Visible-light Driven Photocatalytic H2 Generation and Mechanism

Subscriber access provided by Iowa State University | Library

C: Surfaces, Interfaces, Porous Materials, and Catalysis

Visible-light Driven Photocatalytic H2 Generation and Mechanism Insights on Bi2O2CO3/G-C3N4 Z-scheme Photocatalyst Chengwu Yang, Zhe Xue, Jiaqian Qin, Montree Sawangphruk, Saravanan Rajendran, Xinyu Zhang, and Riping Liu J. Phys. Chem. C, Just Accepted Manuscript • DOI: 10.1021/acs.jpcc.8b10604 • Publication Date (Web): 01 Feb 2019 Downloaded from http://pubs.acs.org on February 5, 2019

Just Accepted “Just Accepted” manuscripts have been peer-reviewed and accepted for publication. They are posted online prior to technical editing, formatting for publication and author proofing. The American Chemical Society provides “Just Accepted” as a service to the research community to expedite the dissemination of scientific material as soon as possible after acceptance. “Just Accepted” manuscripts appear in full in PDF format accompanied by an HTML abstract. “Just Accepted” manuscripts have been fully peer reviewed, but should not be considered the official version of record. They are citable by the Digital Object Identifier (DOI®). “Just Accepted” is an optional service offered to authors. Therefore, the “Just Accepted” Web site may not include all articles that will be published in the journal. After a manuscript is technically edited and formatted, it will be removed from the “Just Accepted” Web site and published as an ASAP article. Note that technical editing may introduce minor changes to the manuscript text and/or graphics which could affect content, and all legal disclaimers and ethical guidelines that apply to the journal pertain. ACS cannot be held responsible for errors or consequences arising from the use of information contained in these “Just Accepted” manuscripts.

is published by the American Chemical Society. 1155 Sixteenth Street N.W., Washington, DC 20036 Published by American Chemical Society. Copyright © American Chemical Society. However, no copyright claim is made to original U.S. Government works, or works produced by employees of any Commonwealth realm Crown government in the course of their duties.

Page 1 of 39 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60

The Journal of Physical Chemistry

Visible-light Driven Photocatalytic H2 Generation and Mechanism Insights on Bi2O2CO3/G-C3N4 Z-scheme Photocatalyst Chengwu Yanga, Zhe Xuea, Jiaqian Qin*b,a,c, Montree Sawangphrukc, Saravanan Rajendrand, Xinyu Zhang*a and Riping Liua

aState

Key Laboratory of Metastable Materials Science and Technology, Yanshan University,

Qinhuangdao 066004, P. R. China bResearch

Unit of Advanced Materials for Energy Storage, Metallurgy and Materials Science

Research Institute, Chulalongkorn University, Bangkok 10330, Thailand cCentre

of Excellence for Energy Storage Technology (CEST),Department of Chemical and

Biomolecular Engineering, School of Energy Science and Engineering, Vidyasirimedhi Institute of Science and Technology, Rayong 21210, Thailand dEscuela

Universitaria de Ingeniería Mecánica (EUDIM), Universidad de Tarapacá, Avda.

General Velásquez 1775, Arica, Chile

*Corresponding Author. Fax: +66 2611 7586 E-mail: [email protected] (J. Qin), [email protected] (X. Zhang)

ABSTRACT Developing a low-cost photocatalyst with efficient performance is significant for practical application of solar-to-fuel conversion. Here, we first adopt a facile method to synthesize Bi2O2CO3 modified g-C3N4 heterojunction via in-situ thermal growth. Bi2O2CO3 nanoparticles on g-C3N4 nanosheets play a vital role in improving photocatalytic activity of splitting water for hydrogen production. The activity of Bi2O2CO3/g-C3N4 heterojunction during 5 hours reaches 965 μmol g-1·h-1, which is much higher than that of pure g-C3N4 (337 μmol g-1·h-1) or others modified g-C3N4 materials. The significantly enhanced photocatalytic activity is

ACS Paragon Plus Environment

The Journal of Physical Chemistry 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60

attributed to direct Z-scheme system construction, resulting in a superior charge carrier separation ability. Theoretical calculations further reveal the redistribution of charge carrier at interface between Bi2O2CO3 and g-C3N4. This work provides new direction to synthesize gC3N4 based heterojunction with high photocatalytic performance for alleviating energy and environmental issues.

Introduction Nowadays, shortage of energy and environmental issues have gained considerable attention in entire world due to the heavy use of fossil fuel, which has become one of urgent problems that needs to be addressed. Semiconductor photocatalytic technology as a neoteric and green technology can facilely convert solar energy to chemical energy, including water splitting, carbon dioxide reduction and organic pollutions degradation, which eventually realizes the solution of energy and environmental issues1-4. Graphite-like carbon nitride nanosheets (g-C3N4) as a metal-free semiconductor photocatalyst has attracted massive interest and enthusiasm of researches due to the intrinsic unique characters5-6. These remarkable physicochemical properties ensure g-C3N4 to become a promising application in the fields of solar energy conversion into clean energy and environmental remediation. Unfortunately, some inevitable drawbacks existed in g-C3N4 material, such as poor visible light response, short lifetime of photogenerated charge carriers, lack of visible light absorption above 460 nm7-8. These shortcomings of g-C3N4 retard photocatalytic activity and further hinder the practical applications. Therefore, several researches have exhausted efforts to cope with this defect, for instance, optimizing morphology9-10, metallic and nonmetallic element doping11-14, surface modification15-16 and forming heterojunction with other material17-20 and so on. In despite of obtaining enhanced photocatalytic activity via modified method (optimizing morphology,


Page 2 of 39

Page 3 of 39 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60


element doping, surface sensitization, etc.), the intrinsic characters of g-C3N4 subject to destroy or the synthetic process is too tedious, which is deleterious to the industrialized application. On the contrary, combining with other semiconductor to form heterojunction can primely maintain the original feature of g-C3N4. Hence, countless examples for g-C3N4 allied with a suitable semiconductor exist so far. A typical case is TiO2, which make charge transport more convenient and lead to high activity7, 21.

