Roles of Two-Dimensional Transition Metal Dichalcogenides as

Review pubs.acs.org/IECR

Roles of Two-Dimensional Transition Metal Dichalcogenides as Cocatalysts in Photocatalytic Hydrogen Evolution and Environmental Remediation Wenchao Peng, Yang Li, Fengbao Zhang, Guoliang Zhang, and Xiaobin Fan* School of Chemical Engineering and Technology, Tianjin University, Tianjin 300072, China ABSTRACT: Photocatalysis has attracted great attention due to its useful environmental applications for hazardous pollutants degradation and sustainable hydrogen evolution. Recently, transition metal dichalcogenide (TMD) based materials have shown great potential in photocatalysis field. Due to their special two-dimensional layered structure and excellent electrochemical catalysis properties, they can be used as effective cocatalysts and supports to modify semiconductors for enhanced photocatalytic activities. By loading TMDs as cocatalysts, stable junctions could be created to facilitate the photogenerated electrons transfer. Moreover, the exposed edges of TMDs are active for hydrogen evolution or oxygen activation, thus leading to the improved performance for semiconductor/TMD composite in photocatalytic H2 evolution and pollutants degradation. This review will focus on the roles of TMDs as cocatalysts for semiconductors in photocatalytic hydrogen evolution and environmental remediation. We expect our work can provide enriched information to harvest the excellent special properties of TMDs as a platform to fabricate more efficient photocatalysts for solar energy utilization.

1. INTRODUCTION Since the discovery of the photocatalytic splitting of water on TiO2 electrodes by Fujishima and Honda in 1972, a large amount of photocatalyts have been developed for solar energy conversion and environment protection.1 Photocatalysis is a semiconductor-mediated process.2 Semiconductors, such as TiO2,3 CdS,4 and BiVO4,5 etc. can absorb and utilize light for chemical reactions due to their unique electronic structure composed of a filled valence band (VB) and an empty conduction band (CB).6 As shown in Figure 1, with light

example, (i) designing materials with different physical properties (crystal structure,9 crystallinity,10 and particle size,11 etc.) for broader light absorbing range or efficient charge separation and migration; (ii) loading proper cocatalysts on the light harvesting semiconductor to promote or accelerate the photocatalytic courses.12 Until now, lots of studies have been published about issue (i).11,13−16 Whereas modifying the semiconductor by loading cocatalysts are more facile methods, which could accept photogenerated charge carriers, provide active sites for photocatalytic process and improve the stability of photocatalysts by suppressing photocorrosion.8 Therefore, cocatalysts play a significant role in improving both the activity and stability of semiconductor photocatalysts. Loading precious metals, such as Pt,17 Au,18 Ag,19 and Pd,20 as cocatalysts could enhance the photocatalytic activity of semiconductors effectively. However, these metals are rare and expensive to apply. Graphene (GR), a versatile carbon material with a single layer and sp2-hybridized carbon lattice, possesses excellent electrical, thermal and mechanical properties.21 As GR can serve as an excellent charge carrier at room temperature (200 000 cm2 V−1 s−1), it has attracted increasing attention in the photocatalysis field.22,23 Using GR as cocatalysts to form electron-conducting surfaces and channels, the photocatalytic activity of composite materials can be greatly increased, mainly owing to the effective separation of the electron−hole pairs.24,25 Since the discovery of the surprising properties of graphene, graphene-like 2D materials have also been hot topics in the material filed. Lots of 2D materials, such as graphitic carbon

Figure 1. Schematic illustration of photocatalytic H2 evolution and organics degradation over a semiconductor photocatalyst loaded with cocatalysts.

irradiation, the electron−hole pairs can be produced and separated, and the photogenerated holes and electrons can be used as oxidant or reductant to perform the pollutant degradation or water reduction, respectively.7 However, the photogenerated electrons and holes in the excited states are unstable and can easily recombine, leading to the low activity of semiconductor photocatalysts.8 A variety of strategies have been employed to increase the utilization efficiency of solar energy in the past few decades. For © 2017 American Chemical Society

Received: Revised: Accepted: Published: 4611

January 25, 2017 March 17, 2017 March 29, 2017 March 29, 2017 DOI: 10.1021/acs.iecr.7b00371 Ind. Eng. Chem. Res. 2017, 56, 4611−4626

Review

Industrial & Engineering Chemistry Research

Figure 2. Crystal structures of TMDs with a typical formula of MX2. (a) Three-dimensional model of the MoS2 crystal structure. (b) Unit cell structures of 2H-MX2 and 1T-MX2. Reprinted with permission from ref 35. Copyright 2015 American Chemical Society.

nitride (g-C 3N 4 ),26−28 transition metal dichalcogenides (TMDs), transition metal oxides, and other 2D compounds started to gain renewed interest in photocatalysis recently.29−31 Similar with graphene, the TMDs are also usually used as cocatalysts for the modification of semiconductors. However, the cocatalytic mechanism is different for them. Graphene is more like a “highway” for electrons transfer, whereas TMDs could accept electrons as active sites.25 Both of these two functions are helpful for the charge separation and photoactivity enhancement. The roles of TMDs in composite photocatalysts can be as follows: (i) TMD acts as active component for light absorption and utilization;32,33 (ii) both TMD and semiconductor act as active components at the same time;34 (iii) TMD acts as cocatalysts, whereas the other semiconductor acts as active component.29 This review will focus on the application of TMDs as cocatalysts for semiconductors in photocatalytic hydrogen evolution and environmental remediation, by which we expect to provide enriched information to harvest the cocatalytic properties of TMDs as a platform to fabricate more efficient photocatalysts for solar energy utilization. The roles and functional mechanism of TMDs cocatalysts in photocatalytic hydrogen evolution and pollutants degradation will be discussed and summarized.

MoS2 into 1T-MoS2,45 whereas an infrared laser could induce the 1T to 2H phase reversion.46 2.2. Roles of TMDs in Photocatalysis. In photocatalytic hydrogen evolution and environmental remediation processes, the TMDs play three different roles for improving both the activity and reliability of semiconductor photocatalysts: (i) TMDs have special 2D layered structure, and can be used as effective supports for anchor of the semiconductor nanoparticles, which could reduce the mobility, provide more active sites, and avoid coalescence and agglomeration of the semiconductors. This is beneficial for keeping the activity and stability of the photocatalysts.47−49 (ii) By loading TMDs as cocatalysts, semiconductor−semiconductor or metal−semiconductor junctions can be formed, and more interfaces could be created.50 Charge separation and immigration can therefore be enhanced, leading to the higher photoactivity.36 As shown in Figure 1, with irradiation, the semiconductor can be excited, and photogenerated electrons can be transferred to the H2evolution cocatalyst and reduce H+ to H2.12 Whereas the holes can migrate to the oxidation cocatalyst and activate the dissolved O2 for the pollutants degradation.51 (iii) Many kinds of TMD materials with different phases have been proved to be active for the electrochemical hydrogen evolution reaction (HER).52,53 Their exposed edge sites could lower the activation energy for photocatalytic H2 evolution.54−56 Moreover, nanoscale MoS2 is a reportedly good O2-activation cocatalyst for oxidation reactions.57 This feature facilitates the formation of superoxide radical anions (O2−) during the photo-oxidation process.22 2.3. Loading Methods of TMDs Cocatalysts for Semiconductors. (a) In Situ Reduction Process. The in situ reduction method is one of the most effective synthetic methods to load the TMD cocatalysts for semiconductors.29 This in situ growth of TMDs on semiconductors is beneficial for an intimate contact, stable junctions could be then created for electrons transfer.58 However, it is difficult to control the morphology and layer number of the loaded TMD cocatalysts using this method.29 In detail, the in situ reduction can be performed using the hydro(solvo)thermal method,23,59 the hotinjection method,60 photoreduction method,61,62 and the thermal annealing method.36,50 Transition metal containing salts, such as Na2MoS4,50 (NH4)2MoS4,62 Na2MoO4,59 and Na2WS4,63 are usually used as the precursors. Thiourea25 or thioacetamide59 can be used both as reductants and sulfur source. Lots of composite photocatalysts, such as MoS2/CdS,64 MoS2/TiO2,59 ZnxCd1−xS/MoS2,65 MoS2/ZnIn2S4,66 ZnS/GR/

2. TMDS AS COCATALYSTS 2.1. Classification of TMDs. Transition metal dichalcogenides (TMDs) are composed of hexagonal layers of metal atoms (M) sandwiched between two chalcogen layers with a MX2 stoichiometry (Figure 2a).35 TMDs exhibit diverse properties related with their composition. MoS2 and WS2 are p-type semiconductors, which have been widely used as cocatalysts for the modification of semiconductor photocatalysts.36,37 WTe2 and TiSe2 are semimetals similar to graphene.38 NbSe2 and VSe2 with single or few-layers are true metals, and schottky junction could be created when they are combined with semiconductors.38,39 The same TMD material could also have different properties depending on their crystalline structure, which can be tailored by changing the number or stacking sequence of layers in their crystals.10 Typically, MoS2 and WS2 have two main phase structure, prismatic trigonal 2H phase and octahedral 1T phase (Figure 2b).35 These two different phases have different properties, and can be transformed to each other under special conditions.40,41 For example, 2H-MoS2 is semiconducting, whereas 1T-MoS2 has metallic properties.42 Bulk 2H-MoS2 has an indirect band gap, but exfoliated MoS2 with 1T phase exhibits direct electronic and optical band gaps.43,44 Lithium insertion method with n-butyllithium as interaction agent can transform the 2H4612

