitride and Carbon Composites as High-Performance Catalysts for CO2 Photocatalytic Conversion. ACS Appl. Mater. Interfaces 2016, 8, 17212−17219. (1766) Yadav, R. K.; Kumar, A.; Park, N.-J.; Yadav, D.; Baeg, J.-O. New Carbon Nanodots-Silica Hybrid Photocatalyst for Highly Selective Solar Fuel Production from CO2. ChemCatChem 2017, 9, 3153−3159. (1767) Wang, W.; Xu, D.; Cheng, B.; Yu, J.; Jiang, C. Hybrid Carbon@TiO2 Hollow Spheres with Enhanced Photocatalytic CO2 Reduction Activity. J. Mater. Chem. A 2017, 5, 5020−5029. (1768) Lin, L.-Y.; Kavadiya, S.; Karakocak, B. B.; Nie, Y.; Raliya, R.; Wang, S. T.; Berezin, M. Y.; Biswas, P. ZnO1−x/Carbon Dots Composite Hollow Spheres: Facile Aerosol Synthesis and Superior CO2 Photoreduction under Uv, Visible and near-Infrared Irradiation. Appl. Catal., B 2018, 230, 36−48. (1769) Zhang, H.; Wang, T.; Wang, J.; Liu, H.; Dao, T. D.; Li, M.; Liu, G.; Meng, X.; Chang, K.; Shi, L.; et al. Surface-Plasmon-Enhanced Photodriven CO2Reduction Catalyzed by Metal-Organic-FrameworkDerived Iron Nanoparticles Encapsulated by Ultrathin Carbon Layers. Adv. Mater. 2016, 28, 3703−3710. (1770) Kongkanand, A.; Martínez Domínguez, R.; Kamat, P. V. Single Wall Carbon Nanotube Scaffolds for Photoelectrochemical Solar Cells. Capture and Transport of Photogenerated Electrons. Nano Lett. 2007, 7, 676−680. (1771) Kim, Y. K.; Park, H. Light-Harvesting Multi-Walled Carbon Nanotubes and CdS Hybrids: Application to Photocatalytic Hydrogen Production from Water. Energy Environ. Sci. 2011, 4, 685−694. (1772) Ago, H.; Kugler, T.; Cacialli, F.; Salaneck, W. R.; Shaffer, M. S. P.; Windle, A. H.; Friend, R. H. Work Functions and Surface Functional Groups of Multiwall Carbon Nanotubes. J. Phys. Chem. B 1999, 103, 8116−8121. (1773) D’Souza, F.; Ito, O. Photosensitized Electron Transfer Processes of Nanocarbons Applicable to Solar Cells. Chem. Soc. Rev. 2012, 41, 86−96. (1774) Silva, C. G.; Faria, J. L. Photocatalytic Oxidation of Phenolic Compounds by Using a Carbon Nanotube-Titanium Dioxide Composite Catalyst. ChemSusChem 2010, 3, 609−618. (1775) Saleh, T. A.; Gupta, V. K. Photo-Catalyzed Degradation of Hazardous Dye Methyl Orange by Use of a Composite Catalyst Consisting of Multi-Walled Carbon Nanotubes and Titanium Dioxide. J. Colloid Interface Sci. 2012, 371, 101−106. (1776) Kang, P.; Zhang, S.; Meyer, T. J.; Brookhart, M. Rapid Selective Electrocatalytic Reduction of Carbon Dioxide to Formate by an Iridium Pincer Catalyst Immobilized on Carbon Nanotube Electrodes. Angew. Chem., Int. Ed. 2014, 53, 8709−8713. (1777) Sastre, F.; Corma, A.; Garcia, H. 185 nm Photoreduction of CO2 to Methane by Water. Influence of the Presence of a Basic Catalyst. J. Am. Chem. Soc. 2012, 134, 14137−14141. (1778) Andreiadis, E. S.; Jacques, P.-A.; Tran, P. D.; Leyris, A.; Chavarot-Kerlidou, M.; Jousselme, B.; Matheron, M.; Pecaut, J.; Palacin, S.; Fontecave, M.; et al. Molecular Engineering of a CobaltBased Electrocatalytic Nanomaterial for H2 Evolution under Fully Aqueous Conditions. Nat. Chem. 2013, 5, 48−53.

(1779) Gui, M. M.; Chai, S.-P.; Xu, B.-Q.; Mohamed, A. R. VisibleLight-Driven MWCNT@TiO2 Core-Shell Nanocomposites and the Roles of Mwcnts on the Surface Chemistry, Optical Properties and Reactivity in CO2 Photoreduction. RSC Adv. 2014, 4, 24007−24013. (1780) Zhao, Y.; Yang, L.; Chen, S.; Wang, X.; Ma, Y.; Wu, Q.; Jiang, Y.; Qian, W.; Hu, Z. Can Boron and Nitrogen Co-Doping Improve Oxygen Reduction Reaction Activity of Carbon Nanotubes? J. Am. Chem. Soc. 2013, 135, 1201−1204. (1781) Zhao, Y.; Nakamura, R.; Kamiya, K.; Nakanishi, S.; Hashimoto, K. Nitrogen-Doped Carbon Nanomaterials as NonMetal Electrocatalysts for Water Oxidation. Nat. Commun. 2013, 4, 2390. (1782) Chen, Y.; Tian, G.; Ren, Z.; Pan, K.; Shi, Y.; Wang, J.; Fu, H. Hierarchical Core-Shell Carbon Nanofiber@ZnIn2S4 Composites for Enhanced Hydrogen Evolution Performance. ACS Appl. Mater. Interfaces 2014, 6, 13841−13849. (1783) Ju, Y.-W.; Yoo, S.; Kim, C.; Kim, S.; Jeon, I.-Y.; Shin, J.; Baek, J.-B.; Kim, G. Fe@N-Graphene Nanoplatelet-Embedded Carbon Nanofibers as Efficient Electrocatalysts for Oxygen Reduction Reaction. Advanced Science 2016, 3, 1500205. (1784) Zhang, J.; Huang, F. Enhanced Visible Light Photocatalytic H2 Production Activity of g-C3N4 Via Carbon Fiber. Appl. Surf. Sci. 2015, 358, 287−295. (1785) Xiang, Q.; Yu, J.; Jaroniec, M. Enhanced Photocatalytic H2Production Activity of Graphene-Modified Titania Nanosheets. Nanoscale 2011, 3, 3670−3678. (1786) Lightcap, I. V.; Kosel, T. H.; Kamat, P. V. Anchoring Semiconductor and Metal Nanoparticles on a Two-Dimensional Catalyst Mat. Storing and Shuttling Electrons with Reduced Graphene Oxide. Nano Lett. 2010, 10, 577−583. (1787) Williams, G.; Seger, B.; Kamat, P. V. TiO2-Graphene Nanocomposites. Uv-Assisted Photocatalytic Reduction of Graphene Oxide. ACS Nano 2008, 2, 1487−1491. (1788) Li, Q.; Guo, B. D.; Yu, J. G.; Ran, J. R.; Zhang, B. H.; Yan, H. J.; Gong, J. R. Highly Efficient Visible-Light-Driven Photocatalytic Hydrogen Production of CdS-Cluster-Decorated Graphene Nanosheets. J. Am. Chem. Soc. 2011, 133, 10878−10884. (1789) Zhang, J.; Qi, L.; Ran, J.; Yu, J.; Qiao, S. Z. Ternary NiS/ ZnxCd1‑xS/Reduced Graphene Oxide Nanocomposites for Enhanced Solar Photocatalytic H2-Production Activity. Adv. Energy Mater. 2014, 4, 1301925. (1790) Tamura, J.; Ono, A.; Sugano, Y.; Huang, C.; Nishizawa, H.; Mikoshiba, S. Electrochemical Reduction of CO2 to Ethylene Glycol on Imidazolium Ion-Terminated Self-Assembly Monolayer-Modified Au Electrodes in an Aqueous Solution. Phys. Chem. Chem. Phys. 2015, 17, 26072−26078. (1791) Upadhyay, R. K.; Soin, N.; Roy, S. S. Role of Graphene/Metal Oxide Composites as Photocatalysts, Adsorbents and Disinfectants in Water Treatment: A Review. RSC Adv. 2014, 4, 3823−3851. (1792) Yang, M.-Q.; Xu, Y.-J. Photocatalytic Conversion of CO2 over Graphene-Based Composites: Current Status and Future Perspective. Nanoscale Horizons 2016, 1, 185−200. (1793) An, X.; Yu, X.; Yu, J. C.; Zhang, G. CdS Nanorods/Reduced Graphene Oxide Nanocomposites for Photocatalysis and Electrochemical Sensing. J. Mater. Chem. A 2013, 1, 5158−5164. (1794) Zhang, J.; Yu, J.; Jaroniec, M.; Gong, J. R. Noble Metal-Free Reduced Graphene Oxide-ZnxCd1‑XS Nanocomposite with Enhanced Solar Photocatalytic H2-Production Performance. Nano Lett. 2012, 12, 4584−4589. (1795) Hsu, H. C.; Shown, I.; Wei, H. Y.; Chang, Y. C.; Du, H. Y.; Lin, Y. G.; Tseng, C. A.; Wang, C. H.; Chen, L. C.; Lin, Y. C.; et al. Graphene Oxide as a Promising Photocatalyst for CO2 to Methanol Conversion. Nanoscale 2013, 5, 262−268. (1796) Li, W.; Jiang, X.; Yang, H.; Liu, Q. Solvothermal Synthesis and Enhanced CO2 Adsorption Ability of Mesoporous Graphene Oxide-ZnO Nanocomposite. Appl. Surf. Sci. 2015, 356, 812−816. (1797) Tit, N.; Said, K.; Mahmoud, N. M.; Kouser, S.; Yamani, Z. H. Ab-Initio Investigation of Adsorption of CO and CO2 Molecules on HD