Unsatisfactorily, TiO2 can not be inspired by visible light due to the wide band gap. Beyond

this case, the other particularly suitable semiconductor is Bi-based materials. They have recently drawn increasing attention and tremendous efforts as the fact of visible light responsive activity, caused by an upshift of valence band from the hybridized O2p and Bi6S2 orbitals22. Bismuth subcarbonate (Bi2O2CO3) as a novel containing bismuth semiconductor constitutes by the alternation of Bi2O22+ and CO32- layers and belongs to Aurivillius-type oxides family. Various methods have been adopted to fabricate Bi2O2CO3/g-C3N4 heterojunction, such as ultrasonic assistance23, chemical precipitation24 and hydrothermal strategy25. These chosen methods led poor control on contact between g-C3N4 and Bi2O2CO3, this is due to the utilization of a post syntheses technology approach. Such poor contact control inevitably not only amplifies internal resistance and impedes charge migration, but also even strongly limits the photocatalytic stability. In this work, we conversely design a one-step in-situ thermal growth to construct Bi2O2CO3/g-C3N4 heterojunction via the use of urea precursor and bismuth organics. The desired strategy allows Bi2O2CO3 nanoparticles to grow on different position of g-C3N4 nanosheets. It accomplishes the uniform dispersion of Bi2O2CO3 and close contact between two components. In the prepared heterojunction, Bi2O2CO3 phase plays a crucial role in enlarging surface area, enhancing visible light absorption, improving charge carriers transfer and reducing band gap. Differing with previous reports only concentrating photodegradation



contaminant, Bi2O2CO3/g-C3N4 heterojunction exhibits enviable photocatalytic water splitting activity for hydrogen production above 460 nm. A reasonable photocatalytic mechanism is proposed and the as-prepared heterojunction is identified to be a direct Z-scheme photocatalytic system through a series of characterization and analyzation. Theoretical calculations further verify this system and reveal the redistribution of charge carriers. The obtained Bi2O2CO3/gC3N4 material with outstanding features via a facile method provide a promising candidate in the field of solar-to-fuel conversion. Experimental section Chemical reagent Urea precursor was obtained from Tianjin kaitong chemical reagent Co., Ltd, China. Bismuth citrate, bismuth subcarbonate (BO), triethanolamine (TEOA), and chloroplatinic acid (H2PtCl6) were purchased from Chengdu aike reagent Co., Ltd, China. Sodium sulfate anhydrous (Na2SO4) was purchased from Tianjin kemiou chemical reagent CO., Ltd, China. Ultrapure water utilized in the experiment was yielded by UPH-20L. Chemical regents were of analytical grade and used as received. All experiments were accomplished at room humidity and temperature. Materials synthesis Bi2O2CO3/g-C3N4 heterojunction photocatalyst materials were synthesized by a viable insitu heat treatment method. In a typical process, a desired amount of bismuth citrate was ground with 30 g of urea for 20 min in agate mortar at room temperature. The obtained homogenous mixture was put into a combustion boat and subsequently annealed to 500 °C for 2h with 10 °C min-1 heating rate under air atmosphere in muffle furnace. After the muffle furnace naturally cooled down to room temperature, the gained hazel product was ground into fine powder. A series of samples were fabricated and the final mass proportions of Bi2O2CO3 in heterojunction photocatalyst materials detected by inductively coupled plasma atomic emission spectrometry


Page 4 of 39

Page 5 of 39 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60


(ICAP 6300 Radial) were 0.19, 0.40, 0.64, 0.83 and 1.03 %, marked as BC1, BC2, BC3, BC4 and BC5, respectively. The pristine g-C3N4 represented as CN was obtained by the consistent condition without bismuth citrate. Materials characterization The phase and composition of Bi2O2CO3/g-C3N4 heterojunction were confirmed by Rigaku D/MAX-Rb with Cu Kα radiation and 1°/min scanning rate from 10° to 80°. The morphologies and microstructures were observed by field-emission scanning electron microscopy (FE-SEM) on Hitachi S4800 and transmission electron microscopy (TEM) on FEI Tecnai F20 G2 S-TWIN. The surface information related to pore diameter and specific surface area of all the materials was recorded on ASAP 2020 HD88 with Brunauer−Emmett−Teller (BET) method. Diffusion absorption spectra were conducted on CRAIC 20/30PV for the optical properties of the asprepared samples at the wavelength range from 280 to 800 nm. Photoluminescence (PL) spectra were implemented using JobinYvon Nanolog-3 spectrofluorometer at the emission wavelength of 325 nm under room temperature. Fourier-transform infrared (FTIR) spectra were collected by E55+ FRA106 in the wavenumber range of 400-2000 cm-1. ESCALAB 250XI with monochromatic Al Kα radiation (1486.6 eV) was employed to detect X-ray photoelectron spectroscopy (XPS), and the binding energy was calibrated by C1s line at 248.6 eV. Electron paramagnetic resonance (EPR) measurement was performed on HAD-FD-ESRII at 77 K in the dark. Ultraviolet photoelectron spectra (UPS) were accomplished with a monochromatic He I light source (21.2 eV) and a VG Scienta R4000 analyzer to measure valence band (VB) of the as-prepared samples. The photoelectrochemical (PEC) performances in the dark or under visible light illumination were performed on CHI660E. 20 mg of photocatalyst was made a slurry with ethanol (1.5 ml), terpilenol (2 ml) and ethocel (50 mg), stired for 2h at 80 ℃. The above slurry was uniformly coated on ITO glass (1×1 cm2) as working electrode by the doctor blade technique. Then, the electrode was dired and calcinated