DOI: 10.1021/acs.iecr.7b00371 Ind. Eng. Chem. Res. 2017, 56, 4611−4626

Review

Industrial & Engineering Chemistry Research MoS2,67 TiO2/GR/MoS2,25 and In2S3/MoS2/CdS,68 were synthesized using the in situ hydro(solvo)methods. High temperature and pressure were usually needed for obtaining TMDs with good crystalline and better cocatalytic activity. Peng et al. succeeded to control the reaction temperature below the boiling point of water under atmosphere, and amorphous MoS 2 was loaded on g-C 3N4 with NH 4OHCl as the reductant.69 This MoS2−g-C3N4 composite exhibited enhanced activity for the degradation of methylene orange under simulated solar light condition. The annealing method could form stable junctions under higher temperature and H2S atmosphere conditions. With this method, MoS2/CdS,36,50 WS2/CdS63 have been synthesized with enhanced photocatalytic activity. The thermal treatment can also be combined with ball-milling process, and little solvent will be needed using this method.70 The hydro(solvo)thermal and annealing methods are very facile and cost-effective, which have great potential to be applied on a large scale. Hot-injection is also a kind of in situ loading method, by which the single layer TMDs nanosheets could be loaded.60 In situ photodeposition of TMDs could be performed at room temperature, and no extra reductant is needed.71 (b) Postloading Method. The loading of TMDs for semiconductor photocatalysts could also be performed using the postloading method. In this method, the TMDs cocatalysts will be synthesized first; an extra loading process was then used to combine the semiconductors and the cocatalysts. Due to the separate treatment toward the cocatalysts and the semicondutors, TMDs with different morphology and phases could be loaded. The shape of the semiconductor will also be remained after the loading process. However, the interfacial contact will be a little weaker compared to the composites from in situ method.72 Specially, loading of 1T-TMD need to prevent the phase transform back to 2H-TMD, low temperature and dark condition are therefore needed. Sonication assisted mixing method is always used for the combination process at room temperature. Using this method, the hydrothermal produced 2H-MoS2 can be supported on gC3N4 without breaking the sheet structure of g-C3N4.73 Especially, the exfoliation process could also be used to obtain different phase TMDs with single or fewer layers before the loading. For example, the bulk 2H-MoS2 can be exfoliated using the lithium insertion first, following with a combination process with CdS to obtain the 1T-MoS2−CdS photocatalyst for H2 evolution.34 The TMDs can also be combined with another cocatalyst, e.g., graphene, to synthesize a binary cocatalyst. The subsequent hydrothermal treatment can then deposit semiconductors, such as TiO2, CdS on the binary cocatalyst for the final ternary photocatalysts.25 Jia et al. synthesized CdS−GR− MoS2 ternary photocatalysts using this postloading method.74 The distribution of CdS and MoS2 on the surface of GR was very uniform, which is helpful to obtain high activity for photocatalytic H2 generation.

sections, detailed introductions for MoS2, WS2, and other TMDs based photocatalysts for hydrogen evolution will be introduced, separately. 3.1. MoS2 Based Photocatalysts. MoS2 is the most frequently used TMD cocatalyst for the modification of semiconductors. Attributing to its facile loading and costeffective, MoS2 has been regarded as ideal substitute for noble metals in photocatalytic H2 evolution.29 To date, many semiconductors, e.g., CdS,36,50 TiO2,58 ZnO,84 ZnIn2S4,61 gC3N4,85 SrTiO3,82 etc., have been modified with MoS2 aiming for the enhancement of H2 evolution activity. Zong et al. synthesized MoS2/CdS composite by impregnating CdS in (NH4)2MoS4 aqueous solution and the following annealing treatment in H2S flow.50 Intimate contact could be found between CdS and MoS2 (Figure 3a,b). The photocatalytic activity of CdS for H2 generation was greatly enhanced after loading MoS2 as cocatalyst, even higher than that of Pt/ CdS under the same reaction conditions (Figure 3c,d).50 In their following work, the origin of the activity enhancement was investigated. They found that the activity of MoS2/CdS was influenced by the following items: the chemical state of the Mo species, the junctions between CdS and MoS2, the surface area, and the crystallinity of the catalyst.36 A ball-milling combined calcination method was also developed for the synthesis of MoS2/CdS photocatalysts with little organic solvent added.70 Due to the uniform loading of MoS2 on the surface of CdS and intimate contact between these two components, greatly enhanced activity for H2 generation of 1315 μmol h−1 can be achieved. Hydro(solv)thermal is the most frequently used method for the loading of MoS2. Zhang et al. fabricated MoS2/CdS photocatalyst via a one-pot solvothermal reaction in a DMSO suspension containing MoS2 nanosheets and Cd(Ac)2·H2O.47 DMSO here also can act as the sulfur source for the formation of CdS. The obtained hybrid was a sandwich-like p−n junction heterostructure with large specific surface area and narrower bandgap. Xiong et al. used a hydrothermal method for the synthesis of the same hybrid. The loaded MoS2 ultrathin nanoplates were found with rich defects present (Figure 4), which showed excellent promotion effect for CdS during the photocatalytic hydrogen evolution.83 It is reported that the appearance of Mo5+ and S22− was due to the defect-rich structure of the MoS2 ultrathin nanoplate, which could provide more active sites for the hydrogen evolution. Until now, the most efficient MoS2/CdS photocatalyst was obtained via a facile one-pot wet-chemical method.60 In that case, CdO was used as the precursors for CdS, whereas oleylamine and oleic acid were used to control the growth of the CdS nanoparticles on the surface of MoS2. Very small CdS nanoparticles with 6−11 nm diameters and single-layer MoS2 nanosheets were formed using this method (Figure 5). The H2 evolution rate can be as more as 1472 μmol h−1, nearly 12 times than that of pure CdS (119 mmol h−1). TiO2 is the most widely used photocatalyst with good antiphotocorrosion properties. Pure TiO2 was only active for UV light, which limited its applications.95 Zhu et al. synthesized MoS2−TiO2 composite photocatalysts via mechanochemistry with bulk MoS2 as the precursor.48 After MoS2 was loaded as cocatalyst, the absorption intensity of the MoS2−TiO2 samples in the range of 400−700 nm could be increased obviously (Figure 6a). Moreover, intimate interactions existed between the MoS2 and TiO2, which can lead to the red shift of the characteristic Raman peaks for TiO2, indicating an increased

3. APPLICATION FOR PHOTOCATALYTIC H2 EVOLUTION Table 1 summarizes the recent progress of TMDs based photocatalysts, including their synthesis methods and their applications for photocatalytic hydrogen evolution. Lactic acid and Na2S/Na2SO3 solution were usually used as sacrificial agents to obtain high H2 evolution rates. The presence of Na2S and Na2SO3 could also protect the TMDs from photocorrosion, thus can increase their stability.75,76 In the following 4613


one-pot solvothermal

one-pot hydrothermal

MoS2/CdS

ZnS−MoS2/GR

4614

0.1 M Na2S and 0.1 M Na2SO3 10 vol % triethanolamine 15% mixed Methanol-H2O 20% mixed Methanol-H2O 10 vol % triethanolamine 10 vol % lactic acid 10 vol % lactic acid water and methanol (3:1 in volume) water and methanol (3:1 in volume) 0.005 M oxalic acid

two-step solvothermal hydrothermal postmixing

in situ photo deposition


hydrothermal in situ photo deposition mechanochemistry hydrothermal solvothermal

thermal annealing in H2S impregnation−sulfidation postloading

gas−solid reaction

in situ thermal method

CdS−MoS2/GR MoS2/TiO2 CdS:N-MoS2

MoS2/SrZrO3

MoS2/CdS

MoS2/ZnO MoS2/g-C3N4 MoS2/TiO2 MoS2/TiO2 MoS2/pyridine-modified g-C3N4 WS2/CdS WS2/mpg-CN 1T-WS2/TiO2

g-C3N4/WS2

WS2/TiSi2

Na2S (0.35 M) and Na2SO3 (0.25 M) (0.02 M) SO32−/(0.1 M) S2−

10 vol % lactic acid 0.35 M/0.25 M Na2S−Na2SO3 10 vol % lactic acid

postmixing postmixing hydrothermal

0.005 M Na2S and 0.005 M Na2SO3 25 vol % methanol/H2O 25 vol % methanol/H2O 10 vol % lactic acid

10 vol % lactic acid

10 vol % lactic acid 10 vol % lactic acid EY/photosensitizer 0.5 M Na2SO3 and 0.43 M Na2S

10 vol % lactic acid

25% (v/v) ethanol/water 0.35 M Na2S and 0.25 M Na2SO3 solution 20 vol % lactic solution 10 vol % lactic acid

10 vol % lactic acid 10 vol % lactic solution 10 vol % lactic solution

sacrificial agents

TiO2/1T-MoS2 TiO2/2H-MoS2 In2S3/MoS2/CdS

CdS−MoS2−GR

CdS−MoS2−rGO MoS2/ZnxCd1−xS MoS2/TiO2 MoS2/ZnIn2S4

thermal annealing in H2S thermal annealing in H2S ball-milling combined calcination two-step hydrothermal hydrothermal

synthesis method

hydrothermal in situ photoassisted deposition donication assisted postloading in situ photodeposition postultrasonic mixing hydrothermal thermal annealing in H2S

CdS−MoS2/GR MoS2/ZnIn2S4

TiO2−MoS2/GR MoS2@TiO2

MoS2/CdS MoS2/CdS MoS2/CdS

catalyst

W W W W

Xe Xe Xe Xe

lamp lamp lamp lamp

λ ≥ 420 nm 34 mW/cm2 λ> 420 nm (λ > 420 nm) (λ > 420 nm)

morphology

sheets/sheets particles/sheets

420 μmol h−1 12 μmol h−1 2570 μmol h−1 g−1 101 μmol h−1 g−1 596.4 μmol g−1

300W Xe lamp λ > 420 nm 300W Xe lamp λ > 420 nm 300 W Xe source AM 1.5 300W Xe lamp λ > 420 nm 100 mW/cm2 150W Xe lamp λ > 420 nm

nanoplates/ nanoparticles particles/sheets sheets/sheets particles/sheets nanosheets/nanobelts nanoflower/ nanosheets particles/sheets sheets/sheets particles/sheets

particles/sheets particles/sheets nanorods/particles/ sheets nanorods/sheets nanosheets/nanofibers nanosheets/ nanoparticles particles/sheets

particles/sheets

particles/sheets particles/sheets nanosheets/nanowire microspheres/ nanosheets particles/sheets

particles/sheets

particles/sheets core−shell nanobelts/ sheets particles/sheets particles/sheets

particles/sheets particles/sheets particles/sheets

768 μmol h−1 g−1 252 μmol h−1 g−1 150.7 μmol h−1 75 μmol h−1 g−1 25 μmol h−1 5.0% at 420 nm

54.4% at 420 nm

10.5% at 450 nm

9.8% at 420 nm

28.1% at 420 nm

9.7% at 365 nm

7.3% at 400 nm

quantum efficiency (%)

300 W Xe lamp 300W Xe lamp λ > 400 nm 600 mW/cm2 300 W Xe lamp 250−380 nm 300 W Xe lamp 100 mW/cm2 300W Xe lamp λ > 400 nm

381.6 μmol h

5.31 mmol h−1

100 W mercury lamp λ = 365 nm 300 W xenon lamp (λ > 420 nm)

621.3 μmol h−1 1.68 mmol h−1 g−1 9.11 mmol h−1 g−1

350 W xenon arc lamp (λ ≥ 420 nm) 300 W xenon arc lamp 320−780 nm Xe lamp (300 W) (λ > 420 nm)

−1

2.0 mmol h−1 g−1 175 μmol h−1 g−1 31.29 μmol h−1

2258 μmol h−1 g−1

137 μmol h−1

99 mol h−1 1061.8 μmol g−1 16.7 mmol h−1 g−1 153 μmol g−1

3.067 mL h−1

300 W Xe Lamp λ < 400 nm 2.7 mW/cm2 300 W Xe Lamp λ < 400 nm 2.7 mW/cm2 300 W Xe Lamp (λ ≥ 420 nm)

300 W xenon arc lamp (λ ≥ 420 nm) 0.5 sun 50 mW/cm2 300 W Xe lamp 125 mW/cm2

350 150 300 300

500 W UV−vis lamp

165.3 μmol h−1 1.6 mmol h −1 g−1 600 mW/cm2 1.8 mmol h−1 8.047 mmol h−1 g−1

350 W Xe arc lamp 20 mW/cm−2 λ = 365 nm 300 W xenon arc lamp 280−700 nm 600 mW/cm2 300 W Xe lamp (λ > 420 nm) 300W Xe lamp λ > 420 nm

activity 540 μmol h−1 533 μmol h−1 1315 μmol h−1

light source 300 W Xe lamp (λ > 420 nm) 300 W Xe lamp (λ > 420 nm) 300 W Xe lamp (λ > 420 nm)

Table 1. Summary of TMDs Based Composite for Photocatalytic H2 Evolution

91

90

63 88 89

84 85 48 86 87

83

82

64 80 81

79 79 68

67

47

71 65 58 78

72

77 61

25 59

50 36 70

ref.