Chemical Reviews

Review

Graphene: Role of Intrinsic Defects on Gas Sensing. Appl. Surf. Sci. 2017, 394, 219−230. (1798) Li, W.; Yang, H.; Jiang, X.; Liu, Q. Highly Selective CO2 Adsorption of ZnO Based N-Doped Reduced Graphene Oxide Porous Nanomaterial. Appl. Surf. Sci. 2016, 360, 143−147. (1799) Hou, J. G.; Cao, S. Y.; Wu, Y. Z.; Liang, F.; Ye, L.; Lin, Z. S.; Sun, L. C. Perovskite-Based Nanocubes with Simultaneously Improved Visible-Light Absorption and Charge Separation Enabling Efficient Photocatalytic CO2 Reduction. Nano Energy 2016, 30, 59−68. (1800) Putri, L. K.; Ong, W.-J.; Chang, W. S.; Chai, S.-P. Heteroatom Doped Graphene in Photocatalysis: A Review. Appl. Surf. Sci. 2015, 358, 2−14. (1801) Zhou, D.; Cheng, Q.-Y.; Cui, Y.; Wang, T.; Li, X.; Han, B.-H. Graphene-Terpyridine Complex Hybrid Porous Material for Carbon Dioxide Adsorption. Carbon 2014, 66, 592−598. (1802) Song, K. S.; Coskun, A. Catalyst-Free Synthesis of Porous Graphene Networks as Efficient Sorbents for CO2 and H2. ChemPlusChem 2015, 80, 1127−1132. (1803) Chowdhury, S.; Balasubramanian, R. Three-Dimensional Graphene-Based Porous Adsorbents for Postcombustion CO 2 Capture. Ind. Eng. Chem. Res. 2016, 55, 7906−7916. (1804) Parshetti, G. K.; Chowdhury, S.; Balasubramanian, R. Plant Derived Porous Graphene Nanosheets for Efficient CO2Capture. RSC Adv. 2014, 4, 44634−44643. (1805) Zhang, X.; Huang, H.; Liu, J.; Liu, Y.; Kang, Z. Carbon Quantum Dots Serving as Spectral Converters through Broadband Upconversion of near-Infrared Photons for Photoelectrochemical Hydrogen Generation. J. Mater. Chem. A 2013, 1, 11529−11533. (1806) Li, Q.; Cui, C.; Meng, H.; Yu, J. Visible-Light Photocatalytic Hydrogen Production Activity of ZnIn2S4 Microspheres Using Carbon Quantum Dots and Platinum as Dual Cocatalysts. Chem. - Asian J. 2014, 9, 1766−1770. (1807) Sun, Y.-P.; Zhou, B.; Lin, Y.; Wang, W.; Fernando, K. A. S.; Pathak, P.; Meziani, M. J.; Harruff, B. A.; Wang, X.; Wang, H.; et al. Quantum-Sized Carbon Dots for Bright and Colorful Photoluminescence. J. Am. Chem. Soc. 2006, 128, 7756−7757. (1808) Liu, J.; Liu, Y.; Liu, N.; Han, Y.; Zhang, X.; Huang, H.; Lifshitz, Y.; Lee, S.-T.; Zhong, J.; Kang, Z. Metal-Free Efficient Photocatalyst for Stable Visible Water Splitting via a Two-Electron Pathway. Science 2015, 347, 970−974. (1809) Hu, Y.; Gao, X.; Yu, L.; Wang, Y.; Ning, J.; Xu, S.; Lou, X. W. Carbon-Coated CdS Petalous Nanostructures with Enhanced Photostability and Photocatalytic Activity. Angew. Chem. 2013, 125, 5746− 5749. (1810) Martindale, B. C. M.; Hutton, G. A. M.; Caputo, C. A.; Prantl, S.; Godin, R.; Durrant, J. R.; Reisner, E. Enhancing Light Absorption and Charge Transfer Efficiency in Carbon Dots through Graphitization and Core Nitrogen Doping. Angew. Chem., Int. Ed. 2017, 56, 6459−6463. (1811) Varela, A. S.; Ranjbar Sahraie, N.; Steinberg, J.; Ju, W.; Oh, H.-S.; Strasser, P. Metal-Doped Nitrogenated Carbon as an Efficient Catalyst for Direct CO2 Electroreduction to CO and Hydrocarbons. Angew. Chem., Int. Ed. 2015, 54, 10758−10762. (1812) Huan, T. N.; Ranjbar, N.; Rousse, G.; Sougrati, M.; Zitolo, A.; Mougel, V.; Jaouen, F.; Fontecave, M. Electrochemical Reduction of CO2 Catalyzed by Fe-N-C Materials: A Structure-Selectivity Study. ACS Catal. 2017, 7, 1520−1525. (1813) Li, X. G.; Bi, W. T.; Chen, M. L.; Sun, Y. X.; Ju, H. X.; Yan, W. S.; Zhu, J. F.; Wu, X. J.; Chu, W. S.; Wu, C. Z.; et al. Exclusive NiN-4 Sites Realize near-Unity CO Selectivity for Electrochemical CO2 Reduction. J. Am. Chem. Soc. 2017, 139, 14889−14892. (1814) Varela, A. S.; Kroschel, M.; Leonard, N. D.; Ju, W.; Steinberg, J.; Bagger, A.; Rossmeisl, J.; Strasser, P. Ph Effects on the Selectivity of the Electrocatalytic CO2 Reduction on Graphene-Embedded Fe−N− C Motifs: Bridging Concepts between Molecular Homogeneous and Solid-State Heterogeneous Catalysis. ACS Energy Letters 2018, 3, 812− 817. (1815) Pan, F.; Zhang, H.; Liu, K.; Cullen, D.; More, K.; Wang, M.; Feng, Z.; Wang, G.; Wu, G.; Li, Y. Unveiling Active Sites of CO2

Reduction on Nitrogen-Coordinated and Atomically Dispersed Iron and Cobalt Catalysts. ACS Catal. 2018, 8, 3116−3122. (1816) Ju, W.; Bagger, A.; Hao, G. P.; Varela, A. S.; Sinev, I.; Bon, V.; Roldan Cuenya, B.; Kaskel, S.; Rossmeisl, J.; Strasser, P. Understanding Activity and Selectivity of Metal-Nitrogen-Doped Carbon Catalysts for Electrochemical Reduction of CO2. Nat. Commun. 2017, 8, 944. (1817) Lessio, M.; Senftle, T. P.; Carter, E. A. Is the Surface Playing a Role During Pyridine-Catalyzed CO2 Reduction on P-GaP Photoelectrodes? ACS Energy Letters 2016, 1, 464−468. (1818) Keith, J. A.; Carter, E. A. Theoretical Insights into Electrochemical CO2Reduction Mechanisms Catalyzed by SurfaceBound Nitrogen Heterocycles. J. Phys. Chem. Lett. 2013, 4, 4058− 4063. (1819) Keith, J. A.; Carter, E. A. Correction to “Theoretical Insights into Electrochemical CO2 Reduction Mechanisms Catalyzed by Surface-Bound Nitrogen Heterocycles. J. Phys. Chem. Lett. 2015, 6, 568−568. (1820) Lim, C.-H.; Holder, A. M.; Hynes, J. T.; Musgrave, C. B. Reduction of CO2 to Methanol Catalyzed by a Biomimetic OrganoHydride Produced from Pyridine. J. Am. Chem. Soc. 2014, 136, 16081− 16095. (1821) Lessio, M.; Carter, E. A. What Is the Role of Pyridinium in Pyridine-Catalyzed CO2 Reduction on P-GaP Photocathodes? J. Am. Chem. Soc. 2015, 137, 13248−13251. (1822) Lim, C.-H.; Holder, A. M.; Hynes, J. T.; Musgrave, C. B. Catalytic Reduction of CO2 by Renewable Organohydrides. J. Phys. Chem. Lett. 2015, 6, 5078−5092. (1823) Muñoz-García, A. B.; Carter, E. A. Non-Innocent Dissociation of H2O on GaP(110): Implications for Electrochemical Reduction of CO2. J. Am. Chem. Soc. 2012, 134, 13600−13603. (1824) Kronawitter, C. X.; Lessio, M.; Zhao, P.; Riplinger, C.; Boscoboinik, A.; Starr, D. E.; Sutter, P.; Carter, E. A.; Koel, B. E. Observation of Surface-Bound Negatively Charged Hydride and Hydroxide on Gap(110) in H2O Environments. J. Phys. Chem. C 2015, 119, 17762−17772. (1825) Senftle, T. P.; Lessio, M.; Carter, E. A. Interaction of Pyridine and Water with the Reconstructed Surfaces of GaP(111) and CdTe(111) Photoelectrodes: Implications for CO2 Reduction. Chem. Mater. 2016, 28, 5799−5810. (1826) Lim, C. H.; Holder, A. M.; Musgrave, C. B. Mechanism of Homogeneous Reduction of CO2 by Pyridine: Proton Relay in Aqueous Solvent and Aromatic Stabilization. J. Am. Chem. Soc. 2013, 135, 142−154. (1827) Lv, T.; Pan, L. K.; Liu, X. J.; Sun, Z. Enhanced Photocatalytic Degradation of Methylene Blue by ZnO-Reduced Graphene OxideCarbon Nanotube Composites Synthesized Via Microwave-Assisted Reaction. Catal. Sci. Technol. 2012, 2, 2297−2301. (1828) Wang, C.; Cao, M. H.; Wang, P. F.; Ao, Y. H.; Hou, J.; Qian, J. Preparation of Graphene-Carbon Nanotube-TiO2 Composites with Enhanced Photocatalytic Activity for the Removal of Dye and Cr (Vi). Appl. Catal., A 2014, 473, 83−89. (1829) Zhang, L. L.; Xiong, Z. G.; Zhao, X. S. Pillaring Chemically Exfoliated Graphene Oxide with Carbon Nanotubes for Photocatalytic Degradation of Dyes under Visible Light Irradiation. ACS Nano 2010, 4, 7030−7036. (1830) Yu, Y. L.; Zheng, W. J.; Cao, Y. A. TiO2-Pd/C Composited Photocatalyst with Improved Photocatalytic Activity for Photoreduction of CO2 into CH4. New J. Chem. 2017, 41, 3204−3210. (1831) Gui, M. M.; Wong, W. M. P.; Chai, S.-P.; Mohamed, A. R. One-Pot Synthesis of Ag-MWCNT@TiO2 Core-Shell Nanocomposites for Photocatalytic Reduction of CO2 with Water under Visible Light Irradiation. Chem. Eng. J. 2015, 278, 272−278. (1832) Ong, W. J.; Gui, M. M.; Chai, S. P.; Mohamed, A. R. Direct Growth of Carbon Nanotubes on Ni/TiO2 as Next Generation Catalysts for Photoreduction of CO2 to Methane by Water under Visible Light Irradiation. RSC Adv. 2013, 3, 4505−4509. (1833) Le Goff, A.; Artero, V.; Jousselme, B.; Tran, P. D.; Guillet, N.; Métayé, R.; Fihri, A.; Palacin, S.; Fontecave, M. From Hydrogenases to HE