Page 6 of 39

at 400 ℃ for 30 min under vacuum condition. Pt foil (1×1 cm2) as the counter electrode, Ag/AgCl as the reference electrode and the work electrode constitute a typical three-electrode cell. The electrolyte was 0.2 M Na2SO4 aqueous solution. To clearly distinguish photoelectrochemical property of CN and BC3, the photoconversion efficiency was calculated via the equation (1) 26: Photoconversion efficiency (%) =

jp(E0rev - |Emeas - Eaoc|) I0

× 100 %

(1)

where jp is the current density of working electrode at the corresponding measure potential, E0rev is the standard reversible potential (1.23 eV NHE-1), Emeas and Eaoc are the potential of working electrode and open circuit potential under illumination respectively, I0 is the incident light intensity. Theoretical calculation details Density function theory (DFT)27 with the generalized gradient approximation (GGA)28 and the Perdew-Burke-Eznerhof (PBE) function implemented in the Vienna Ab initio Simulation Package (VASP)29-30 were employed for theoretical calculation. The projector augmented wave (PAW)31 method with plane-wave cutoff energy (500 eV) was used to describe the ion-electron interactions. The van der Waals-like interactions were corrected via the approach of Grimme (DFT-D2)32. Accurate electronic structures were obtained by HSE06 hybrid functional33. A kpoints sampling of 11×9×3 and a vacuum of 15 Å along the Z direction were adopted in this theoretical calculation. 1×2 unit of monolayer g-C3N4 was matched with 2×1 unit of four layers Bi2O2CO3 (100) surface for Bi2O2CO3/g-C3N4 heterostructure. The convergence criteria for the energy and force were set to 1.0×10-6 eV and 0.01 eV Å-1, respectively. Photocatalytic characterization Photocatalytic water splitting reaction for hydrogen production was taken place in a seal 100 ml quartz reactor. The hydrogen gas in the reactor was periodically analyzed by GC2014C gas chromatography system equipped with TCD detector. 300 W Xenon lamp with UV cutoff filter


Page 7 of 39 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60


(λ>420 nm) was served as visible light source. In a typical photocatalytic reaction routine, 50 mg of the as-prepared photocatalyst was introduced into 80 ml of mix solution containing H2PtCl6 (4 ml, 1 g L-1), TEOA (8 ml) and ultrapure water (68 ml) and then sonicated for 5 min to form homogenously dispersed suspension. To further explore the photocatalytic activities of all the materials, apparent quantum efficiency (AQE) was determinated using monochromatic light irradiation (λ=420, 475 and 520 nm) at same condition. The average irradiation intensities of monochromatic light (λ=420, 475 and 520 nm) were measured by Radiometer FZ-A. The photocatalytic reaction maintained for 5h under monochromatic light irradiation. Apparent quantum efficiency was calculated according to the following equation (2): AQE (%) =

2 × the number of produced hydrogen molecules the number of incident photons

× 100 %

(2)

Results and Discussion A succinct fabrication routine for heterojunction materials was schematically depicted in Figure 1a. Bismuth citrate particles are encircled by urea or adhered on the surface in blending process, and the mixture finally produces Bi2O2CO3/g-C3N4 material during calcination. After combination, the color transforms from brilliant yellow of pristine g-C3N4 to yellowish-brown (Figure S1), which predicatively elevate the light absorption capacity. From the SEM image (Figure 1b), the morphology of Bi2O2CO3/g-C3N4 heterojunction exhibits typical twodimensional layered structure and scarcely change compared with g-C3N4 (Figure S2), reflecting that adding bismuth citrate into urea is free of influencing the final morphology of g-C3N4. N2 absorption-desorption isotherms of g-C3N4 and Bi2O2CO3/g-C3N4 display same type IV hysteresis loops (Figure S3a), indicating that the mesoporous structure on g-C3N4 is maintained after integrating Bi2O2CO3 nanoparticles. The specific surface area determined for Bi2O2CO3/g-C3N4 is 56 m2 g-1, and the main pore diameter is 23 nm, while the corresponding results of g-C3N4 are 48 m2 g-1 and 26 nm, respectively (Figure S3b). The pyrolysis of bismuth



citrate during calcination releases a mass of carbon dioxide gas and further influences the polymerization reaction of urea, partly resulting in these changes between g-C3N4 and Bi2O2CO3/g-C3N4. As observed from TEM images of Bi2O2CO3/g-C3N4 (Figure. 1c-e), Bi2O2CO3 nanoparticles with the sizes of 50-150 nm not only locate at the surface and margin of g-C3N4 sheet, but also intercalate into the interlayer. Bismuth citrate particles encircled or adhered by urea can gain this phenomenon after calcination. It reveals the intimate contact between Bi2O2CO3 nanoparticles and g-C3N4. These Bi2O2CO3 nanoparticles in g-C3N4 are favor of extending the distance between the layers and eventually increase the specific surface area, which is in good agreement with the BET results. Bi2O2CO3 nanoparticles consist of many crystalline grains with about 20 nm diameters and the lattice spacing is 0.298 nm, corresponding to (1 6 1) crystal plane of Bi2O2CO3 (Figure 2a,b). However, when bismuth citrate endure calcination at same heat treatment procedure without any addition of urea, the obtained material is pure Bi2O3 powder featured high crystallinity (Figure S4). It can be inferred that Bi-O bonds in Bi2O3 transforms to Bi-O-C bonds of Bi2O2CO3 because of the decomposition of urea creating an enriched carbon dioxide atmosphere during calcination, which emphasizes the significant effect of urea on fabricating Bi2O2CO334. Figure 2c-g shown each element mapping in Bi2O2CO3/g-C3N4 material. Noting that nitrogen element also exists on the surface of Bi2O2CO3 nanoparticle, because a small amount of g-C3N4 adhere to Bi2O2CO3 nanoparticle, directly proving the close contact between the two phases. The phase composition and chemical structure of pure g-C3N4 and the as-prepared samples were first characterized by X-ray diffraction patterns (XRD) and Fourier transform infrared spectroscopy (FTIR) (Figure 3a,b). The XRD and FTIR results of g-C3N4 modified by Bi2O2CO3 are very similar to that of pure g-C3N4, corroborating that the fundamental structure of g-C3N4 is retained. The main diffraction peaks are indexed to (1 0 0) at ~13.0° and (0 0 2) at ~27.2°, ascribed to the in-plane repeating heptazine framework structure and the interlayer