Industrial & Engineering Chemistry Research Review


Review

92 93 94 nanosheets/nanorods particles/particles particles/sheets 1842 μmol h−1 g−1 2.5 mmol h−1 g−1 4.06 μmol h−1 500W arc lamp λ > 420 nm 300W Xe lamp λ > 420 nm 300W Xe lamp λ > 420 nm

21.2% at 420 nm

37

0.35m Na2S and 0.25m Na2SO3 0.35 M Na2S and 0.25 M Na2SO3 15 vol % triethanolamine

Figure 4. (A) Scanning electron microscopy (SEM), (B) TEM, (C) HRTEM, and (D) cross-sectional HRTEM images of the as-prepared MoS2 ultrathin nanoplate. (E) XRD patterns of the resulted MoS2 ultrathin nanoplate. The inset in panel C is the corresponding SAED of the ultrathin nanoplate. Reprinted with permission from ref 83. Copyright 2015 Royal Society of Chemistry.

WS2/graphene−CdS NiS2/CdLa2S4 NiS2/g-C3N4

morphology

nanosheets/nanorods 28.9% at 420 nm 1222 μmol h−1 300 W arc lamp λ ≥ 400 nm 20 vol % lactic acid

Figure 3. (a) High resolution transmission electron microscopy (HRTEM) image of 1 wt % MoS2/CdS. (b) Magnified HRTEM image of the selected frame from image a. (c) Rate of H2 evolution on MoS2/ CdS photocatalysts loaded with different amounts of MoS2 under visible light (λ > 420 nm). (d) Rate of H2 evolution on CdS loaded with 0.2 wt % of different cocatalysts. Reproduced with permission from ref 36. Copyright 2008 American Chemical Society.

ultrasonic/exfoliation method solvothermal hydrothermal hydrothermal

quantum efficiency (%) activity light source sacrificial agents synthesis method catalyst

Table 1. continued

WS2/CdS

ref.


Figure 5. TEM images of WS2−CdS nanohybrids obtained at different reaction times. The reaction time is (a) 5, (b) 30, (c) 60 min. (d) Schematic illustration of the shape evolution of WS2−CdS nanohybrids. Reprinted with permission from ref 60. Copyright 2015 Wiley-VCH. 4615


Review


plane, the photogenerated electrons do not need to transfer to the edge sites for protons reduction, unlike the case for 2HMoS2. This will shorten the transfer distance of electrons, thus decreasing the possibility of charge recombination (Figure 8).

Figure 6. (a) UV−vis DRS of TiO 2 and the MoS 2 −TiO 2 photocatalysts with different MoS2 loading amounts. (b) Raman spectra of TiO2, various MoS2−TiO2 and MoS2 samples. Reprinted with permission from ref 48. Copyright 2015 Royal Society of Chemistry. Figure 8. Schematic illustrating charge-transfer behavior and H2 evolution active sites for 1T-MoS2 and 2H-MoS2. Reproduced with permission from ref 79. Copyright 2015 Springer.

charge separation efficiency (Figure 6b). The broadened light absorption range, intimate interactions, and the superior conductivity of MoS2 leaded the enhanced activity for H2 generation. A maximum H2 evolution rate of 150.7 μmol h−1 can be obtained, which was 48.6 times higher than that of pure TiO2. Shen et al. prepared one-dimensional MoS2 nanosheet/ TiO2 nanowire hybrid nanostructures via a simple hydrothermal way (Figure 7).58 By coating with a few layers of MoS2,

Other semiconductors, such as ZnS,67 ZnxCd 1−x S,65 ZnIn2S4,61,66,78 and SrZrO3,82 could also be modified by loading MoS2 as cocatalyst. The largest H2 evolution rate of 8.407 mmol h−1 g−1 was achieved by MoS2/ZnIn2S4, and the loading of MoS2 was realized by in situ photoassisted deposition process. The g-C3N4, as a typical metal-free photocatalyst, could also be enhanced by loading MoS2 as the cocatalyst.96 The H2 production rate is however relative low (26.8 μmol h−1) without the addition of Pt.96−98 3.2. WS2 Based Photocatalysts. WS2 is another frequently used TMD cocatalyst for the modification of semiconductors. Compared to the MoS2, WS2 is more difficult to be exfoliated into thinner nanosheets, but it has better performance for the HER with earlier overpotential and lower Tafel slope.52 Zong and co-workers loaded WS2 on CdS using an impregnation− sulfidation approach. The photocatalytic H2 evolution rate can be increased to 420 μmol h−1, and the enhanced activity was attributed to the junction formed between WS2 and CdS.63 This H2 generation rate was smaller than the MoS2/CdS composite (540 μmol h−1) synthesized using the same method, indicating the cocatalytic effect of MoS2 was better than WS2 in this system.50 Using CdS nanorods as a substitute of CdS nanoparticles, He et al. synthesized the WS2 nanosheets−CdS nanorods composite by an ultrasonic/exfoliation method.37 Compared to the MoS2, WS2 nanosheets are more capable of covering the CdS surface with tighter contact (Figure 9). The largest hydrogen evolution rate of 1222 μmol h−1 can be achieved with a WS2-to-CdS mass ratio of 1.6:1 under visiblelight irradiation (λ ≥ 400 nm). The authors also attributed the enhanced activity to the heterojunctions between WS2 and CdS. The corresponding apparent quantum yield (AQY) was calculated to be 28.9% under monochromatic irradiation of 420 nm.37 Loading of nanosized WS2 cocatalyst could extend the adsorption edge of TiO2 into visible light region. Using photodeposition method, Jing et al. synthesized WS2 sensitized mesoporous TiO2 composite, and a H2 evolution rate of ∼700 μmol h−1 could be obtained under visible light (λ > 430 nm) without the addition of Pt.99 Mahler et al. developed a synthetic protocol (Figure 10) for producing colloidal WS2 monolayers with prismatic 2H phase or distorted octahedral 1T phase.89 For the synthesis of 1TWS2, WCl6 was used as precursors, and oleylamine was used as

Figure 7. (a) SEM image of pure TiO2 nanowires. The inset shows their porous structure; (b) SEM image of as-synthesized MoS2 nanosheet−TiO2 nanowire hybrid structures; (c) XRD patterns of the samples; (d) HRTEM image of as-synthesized MoS2−TiO2 hybrid structures. Reprinted with permission from ref 58. Copyright 2015 Royal Society of Chemistry.

more exposed edges of MoS2 can be provided. The contact between them was very tight (Figure 7d). These 1D hybrid nanostructures exhibited high activity with an enhanced hydrogen evolution rate of 1.67 mmol h−1 g−1 under visible light (λ > 420 nm). Bai and co-workers exfoliated the bulk MoS2 into 1T phase MoS2 nanosheets using the lithium insertion method.79 Using them as supports, TiO2−MoS2 (1T) was synthesized. The TiO2−MoS2 (1T) was found with better activity than that supported on bulk MoS2 (2H). They thought that the 1T-MoS2 nanosheets not only act as electron delivery channels, but also offer active sites for H2 evolution on their basal plane and edges. Due to the presence of active sites on the 1T-MoS2 basal 4616


Review


WS2 can also be used for the modification of metal-free gC3N4 to increase the charge separation. Hou et al. prepared the WS2-mesoporous g-C3N4 (mpg-CN) composite photocatalyst via an impregnation−sulfidation approach.88 The hydrogen evolution rate reached an optimum of 12 μmol h−1 with a loading percentage of 0.3 wt %. This enhanced activity of WS2/ mpg-CN was mainly attributed to the thin layered junctions formed between WS2 and mpg-CN and the great performance of WS2 for HER. 3.3. NiS2 Based Photocatalysts. Due to the smaller intrinsic resistance of NiS2 compared to NiS, the NiS2 shows better electrochemical HER activity.100 NiS2 should be therefore more efficient to utilize the photogenerated electron for water reduction. Yuan et al. loaded NiS2 for the modification of CdLa2S4 via a hydrothermal process.93 With the optimum of 2 wt % NiS2 loading, a H2 production rate of 2.5 mmol h−1 g−1 could be obtained. They attributed the high activity to the enhanced separation of photogenerated electrons and holes as well as the activation effect of NiS2 for H2 evolution. They also proved that the presence of NiS2 can dramatically increase the H2 production rate to 4.06 μmol h−1 for g-C3N4, which is 3 times higher than that of 1 wt % Pt loaded g-C3N4.94

Figure 9. Model and HR-TEM image for the CdS nanorods@WS2 nanosheets composite; the histogram shows the average hydrogen evolution rate of WS2−CdS synthesized using different dispersing agents. Reproduced with permission from ref 37. Copyright 2016 American Chemical Society.