Chemical Reviews

Review

Noble Metal−Free Catalytic Nanomaterials for H2 Production and Uptake. Science 2009, 326, 1384−1387. (1834) Kang, P.; Cheng, C.; Chen, Z.; Schauer, C. K.; Meyer, T. J.; Brookhart, M. Selective Electrocatalytic Reduction of CO2 to Formate by Water-Stable Iridium Dihydride Pincer Complexes. J. Am. Chem. Soc. 2012, 134, 5500−5503. (1835) Kang, P.; Meyer, T. J.; Brookhart, M. Selective Electrocatalytic Reduction of Carbon Dioxide to Formate by a Water-Soluble Iridium Pincer Catalyst. Chem. Sci. 2013, 4, 3497−3502. (1836) Sanz, R.; Calleja, G.; Arencibia, A.; Sanz-Perez, E. S. Development of High Efficiency Adsorbents for CO2 Capture Based on a Double-Functionalization Method of Grafting and Impregnation. J. Mater. Chem. A 2013, 1, 1956−1962. (1837) Li, L.; Zhang, S.; Xu, L.; Wang, J.; Shi, L.-X.; Chen, Z.-N.; Hong, M.; Luo, J. Effective Visible-Light Driven CO2 Photoreduction Via a Promising Bifunctional Iridium Coordination Polymer. Chem. Sci. 2014, 5, 3808−3813. (1838) Lee, Y.; Kim, S.; Kang, J. K.; Cohen, S. M. Photocatalytic CO2 Reduction by a Mixed Metal (Zr/Ti), Mixed Ligand Metal-Organic Framework under Visible Light Irradiation. Chem. Commun. 2015, 51, 5735−5738. (1839) Dhakshinamoorthy, A.; Asiri, A. M.; Garcia, H. Metal-Organic Framework (MOF) Compounds: Photocatalysts for Redox Reactions and Solar Fuel Production. Angew. Chem., Int. Ed. 2016, 55, 5414− 5445. (1840) Yadav, R. K.; Kumar, A.; Park, N.-J.; Kong, K.-J.; Baeg, J.-O. A Highly Efficient Covalent Organic Framework Film Photocatalyst for Selective Solar Fuel Production from CO2. J. Mater. Chem. A 2016, 4, 9413−9418. (1841) Wang, D.; Huang, R.; Liu, W.; Sun, D.; Li, Z. Fe-Based MOFs for Photocatalytic CO2 Reduction: Role of Coordination Unsaturated Sites and Dual Excitation Pathways. ACS Catal. 2014, 4, 4254−4260. (1842) Sadeghi, N.; Sharifnia, S.; Sheikh Arabi, M. A PorphyrinBased Metal Organic Framework for High Rate Photoreduction of CO2 to CH4 in Gas Phase. J. CO2 Util. 2016, 16, 450−457. (1843) Wang, S.; Wang, X. Imidazolium Ionic Liquids, Imidazolylidene Heterocyclic Carbenes, and Zeolitic Imidazolate Frameworks for CO2 Capture and Photochemical Reduction. Angew. Chem., Int. Ed. 2016, 55, 2308−2320. (1844) Chen, Y.; Wang, D. K.; Deng, X. Y.; Li, Z. H. Metal-Organic Frameworks (MOFs) for Photocatalytic CO2 Reduction. Catal. Sci. Technol. 2017, 7, 4893−4904. (1845) Sun, M. Y.; Yan, S. Y.; Sun, Y. J.; Yang, X. H.; Guo, Z. F.; Du, J. F.; Chen, D. S.; Chen, P.; Xing, H. Z. Enhancement of Visible-LightDriven CO2 Reduction Performance Using an Amine-Functionalized Zirconium Metal-Organic Framework. Dalton Trans. 2018, 47, 909− 915. (1846) Xu, H.-Q.; Hu, J.; Wang, D.; Li, Z.; Zhang, Q.; Luo, Y.; Yu, S.H.; Jiang, H.-L. Visible-Light Photoreduction of CO2 in a MetalOrganic Framework: Boosting Electron-Hole Separation Via Electron Trap States. J. Am. Chem. Soc. 2015, 137, 13440−13443. (1847) Chen, D.; Xing, H.; Wang, C.; Su, Z. Highly Efficient VisibleLight-Driven CO2Reduction to Formate by a New Anthracene-Based Zirconium MOF Via Dual Catalytic Routes. J. Mater. Chem. A 2016, 4, 2657−2662. (1848) Kajiwara, T.; Fujii, M.; Tsujimoto, M.; Kobayashi, K.; Higuchi, M.; Tanaka, K.; Kitagawa, S. Photochemical Reduction of Low Concentrations of CO2 in a Porous Coordination Polymer with a Ruthenium(II)-Co Complex. Angew. Chem., Int. Ed. 2016, 55, 2697− 2700. (1849) Zhao, J.; Wang, Q.; Sun, C. Y.; Zheng, T. T.; Yan, L. K.; Li, M. T.; Shao, K. Z.; Wang, X. L.; Su, Z. M. A Hexanuclear Cobalt Metal-Organic Framework for Efficient CO2 Reduction under Visible Light. J. Mater. Chem. A 2017, 5, 12498−12505. (1850) Logan, M. W.; Ayad, S.; Adamson, J. D.; Dilbeck, T.; Hanson, K.; Uribe-Romo, F. J. Systematic Variation of the Optical Bandgap in Titanium Based Isoreticular Metal-Organic Frameworks for Photocatalytic Reduction of CO2 under Blue Light. J. Mater. Chem. A 2017, 5, 11854−11863.