Page 8 of 39

Page 9 of 39 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60


stacking hexatomic rings system, respectively. It is worth noting that diffraction peak of (0 0 2) shifts to reduced value about 0.18° after adding Bi2O2CO3 due to the increasing interlayer distance, which is in accord with the TEM analysis. According to the intensity of two diffraction peaks, the crystallinity is increased after modification, related to the completed polymerization of urea precursor by bismuth citrate addition, which results in the elimination of hydrogen bonds in intralayer framework and surface defects that often act as electron trap sites to hamper photoelectron transfer across the plane35. There are no other diffraction peaks for the heterojunction materials on account of the low addition of bismuth citrate in the synthetic process. In order to further ascertain the doped phase, a sample with more additive precursor of bismuth citrate, labeled as BC6, was synthesized (Figure S5). The characteristic peaks at 23.98°, 29.68° and 32.3° are consistent with these of orthorhombic Bi2O2CO3 phase rather than Bi2O3, verifying the successful construction of Bi2O2CO3/g-C3N4 heterojunction. As shown in Figure 3b, for containing g-C3N4 materials, the absorption peak at 812 cm-1 represents the typical bending mode of tri-s-triazine structure36. The bands in the region from 1250 to 1634 cm-1 can trance to the characteristic skeletal stretching vibrations of C-N aromatic rings37. For Bi2O2CO3, the absorption peaks at 550 and 845 cm-1 assign to the stretching mode of Bi-O-Bi group and bending mode of CO32- group respectively, while the peaks at 1387 and 1466 cm-1 are associated with antisymmetric vibration of CO32- group38-39. As the accessorial mass ratio of Bi2O2CO3 in heterojunctions, the absorption intensities at 812 and 1250~1634 cm-1 progressively enhance, implying that coupling with Bi2O2CO3 into g-C3N4 has a positive effect on the formation of tri-s-triazine structure and C-N heterocycles of g-C3N4, which is in agreement with the XRD results. To investigate chemical structure and electron transfer on element atom, XPS spectrum was employed. A small Bi4f and O1s peak are bulged on the survey scan spectra of Bi2O2CO3/g-C3N4 (Figure S6a). The C1s spectra contain two intense peaks, C-C bond (284.6



eV) and C-(N)3 (~288.2 eV), which derive from the adventitious carbon and sp2 hybridized carbon of g-C3N4, respectively (Figure 3c)40-41. It can be observed that the combination of Bi2O2CO3 shifts C-(N)3 peak toward higher binding energy, indicating that Bi2O2CO3 chemically interact with carbon atoms in C-(N)3 to form new carbon bond. Besides, two deconvolution peaks at 285.10 and 288.85 eV on C1s spectrum are associated with C=C bond and carbonate ion of Bi2O2CO3, again testifying the formation of Bi2O2CO3/g-C3N439, 42. The N1s spectra of g-C3N4 and Bi2O2CO3/g-C3N4 can be resolved into two peaks located at ~398.50 and ~400.00 eV, corresponding to sp2 hybridized nitrogen atom (C-N=C)20, 36 and bridging nitrogen atom with carbon (N-(C)3)43, respectively (Figure 3d). Noticeably, similar to the shift trend of C-(N)3 bond, the binding energy of nitrogen atom on C-N=C and N-(C)3 of Bi2O2CO3/g-C3N4 possesses higher binding energy in opposite to that of g-C3N4, which also indicates that Bi2O2CO3 interact with sp2 hybridized nitrogen and bridging nitrogen. The porbital electrons of sp2 hybridized carbon and nitrogen couple into a π bond to form conjugated system. The sp3 hybridized nitrogen in N-(C)3 bond has lone pair electrons. The escape of electrons in conjugated system and sp3 hybridized nitrogen will lead to the decreased electron density, which results in C1s and N1s peaks of g-C3N4 shifting toward the higher binding energy. Oppositely, the other atom receiving electron will increase electron density and reduce corresponding binding energy. The coincident variation is enclosed from Bi4f spectrum of Bi2O2CO3/g-C3N4. The Bi4f spectrum is deconvoluted into two peaks at 159.26 and 164.51 eV, identified as 4f7/2 and 4f5/2 component of Bi3+ ion respectively44-45 (Figure S6b). Nevertheless, for Bi2O2CO3, the 4f7/2 asymmetric peak is separated into two parts at 158.47 and 159.56 eV respectively and the 4f5/2 peak is similarly divided into two parts at163.76 and 164.56 eV (Figure S6c). The peaks at the binding energy of 158.47 and 163.76 eV are attributed to Bi metal or low chemical state of bismuth ion, while the peaks at 159.56 and 164.56 eV result from the presence of Bi3+ oxidation state44, 46. Obviously, the binding energy of Bi3+ ion is


Page 10 of 39

Page 11 of 39 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60


reduced after the formation of the Bi2O2CO3/g-C3N4 heterojunction. The electrons of carbon and nitrogen atoms in g-C3N4 enter into the unoccupied p-orbital of bismuth atoms to form a weak Bi-C and Bi-N bonds, which alters the electron density of corresponding atoms and finally results in the shifts of binding energy. The electronic structure information was further studied by electron paramagnetic resonance (EPR) at 77k in the dark. As shown in Figure S7, EPR signals arise at same g value (2.003) indexing as superoxide species O2- due to the reduction of absorbed oxygen molecule on the surface by unpaired electrons47. Contrast to gC3N4, an intense EPR signal presents the increasement of delocalization electrons and redistribution on heterojunction system48. It further confirms the changes of atomic electron density and the form of Bi-C and Bi-N bonds. Based on the analysis of TEM and XPS results, it is rational to infer that the derived Bi2O2CO3 nanoparticles are not pure phase and nitrogen element enteres into the lattice to produce nitrogen dopping Bi2O2CO3. The photocatalytic hydrogen evaluation measurements were completed in triethanolamine (TEOA) aqueous solution under illumination (Figure 4a). The photocatalytic activity (R0) of bare g-C3N4 is 337 μmol g-1·h-1, whilst for Bi2O2CO3 modified g-C3N4, the photocatalytic activities (R) receive arresting enhancement. Indeed, the best photocatalytic activity is 965 μmol g-1·h-1 and almost 3 times higher than that of g-C3N4. It proves that cooperating with Bi2O2CO3 ameliorator can effectively boost the photocatalytic activity for hydrogen production. The cyclic photocatalytic experiment for 15 hours (Figure 4b) discloses that Bi2O2CO3/g-C3N4 heterojunction material has stabilized photocatalytic performance, while g-C3N4 shows an inferior photocatalytic stability with obvious decrease of hydrogen production in sequential cyclic experiment. It elucidates that Bi2O2CO3/g-C3N4 heterojunction can be nominated to the practical application of energy conversion from solar energy to chemical energy in opposite to pristine g-C3N4. Moreover, photocatalytic activity of Bi2O2CO3/g-C3N4 is much higher than other g-C3N4 heterojunctions with metallic compound reported previously (Figure 4c49-58 and