4. APPLICATION FOR POLLUTANTS DEGRADATION 4.1. MoS2 Based Photocatalysts. Photocatalysis is also an attractive technology for the degradation of pollutants in water using solar energy.120 Some examples of the recent TMDs based photocatalysts for pollutants degradation are shown in Table 2. A large number of semiconductor materials, such as metal oxides and metal sulfides (e.g., TiO2, WO3, CdS, ZnS, and ZnO), have been developed as active catalysts for photocatalytic organic degradation.22,121−124 TMDs materials have been proved to be effective cocatalysts not only for photocatalytic H2 evolution but also for organics degradation. Except for the photocatalytic hydrogen evolution, Bai et al. also evaluated the advantage of MoS2 as cocatalyst for TiO2 in photodegradation of RhB. A degradation activity order similar to H2 generation was conclude as TiO2−MoS2(1T) >TiO2 > TiO2−MoS2(2H).79 Liu et al. loaded MoS2 nanoparticles on the surface of TiO2 nanobelts by a simple hydrothermal method. Compared to the pure TiO2 nanobelts, the light absorption edge of MoS2 modified samples are red-shifted, which can be attributed to the strong chemical bonding between TiO2 and MoS2 (Figure 12a). The transient photocurrent was also increased after the loading of MoS2, indicating a more efficient charge separation efficiency (Figure 12b). The photocatalytic degradation rate of RhB was therefore increased with a pseudo-first-order reaction kinetics, and the heterojunction structures containing 40 wt % MoS2 possess the highest photocatalytic activity.108 Bismuth oxybromide (BiOBr) has recently attracted much attention. Its photocatalytic activity, however, was limited by the high recombination rate of the photogenerated electron− hole pairs.125 Di et al. synthesized MoS2/BiOBr composite using a facile hydrothermal method with MoS2 as support.101 The obtained samples were composed of numerous microspheres with different diameters. Loading MoS2 as cocatalyst for BiOBr can create more interface area and reduce the barrier for electron transfer, thus accelerating the charge transfer (Figure 13). By using tert-butanol as hydroxyl radical trapping agents and disodium ethylenediaminetetraacetate as holes scavenger, they proved that both holes and hydroxyl radicals

Figure 10. Synthetic protocols for producing colloidal WS 2 monolayers with 1T or 2H phase structure. Reprinted with permission from ref 89. Copyright 2014 American Chemical Society.

solvent. An extra hexamethyldisilazane (HMDS) was needed to obtain 2H-WS2 using this method. Loading the generated 1TWS2 nanosheets with P25−TiO2 by a simple adsorption protocol, the H2 evolution rate can be increased by more than 3-fold to 2570 μmol g−1 h−1 compared to bare P25. Combined with 2H-WS2, the hydrogen evolution rate however decreased (Figure 11). They attributed this activity diminishing to the extra recombination centers introduced by the addition of semiconducting 2H-WS2 layers.89

Figure 11. (a) Electronic band alignment between TiO2 and synthesized 1T-WS2 and 2H-WS2 nanostructures. (b) Photocatalytic hydrogen production rates for P25−TiO2 and the TiO2:1T-WS2 and TiO2:2H-WS2 nanocomposites. Reprinted with permission from ref 89. Copyright 2014 American Chemical Society. 4617


4618

NiS2/g-C3N4

WS2−Bi2WO6/ Bi3.84W0.16O6.24 CoS2−GR/TiO2

sonochemical and hydrothermal method hydrothermal

combination of anodization and hydrothermal precipitation in situ photoreduction deposition hydrothermal

MoS2@TiO2

Ag3PO4/MoS2 WS2/TiO2

in situ hydrothermal

BiVO4@MoS2

deposition

MoS2/Ag3PO4

solvothermal

two-step hydrothermal

MoS2/SrTiO3

MoS2/C3N4

two-step hydrothermal

MoS2/TiO2

microwave process

aqueous chemical method two-step hydrothermal

MoS2−α-S MoS2/BiVO4

MoS2/BiOBr

hydothermal one-pot solvothermal

TiO2@MoS2 MoS2−GR−TiO2

anion-exchange strategy

sonicated mixing solvothermal

MoS2/Bi2S3

hydrothermal-deposition

Ag3PO4−MoS2/ GR 1T-MoS2/TiO2 MoS2/Bi2MoO6

two-step hydrothermal hydrothermal


MoS2/CdS

MoS2/SnO2 MoS2/CdS

solvothermal

synthesis method

MoS2/BiOBr

catalyst

20 W tungsten halogen lamp 150 W Xe lamp 500 W xenon lamp (λ > 420 nm) 500 W xenon lamp (λ ≥ 400 nm) 500 W xenon lamp 100 W UV-light

MB 10 mg L−1 RhB 10 mg L−1 MB 8 mg L−1 MB 40 mg L−1 RhB 10 mg L−1 MO 30 mg L−1

DP of 87% in 6 h DP of 74.4% in 3 h

300 W xenon lamp (λ ≥ 400 nm) 300 W xenon lamp (λ ≥ 400 nm) 500 W xenon lamp (λ ≥ 400 nm)

ciprofloxacin (CIP) 10 mg L−1 MO 10 mg L−1 crystal violet 25 mg L−1

250 W xenon lamp (λ > 400 nm)

MB 2.0 × 10−5 mol/L RhB 10 mg L−1

MB 20 mg L−1 4-chlorophenol 2.2 × 10−4 M RhB 10−5 M

230 W long-wave mercury lamp λ = 365 nm 35 W Xe arc lamp (λ ≥ 420 nm) 300W tungsten halogen lamp (λ > 400 nm) 300W Xe lamp 320 nm ≤ λ≤ 780 nm 8 W halogen lamp 400−790 nm

RhB 10 mg L−1

DP of ∼95% in 30 min

300 W xenon lamp (λ ≥ 400 nm)

Cr(VI) 5 mg L−1

kapp 0.00818 min−1

DP of >90% in 90 min

DP of ∼100% in 60 min

DP of 98.2% in 60 min DP of >60% in 60 min

DP of 85.3% in 120 min


0.047 min−1 DP of 94.1% in 45 min

Rate constant (k) 0.2228 min−1

150 W mercury lamp 500 W Xe-illuminator

300 W Xe lamp (λ > 400 nm)

RhB 10 mg L−1 Bisphenol A 20 mg L−1 RhB 10 mg L−1 MB 10 mg L−1


k 0.0239 min−1

DP of 80% in 150 min DP of 94.2% in 120 min

DP of 90% in 100 min DP of 80% in 80 min

DP of >99% in 30 min DP of 100% in 80 min

300 W Xe lamp (λ > 400 nm) 150 W Xe lamp (λ > 420 nm)

500 W xenon lamp (λ > 420 nm)

300 W Xe arc lamp (λ > 420 nm)

activity

MB and RhB 2 × 10−5 M 2,4-dichlorophenol 20 mg L−1 RhB 10−5 mol L−1 RhB 10 mg L−1

300 W Xe lamp (λ >400 nm)

light source degradation percentage (DP) of 94% in 50 min average rate constants kapp (min−1) 5.83 × 10−3 for MB 3.16 × 10−3 for RhB DP of >99% in 20 min

RhB 10 mg L

−1

pollutants

Table 2. Summary of TMDs Based Photocatalysts for Pollutants Degradation morphology

5.4 times than g-C3N4

7.2 times higher than pure C3 N 4 DP of 400 nm).111 They also investigated the time dependent morphology evolution of the samples to show the growth mechanism of the 2D MoS2 nanosheet-coated Bi2S3 discoid composites (Figure 14). On the basis of the analysis, they attributed the enhanced activity to the matched energy band, the intimate interfacial contact between MoS2 and Bi2S3, and the strong adsorption ability toward Cr(VI) in aqueous solution. Yan et al. synthesized graphene-like MoS2/g-C3N4 composite using a facile ethylene glycol (EG)-assisted solvothermal method. The obtained samples were effective for MO degradation under visible light.113 They used ESR spin trap technique (with 5,5-dimethyl-1-pyrroline N-oxide (DMPO)) to identify the possible radical species during the photocatalysis process, by which they confirmed that O2•− was the main active oxidizing species for organics degradation (Figure 15).113 Loading MoS2 on the surface of BiVO4, Zhao et al. fabricated BiVO4@p-MoS2 with core−shell structure; the photocatalytic activity and the light absorption range were tunable by control

Figure 15. ESR spectra of radical adducts trapped by DMPO: (A) DMPO-O2•− radical species detected for a GL-MoS2/C3N4 (0.1%) dispersion in methanol, (B) DMPO-·OH radical species detected for a GL-MoS 2 /C 3N 4 (0.1%) dispersion in water. Reprinted with permission from ref 113. Copyright 2016 John Wiley & Sons, Inc.

the loading amount of MoS2. The BiVO4@MoS2 (10 wt %) sample with 300 nm MoS2 shell showed the highest photoreduction and photooxidation activities.114 4.2. WS2 and Other TMDs Based Photocatalysts. As early as 2004, Ho et al. had successfully modified TiO2 with MoS2 and WS2 clusters using an in situ photoreduction deposition method.62 They used ESR technology to confirm the presence of Ti3+ radical, which was the evidence for the photogenerated electrons transfer from the CB of MS2 to that of TiO2 under visible light. The obtained samples were then evaluated for the photocatalytic degradation of MB and 4chlorophenol under visible light (λ > 400 nm). Both MoS2 and WS2 nanocluster sensitized TiO2 exhibit high photocatalytic activity, and the enhancement effect of WS2 was better than that of MoS2. Zou et al. synthesized novel heterostructured composite of few layered WS2−Bi2WO6/Bi3·84W0.16O6.24 with a facile hydrothermal method.117 The formation mechanism of the composite is proposed in Figure 16, which contained the 4619


Review


Figure 16. Formation mechanism of the few-layer WS2−BWO composite. Reprinted with permission from ref 117. Copyright 2015 Elsevier. Figure 18. Morphology characterization of the TiO2−MoS2/GR composite. TEM (a, b) and HRTEM (c, d) images of the TiO2− MoS2/GR composite. Reprinted with permission from ref 25, Copyright 2015 American Chemical Society.

liquid exfoliation of WS2 and the following growth of BWO on the surface of WS2. The exfoliated WS2 was with negative ζpotential and native vacancy defects, which are beneficial for the adsorption of Bi3+ and the subsequent formation process. As shown in Figure 17, the impact of scavengers on RhB

graphene cocatalysts. The activity for H2 evolution was different by adjusting the GR percentage of MoS2/GR cocatalysts and the percentage of the hybrid for the ternary photocatalysts. Even without a noble-metal cocatalyst, the TiO2/MoS2/ graphene composite could reach a high H2 production rate of 165.3 μmol h−1 after optimization, and the AQY reaches 9.7% at 365 nm. For the enhancement mechanism analysis, they thought that GR could transport the photogenerated electrons rapidly, and the MoS2 nanosheets can accept electrons and act as active sites for H2 evolution (Figure 19).