(1851) Kornienko, N.; Zhao, Y.; Kley, C. S.; Zhu, C.; Kim, D.; Lin, S.; Chang, C. J.; Yaghi, O. M.; Yang, P. Metal-Organic Frameworks for Electrocatalytic Reduction of Carbon Dioxide. J. Am. Chem. Soc. 2015, 137, 14129−14135. (1852) Pipelzadeh, E.; Rudolph, V.; Hanson, G.; Noble, C.; Wang, L. Z. Photoreduction of CO2 on ZIF-8/TiO2 Nanocomposites in a Gaseous Photoreactor under Pressure Swing. Appl. Catal., B 2017, 218, 672−678. (1853) Liu, S.; Chen, F.; Li, S.; Peng, X.; Xiong, Y. Enhanced Photocatalytic Conversion of Greenhouse Gas CO2 into Solar Fuels over g-C3N4 Nanotubes with Decorated Transparent ZIF-8 Nanoclusters. Appl. Catal., B 2017, 211, 1−10. (1854) Wang, S.; Yao, W.; Lin, J.; Ding, Z.; Wang, X. Cobalt Imidazolate Metal−Organic Frameworks Photosplit CO2 under Mild Reaction Conditions. Angew. Chem., Int. Ed. 2014, 53, 1034−1038. (1855) Li, R.; Hu, J.; Deng, M.; Wang, H.; Wang, X.; Hu, Y.; Jiang, H.-L.; Jiang, J.; Zhang, Q.; Xie, Y.; et al. Integration of an Inorganic Semiconductor with a Metal−Organic Framework: A Platform for Enhanced Gaseous Photocatalytic Reactions. Adv. Mater. 2014, 26, 4783−4788. (1856) He, X.; Gan, Z. R.; Fisenko, S.; Wang, D. W.; El-Kaderi, H. M.; Wang, W. N. Rapid Formation of Metal-Organic Frameworks (MOFs) Based Nanocomposites in Microdroplets and Their Applications for CO2 Photoreduction. ACS Appl. Mater. Interfaces 2017, 9, 9688−9698. (1857) Sheberla, D.; Bachman, J. C.; Elias, J. S.; Sun, C. J.; ShaoHorn, Y.; Dinca, M. Conductive MOF Electrodes for Stable Supercapacitors with High Areal Capacitance. Nat. Mater. 2017, 16, 220−224. (1858) Feng, D. W.; Lei, T.; Lukatskaya, M. R.; Park, J.; Huang, Z. H.; Lee, M.; Shaw, L.; Chen, S. C.; Yakovenko, A. A.; Kulkarni, A.; et al. Robust and Conductive Two-Dimensional Metal-Organic Frameworks with Exceptionally High Volumetric and Areal Capacitance. Nature Energy 2018, 3, 30−36. (1859) Kumari, G.; Zhang, X.; Devasia, D.; Heo, J.; Jain, P. K. Watching Visible Light-Driven CO2 Reduction on a Plasmonic Nanoparticle Catalyst. ACS Nano 2018, 12, 8330−8340. (1860) Liu, E.; Hu, Y.; Li, H.; Tang, C.; Hu, X.; Fan, J.; Chen, Y.; Bian, J. Photoconversion of CO2 to Methanol over Plasmonic Ag/ TiO2 Nano-Wire Films Enhanced by Overlapped Visible-LightHarvesting Nanostructures. Ceram. Int. 2015, 41, 1049−1057. (1861) Low, J. X.; Qiu, S. Q.; Xu, D. F.; Jiang, C. J.; Cheng, B. Direct Evidence and Enhancement of Surface Plasmon Resonance Effect on Ag-Loaded TiO2 Nanotube Arrays for Photocatalytic CO2 Reduction. Appl. Surf. Sci. 2018, 434, 423−432. (1862) He, Z.-Q.; Tong, L.-L.; Zhang, Z.-P.; Chen, J.-M.; Song, S. Ag/Ag2WO4 Plasmonic Catalyst for Photocatalytic Reduction of CO2 under Visible Light. Acta Phys-Chim. Sin. 2015, 31, 2341−2348. (1863) Yu, S.; Huang, H.; Dong, F.; Li, M.; Tian, N.; Zhang, T.; Zhang, Y. Synchronously Achieving Plasmonic Bi Metal Deposition and I-Doping by Utilizing BiOIO3 as the Self-Sacrificing Template for High-Performance Multifunctional Applications. ACS Appl. Mater. Interfaces 2015, 7, 27925−27933. (1864) Knight, M. W.; King, N. S.; Liu, L.; Everitt, H. O.; Nordlander, P.; Halas, N. J. Aluminum for Plasmonics. ACS Nano 2014, 8, 834−840. (1865) Ramadurgam, S.; Lin, T.-G.; Yang, C. Aluminum Plasmonics for Enhanced Visible Light Absorption and High Efficiency Water Splitting in Core−Multishell Nanowire Photoelectrodes with Ultrathin Hematite Shells. Nano Lett. 2014, 14, 4517−4522. (1866) Hao, Q.; Wang, C.; Huang, H.; Li, W.; Du, D.; Han, D.; Qiu, T.; Chu, P. K. Aluminum Plasmonic Photocatalysis. Sci. Rep. 2015, 5, 15288. (1867) Zhou, L.; Zhang, C.; McClain, M. J.; Manjavacas, A.; Krauter, C. M.; Tian, S.; Berg, F.; Everitt, H. O.; Carter, E. A.; Nordlander, P.; et al. Aluminum Nanocrystals as a Plasmonic Photocatalyst for Hydrogen Dissociation. Nano Lett. 2016, 16, 1478−1484. HF


Chemical Reviews

Review

Conversion Efficiency for Photothermal Ablation of Cancer Cells in Vivo. ACS Nano 2011, 5, 9761−9771. (1886) Tian, Q. W.; Tang, M. H.; Sun, Y. G.; Zou, R. J.; Chen, Z. G.; Zhu, M. F.; Yang, S. P.; Wang, J. L.; Wang, J. H.; Hu, J. Q. Hydrophilic Flower-Like CuS Superstructures as an Efficient 980 nm Laser-Driven Photothermal Agent for Ablation of Cancer Cells. Adv. Mater. 2011, 23, 3542−3547. (1887) Yang, K.; Hu, L. L.; Ma, X. X.; Ye, S. Q.; Cheng, L.; Shi, X. Z.; Li, C. H.; Li, Y. G.; Liu, Z. Multimodal Imaging Guided Photothermal Therapy Using Functionalized Graphene Nanosheets Anchored with Magnetic Nanoparticles. Adv. Mater. 2012, 24, 1868−1872. (1888) Robinson, J. T.; Tabakman, S. M.; Liang, Y. Y.; Wang, H. L.; Sanchez Casalongue, H.; Vinh, D.; Dai, H. J. Ultrasmall Reduced Graphene Oxide with High near-Infrared Absorbance for Photothermal Therapy. J. Am. Chem. Soc. 2011, 133, 6825−6831. (1889) Tian, B.; Wang, C.; Zhang, S.; Feng, L. Z.; Liu, Z. Photothermally Enhanced Photodynamic Therapy Delivered by Nano-Graphene Oxide. ACS Nano 2011, 5, 7000−7009. (1890) Akhavan, O.; Ghaderi, E.; Aghayee, S.; Fereydooni, Y.; Talebi, A. The Use of a Glucose-Reduced Graphene Oxide Suspension for Photothermal Cancer Therapy. J. Mater. Chem. 2012, 22, 13773− 13781. (1891) Akhavan, O.; Ghaderi, E. Graphene Nanomesh Promises Extremely Efficient in Vivo Photothermal Therapy. Small 2013, 9, 3593−3601. (1892) Gan, Z. X.; Wu, X. L.; Meng, M.; Zhu, X. B.; Yang, L.; Chu, P. K. Photothermal Contribution to Enhanced Photocatalytic Performance of Graphene-Based Nanocomposites. ACS Nano 2014, 8, 9304− 9310. (1893) Abdellah, M.; El-Zohry, A. M.; Antila, L. J.; Windle, C. D.; Reisner, E.; Hammarstrom, L. Time-Resolved IR Spectroscopy Reveals a Mechanism with TiO2 as a Reversible Electron Acceptor in a TiO2Re Catalyst System for CO2 Photoreduction. J. Am. Chem. Soc. 2017, 139, 1226−1232. (1894) Byeon, J. H.; Kim, Y. W. Au-TiO2 Nanoscale Heterodimers Synthesis from an Ambient Spark Discharge for Efficient Photocatalytic and Photothermal Activity. ACS Appl. Mater. Interfaces 2014, 6, 763−767. (1895) Nikitenko, S. I.; Chave, T.; Cau, C.; Brau, H. P.; Flaud, V. Photothermal Hydrogen Production Using Noble-Metal-Free Ti@ TiO2 Core-Shell Nanoparticles under Visible-NIR Light Irradiation. ACS Catal. 2015, 5, 4790−4795. (1896) Hoch, L. B.; O’Brien, P. G.; Jelle, A.; Sandhel, A.; Perovic, D. D.; Mims, C. A.; Ozin, G. A. Nanostructured Indium Oxide Coated Silicon Nanowire Arrays: A Hybrid Photothermal/Photochemical Approach to Solar Fuels. ACS Nano 2016, 10, 9017−9025. (1897) Wang, F. F.; Huang, Y. J.; Chai, Z. G.; Zeng, M.; Li, Q.; Wang, Y.; Xu, D. S. Photothermal-Enhanced Catalysis in Core-Shell Plasmonic Hierarchical Cu7S4 Microsphere@Zeolitic Imidazole Framework-8. Chem. Sci. 2016, 7, 6887−6893. (1898) Ha, M. N.; Lu, G.; Liu, Z.; Wang, L.; Zhao, Z. 3DOMLaSrCoFeO6‑δ as a Highly Active Catalyst for the Thermal and Photothermal Reduction of CO2 with H2O to CH4. J. Mater. Chem. A 2016, 4, 13155−13165. (1899) Ren, J.; Ouyang, S.; Xu, H.; Meng, X.; Wang, T.; Wang, D.; Ye, J. Targeting Activation of CO2 and H2 over Ru-Loaded Ultrathin Layered Double Hydroxides to Achieve Efficient Photothermal CO2 Methanation in Flow-Type System. Adv. Energy Mater. 2017, 7, 1601657. (1900) Jia, J.; O’Brien, P. G.; He, L.; Qiao, Q.; Fei, T.; Reyes, L. M.; Burrow, T. E.; Dong, Y. C.; Liao, K.; Varela, M.; et al. Visible and nearInfrared Photothermal Catalyzed Hydrogenation of Gaseous CO2 over Nanostructured Pd@Nb2O5. Advanced Science 2016, 3, 1600189. (1901) Low, J.; Zhang, L.; Zhu, B.; Liu, Z.; Yu, J. TiO2 Photonic Crystals with Localized Surface Photothermal Effect and Enhanced Photocatalytic CO2 Reduction Activity. ACS Sustainable Chem. Eng. 2018, 6, 15653. (1902) Barber, J. Photosynthetic Energy Conversion: Natural and Artificial. Chem. Soc. Rev. 2009, 38, 185−196.