Table S1). Additionally, in order to understand the effect of calcination temperature on photocatalytic activity, three Bi2O2CO3/g-C3N4 samples with same reactant ratio were obtained at 470, 500 and 530 ℃. The photogenerated rates are 191 and 759 μmol g-1·h-1 for 470 and 530 ℃, respectively (Figure S8). The photocatalytic activities of Bi2O2CO3/g-C3N4 calcinate at 470 and 530 ℃ is low than that obtained 500 ℃, even worse than g-C3N4. For 530 ℃, the characteristic peak of Bi2O2CO3 shows in XRD pattern (Figure S9), indicating that the ratio of Bi2O2CO3 in heterojunction becomes large. For another, the (0 0 2) peak of g-C3N4 generates a distinct right shift, indicating that the distance between interlayers of hexatomic rings system decreases. It may result from that the larger Bi2O2CO3 particles formed by agglomeration effect squeeze g-C3N4 nanosheets instead of implant into the interlayers. Calcination temperature can decide the pyrolysis of urea and bismuth citrate and the interaction of them, which alters the ratio of Bi2O2CO3 and the general structure of g-C3N4. It can be concluded that calcination temperature for fabricating pure g-C3N4 and Bi2O2CO3/g-C3N4 materials plays a vital role in affecting phase composition, structure and in the end photocatalytic activity for hydrogen production. The amount of hydrogen of g-C3N4 and Bi2O2CO3/g-C3N4 under monochromatic light irradiation (λ=420, 475 and 520 nm) was shown in Figure 4d. The apparent quantum efficiency (AQE) was calculated and listed in Table S2. The AQE of BC3 is 7.14 % at λ=420 nm, which is higher than that of g-C3N4, 3.48 %. UV-VIS diffuse absorption spectra and PL spectra of Bi2O2CO3 modified g-C3N4 materials together with pristine g-C3N4 were illustrated in Figure 5. Apparently, the enhanced absorption ability in the region of 280-800 nm are obtained in comparison with pure g-C3N4 (Figure 5a). It seems that the absorption ability of heterojunction is increased just because of Bi2O2CO3, gC3N4 cannot absorb the wavelengths higher than its absorption edge. So the higher wavelengths absorbed by Bi2O2CO3 are useless for g-C3N4. The corresponding band gap energies estimated


Page 12 of 39

Page 13 of 39 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60


using Tauc plots (Figure S10) are 2.51 and 2.29 eV for g-C3N4 and Bi2O2CO3/g-C3N4, respectively. Generally, the enhancement of optical property along with the narrowing band gap benefit more photons joining into photocatalytic reaction and strengthen the photocatalytic activity. The UV-VIS diffuse absorption spectrum of Bi2O2CO3 with the corresponding Tauc plots were shown in Figure S11. In Figure 5b, the PL intensities are reduced drastically with the increasement of Bi2O2CO3, probably due to the fast migration of electron between g-C3N4 and Bi2O2CO3 via the formed Bi-C and Bi-O bonds, which testifies the positive effect of Bi2O2CO3 ameliorator on suppressing the recombination of photoinduced charge carriers. Simultaneously, the interaction between g-C3N4 and Bi2O2CO3 results in the shift of emission peaks from 452 to 462 nm. Photoelectrochemical (PEC) experiment was accomplished to get deep insight into the charge transfer and band alignment. The saltatorial current density of Bi2O2CO3/g-C3N4 in transient photocurrent response measurement is approximately three times higher than that of g-C3N4, revealing that Bi2O2CO3 modified g-C3N4 materials possess prominent photoelectronic activity (Figure 6a). This result demonstrates that more active photogenerated electrons generate and participate in reduction of water to improve photocatalytic rate. From electrochemical impedance spectra (EIS) (Figure S12a), the arc radius of Bi2O2CO3/g-C3N4 is smaller than that of g-C3N4. The close interface in Bi2O2CO3/g-C3N4 broaden channel of charge mobility and reduce inner resistance, which realizes the low recombination rate of photogenerated charge carriers. In addition, the Mott-schottky plots (MS) were utilized to determine the position of conduction band and further reckon the band alignment (Figure 6b). After doping Bi2O2CO3, the slope is minished as compared to g-C3N4, indicating the enhancement of charge transfer efficiency, which matches these above results. The flat band potentials of g-C3N4 and heterojunction are -1.22 and -1.13 eV respectively, while the corresponding calculated conduction band potentials locate at -1.02 and -0.93 eV. Based on the



band gap energy, the valence band potentials as the subtraction of band gap and conduction band potential are 1.49 and 1.36 eV, respectively. The flat band potential, band gap and band position were summarized in Table S3. Besides, ultraviolet photoelectron spectra (UPS) were obtained to further measure valence band and analyze band position precisely (Figure 6c,d). The valence band of g-C3N4 and heterojunction in vacuum level are 5.89 and 5.76 eV, respectively, and the corresponding conduction band are 3.38 and 3.47 eV. This is in line with the results calculated from PEC measurements. The UPS results of Bi2O2CO3 were shown in Figure S13. When g-C3N4 and Bi2O2CO3 with different fermi levels construct a heterojunction, a built-in electric field with the direction from g-C3N4 surface to Bi2O2CO3 will be created at the interface59. Under electric field driving, electrons and holes reversely transfer to form electron flow, which prolongs lifetime of electrons and holes and increases photocurrent response. The photoconversion efficiency as a function of the applied potential is enhanced after decorating Bi2O2CO3, confirming that the presence can facilitate the transformation from light energy to chemical energy (Figure S12b). Theoretical calculations were performed using density function theory to get deep insight into the electronic structure and electronic behavior of the formed Bi2O2CO3/g-C3N4 heterojunction. The calculated band gap of pure g-C3N4 and Bi2O2CO3 are 2.72 and 2.51 eV respectively (Figure 7a), coinciding with the experimental band gap (2.51 eV for g-C3N4, 2.91 eV for Bi2O2CO3). The planar-averaged charge density difference was depicted in Figure 7b. Yellow region and cyan region respectively represent electron accumulation and depletion. The redistribution of electrons and holes occurs at the contacted interface between g-C3N4 and Bi2O2CO3. For the calculation results, electrons transfer from Bi2O2CO3 nanoparticle (∆ρ0), rending that residual holes gather in Bi2O2CO360. It demonstrates that g-C3N4 can act as a charge sink to accept electron. Figure 7c shown the total density of state and partial density of state of the Bi2O2CO3/g-C3N4 heterojunction. The conduction band