Figure 17. Effects of different scavengers and oxygen on photodegradation of RhB over the few-layer WS2−BWO under visible-light irradiation. Reprinted with permission from ref 117. Copyright 2015 Elsevier.

degradation follows this order: benzoquinone > sodium oxalate > isopropyl alcohol. Therefore, the ·O2− was the main active species in the degradation process, the second is h+, and the · OH contributed slightly. Zhu et al. synthesized NiS2/g-C3N4 composites using a facile hydrothermal method. Their activity for RhB photodegradation could be tuned by changing the loading amounts of NiS2.119

Figure 19. Schematic illustration of the charge transfer in TiO2/MG composites. Reprinted with permission from ref 25. Copyright 2015 American Chemical Society.

5. TMD/GR BASED TERNARY PHOTOCATALYSTS As GR can serve as an excellent charge carrier at room temperature (200 000 cm2 V−1 s−1), it has attracted increasing attention in the photocatalysis field.22,23 The TMDs materials can be combined with GR to form TMD/GR layered structures, which can be used as hybrid cocatalysts for the modification of semiconductors. Xiang et al. report a new composite material consisting of TiO2 nanoparticles supported on the layered MoS2/graphene hybrid (Figure 18).25 Intimate contact could be observed between TiO2 and the 2D MoS2/

By using both GR and MoS2 as the cocatalysts, CdS with different morphology can be modified for higher activities. Chang et al. supported MoS2 on nanosized GR using hydrothermal method. After that, 3D hierarchical MoS2/GR− CdS composites with diameters of 100 to 300 nm were synthesized with the help of polyvinylpyrrolidone (PVP) (Figure 20).77 The photocatalytic H2 evolution activity of the proposed MoS2/GR−CdS composite was then tested in lactic acid solution. A H2 evolution rate of 1.8 mmol/h corresponding 4620


Review


the high photoactivity. Therefore, new and effective loading methods should be developed for real application. Second, the active sites of the TMDs are origin from their defects and edges. Synthesis of TMDs with smaller scales or porous structures to expose more active sites are still needed. Third, to increase the electric conductivity of the TMDs modified photocatalysts is another important solution. By adding a small percentage of graphene or carbon nanotube, more efficient charge separation could be achieved, thus leading to the photoactivity enhancement. Although more in-depth studies are still needed for real application, TMD based photocatalysts have great potential to address various environmental and energy-related problems.

■

Figure 20. (a) Schematic illustration of growth mechanism of MoS2/ GR−CdS composites. TEM images of GO (b) and nanosized rGO (c). SEM (d) and TEM (e) images of as-prepared MoS2/GR composite. The inset of panel e is the HRTEM image of MoS2/GR composite. (f and g) SEM images of CdS−MoS2/GR composites. TEM (h) and HRTEM (i and j) images of the CdS−MoS2/GR composite. Reprinted with permission from ref 77. Copyright 2014 American Chemical Society.

AUTHOR INFORMATION

Corresponding Author

*X. Fan. Phone: +86-22-27890090. E-mail: [email protected]. cn. ORCID

Wenchao Peng: 0000-0002-1515-8287 Yang Li: 0000-0003-3003-9857 Xiaobin Fan: 0000-0002-9615-3866

to an AQE of 28.1% at 420 nm was achieved, even higher than that of Pt/CdS. Jia et al. synthesized a graphene dispersed CdS−MoS2 nanocrystal, and the largest H2 evolution rate can reach 3.067 mmol/h.74 For the first time, they used time-resolved photoluminescence for the description of the crucial roles of graphene and MoS2 (Figure 21). In the ternary photocatalysts,

Notes

The authors declare no competing financial interest. Biographies

Figure 21. (a) Photocatalytic hydrogen evolution rates over CdS−GO (100:x), CdS−MoS2 (100:x), and CdS−graphene−MoS2 (100:x:2), (b) Photoluminescence decay profiles of CdS, CdS−MoS2 (100:1) and CdS−graphene−MoS2 (100:0.2:1). Reproduced with permission from ref 74. Copyright 2014 Royal Society of Chemistry.

Wenchao Peng received his BS in chemistry from Nankai University and his Ph.D. in chemical engineering in 2011 from Tianjin University. Afterwards, he worked as a post doctor in Curtin University and Hong Kong University from 2011 to 2014. He is currently a faculty member at school of chemical engineering and technology, Tianjin University, China. His research interests include synthesis of nanomaterials and their applications for catalysis, electrocatalysis, and photocatalysis.

WS2 was not so efficient as MoS2, and the H2 evolution rate can only reach 1.842 mmol/h for the CdS−WS2/graphene with an apparent quantum efficiency of 21.2% at 420 nm.92

6. CONCLUSIONS AND PERSPECTIVE This short review focuses on recent developments in the synthesis of TMDs based composites for photocatalytic H2 evolution and pollutants degradation. 2D layered TMDs can be used as effective cocatalysts for the modification of kinds of materials, such as oxides, sulfides, and salts, via different methods including the in situ reduction and postcombination. Due to the superior cocatalytic properties, 2D TMDs nanosheets are postulated to have great potential to replace conventional noble-metal cocatalysts. There are still many challenges to apply the TMDs based composites for real application. First, intimate contact between the semiconductor and the TMDs should be created to facilitate the photogenerated electrons transfer. The formation of stable junction is the most important factor responsible for 4621


Review


Chemical Engineering, Tianjin University, in 2006 and 2009, respectively. He joined Tianjin University in 2009 as a lecturer and got promoted to associate professor and professor in 2011 and 2013, respectively. His research interests include the preparation and applications of new nanomaterials and green chemistry.

Yang Li received her BS and Ph.D. from school of chemical engineering and technology, Tianjin University, in 2007 and 2012, respectively. She joined Tianjin University in 2012. Her research interests include the preparation and applications of new nanomaterials and green chemistry.

■

ACKNOWLEDGMENTS This research was supported by the project No. 21506158 and No. 21676198 from the National Natural Science Foundation of China (NSFC). This invited contribution is part of the I&EC Research special issue for the 2017 Class of Influential Researchers.

■

REFERENCES

(1) Inoue, T.; Fujishima, A.; Konishi, S.; Honda, K. Photoelectrocatalytic reduction of carbon dioxide in aqueous suspensions of semiconductor powders. Nature 1979, 277, 637−638. (2) Chen, X. B.; Shen, S. H.; Guo, L. J.; Mao, S. S. Semiconductorbased Photocatalytic Hydrogen Generation. Chem. Rev. 2010, 110, 6503−6570. (3) Leng, M.; Chen, Y.; Xue, J. M. Synthesis of TiO2 nanosheets via an exfoliation route assisted by a surfactant. Nanoscale 2014, 6, 8531− 8534. (4) Bao, N.; Shen, L.; Takata, T.; Domen, K.; Gupta, A.; Yanagisawa, K.; Grimes, C. A. Facile cd-thiourea complex thermolysis synthesis of phase-controlled CdS nanocrystals for photocatalytic hydrogen production under visible light. J. Phys. Chem. C 2007, 111, 17527− 17534. (5) Ng, Y. H.; Iwase, A.; Kudo, A.; Amal, R. Reducing Graphene Oxide on a Visible-Light BiVO4 Photocatalyst for an Enhanced Photoelectrochemical Water Splitting. J. Phys. Chem. Lett. 2010, 1, 2607−2612. (6) Kudo, A.; Miseki, Y. Heterogeneous photocatalyst materials for water splitting. Chem. Soc. Rev. 2009, 38, 253−278. (7) Rajeshwar, K.; de Tacconi, N. R. Solution combustion synthesis of oxide semiconductors for solar energy conversion and environmental remediation. Chem. Soc. Rev. 2009, 38, 1984−1998. (8) Yang, J. H.; Wang, D. G.; Han, H. X.; Li, C. Roles of Cocatalysts in Photocatalysis and Photoelectrocatalysis. Acc. Chem. Res. 2013, 46, 1900−1909. (9) Bi, Y.; Ouyang, S.; Umezawa, N.; Cao, J.; Ye, J. Facet Effect of Single-Crystalline Ag3PO4 Sub-microcrystals on Photocatalytic Properties. J. Am. Chem. Soc. 2011, 133, 6490−6492. (10) Voiry, D.; Mohite, A.; Chhowalla, M. Phase engineering of transition metal dichalcogenides. Chem. Soc. Rev. 2015, 44, 2702− 2712. (11) Ji, J. Y.; Ji, H. X.; Zhang, L. L.; Zhao, X.; Bai, X.; Fan, X. B.; Zhang, F. B.; Ruoff, R. S. Graphene-Encapsulated Si on UltrathinGraphite Foam as Anode for High Capacity Lithium-Ion Batteries. Adv. Mater. 2013, 25, 4673−4677. (12) 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. (13) Qu, Y.; Duan, X. Progress, challenge and perspective of heterogeneous photocatalysts. Chem. Soc. Rev. 2013, 42, 2568−2580. (14) Xiang, Q.; Yu, J.; Jaroniec, M. Graphene-based semiconductor photocatalysts. Chem. Soc. Rev. 2012, 41, 782−796. (15) 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. (16) Osterloh, F. E. Inorganic nanostructures for photoelectrochemical and photocatalytic water splitting. Chem. Soc. Rev. 2013, 42, 2294− 2320. (17) Wu, K. F.; Zhu, H. M.; Liu, Z.; Rodriguez-Cordoba, W.; Lian, T. Q. Ultrafast Charge Separation and Long-Lived Charge Separated

Fengbao Zhang is currently a professor at the Department of Chemical Engineering, Tianjin University, China. He received his BSc, MSc and PhD from Tianjin University in 1984, 1987 and 1991, respectively, majoring in chemical engineering. His research interests include new nanomaterials and green chemistry.

Guoliang Zhang is currently a professor at the Department of Chemical Engineering, Tianjin University, China. He received his BSc and MSc from Tianjin University in 1982 and 1988, respectively, majoring in chemical engineering. His research interests include new nanomaterials and green chemistry.