(1868) Zhang, Z.; Huang, J.; Fang, Y.; Zhang, M.; Liu, K.; Dong, B. A Nonmetal Plasmonic Z-Scheme Photocatalyst with Uv- to Nir-Driven Photocatalytic Protons Reduction. Adv. Mater. 2017, 29, 1606688. (1869) Lu, N.; Zhang, Z.; Wang, Y.; Liu, B.; Guo, L.; Wang, L.; Huang, J.; Liu, K.; Dong, B. Direct Evidence of IR-Driven Hot Electron Transfer in Metal-Free Plasmonic W18O49/Carbon Heterostructures for Enhanced Catalytic H2 Production. Appl. Catal., B 2018, 233, 19−25. (1870) Zhang, Z.; Jiang, X.; Liu, B.; Guo, L.; Lu, N.; Wang, L.; Huang, J.; Liu, K.; Dong, B. IR-Driven Ultrafast Transfer of Plasmonic Hot Electrons in Nonmetallic Branched Heterostructures for Enhanced H2Generation. Adv. Mater. 2018, 30, 1705221. (1871) Liu, L.; Zhong, H.; Bai, Z.; Zhang, T.; Fu, W.; Shi, L.; Xie, H.; Deng, L.; Zou, B. Controllable Transformation from Rhombohedral Cu1.8S Nanocrystals to Hexagonal CuS Clusters: Phase- and Composition-Dependent Plasmonic Properties. Chem. Mater. 2013, 25, 4828−4834. (1872) Zhao, Y.; Pan, H.; Lou, Y.; Qiu, X.; Zhu, J.; Burda, C. Plasmonic Cu2−xS Nanocrystals: Optical and Structural Properties of Copper-Deficient Copper(I) Sulfides. J. Am. Chem. Soc. 2009, 131, 4253−4261. (1873) Alsaif, M. M. Y. A.; Chrimes, A. F.; Daeneke, T.; Balendhran, S.; Bellisario, D. O.; Son, Y.; Field, M. R.; Zhang, W.; Nili, H.; Nguyen, E. P.; et al. High-Performance Field Effect Transistors Using Electronic Inks of 2D Molybdenum Oxide Nanoflakes. Adv. Funct. Mater. 2016, 26, 91−100. (1874) Alsaif, M. M. Y. A.; Latham, K.; Field, M. R.; Yao, D. D.; Medehkar, N. V.; Beane, G. A.; Kaner, R. B.; Russo, S. P.; Ou, J. Z.; Kalantar-Zadeh, K. Tunable Plasmon Resonances in Two-Dimensional Molybdenum Oxide Nanoflakes. Adv. Mater. 2014, 26, 3931−3937. (1875) Yin, H.; Kuwahara, Y.; Mori, K.; Cheng, H.; Wen, M.; Yamashita, H. High-Surface-Area Plasmonic MoO3‑xRational Synthesis and Enhanced Ammonia Borane Dehydrogenation Activity. J. Mater. Chem. A 2017, 5, 8946−8953. (1876) Lou, Z.; Kim, S.; Zhang, P.; Shi, X.; Fujitsuka, M.; Majima, T. In Situ Observation of Single Au Triangular Nanoprism Etching to Various Shapes for Plasmonic Photocatalytic Hydrogen Generation. ACS Nano 2017, 11, 968−974. (1877) Cortie, M. B.; McDonagh, A. M. Synthesis and Optical Properties of Hybrid and Alloy Plasmonic Nanoparticles. Chem. Rev. 2011, 111, 3713−3735. (1878) Boyer, D.; Tamarat, P.; Maali, A.; Lounis, B.; Orrit, M. Photothermal Imaging of Nanometer-Sized Metal Particles among Scatterers. Science 2002, 297, 1160−1163. (1879) Huang, X. H.; El-Sayed, I. H.; Qian, W.; El-Sayed, M. A. Cancer Cell Imaging and Photothermal Therapy in the near-Infrared Region by Using Gold Nanorods. J. Am. Chem. Soc. 2006, 128, 2115− 2120. (1880) Nam, J.; Won, N.; Jin, H.; Chung, H.; Kim, S. Ph-Induced Aggregation of Gold Nanoparticles for Photothermal Cancer Therapy. J. Am. Chem. Soc. 2009, 131, 13639−13645. (1881) Chen, J. Y.; Glaus, C.; Laforest, R.; Zhang, Q.; Yang, M. X.; Gidding, M.; Welch, M. J.; Xia, Y. N. Gold Nanocages as Photothermal Transducers for Cancer Treatment. Small 2010, 6, 811−817. (1882) Shi Kam, N. W.; O’Connell, M.; Wisdom, J. A.; Dai, H. J. Carbon Nanotubes as Multifunctional Biological Transporters and near-Infrared Agents for Selective Cancer Cell Destruction. Proc. Natl. Acad. Sci. U. S. A. 2005, 102, 11600−11605. (1883) Moon, H. K.; Lee, S. H.; Choi, H. C. In Vivo near-Infrared Mediated Tumor Destruction by Photothermal Effect of Carbon Nanotubes. ACS Nano 2009, 3, 3707−3713. (1884) Zhou, M.; Zhang, R.; Huang, M. A.; Lu, W.; Song, S. L.; Melancon, M. P.; Tian, M.; Liang, D.; Li, C. A Chelator-Free Multifunctional [64Cu]CuS Nanoparticle Platform for Simultaneous Micro-Pet/Ct Imaging and Photothermal Ablation Therapy. J. Am. Chem. Soc. 2010, 132, 15351−15358. (1885) Tian, Q. W.; Jiang, F. R.; Zou, R. J.; Liu, Q.; Chen, Z. G.; Zhu, M. F.; Yang, S. P.; Wang, J. L.; Wang, J. H.; Hu, J. Q. Hydrophilic Cu9S5 Nanocrystals: A Photothermal Agent with a 25.7% Heat HG