Page 14 of 39

Page 15 of 39 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60


is mainly constituted by Bi6p and O2p, while N2p has dominating contribution on valence band. The obtained band gap of Bi2O2CO3/g-C3N4 heterojunction is 2.30 eV and has inappreciable difference with the experimental band gap, evidencing the positive effect of Bi2O2CO3 ameliorator on modulating band gap of g-C3N4. According to the aforementioned detection and analysis, two possible heterojunction systems can be proposed. As drawn in Figure 7d, under visible light irradiation, the photoexcited electrons in the conduction band of g-C3N4 transfer to the conduction band of Bi2O2CO3, and the remaining holes in the valence band of g-C3N4 departure to the valence band of Bi2O2CO3. This situation engenders that all the photoexcited electrons located at the conduction band of Bi2O2CO3 lack adequate activity to split water for hydrogen gas, due to the fact that the conduction band potential of Bi2O2CO3 is really positive than the reduction potential of water. On the other hand, similar to electrons, the photogenerated holes in the valance band of Bi2O2CO3 are in a weak position for oxidizing water or react with TEOA sacrificial agent. As a result, if Bi2O2CO3/g-C3N4 heterojunction constitutes a photocatalytic system like Figure 7d, it hardly reacts with water to produce hydrogen or its photocatalytic activity is no match for pristine g-C3N4, which is not in accord with the results of photocatalytic hydrogen evaluation measurement. On the contrary, photocatalytic system depicted in Figure 7e is a direct typical Z-scheme photocatalyst. Composition and microstructure variation of Bi2O2CO3 can endow visible light absorption ability and realize visible-light driven photocatalytic activity, such as surface defect engineering61-62, element doping63-64, morphology modification65-66, vacancy modulation67 and so on. Nitrogen atoms enter into Bi2O2CO3 lattice during heat treatment process and render the improved visible light response. Meanwhile, the irregular morphology of Bi2O2CO3 may also alter the optical property instead of flower-like structure that Bi2O2CO3 generally has not visible light activity65. In Z-scheme system, the photoexcited electrons derived from Bi2O2CO3 phase migrate to the valance band of g-C3N4 via the intimate interface between the two phases



under the built-in electric field driving, and rapidly move up to the conduction band of g-C3N4. Photogenerated holes in Bi2O2CO3 is restrained to transfer to g-C3N4. Subsequently, electrons and holes accumulate in conduction band of g-C3N4 and valance band of Bi2O2CO3, respectively. These electrons with high reduction ability can further work with water to produce hydrogen, and the holes restored in valance band of Bi2O2CO3 can generate hydroxyl radical (·OH) utilizing water (Figure 8). The above analysis is confirmed by theoretical calculation and UPS results. The Z-scheme system realizes the effective separation of photoinduced electron-hole pairs and finally caters the higher photocatalytic activity compared with pristine g-C3N4. In consideration of the excellent photocatalytic activity of Bi2O2CO3/g-C3N4 heterojunction, of course, it is necessary to anatomize the essence of positive effect of Bi2O2CO3 on photocatalytic performance. Coupling with Bi2O2CO3 into g-C3N4 can enlarge the surface area and the distance between layers, which not only affords more active sites for the reaction of electrons and water, also facilitates the solution circulation in the heterojunction inner. The photocatalytic performance is sensitive with crystallinity of photocatalyst. Bi2O2CO3/g-C3N4 exhibits a high crystallinity compared with pure g-C3N4, implying the reducing hydrogen bonds and crystal defects on the surface. These bonds and defects can retard electron transfer in the nanosheets and lead to a poor photocatalytic activity. For another, Bi2O2CO3/g-C3N4 heterojunction has deep color and narrowing band gap in contrast with gC3N4, resulting in more effective photons participating into the photocatalytic reaction. In addition, the g-C3N4 based heterojunction formed a direct Z-scheme system along with poor transfer resistance makes the efficient suppression of the charge carriers recombination. Hence, these synergistic effects exited in Bi2O2CO3/g-C3N4 heterojunction create an excellent photocatalytic performance. Conclusions


Page 16 of 39

Page 17 of 39 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60


In summary, an efficient photocatalytic heterojunction composed by g-C3N4 and Bi2O2CO3 was successfully synthesized via one-step in-situ thermal growth. The introducing Bi2O2CO3 nanoparticles are immobilized on the different position of g-C3N4, namely, surface, edge and interlayers, which signally extends the distance between the layers and enlarges the surface area. Meanwhile, Bi2O2CO3 nanoparticles in the as-prepared heterojunction have significant effect on enhancing visible light absorption efficiency, adjusting band gap and restraining the recombination of photogenerated electron-hole pairs, resulting in the superior photocatalytic activity of Bi2O2CO3/g-C3N4 heterojunction for hydrogen production. According to the analytic results of a series of detection means, a reasonable photocatalytic mechanism is also proposed and the as-prepared heterojunction is identified to be a direct Zscheme photocatalytic system. This work provides for synthesizing g-C3N4 based heterojunction with excellent photocatalytic performance develop a promising candidate for alleviating energy risk and environmental issues. Supporting Information The Supporting Information is available free of charge on Pictures of all the samples; morphology of g-C3N4, surface information; XRD patterns of Bi2O3 and BC6; survey scan XPS spectra, high-resolution XPS spectra of Bi4f; EPR spectra; photocatalytic hydrogen evaluation and XRD patterns of heterojunction obtained at different calcination temperature; Tauc plots; UV-VIS diffuse adsorption spectrum, ultraviolet photoelectron spectra and band alignment of Bi2O2CO3; electrochemical impedance spectra and the calculated photoconversion efficiency; photocatalytic activity comparison with other semiconductor photocatalysts; apparent quantum efficiency as well as the calculated method; the list of flat band potential, band gap and band position. Acknowledgments This research is financially supported by the Thailand Research Fund (RSA6080017). We also



gratefully acknowledge the NSFC (grant 51421091), National Science Foundation for Distinguished Young Scholars for Hebei Province of China (grant E2016203376), Asahi Glass Foundation, and The Energy Conservation Promotion Fund from the Energy Policy and Planning Office, Ministry of Energy.