Xiaobin Fan is currently a professor at Tianjin University, China. He received his BSc in 2003 from Nankai University with the major in chemistry. Then he received his MSc and PhD from Department of 4622


Review


under Visible Light Irradiation. J. Phys. Chem. C 2010, 114, 1963− 1968. (37) He, J.; Chen, L.; Yi, Z. Q.; Au, C. T.; Yin, S. F. CdS Nanorods Coupled with WS2 Nanosheets for Enhanced Photocatalytic Hydrogen Evolution Activity. Ind. Eng. Chem. Res. 2016, 55, 8327−8333. (38) Chhowalla, M.; Shin, H. S.; Eda, G.; Li, L.-J.; Loh, K. P.; Zhang, H. The chemistry of two-dimensional layered transition metal dichalcogenide nanosheets. Nat. Chem. 2013, 5, 263−275. (39) Li, X.; Wang, J.; Xu, D.; Sun, Z.; Zhao, Q.; Peng, W.; Li, Y.; Zhang, G.; Zhang, F.; Fan, X. NbSe2 Nanosheet Supported PbBiO2Br as a High Performance Photocatalyst for the Visible Light-driven Asymmetric Alkylation of Aldehyde. ACS Sustainable Chem. Eng. 2015, 3, 1017−1022. (40) Zeng, Z.; Yin, Z.; Huang, X.; Li, H.; He, Q.; Lu, G.; Boey, F.; Zhang, H. Single-Layer Semiconducting Nanosheets: High-Yield Preparation and Device Fabrication. Angew. Chem., Int. Ed. 2011, 50, 11093−11097. (41) Zeng, Z.; Sun, T.; Zhu, J.; Huang, X.; Yin, Z.; Lu, G.; Fan, Z.; Yan, Q.; Hng, H. H.; Zhang, H. An Effective Method for the Fabrication of Few-Layer-Thick Inorganic Nanosheets. Angew. Chem., Int. Ed. 2012, 51, 9052−9056. (42) Lin, Y.-C.; Dumcenco, D. O.; Huang, Y.-S.; Suenaga, K. Atomic mechanism of the semiconducting-to-metallic phase transition in single-layered MoS2. Nat. Nanotechnol. 2014, 9, 391−396. (43) Wang, H.; Lu, Z.; Kong, D.; Sun, J.; Hymel, T. M.; Cui, Y. Electrochemical Tuning of MoS2 Nanoparticles on Three-Dimensional Substrate for Efficient Hydrogen Evolution. ACS Nano 2014, 8, 4940−4947. (44) Voiry, D.; Salehi, M.; Silva, R.; Fujita, T.; Chen, M.; Asefa, T.; Shenoy, V. B.; Eda, G.; Chhowalla, M. Conducting MoS2 Nanosheets as Catalysts for Hydrogen Evolution Reaction. Nano Lett. 2013, 13, 6222−6227. (45) Li, H.; Wu, J. M. T.; Yin, Z. Y.; Zhang, H. Preparation and Applications of Mechanically Exfoliated Single-Layer and Multi layer MoS2 and WSe2 Nanosheets. Acc. Chem. Res. 2014, 47, 1067−1075. (46) Fan, X.; Xu, P.; Zhou, D.; Sun, Y.; Li, Y. C.; Nguyen, M. A. T.; Terrones, M.; Mallouk, T. E. Fast and Efficient Preparation of Exfoliated 2H MoS2 Nanosheets by Sonication-Assisted Lithium Intercalation and Infrared Laser-Induced 1T to 2H Phase Reversion. Nano Lett. 2015, 15, 5956−5960. (47) Zhang, J.; Zhu, Z. P.; Feng, X. L. Construction of TwoDimensional MoS2/CdS p-n Nanohybrids for Highly Efficient Photocatalytic Hydrogen Evolution. Chem. - Eur. J. 2014, 20, 10632−10635. (48) Zhu, Y. Y.; Ling, Q.; Liu, Y. F.; Wang, H.; Zhu, Y. F. Photocatalytic H2 evolution on MoS2-TiO2 catalysts synthesized via mechanochemistry. Phys. Chem. Chem. Phys. 2015, 17, 933−940. (49) Vattikuti, S. V. P.; Byon, C.; Reddy, C. V.; Ravikumar, R. Improved photocatalytic activity of MoS2 nanosheets decorated with SnO2 nanoparticles. RSC Adv. 2015, 5, 86675−86684. (50) Zong, X.; Yan, H. J.; Wu, G. P.; Ma, G. J.; Wen, F. Y.; Wang, L.; Li, C. Enhancement of photocatalytic H2 evolution on CdS by loading MoS2 as cocatalyst under visible light irradiation. J. Am. Chem. Soc. 2008, 130, 7176−7177. (51) Peng, W. C.; Wang, X.; Li, X. Y. The synergetic effect of MoS2 and graphene on Ag3PO4 for its ultra-enhanced photocatalytic activity in phenol degradation under visible light. Nanoscale 2014, 6, 8311− 8317. (52) Ambrosi, A.; Sofer, Z.; Pumera, M. 2H –> 1T phase transition and hydrogen evolution activity of MoS2, MoSe2, WS2 and WSe2 strongly depends on the MX2 composition. Chem. Commun. 2015, 51, 8450−3. (53) Li, Y. G.; Wang, H. L.; Xie, L. M.; Liang, Y. Y.; Hong, G. S.; Dai, H. J. MoS2 Nanoparticles Grown on Graphene: An Advanced Catalyst for the Hydrogen Evolution Reaction. J. Am. Chem. Soc. 2011, 133, 7296−7299. (54) Morales-Guio, C. G.; Stern, L. A.; Hu, X. L. Nanostructured hydrotreating catalysts for electrochemical hydrogen evolution. Chem. Soc. Rev. 2014, 43, 6555−6569.

State in Photocatalytic CdS-Pt Nanorod Heterostructures. J. Am. Chem. Soc. 2012, 134, 10337−10340. (18) Singh, R.; Pal, B. Highly enhanced photocatalytic activity of Au nanorod-CdS nanorod heterocomposites. J. Mol. Catal. A: Chem. 2013, 378, 246−254. (19) Huang, S.; Lin, Y.; Yang, J. H.; Li, X. R.; Zhang, J.; Yu, J. G.; Shi, H. L.; Wang, W. Z.; Yu, Y. Enhanced photocatalytic activity and stability of semiconductor by Ag doping and simultaneous deposition: the case of CdS. RSC Adv. 2013, 3, 20782−20792. (20) Su, R.; Tiruvalam, R.; He, Q.; Dimitratos, N.; Kesavan, L.; Hammond, C.; Lopez-Sanchez, J. A.; Bechstein, R.; Kiely, C. J.; Hutchings, G. J.; Besenbacher, F. Promotion of Phenol Photodecomposition over TiO2 Using Au, Pd, and Au-Pd Nanoparticles. ACS Nano 2012, 6, 6284−6292. (21) Novoselov, K. S.; Geim, A. K.; Morozov, S. V.; Jiang, D.; Zhang, Y.; Dubonos, S. V.; Grigorieva, I. V.; Firsov, A. A. Electric field effect in atomically thin carbon films. Science 2004, 306, 666−669. (22) Xiang, Q. J.; Yu, J. G.; Jaroniec, M. Graphene-based semiconductor photocatalysts. Chem. Soc. Rev. 2012, 41, 782−796. (23) Chen, Z.; Liu, S. Q.; Yang, M. Q.; Xu, Y. J. Synthesis of Uniform CdS Nanospheres/Graphene Hybrid Nanocomposites and Their Application as Visible Light Photocatalyst for Selective Reduction of Nitro Organics in Water. ACS Appl. Mater. Interfaces 2013, 5, 4309− 4319. (24) Peng, W. C.; Li, X. Y. Synthesis of a sulfur-graphene composite as an enhanced metal-free photocatalyst. Nano Res. 2013, 6, 286−292. (25) Xiang, Q. J.; Yu, J. G.; 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. (26) Zhou, L.; Zhang, H.; Sun, H.; Liu, S.; Tade, M. O.; Wang, S.; Jin, W. Recent advances in non-metal modification of graphitic carbon nitride for photocatalysis: a historic review. Catal. Sci. Technol. 2016, 6, 7002−7023. (27) Sun, H.; Zhou, G.; Wang, Y.; Suvorova, A.; Wang, S. A New Metal-Free Carbon Hybrid for Enhanced Photocatalysis. ACS Appl. Mater. Interfaces 2014, 6, 16745−16754. (28) Sun, H.; Wang, S. 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. (29) Lu, Q.; Yu, Y.; Ma, Q.; Chen, B.; Zhang, H. 2D TransitionMetal-Dichalcogenide-Nanosheet-Based Composites for Photocatalytic and Electrocatalytic Hydrogen Evolution Reactions. Adv. Mater. 2016, 28, 1917−1933. (30) Huang, X.; Tan, C.; Yin, Z.; Zhang, H. 25th Anniversary Article: Hybrid Nanostructures Based on Two-Dimensional Nanomaterials. Adv. Mater. 2014, 26, 2185−2204. (31) Xu, M. S.; Liang, T.; Shi, M. M.; Chen, H. Z. Graphene-Like Two-Dimensional Materials. Chem. Rev. 2013, 113, 3766−3798. (32) Sang, Y.; Zhao, Z.; Zhao, M.; Hao, P.; Leng, Y.; Liu, H. From UV to Near-Infrared, WS2 Nanosheet: A Novel Photocatalyst for Full Solar Light Spectrum Photodegradation. Adv. Mater. 2015, 27, 363− 369. (33) Atkin, P.; Daeneke, T.; Wang, Y.; Carey, B. J.; Berean, K. J.; Clark, R. M.; Ou, J. Z.; Trinchi, A.; Cole, I. S.; Kalantar-zadeh, K. 2D WS2/carbon dot hybrids with enhanced photocatalytic activity. J. Mater. Chem. A 2016, 4, 13563−13571. (34) Du, P.; Zhu, Y.; Zhang, J.; Xu, D.; Peng, W.; Zhang, G.; Zhang, F.; Fan, X. Metallic 1T phase MoS2 nanosheets as a highly efficient cocatalyst for the photocatalytic hydrogen evolution of CdS nanorods. RSC Adv. 2016, 6, 74394−74399. (35) Lv, R.; Robinson, J. A.; Schaak, R. E.; Sun, D.; Sun, Y.; Mallouk, T. E.; Terrones, M. Transition Metal Dichalcogenides and Beyond: Synthesis, Properties, and Applications of Single- and Few-Layer Nanosheets. Acc. Chem. Res. 2015, 48, 56−64. (36) Zong, X.; Wu, G. P.; Yan, H. J.; Ma, G. J.; Shi, J. Y.; Wen, F. Y.; Wang, L.; Li, C. Photocatalytic H2 Evolution on MoS2/CdS Catalysts 4623