Chemical Reviews

Review

(1903) Fillol, J. L.; Codolà, Z.; Garcia-Bosch, I.; Gómez, L.; Pla, J. J.; Costas, M. Efficient Water Oxidation Catalysts Based on Readily Available Iron Coordination Complexes. Nat. Chem. 2011, 3, 807− 813. (1904) Toma, F. M.; Sartorel, A.; Iurlo, M.; Carraro, M.; Parisse, P.; Maccato, C.; Rapino, S.; Gonzalez, B. R.; Amenitsch, H.; Da Ros, T.; et al. Efficient Water Oxidation at Carbon Nanotube−Polyoxometalate Electrocatalytic Interfaces. Nat. Chem. 2010, 2, 826−831. (1905) Yin, Q.; Tan, J. M.; Besson, C.; Geletii, Y. V.; Musaev, D. G.; Kuznetsov, A. E.; Luo, Z.; Hardcastle, K. I.; Hill, C. L. A Fast Soluble Carbon-Free Molecular Water Oxidation Catalyst Based on Abundant Metals. Science 2010, 328, 342−345. (1906) Liang, Y.; Li, Y.; Wang, H.; Dai, H. Strongly Coupled Inorganic/Nanocarbon Hybrid Materials for Advanced Electrocatalysis. J. Am. Chem. Soc. 2013, 135, 2013−2036. (1907) Hurst, J. K. In Pursuit of Water Oxidation Catalysts for Solar Fuel Production. Science 2010, 328, 315−316. (1908) Rosen, J.; Hutchings, G. S.; Jiao, F. Ordered Mesoporous Cobalt Oxide as Highly Efficient Oxygen Evolution Catalyst. J. Am. Chem. Soc. 2013, 135, 4516−4521. (1909) Reece, S. Y.; Hamel, J. A.; Sung, K.; Jarvi, T. D.; Esswein, A. J.; Pijpers, J. J. H.; Nocera, D. G. Wireless Solar Water Splitting Using Silicon-Based Semiconductors and Earth-Abundant Catalysts. Science 2011, 334, 645−648. (1910) Smith, R. D. L.; Prévot, M. S.; Fagan, R. D.; Zhang, Z.; Sedach, P. A.; Siu, M. K. J.; Trudel, S.; Berlinguette, C. P. Photochemical Route for Accessing Amorphous Metal Oxide Materials for Water Oxidation Catalysis. Science 2013, 340, 60−63. (1911) Hu, X. L.; Cossairt, B. M.; Brunschwig, B. S.; Lewis, N. S.; Peters, J. C. Electrocatalytic Hydrogen Evolution by Cobalt Difluoroboryl-Diglyoximate Complexes. Chem. Commun. 2005, 41, 4723−4725. (1912) Cobo, S.; Heidkamp, J.; Jacques, P.-A.; Fize, J.; Fourmond, V.; Guetaz, L.; Jousselme, B.; Ivanova, V.; Dau, H.; Palacin, S.; et al. A Janus Cobalt-Based Catalytic Material for Electro-Splitting of Water. Nat. Mater. 2012, 11, 802−807. (1913) Liang, Y.; Li, Y.; Wang, H.; Zhou, J.; Wang, J.; Regier, T.; Dai, H. Co3O4 Nanocrystals on Graphene as a Synergistic Catalyst for Oxygen Reduction Reaction. Nat. Mater. 2011, 10, 780−786. (1914) Zhang, G.; Zang, S.; Wang, X. Layered Co(OH)2 Deposited Polymeric Carbon Nitrides for Photocatalytic Water Oxidation. ACS Catal. 2015, 5, 941−947. (1915) Zhang, F.; Yamakata, A.; Maeda, K.; Moriya, Y.; Takata, T.; Kubota, J.; Teshima, K.; Oishi, S.; Domen, K. Cobalt-Modified Porous Single-Crystalline LaTiO2N for Highly Efficient Water Oxidation under Visible Light. J. Am. Chem. Soc. 2012, 134, 8348−8351. (1916) Li, R.; Chen, Z.; Zhao, W.; Zhang, F.; Maeda, K.; Huang, B.; Shen, S.; Domen, K.; Li, C. Sulfurization-Assisted Cobalt Deposition on Sm2Ti2S2O5 Photocatalyst for Water Oxidation under Visible Light Irradiation. J. Phys. Chem. C 2013, 117, 376−382. (1917) Higashi, M.; Domen, K.; Abe, R. Highly Stable Water Splitting on Oxynitride Taon Photoanode System under Visible Light Irradiation. J. Am. Chem. Soc. 2012, 134, 6968−6971. (1918) Ma, S. S. K.; Hisatomi, T.; Maeda, K.; Moriya, Y.; Domen, K. Enhanced Water Oxidation on Ta3N5 Photocatalysts by Modification with Alkaline Metal Salts. J. Am. Chem. Soc. 2012, 134, 19993−19996. (1919) Zhang, J. S.; Grzelczak, M.; Hou, Y. D.; Maeda, K.; Domen, K.; Fu, X. Z.; Antonietti, M.; Wang, X. C. Photocatalytic Oxidation of Water by Polymeric Carbon Nitride Nanohybrids Made of Sustainable Elements. Chem. Sci. 2012, 3, 443−446. (1920) Grätzel, M. Artificial Photosynthesis: Water Cleavage into Hydrogen and Oxygen by Visible Light. Acc. Chem. Res. 1981, 14, 376−384. (1921) Maeda, K.; Xiong, A. K.; Yoshinaga, T.; Ikeda, T.; Sakamoto, N.; Hisatomi, T.; Takashima, M.; Lu, D. L.; Kanehara, M.; Setoyama, T.; et al. Photocatalytic Overall Water Splitting Promoted by Two Different Cocatalysts for Hydrogen and Oxygen Evolution under Visible Light. Angew. Chem., Int. Ed. 2010, 49, 4096−4099.

(1922) Ma, S. S. K.; Maeda, K.; Abe, R.; Domen, K. Visible-LightDriven Nonsacrificial Water Oxidation over Tungsten Trioxide Powder Modified with Two Different Cocatalysts. Energy Environ. Sci. 2012, 5, 8390−8397. (1923) Huang, L.; Wang, X.; Yang, J.; Liu, G.; Han, J.; Li, C. Dual Cocatalysts Loaded Type I CdS/ZnS Core/Shell Nanocrystals as Effective and Stable Photocatalysts for H2 Evolution. J. Phys. Chem. C 2013, 117, 11584−11591. (1924) Wang, D.; Hisatomi, T.; Takata, T.; Pan, C.; Katayama, M.; Kubota, J.; Domen, K. Core/Shell Photocatalyst with Spatially Separated Cocatalysts for Efficient Reduction and Oxidation of Water. Angew. Chem., Int. Ed. 2013, 52, 11252−11256. (1925) Li, R.; Zhang, F.; Wang, D.; Yang, J.; Li, M.; Zhu, J.; Zhou, X.; Han, H.; Li, C. Spatial Separation of Photogenerated Electrons and Holes among {010} and {110} Crystal Facets of BiVO4. Nat. Commun. 2013, 4, 1432. (1926) Kim, W.; McClure, B. A.; Edri, E.; Frei, H. Coupling Carbon Dioxide Reduction with Water Oxidation in Nanoscale Photocatalytic Assemblies. Chem. Soc. Rev. 2016, 45, 3221−3243. (1927) Ampelli, C.; Centi, G.; Passalacqua, R.; Perathoner, S. Synthesis of Solar Fuels by a Novel Photoelectrocatalytic Approach. Energy Environ. Sci. 2010, 3, 292−301. (1928) Zhang, M.; Cheng, J.; Xuan, X. X.; Zhou, J. H.; Cen, K. F. CO2 Synergistic Reduction in a Photoanode-Driven Photoelectrochemical Cell with a Pt-Modified TiO2Nanotube Photoanode and a Pt Reduced Graphene Oxide Electrocathode. ACS Sustainable Chem. Eng. 2016, 4, 6344−6354. (1929) Cheng, J.; Zhang, M.; Wu, G.; Wang, X.; Zhou, J.; Cen, K. Photoelectrocatalytic Reduction of CO2 into Chemicals Using PtModified Reduced Graphene Oxide Combined with Pt-Modified TiO2 Nanotubes. Environ. Sci. Technol. 2014, 48, 7076−7084. (1930) Cheng, J.; Zhang, M.; Liu, J.; Zhou, J.; Cen, K. A Cu Foam Cathode Used as a Pt-RGO Catalyst Matrix to Improve CO2 Reduction in a Photoelectrocatalytic Cell with a TiO2 Photoanode. J. Mater. Chem. A 2015, 3, 12947−12957. (1931) Nie, R.; Ma, W. J.; Dong, Y. P.; Xu, Y. J.; Wang, J. Y.; Wang, J. G.; Jing, H. W. Artificial Photosynthesis of Methanol by Mn:CdS and CdSeTe Quantum Dot Cosensitized Titania Photocathode in ImineBased Ionic Liquid Aqueous Solution. ChemCatChem 2018, 10, 3342− 3350. (1932) Li, M.; Li, P.; Chang, K.; Liu, H.; Hai, X.; Zhang, H.; Ye, J. Design of a Photoelectrochemical Device for the Selective Conversion of Aqueous CO2 to CO: Using Mesoporous Palladium-Copper Bimetallic Cathode and Hierarchical ZnO-Based Nanowire Array Photoanode. Chem. Commun. 2016, 52, 8235−8238. (1933) Song, J. T.; Iwasaki, T.; Hatano, M. Photoelectrochemical CO2 Reduction on 3C-SiC Photoanode in Aqueous Solution. Japanese Journal of Applied Physics 2015, 54, 04DR05. (1934) Aoi, S.; Mase, K.; Ohkubo, K.; Suenobu, T.; Fukuzumi, S. Selective CO Production in Photoelectrochemical Reduction of CO2 with a Cobalt Chlorin Complex Adsorbed on Multiwalled Carbon Nanotubes in Water. ACS Energy Letters 2017, 2, 532−536. (1935) Yang, X.; Fugate, E. A.; Mueanngern, Y.; Baker, L. R. Photoelectrochemical CO2 Reductio N to Acetate on Iron-Copper Oxide Catalysts. ACS Catal. 2017, 7, 177−180. (1936) Kecsenovity, E.; Endrodi, B.; Papa, Z.; Hernadi, K.; Rajeshwar, K.; Janaky, C. Decoration of Ultra-Long Carbon Nanotubes with Cu2O Nanocrystals: A Hybrid Platform for Enhanced Photoelectrochemical CO2 Reduction. J. Mater. Chem. A 2016, 4, 3139−3147. (1937) Yuan, J.; Zheng, L.; Hao, C. Role of Pyridine in Photoelectrochemical Reduction of CO2 to Methanol at a CuInS2 Thin Film Electrode. RSC Adv. 2014, 4, 39435−39438. (1938) LaTempa, T. J.; Rani, S.; Bao, N.; Grimes, C. A. Generation of Fuel from CO2 Saturated Liquids Using a P-Si Nanowire∥N-TiO2 Nanotube Array Photoelectrochemical Cell. Nanoscale 2012, 4, 2245− 2250. (1939) Kong, Q.; Kim, D.; Liu, C.; Yu, Y.; Su, Y.; Li, Y.; Yang, P. Directed Assembly of Nanoparticle Catalysts on Nanowire PhotoHH