Notes The authors declare no conflict of interest. References 1. Chen, X.; Liu, L.; Yu, P. Y.; Mao, S. S. Increasing Solar Absorption for Photocatalysis with Black Hydrogenated Titanium Dioxide Nanocrystals. Science 2011, 331, 746-750. 2. 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 TwoElectron Pathway. Science 2015, 347, 970-974. 3. Yin, H.; Yi, J.; Yang, Z.-W.; Xu, Z.-Y.; Xie, S.-J.; Li, L.; Li, C.-Y.; Xu, J.; Zhang, H.; Zhang, S.-J. et al. Plasmon Enhanced Quantum Dots Fluorescence and Energy Conversion in Water Splitting Using Shell-Isolated Nanoparticles. Nano Energy 2017, 42, 232-240. 4. 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-n/a. 5. Cao, S.; Low, J.; Yu, J.; Jaroniec, M. Polymeric Photocatalysts Based on Graphitic Carbon Nitride. Adv. Mater. 2015, 27, 2150-2176. 6. Liu, C.; Huang, H.; Ye, L.; Yu, S.; Tian, N.; Du, X.; Zhang, T.; Zhang, Y. IntermediateMediated Strategy to Horn-Like Hollow Mesoporous Ultrathin G-C3n4 Tube with Spatial Anisotropic Charge Separation for Superior Photocatalytic H2 Evolution. Nano Energy 2017, 41, 738-748. 7. Fu, J.; Yu, J.; Jiang, C.; Cheng, B. G-C3n4-Based Heterostructured Photocatalysts. Advanced Energy Materials 2018, 8, 1701503. 8. Wen, J.; Xie, J.; Chen, X.; Li, X. A Review on G-C3n4-Based Photocatalysts. Appl. Surf. Sci. 2017, 391, 72-123. 9. Li, X.-H.; Zhang, J.; Chen, X.; Fischer, A.; Thomas, A.; Antonietti, M.; Wang, X. Condensed Graphitic Carbon Nitride Nanorods by Nanoconfinement: Promotion of Crystallinity on Photocatalytic Conversion. Chem. Mater. 2011, 23, 4344-4348. 10. Sun, J.; Zhang, J.; Zhang, M.; Antonietti, M.; Fu, X.; Wang, X. Bioinspired Hollow Semiconductor Nanospheres as Photosynthetic Nanoparticles. Nature Communications 2012, 3, 1139. 11. Chen, X.; Zhang, J.; Fu, X.; Antonietti, M.; Wang, X. Fe-G-C3n4-Catalyzed Oxidation of Benzene to Phenol Using Hydrogen Peroxide and Visible Light. J. Am. Chem. Soc. 2009, 131, 11658-11659. 12. Zhang, Y.; Mori, T.; Ye, J.; Antonietti, M. Phosphorus-Doped Carbon Nitride Solid: Enhanced Electrical Conductivity and Photocurrent Generation. J. Am. Chem. Soc. 2010, 132, 6294-6295. 13. Liu, G.; Niu, P.; Sun, C.; Smith, S. C.; Chen, Z.; Lu, G. Q.; Cheng, H.-M. Unique


Page 18 of 39

Page 19 of 39 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60


Electronic Structure Induced High Photoreactivity of Sulfur-Doped Graphitic C3n4. J. Am. Chem. Soc. 2010, 132, 11642-11648. 14. Wang, X.; Chen, X.; Thomas, A.; Fu, X.; Antonietti, M. Metal-Containing Carbon Nitride Compounds: A New Functional Organic–Metal Hybrid Material. Adv. Mater. 2009, 21, 1609-1612. 15. Maeda, K.; Wang, X.; Nishihara, Y.; Lu, D.; Antonietti, M.; Domen, K. Photocatalytic Activities of Graphitic Carbon Nitride Powder for Water Reduction and Oxidation under Visible Light. J. Phys. Chem. C 2009, 113, 4940-4947. 16. Di, Y.; Wang, X.; Thomas, A.; Antonietti, M. Making MetalCarbon Nitride Heterojunctions for Improved Photocatalytic Hydrogen Evolution with Visible Light. ChemCatChem 2010, 2, 834-838. 17. 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-Environ 2017, 219, 693-704. 18. Xue, W.; Hu, X.; Liu, E.; Fan, J. Novel Reduced Graphene Oxide-Supported Cd0.5zn0.5s/G-C3n4 Z-Scheme Heterojunction Photocatalyst for Enhanced Hydrogen Evolution. Appl. Surf. Sci. 2018, 447, 783-794. 19. Meng, J.; Lan, Z.; Chen, T.; Lin, Q.; Liu, H.; Wei, X.; Lu, Y.; Li, J.; Zhang, Z. Organic– Organic Hybrid G-C3n4/Ethanediamine Nanosheets for Photocatalytic H2 Evolution. J. Phys. Chem. C 2018, 122, 24725-24731. 20. Yang, C.; Qin, J.; Xue, Z.; Ma, M.; Zhang, X.; Liu, R. Rational Design of CarbonDoped Tio2 Modified G-C3n4 Via in-Situ Heat Treatment for Drastically Improved Photocatalytic Hydrogen with Excellent Photostability. Nano Energy 2017, 41, 1-9. 21. Wu, M.; Zhang, J.; Liu, C.; Gong, Y.; Wang, R.; He, B.; Wang, H. 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. 22. He, R.; Xu, D.; Cheng, B.; Yu, J.; Ho, W. Review on Nanoscale Bi-Based Photocatalysts. Nanoscale Horizons 2018, 3, 464-504. 23. Ma, Y.; Bian, Y.; Tan, P.; Shang, Y.; Liu, Y.; Wu, L.; Zhu, A.; Liu, W.; Xiong, X.; Pan, J. Simple and Facile Ultrasound-Assisted Fabrication of Bi2o2co3/G-C3n4 Composites with Excellent Photoactivity. J. Colloid Interface Sci. 2017, 497, 144-154. 24. Zhang, Q.; Wang, H.; Hu, S.; Lu, G.; Bai, J.; Kang, X.; Liu, D.; Gui, J. Synthesis and Properties of Visible Light Responsive G-C3n4/Bi2o2co3 Layered Heterojunction Nanocomposites. RSC Advances 2015, 5, 42736-42743. 25. Wang, Z.; Huang, Y.; Ho, W.; Cao, J.; Shen, Z.; Lee, S. C. Fabrication of Bi2o2co3/GC3n4 Heterojunctions for Efficiently Photocatalytic No in Air Removal: In-Situ SelfSacrificial Synthesis, Characterizations and Mechanistic Study. Appl. Catal. B-Environ 2016, 199, 123-133. 26. Mor, G. K.; Shankar, K.; Varghese, O. K.; Grimes, C. A. Photoelectrochemical Properties of Titania Nanotubes. J. Mater. Res. 2004, 19, 2989-2996. 27. Hohenberg, P.; Kohn, W. Inhomogeneous Electron Gas. Physical Review 1964, 136, B864-B871. 28. Perdew, J. P.; Burke, K.; Ernzerhof, M. Generalized Gradient Approximation Made Simple. Phys. Rev. Lett. 1996, 77, 3865-3868. 29. Kresse, G. Ab Initio Molecular Dynamics for Liquid Metals. J. Non-Cryst. Solids 1995, 192, 222-229. 30. Kresse, G.; Furthmüller, J. Efficient Iterative Schemes for Ab Initio Total-Energy Calculations Using a Plane-Wave Basis Set. Phys. Rev. B: Condens. Matter 1996, 54, 1116911186.