Review


for cooperative photocatalytic hydrogen production from water. Chem. Commun. 2014, 50, 1185−1188. (73) Ge, L.; Han, C. C.; Xiao, X. L.; Guo, L. L. Synthesis and characterization of composite visible light active photocatalysts MoS2g-C3N4 with enhanced hydrogen evolution activity. Int. J. Hydrogen Energy 2013, 38, 6960−6969. (74) Jia, T.; Kolpin, A.; Ma, C.; Chan, R. C.-T.; Kwok, W.-M.; Tsang, S. C. E. A graphene dispersed CdS-MoS2 nanocrystal ensemble for cooperative photocatalytic hydrogen production from water. Chem. Commun. 2014, 50, 1185−1188. (75) Wang, B.; Li, C.; Hirabayashi, D.; Suzuki, K. Hydrogen evolution by photocatalytic decomposition of water under ultraviolet− visible irradiation over K2La2Ti3−xMxO10+δ perovskite. Int. J. Hydrogen Energy 2010, 35, 3306−3312. (76) Buehler, N.; Meier, K.; Reber, J. F. Photochemical hydrogen production with cadmium sulfide suspensions. J. Phys. Chem. 1984, 88, 3261−3268. (77) Chang, K.; Mei, Z. W.; Wang, T.; Kang, Q.; Ouyang, S. X.; Ye, J. H. MoS2/Graphene Cocatalyst for Efficient Photocatalytic H-2 Evolution under Visible Light Irradiation. ACS Nano 2014, 8, 7078− 7087. (78) Wei, L.; Chen, Y. J.; Lin, Y. P.; Wu, H. S.; Yuan, R. S.; Li, Z. H. MoS2 as non-noble-metal co-catalyst for photocatalytic hydrogen evolution over hexagonal ZnIn2S4 under visible light irradiations. Appl. Catal., B 2014, 144, 521−527. (79) Bai, S.; Wang, L. M.; Chen, X. Y.; Du, J. T.; Xiong, Y. J. Chemically exfoliated metallic MoS2 nanosheets: A promising supporting co-catalyst for enhancing the photocatalytic performance of TiO2 nanocrystals. Nano Res. 2015, 8, 175−183. (80) Liu, C. B.; Wang, L. L.; Tang, Y. H.; Luo, S. L.; Liu, Y. T.; Zhang, S. Q.; Zeng, Y. X.; Xu, Y. Z. Vertical single or few-layer MoS2 nanosheets rooting into TiO2 nanofibers for highly efficient photocatalytic hydrogen evolution. Appl. Catal., B 2015, 164, 1−9. (81) Liu, Q.; Li, X. L.; He, Q.; Khalil, A.; Liu, D. B.; Xiang, T.; Wu, X. J.; Song, L. Gram-Scale Aqueous Synthesis of Stable Few-Layered 1TMoS2: Applications for Visible-Light-Driven Photocatalytic Hydrogen Evolution. Small 2015, 11, 5556−5564. (82) Tian, Q. W.; Zhang, L.; Liu, J. H.; Li, N. X.; Ma, Q. H.; Zhou, J. C.; Sun, Y. M. Synthesis of MoS2/SrZrO3 heterostructures and their photocatalytic H2 evolution under UV irradiation. RSC Adv. 2015, 5, 734−739. (83) Xiong, J. H.; Liu, Y. H.; Wang, D. K.; Liang, S. J.; Wu, W. M.; Wu, L. An efficient cocatalyst of defect-decorated MoS2 ultrathin nanoplates for the promotion of photocatalytic hydrogen evolution over CdS nanocrystal. J. Mater. Chem. A 2015, 3, 12631−12635. (84) Yuan, Y. J.; Wang, F.; Hu, B.; Lu, H. W.; Yu, Z. T.; Zou, Z. G. Significant enhancement in photocatalytic hydrogen evolution from water using a MoS2 nanosheet-coated ZnO heterostructure photocatalyst. Dalton Trans. 2015, 44, 10997−11003. (85) Zhao, H.; Dong, Y. M.; Jiang, P. P.; Miao, H. Y.; Wang, G. L.; Zhang, J. J. In situ light-assisted preparation of MoS2 on graphitic C3N4 nanosheets for enhanced photocatalytic H2 production from water. J. Mater. Chem. A 2015, 3, 7375−7381. (86) Li, H. D.; Wang, Y. N.; Chen, G. H.; Sang, Y. H.; Jiang, H. D.; He, J. T.; Li, X.; Liu, H. Few-layered MoS2 nanosheets wrapped ultrafine TiO2 nanobelts with enhanced photocatalytic property. Nanoscale 2016, 8, 6101−6109. (87) Li, M. L.; Zhang, L. X.; Fan, X. Q.; Wu, M. Y.; Du, Y. Y.; Wang, M.; Kong, Q. L.; Zhang, L. L.; Shi, J. L. Dual synergetic effects in MoS2/pyridine-modified g-C3N4 composite for highly active and stable photocatalytic hydrogen evolution under visible light. Appl. Catal., B 2016, 190, 36−43. (88) Hou, Y. D.; Zhu, Y. S.; Xu, Y.; Wang, X. C. Photocatalytic hydrogen production over carbon nitride loaded with WS2 as cocatalyst under visible light. Appl. Catal., B 2014, 156, 122−127. (89) 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.

(55) Morales-Guio, C. G.; Hu, X. L. Amorphous Molybdenum Sulfides as Hydrogen Evolution Catalysts. Acc. Chem. Res. 2014, 47, 2671−2681. (56) Yan, Y.; Xia, B. Y.; Xu, Z. C.; Wang, X. Recent Development of Molybdenum Sulfides as Advanced Electrocatalysts for Hydrogen Evolution Reaction. ACS Catal. 2014, 4, 1693−1705. (57) Gao, Q. S.; Giordano, C.; Antonietti, M. Biomimetic Oxygen Activation by MoS2/Ta3N5 Nanocomposites for Selective Aerobic Oxidation. Angew. Chem., Int. Ed. 2012, 51, 11740−11744. (58) Shen, M.; Yan, Z. P.; Yang, L.; Du, P. W.; Zhang, J. Y.; Xiang, B. MoS2 nanosheet/TiO2 nanowire hybrid nanostructures for enhanced visible-light photocatalytic activities. Chem. Commun. 2014, 50, 15447−15449. (59) Zhou, W. J.; Yin, Z. Y.; Du, Y. P.; Huang, X.; Zeng, Z. Y.; Fan, Z. X.; Liu, H.; Wang, J. Y.; Zhang, H. Synthesis of Few-Layer MoS2 Nanosheet-Coated TiO2 Nanobelt Heterostructures for Enhanced Photocatalytic Activities. Small 2013, 9, 140−147. (60) Chen, J. Z.; Wu, X. J.; Yin, L. S.; Li, B.; Hong, X.; Fan, Z. X.; Chen, B.; Xue, C.; Zhang, H. One-pot Synthesis of CdS Nanocrystals Hybridized with Single-Layer Transition-Metal Dichalcogenide Nanosheets for Efficient Photocatalytic Hydrogen Evolution. Angew. Chem., Int. Ed. 2015, 54, 1210−1214. (61) Chen, G. P.; Ding, N.; Li, F.; Fan, Y. Z.; Luo, Y. H.; Li, D. M.; Meng, Q. B. Enhancement of photocatalytic H2 evolution on ZnIn2S4 loaded with in-situ photo-deposited MoS2 under visible light irradiation. Appl. Catal., B 2014, 160, 614−620. (62) Ho, W. K.; Yu, J. C.; Lin, J.; Yu, J. G.; Li, P. S. Preparation and photocatalytic behavior of MoS2 and WS2 nanocluster sensitized TiO2. Langmuir 2004, 20, 5865−5869. (63) Zong, X.; Han, J. F.; Ma, G. J.; Yan, H. J.; Wu, G. P.; Li, C. Photocatalytic H2 Evolution on CdS Loaded with WS2 as Cocatalyst under Visible Light Irradiation. J. Phys. Chem. C 2011, 115, 12202− 12208. (64) Lang, D.; Shen, T. T.; Xiang, Q. J. Roles of MoS2 and Graphene as Cocatalysts in the Enhanced Visible-Light Photocatalytic H2 Production Activity of Multiarmed CdS Nanorods. ChemCatChem 2015, 7, 943−951. (65) Lu, Y. T.; Wang, D. D.; Yang, P.; Du, Y. K.; Lu, C. Coupling ZnxCd1-xS nanoparticles with graphene-like MoS2: superior interfacial contact, low overpotential and enhanced photocatalytic activity under visible-light irradiation. Catal. Sci. Technol. 2014, 4, 2650−2657. (66) Tian, G. H.; Chen, Y. J.; Ren, Z. Y.; Tian, C. G.; Pan, K.; Zhou, W.; Wang, J. Q.; Fu, H. G. Enhanced Photocatalytic Hydrogen Evolution over Hierarchical Composites of ZnIn2S4 Nanosheets Grown on MoS2 Slices. Chem. - Asian J. 2014, 9, 1291−1297. (67) Zhu, B. L.; Lin, B. Z.; Zhou, Y.; Sun, P.; Yao, Q. R.; Chen, Y. L.; Gao, B. F. Enhanced photocatalytic H2 evolution on ZnS loaded with graphene and MoS2 nanosheets as cocatalysts. J. Mater. Chem. A 2014, 2, 3819−3827. (68) Jiang, W. J.; Liu, Y. F.; Zong, R. L.; Li, Z. P.; Yao, W. Q.; Zhu, Y. F. Photocatalytic hydrogen generation on bifunctional ternary heterostructured In2S3/MoS2/CdS composites with high activity and stability under visible light irradiation. J. Mater. Chem. A 2015, 3, 18406−18412. (69) Peng, W.-c.; Li, X.-y. Synthesis of MoS2/g-C3N4 as a solar lightresponsive photocatalyst for organic degradation. Catal. Commun. 2014, 49, 63−67. (70) Chen, G. P.; Li, D. M.; Li, F.; Fan, Y. Z.; Zhao, H. F.; Luo, Y. H.; Yu, R. C.; Meng, Q. B. Ball-milling combined calcination synthesis of MoS2/CdS photocatalysts for high photocatalytic H-2 evolution activity under visible light irradiation. Appl. Catal., A 2012, 443, 138−144. (71) Li, Y. X.; Wang, H.; Peng, S. Q. Tunable Photodeposition of MoS2 onto a Composite of Reduced Graphene Oxide and CdS for Synergic Photocatalytic Hydrogen Generation. J. Phys. Chem. C 2014, 118, 19842−19848. (72) Jia, T. T.; Kolpin, A.; Ma, C. S.; Chan, R. C. T.; Kwok, W. M.; Tsang, S. C. E. A graphene dispersed CdS-MoS2 nanocrystal ensemble 4624