Chemical Reviews

Review

electrodes for Photoelectrochemical CO2 Reduction. Nano Lett. 2016, 16, 5675−5680. (1940) Magesh, G.; Kim, E. S.; Kang, H. J.; Banu, M.; Kim, J. Y.; Kim, J. H.; Lee, J. S. A Versatile Photoanode-Driven Photoelectrochemical System for Conversion of CO2 to Fuels with High Faradaic Efficiencies at Low Bias Potentials. J. Mater. Chem. A 2014, 2, 2044−2049. (1941) Sahara, G.; Abe, R.; Higashi, M.; Morikawa, T.; Maeda, K.; Ueda, Y.; Ishitani, O. Photoelectrochemical CO2 Reduction Using a Ru(II)-Re(I) Multinuclear Metal Complex on a P-Type Semiconducting Nio Electrode. Chem. Commun. 2015, 51, 10722−10725. (1942) He, D.; Jin, T.; Li, W.; Pantovich, S.; Wang, D.; Li, G. Photoelectrochemical CO2 Reduction by a Molecular Cobalt(II) Catalyst on Planar and Nanostructured Si Surfaces. Chem. - Eur. J. 2016, 22, 13064−13067. (1943) Jang, J.-W.; Cho, S.; Magesh, G.; Jang, Y. J.; Kim, J. Y.; Kim, W. Y.; Seo, J. K.; Kim, S.; Lee, K.-H.; Lee, J. S. Aqueous-Solution Route to Zinc Telluride Films for Application to CO2 Reduction. Angew. Chem., Int. Ed. 2014, 53, 5852−5857. (1944) Jang, Y. J.; Jang, J.-W.; Lee, J.; Kim, J. H.; Kumagai, H.; Lee, J.; Minegishi, T.; Kubota, J.; Domen, K.; Lee, J. S. Selective CO Production by Au Coupled ZnTe/ZnO in the Photoelectrochemical CO2 Reduction System. Energy Environ. Sci. 2015, 8, 3597−3604. (1945) Jang, Y. J.; Jeong, I.; Lee, J.; Lee, J.; Ko, M. J.; Lee, J. S. Unbiased Sunlight-Driven Artificial Photosynthesis of Carbon Monoxide from CO2 Using a ZnTe-Based Photocathode and a Perovskite Solar Cell in Tandem. ACS Nano 2016, 10, 6980−6987. (1946) Schreier, M.; Heroguel, F.; Steier, L.; Ahmad, S.; Luterbacher, J. S.; Mayer, M. T.; Luo, J. S.; Gratzel, M. Solar Conversion of CO2 to Co Using Earth-Abundant Electrocatalysts Prepared by Atomic Layer Modification of CuO. Nature Energy 2017, 2, 17087. (1947) Chen, Y. K.; Lewis, N. S.; Xiang, C. X. Modeling and Simulation of the Spatial and Light-Intensity Dependence of Product Distributions in an Integrated Photoelectrochemical CO2 Reduction System. ACS Energy Letters 2016, 1, 273−280. (1948) Singh, M. R.; Clark, E. L.; Bell, A. T. Thermodynamic and Achievable Efficiencies for Solar-Driven Electrochemical Reduction of Carbon Dioxide to Transportation Fuels. Proc. Natl. Acad. Sci. U. S. A. 2015, 112, E6111−E6118. (1949) Arai, T.; Sato, S.; Uemura, K.; Morikawa, T.; Kajino, T.; Motohiro, T. Photoelectrochemical Reduction of CO2 in Water under Visible-Light Irradiation by a P-Type InP Photocathode Modified with an Electropolymerized Ruthenium Complex. Chem. Commun. 2010, 46, 6944−6946. (1950) Chang, X.; Wang, T.; Zhang, P.; Wei, Y.; Zhao, J.; Gong, J. Stable Aqueous Photoelectrochemical CO2 Reduction by a Cu2O Dark Cathode with Improved Selectivity for Carbonaceous Products. Angew. Chem., Int. Ed. 2016, 55, 8840−8845. (1951) Chu, S.; Fan, S. Z.; Wang, Y. J.; Rossouw, D.; Wang, Y. C.; Botton, G. A.; Mi, Z. T. Tunable Syngas Production from CO2 and H2O in an Aqueous Photoelectrochemical Cell. Angew. Chem., Int. Ed. 2016, 55, 14262−14266. (1952) Kang, U.; Choi, S. K.; Ham, D. J.; Ji, S. M.; Choi, W.; Han, D. S.; Abdel-Wahab, A.; Park, H. Photosynthesis of Formate from CO2 and Water at 1% Energy Efficiency Via Copper Iron Oxide Catalysis. Energy Environ. Sci. 2015, 8, 2638−2643. (1953) Deguchi, M.; Yotsuhashi, S.; Hashiba, H.; Yamada, Y.; Ohkawa, K. Enhanced Capability of Photoelectrochemical CO2 Conversion System Using an AlGaN/GaN Photoelectrode. Japanese Journal of Applied Physics 2013, 52, No. 08JF07. (1954) Deguchi, M.; Yotsuhashi, S.; Yamada, Y.; Ohkawa, K. Photoelectrochemical CO2 Conversion to Hydrocarbons Using an AlGaN/GaN-Si Tandem Photoelectrode. Adv. Condens. Matter Phys. 2015, 537860. (1955) de Brito, J. F.; Araujo, A. R.; Rajeshwar, K.; Zanoni, M. V. B. Photoelectrochemical Reduction of CO2 on Cu/Cu2O Films: Product Distribution and pH Effects. Chem. Eng. J. 2015, 264, 302−309. (1956) Guaraldo, T. T.; de Brito, J. F.; Wood, D.; Zanoni, M. V. B. A New Si/TiO2/Pt P-N Junction Semiconductor to Demonstrate

Photoelectrochemical CO2 Conversion. Electrochim. Acta 2015, 185, 117−124. (1957) Hasan, M. R.; Abd Hamid, S. B.; Basirun, W. J.; Meriam Suhaimy, S. H.; Che Mat, A. N. A Sol-Gel Derived, Copper-Doped, Titanium Dioxide-Reduced Graphene Oxide Nanocomposite Electrode for the Photoelectrocatalytic Reduction of CO2 to Methanol and Formic Acid. RSC Adv. 2015, 5, 77803−77813. (1958) Huang, X. F.; Cao, T. C.; Liu, M. C.; Zhao, G. H. Synergistic Photoelectrochemical Synthesis of Formate from CO2 on {121} Hierarchical Co3O4. J. Phys. Chem. C 2013, 117, 26432−26440. (1959) Huang, X. F.; Shen, Q.; Liu, J. B.; Yang, N. J.; Zhao, G. H. A CO2Adsorption-Enhanced Semiconductor/Metal-Complex Hybrid Photoelectrocatalytic Interface for Efficient Formate Production. Energy Environ. Sci. 2016, 9, 3161−3171. (1960) Kamimura, S.; Murakami, N.; Tsubota, T.; Ohno, T. Fabrication and Characterization of a P-Type Cu3Nb2O8 Photocathode toward Photoelectrochemical Reduction of Carbon Dioxide. Appl. Catal., B 2015, 174, 471−476. (1961) Kaneco, S.; Katsumata, H.; Suzuki, T.; Ohta, K. Photoelectrochemical Reduction of Carbon Dioxide at P-Type Gallium Arsenide and P-Type Indium Phosphide Electrodes in Methanol. Chem. Eng. J. 2006, 116, 227−231. (1962) Song, J. T.; Ryoo, H.; Cho, M.; Kim, J.; Kim, J. G.; Chung, S. Y.; Oh, J. Nanoporous Au Thin Films on Si Photoelectrodes for Selective and Efficient Photoelectrochemical CO2 Reduction. Adv. Energy Mater. 2017, 7, 1601103. (1963) Xu, Y. J.; Wang, S.; Yang, J.; Han, B.; Nie, R.; Wang, J. X.; Dong, Y. P.; Yu, X. G.; Wang, J. G.; Jing, H. W. Highly Efficient Photoelectrocatalytic Reduction of CO2 on the Ti3C2/g-C3N4 Heterojunction with Rich Ti3+ and Pyri-N Species. J. Mater. Chem. A 2018, 6, 15213−15220. (1964) Kaneco, S.; Katsumata, H.; Suzuki, T.; Ohta, K. Photoelectrocatalytic Reduction of CO2 in LiOH/Methanol at MetalModified P-InP Electrodes. Appl. Catal., B 2006, 64, 139−145. (1965) Shen, Q.; Chen, Z.; Huang, X.; Liu, M.; Zhao, G. High-Yield and Selective Photoelectrocatalytic Reduction of CO2 to Formate by Metallic Copper Decorated Co3O4 Nanotube Arrays. Environ. Sci. Technol. 2015, 49, 5828−5835. (1966) Roy, N.; Hirano, Y.; Kuriyama, H.; Sudhagar, P.; Suzuki, N.; Katsumata, K. I.; Nakata, K.; Kondo, T.; Yuasa, M.; Serizawa, I.; et al. Boron-Doped Diamond Semiconductor Electrodes: Efficient Photoelectrochemical CO2 Reduction through Surface Modification. Sci. Rep. 2016, 6, 38010. (1967) Kwak, B. S.; Kang, M. Photocatalytic Reduction of CO2 with H2O Using Perovskite CaxTiyO3. Appl. Surf. Sci. 2015, 337, 138−144. (1968) Huang, C.; Chen, C.; Zhang, M.; Lin, L.; Ye, X.; Lin, S.; Antonietti, M.; Wang, X. Carbon-Doped BN Nanosheets for MetalFree Photoredox. Nat. Commun. 2015, 6, 7698. (1969) Vyas, V. S.; Lotsch, B. V. Materials Chemistry: Organic Polymers Form Fuel from Water. Nature 2015, 521, 41−42. (1970) Vyas, V. S.; Lau, V. W.-h.; Lotsch, B. V. Soft Photocatalysis: Organic Polymers for Solar Fuel Production. Chem. Mater. 2016, 28, 5191−5204. (1971) Schwartzenberg, K. C.; Hamilton, J. W. J.; Lucid, A. K.; Weitz, E.; Notestein, J.; Nolan, M.; Byrne, J. A.; Gray, K. A. Multifunctional Photo/Thermal Catalysts for the Reduction of Carbon Dioxide. Catal. Today 2017, 280, 65−73. (1972) Zhang, W. B.; Wang, L. B.; Wang, K. W.; Khan, M. U.; Wang, M. L.; Li, H. L.; Zeng, J. Integration of Photothermal Effect and Heat Insulation to Efficiently Reduce Reaction Temperature of CO2 Hydrogenation. Small 2017, 13, 1602583. (1973) Zhao, S.; Jin, R.; Jin, R. Opportunities and Challenges in CO2 Reduction by Gold- and Silver-Based Electrocatalysts: From Bulk Metals to Nanoparticles and Atomically Precise Nanoclusters. ACS Energy Letters 2018, 3, 452−462. (1974) Bushuyev, O. S.; De Luna, P.; Dinh, C. T.; Tao, L.; Saur, G.; van de Lagemaat, J.; Kelley, S. O.; Sargent, E. H. What Should We Make with CO2 and How Can We Make It? Joule 2018, 2, 825−832. HI