Review


(108) Liu, H.; Lv, T.; Zhu, C. K.; Su, X.; Zhu, Z. F. Efficient synthesis of MoS2 nanoparticles modified TiO2 nanobelts with enhanced visiblelight-driven photocatalytic activity. J. Mol. Catal. A: Chem. 2015, 396, 136−142. (109) Song, Y. H.; Lei, Y. C.; Xu, H.; Wang, C.; Yan, J.; Zhao, H. Z.; Xu, Y. G.; Xia, J. X.; Yin, S.; Li, H. M. Synthesis of few-layer MoS2 nanosheet-loaded Ag3PO4 for enhanced photocatalytic activity. Dalton Trans. 2015, 44, 3057−3066. (110) Wang, C. X.; Lin, H. H.; Xu, Z. Z.; Cheng, H.; Zhang, C. Onestep hydrothermal synthesis of flowerlike MoS2/CdS heterostructures for enhanced visible-light photocatalytic activities. RSC Adv. 2015, 5, 15621−15626. (111) Weng, B.; Zhang, X.; Zhang, N.; Tang, Z. R.; Xu, Y. J. TwoDimensional MoS2 Nanosheet-Coated Bi2S3 Discoids: Synthesis, Formation Mechanism, and Photocatalytic Application. Langmuir 2015, 31, 4314−4322. (112) Xia, J. X.; Ge, Y. P.; Zhao, D. X.; Di, J.; Ji, M. X.; Yin, S.; Li, H. M.; Chen, R. Microwave-assisted synthesis of few-layered MoS2/ BiOBr hollow microspheres with superior visible-light-response photocatalytic activity for ciprofloxacin removal. CrystEngComm 2015, 17, 3645−3651. (113) Yan, J.; Chen, Z. G.; Ji, H. Y.; Liu, Z.; Wang, X.; Xu, Y. G.; She, X. J.; Huang, L. Y.; Xu, L.; Xu, H.; Li, H. M. Construction of a 2D Graphene-Like MoS2/C3N4 Heterojunction with Enhanced VisibleLight Photocatalytic Activity and Photoelectrochemical Activity. Chem. - Eur. J. 2016, 22, 4764−4773. (114) Zhao, W.; Liu, Y.; Wei, Z. B.; Yang, S. G.; He, H.; Sun, C. Fabrication of a novel p-n heterojunction photocatalyst n-BiVO4@pMoS2 with core-shell structure and its excellent visible-light photocatalytic reduction and oxidation activities. Appl. Catal., B 2016, 185, 242−252. (115) Zheng, L. X.; Han, S. C.; Liu, H.; Yu, P. P.; Fang, X. S. Hierarchical MoS2 Nanosheet@TiO2 Nanotube Array Composites with Enhanced Photocatalytic and Photocurrent Performances. Small 2016, 12, 1527−1536. (116) Zhu, C. S.; Zhang, L.; Jiang, B.; Zheng, J. T.; Hu, P.; Li, S. J.; Wu, M. B.; Wu, W. T. Fabrication of Z-scheme Ag3PO4/MoS2 composites with enhanced photocatalytic activity and stability for organic pollutant degradation. Appl. Surf. Sci. 2016, 377, 99−108. (117) Zou, J. P.; Ma, J.; Luo, J. M.; Yu, J.; He, J. K.; Meng, Y. T.; Luo, Z.; Bao, S. K.; Liu, H. L.; Luo, S. L.; Luo, X. B.; Chen, T. C.; Suib, S. L. Fabrication of novel heterostructured few layered WS2-Bi2WO6/ Bi3.84W0.16O6.24 composites with enhanced photocatalytic performance. Appl. Catal., B 2015, 179, 220−228. (118) Zhu, L.; Jo, S. B.; Ye, S.; Ullah, K.; Meng, Z. D.; Oh, W. C. A green and direct synthesis of photosensitized CoS2-graphene/TiO2 hybrid with high photocatalytic performance. J. Ind. Eng. Chem. 2015, 22, 264−271. (119) Zhu, C. Z.; Jiang, Z. F.; Wei, W.; Chen, L. L.; Liu, D.; Qian, K.; Lu, X. M.; Xie, J. M. Fabrication of noble-metal-free NiS2/g-C3N4 hybrid photocatalysts with visible light-responsive photocatalytic activities. Res. Chem. Intermed. 2016, 42, 6483−6499. (120) Hoffmann, M. R.; Martin, S. T.; Choi, W. Y.; Bahnemann, D. W. Environmental Applications of Semiconductor Photocatalysis. Chem. Rev. 1995, 95, 69−96. (121) Fan, H. G.; Zhao, X. T.; Yang, J. H.; Shan, X. N.; Yang, L. L.; Zhang, Y. J.; Li, X. Y.; Gao, M. ZnO-graphene composite for photocatalytic degradation of methylene blue dye. Catal. Commun. 2012, 29, 29−34. (122) Tian, L. H.; Ye, L. Q.; Liu, J. Y.; Zan, L. Solvothermal synthesis of CNTs-WO3 hybrid nanostructures with high photocatalytic activity under visible light. Catal. Commun. 2012, 17, 99−103. (123) Hu, Z. Y.; Xu, L. B.; Wang, L. L.; Huang, Y.; Xu, L. M.; Chen, J. F. One-step fabrication of N-doped TiO2 inverse opal films with visible light photocatalytic activity. Catal. Commun. 2013, 40, 106− 110. (124) Liu, X. J.; Pan, L. K.; Lv, T.; Zhu, G.; Sun, Z.; Sun, C. Q. Microwave-assisted synthesis of CdS-reduced graphene oxide

(90) Akple, M. S.; Low, J. X.; Wageh, S.; Al-Ghamdi, A. A.; Yu, J. G.; Zhang, J. Enhanced visible light photocatalytic H2 poduction of gC3N4/WS2 composite heterostructures. Appl. Surf. Sci. 2015, 358, 196−203. (91) Chu, D. M.; Zhang, C. Y.; Yang, P.; Du, Y. K.; Lu, C. WS2 as an Effective Noble-Metal Free Cocatalyst Modified TiSi2 for Enhanced Photocatalytic Hydrogen Evolution under Visible Light Irradiation. Catalysts 2016, 6, 136. (92) Xiang, Q. J.; Cheng, F. Y.; Lang, D. Hierarchical Layered WS2/ Graphene-Modified CdS Nanorods for Efficient Photocatalytic Hydrogen Evolution. ChemSusChem 2016, 9, 996−1002. (93) Yuan, Y. P.; Cao, S. W.; Yin, L. S.; Xu, L.; Xue, C. NiS2 Cocatalyst decoration on CdLa2S4 nanocrystals for efficient photocatalytic hydrogen generation under visible light irradiation. Int. J. Hydrogen Energy 2013, 38, 7218−7223. (94) Yin, L. S.; Yuan, Y. P.; Cao, S. W.; Zhang, Z. Y.; Xue, C. Enhanced visible-light-driven photocatalytic hydrogen generation over g-C3N4 through loading the noble metal-free NiS2 cocatalyst. RSC Adv. 2014, 4, 6127−6132. (95) Liu, G.; Zhao, Y.; Sun, C.; Li, F.; Lu, G. Q.; Cheng, H.-M. Synergistic effects of B/N doping on the visible-light photocatalytic activity of mesoporous TiO2. Angew. Chem., Int. Ed. 2008, 47, 4516− 4520. (96) Zheng, D.; Zhang, G.; Hou, Y.; Wang, X. Layering MoS. on soft hollow g-C3N4 nanostructures for photocatalytic hydrogen evolution. Appl. Catal., A 2016, 521, 2−8. (97) Ge, L.; Han, C.; Xiao, X.; Guo, L. Synthesis and characterization of composite visible light active photocatalysts MoS2-g-C3N4 with enhanced hydrogen evolution activity. Int. J. Hydrogen Energy 2013, 38, 6960−6969. (98) Tian, Y.; Ge, L.; Wang, K.; Chai, Y. Synthesis of novel MoS2/gC3N 4 heterojunction photocatalysts with enhanced hydrogen evolution activity. Mater. Charact. 2014, 87, 70−73. (99) Jing, D. W.; Guo, L. J. WS2 sensitized mesoporous TiO2 for efficient photocatalytic hydrogen production from water under visible light irradiation. Catal. Commun. 2007, 8, 795−799. (100) Jiang, N.; Tang, Q.; Sheng, M.; You, B.; Jiang, D.-e.; Sun, Y. Nickel sulfides for electrocatalytic hydrogen evolution under alkaline conditions: a case study of crystalline NiS, NiS 2 , and Ni 3 S 2 nanoparticles. Catal. Sci. Technol. 2016, 6, 1077−1084. (101) Di, J.; Xia, J. X.; Ge, Y. P.; Xu, L.; Xu, H.; Chen, J.; He, M. Q.; Li, H. M. Facile fabrication and enhanced visible light photocatalytic activity of few-layer MoS2 coupled BiOBr microspheres. Dalton Trans. 2014, 43, 15429−15438. (102) Min, Y. L.; He, G. Q.; Xu, Q. J.; Chen, Y. C. Dual-functional MoS2 sheet-modified CdS branch-like heterostructures with enhanced photostability and photocatalytic activity. J. Mater. Chem. A 2014, 2, 2578−2584. (103) Chen, Y. J.; Tian, G. H.; Shi, Y. H.; Xiao, Y. T.; Fu, H. G. Hierarchical MoS2/Bi2MoO6 composites with synergistic effect for enhanced visible photocatalytic activity. Appl. Catal., B 2015, 164, 40− 47. (104) Fu, H.; Yu, K.; Li, H. L.; Li, J. Z.; Guo, B. J.; Tan, Y. H.; Song, C. Q.; Zhu, Z. Q. Enhanced field emission and photocatalytic performance of MoS2 titania nanoheterojunctions via two synthetic approaches. Dalton Trans. 2015, 44, 1664−1672. (105) Gao, W. Y.; Wang, M. Q.; Ran, C. X.; Li, L. Facile one-pot synthesis of MoS2 quantum dots-graphene-TiO2 composites for highly enhanced photocatalytic properties. Chem. Commun. 2015, 51, 1709− 1712. (106) Hu, C. Y.; Zheng, S. Z.; Lian, C. J.; Chen, F.; Lu, T. W.; Hu, Q. H.; Duo, S. W.; Zhang, R. B.; Guan, C. Y. alpha-S nanoparticles grown on MoS2 nanosheets: A novel sulfur-based photocatalyst with enhanced photocatalytic performance. J. Mol. Catal. A: Chem. 2015, 396, 128−135. (107) Li, H. L.; Yu, K.; Lei, X.; Guo, B. J.; Fu, H.; Zhu, Z. Q. Hydrothermal Synthesis of Novel MoS2/BiVO4 Hetero-Nanoflowers with Enhanced Photocatalytic Activity and a Mechanism Investigation. J. Phys. Chem. C 2015, 119, 22681−22689. 4625


Review

Industrial & Engineering Chemistry Research composites for photocatalytic reduction of Cr(VI). Chem. Commun. 2011, 47, 11984−11986. (125) Ai, Z.; Ho, W.; Lee, S. Efficient Visible Light Photocatalytic Removal of NO with BiOBr-Graphene Nanocomposites. J. Phys. Chem. C 2011, 115, 25330−25337.

4626


Roles of Two-Dimensional Transition Metal Dichalcogenides as

Recommend Documents