Chemical Reviews

Review

(1975) Akhter, P.; Hussain, M.; Saracco, G.; Russo, N. Novel Nanostructured-TiO2 Materials for the Photocatalytic Reduction of CO2 Greenhouse Gas to Hydrocarbons and Syngas. Fuel 2015, 149, 55−65. (1976) Li, D.; Ouyang, S.; Xu, H.; Lu, D.; Zhao, M.; Zhang, X.; Ye, J. Synergistic Effect of Au and Rh on SrTiO3 in Significantly Promoting Visible-Light-Driven Syngas Production from CO2 and H2O. Chem. Commun. 2016, 52, 5989−5992. (1977) Tahir, B.; Tahir, M.; Amin, N. A. S. Photo-Induced CO2 Reduction by CH4/H2O to Fuels over Cu-Modified g-C3N4 Nanorods under Simulated Solar Energy. Appl. Surf. Sci. 2017, 419, 875−885. (1978) Urbain, F.; Tang, P. Y.; Carretero, N. M.; Andreu, T.; Gerling, L. G.; Voz, C.; Arbiol, J.; Morante, J. R. A Prototype Reactor for Highly Selective Solar-Driven CO2 Reduction to Synthesis Gas Using Nanosized Earth-Abundant Catalysts and Silicon Photovoltaics. Energy Environ. Sci. 2017, 10, 2256−2266. (1979) Chu, S.; Ou, P. F.; Ghamari, P.; Vanka, S.; Zhou, B. W.; Shih, I.; Song, J.; Mi, Z. T. Photoelectrochemical CO2 Reduction into Syngas with the Metal/Oxide Interface. J. Am. Chem. Soc. 2018, 140, 7869−7877. (1980) Shih, C. F.; Zhang, T.; Li, J.; Bai, C. Powering the Future with Liquid Sunshine. Joule 2018, 2, 1925. (1981) Huang, H.; Mao, M.; Zhang, Q.; Li, Y.; Bai, J.; Yang, Y.; Zeng, M.; Zhao, X. Solar Light Driven CO2 Reduction by CH4 on Silica Cluster Modified Ni Nanocrystals with a High Solar to Fuel Efficiency and Excellent Durability. Adv. Energy Mater. 2018, 8, 1702472. (1982) Stanley, J. N. G.; García-García, I.; Perfrement, T.; Lovell, E. C.; Schmidt, T. W.; Scott, J.; Amal, R. Plasmonic Effects on CO2 Reduction over Bimetallic Ni-Au Catalysts. Chem. Eng. Sci. 2019, 194, 94. (1983) Zhang, L.; Kong, G. G.; Meng, Y. P.; Tian, J. S.; Zhang, L. J.; Wan, S. L.; Lin, J. D.; Wang, Y. Direct Coupling of Thermo- and Photocatalysis for Conversion of CO2-H2O into Fuels. ChemSusChem 2017, 10, 4709−4714. (1984) Poudyal, S.; Laursen, S. Insights into Elevated-Temperature Photocatalytic Reduction of CO2 by H2O. J. Phys. Chem. C 2018, 122, 8045−8057. (1985) Osterloh, F. E. The Low Concentration of CO2 in the Atmosphere Is an Obstacle to a Sustainable Artificial Photosynthesis Fuel Cycle Based on Carbon. ACS Energy Letters 2016, 1, 1060−1061. (1986) Nakajima, T.; Tamaki, Y.; Ueno, K.; Kato, E.; Nishikawa, T.; Ohkubo, K.; Yamazaki, Y.; Morimoto, T.; Ishitani, O. Photocatalytic Reduction of Low Concentration of CO2. J. Am. Chem. Soc. 2016, 138, 13818. (1987) Zou, J.-P.; Wu, D.-D.; Luo, J.; Xing, Q.-J.; Luo, X.-B.; Dong, W.-H.; Luo, S.-L.; Du, H.-M.; Suib, S. L. A Strategy for One-Pot Conversion of Organic Pollutants into Useful Hydrocarbons through Coupling Photodegradation of MB with Photoreduction of CO2. ACS Catal. 2016, 6, 6861−6867. (1988) Dong, W. H.; Wu, D. D.; Luo, J. M.; Xing, Q. J.; Liu, H.; Zou, J. P.; Luo, X. B.; Min, X. B.; Liu, H. L.; Luo, S. L.; et al. Coupling of Photodegradation of RhB with Photoreduction of CO2 over RGo/ SrTi0.95Fe0.05O3‑δ Catalyst: A Strategy for One-Pot Conversion of Organic Pollutants to Methanol and Ethanol. J. Catal. 2017, 349, 218− 225. (1989) Liang, J.; Li, L. Synthesis of N-Doped Graphene-Functionalized Zn1.231Ge0.689N1.218O0.782 Solid Solution as a Photocatalyst for CO2 Reduction and Oxidation of Benzyl Alcohol under Visible-Light Irradiation. J. Mater. Chem. A 2017, 5, 10998−11008. (1990) Chen, Y.; Wang, M.; Ma, Y.; Li, Y.; Cai, J.; Li, Z. Coupling Photocatalytic CO2 Reduction with Benzyl Alcohol Oxidation to Produce Benzyl Acetate over Cu2O/Cu. Catal. Sci. Technol. 2018, 8, 2218−2223. (1991) Huang, Z.; Teramura, K.; Asakura, H.; Hosokawa, S.; Tanaka, T. Efficient Photocatalytic Carbon Monoxide Production from Ammonia and Carbon Dioxide by the Aid of Artificial Photosynthesis. Chem. Sci. 2017, 8, 5797−5801. (1992) Compagnoni, M.; Ramis, G.; Freyria, F. S.; Armandi, M.; Bonelli, B.; Rossetti, I. Innovative Photoreactors for Unconventional

Photocatalytic Processes: The Photoreduction of CO2 and the PhotoOxidation of Ammonia. Rend. Lincei-Sci. Fis. 2017, 28, 151−158. (1993) Bazzo, A.; Urakawa, A. Origin of Photocatalytic Activity in Continuous Gas Phase CO2 Reduction over Pt/TiO2. ChemSusChem 2013, 6, 2095−2102. (1994) Hong, J. D.; Zhang, W.; Ren, J.; Xu, R. Photocatalytic Reduction of CO2A Brief Review on Product Analysis and Systematic Methods. Anal. Methods 2013, 5, 1086−1097. (1995) Hoffmann, M. R.; Moss, J. A.; Baum, M. M. Artificial Photosynthesis: Semiconductor Photocatalytic Fixation of CO2 to Afford Higher Organic Compounds. Dalton Trans. 2011, 40, 5151− 5158. (1996) Kim, D.; Sakimoto, K. K.; Hong, D. C.; Yang, P. D. Artificial Photosynthesis for Sustainable Fuel and Chemical Production. Angew. Chem., Int. Ed. 2015, 54, 3259−3266. (1997) Sheng, H.; Oh, M. H.; Osowiecki, W. T.; Kim, W.; Alivisatos, A. P.; Frei, H. Carbon Dioxide Dimer Radical Anion as Surface Intermediate of Photoinduced CO2 Reduction at Aqueous Cu and CdSe Nanoparticle Catalysts by Rapid-Scan FTIR Spectroscopy. J. Am. Chem. Soc. 2018, 140, 4363−4371.

HJ


Cocatalysts for Selective Photoreduction of CO2 into Solar Fuels

Recommend Documents