31. Blöchl, P. E. Projector Augmented-Wave Method. Phys. Rev. B 1994, 50, 17953-17979. 32. Grimme, S. Semiempirical Gga-Type Density Functional Constructed with a LongRange Dispersion Correction. J. Comput. Chem. 2006, 27, 1787-1799. 33. Heyd, J.; Scuseria, G. E.; Ernzerhof, M. Hybrid Functionals Based on a Screened Coulomb Potential. J. Chem. Phys. 2003, 118, 8207-8215. 34. Shan, W.; Hu, Y.; Bai, Z.; Zheng, M.; Wei, C. In Situ Preparation of G-C3n4/BismuthBased Oxide Nanocomposites with Enhanced Photocatalytic Activity. Appl. Catal. B-Environ 2016, 188, 1-12. 35. Ou, H.; Lin, L.; Zheng, Y.; Yang, P.; Fang, Y.; Wang, X. Tri‐S‐Triazine‐Based Crystalline Carbon Nitride Nanosheets for an Improved Hydrogen Evolution. Adv. Mater. 2017, 29, 1700008. 36. Xu, Q.; Cheng, B.; Yu, J.; Liu, G. Making Co-Condensed Amorphous Carbon/G-C3n4 Composites with Improved Visible-Light Photocatalytic H2-Production Performance Using Pt as Cocatalyst. Carbon 2017, 118, 241-249. 37. Wang, J.; Yang, Z.; Gao, X.; Yao, W.; Wei, W.; Chen, X.; Zong, R.; Zhu, Y. CoreShell G-C3n4@Zno Composites as Photoanodes with Double Synergistic Effects for Enhanced Visible-Light Photoelectrocatalytic Activities. Appl. Catal. B-Environ 2017, 217, 169-180. 38. Cen, W.; Xiong, T.; Tang, C.; Yuan, S.; Dong, F. Effects of Morphology and Crystallinity on the Photocatalytic Activity of (Bio)2co3 Nano/Microstructures. Industrial & Engineering Chemistry Research 2014, 53, 15002-15011. 39. Zhao, W.; Wang, Y.; Wang, A.; Qian, J.; Zhu, W.; Dou, S.; Wang, Q.; Zhong, Q.; Chen, A. Novel Bi2o2co3/Polypyrrole/G-C3n4 Nanocomposites with Efficient Photocatalytic and Nonlinear Optical Properties. RSC Advances 2017, 7, 7658-7670. 40. Li, J.; Yin, Y.; Liu, E.; Ma, Y.; Wan, J.; Fan, J.; Hu, X. In Situ Growing Bi2moo6 on G-C3n4 Nanosheets with Enhanced Photocatalytic Hydrogen Evolution and Disinfection of Bacteria under Visible Light Irradiation. J. Hazard. Mater. 2017, 321, 183-192. 41. 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. 42. Zhao, Z.; Zhou, Y.; Wang, F.; Zhang, K.; Yu, S.; Cao, K. Polyaniline-Decorated {001} Facets of Bi2o2co3 Nanosheets: In Situ Oxygen Vacancy Formation and Enhanced Visible Light Photocatalytic Activity. ACS Appl. Mater. Interfaces 2015, 7, 730-737. 43. Yang, S.; Gong, Y.; Zhang, J.; Zhan, L.; Ma, L.; Fang, Z.; Vajtai, R.; Wang, X.; Ajayan, P. M. Exfoliated Graphitic Carbon Nitride Nanosheets as Efficient Catalysts for Hydrogen Evolution under Visible Light. Adv. Mater. 2013, 25, 2452-2456. 44. Dharmadhikari, V. S.; Sainkar, S. R.; Badrinarayan, S.; Goswami, A. Characterisation of Thin Films of Bismuth Oxide by X-Ray Photoelectron Spectroscopy. J. Electron. Spectrosc. Relat. Phenom. 1982, 25, 181-189. 45. Xia, J.; Ji, M.; Di, J.; Wang, B.; Yin, S.; Zhang, Q.; He, M.; Li, H. Construction of Ultrathin C3n4/Bi4o5i2 Layered Nanojunctions Via Ionic Liquid with Enhanced Photocatalytic Performance and Mechanism Insight. Appl. Catal. B-Environ 2016, 191, 235245. 46. Sun, J.; Wu, S.; Yang, S.-Z.; Li, Q.; Xiong, J.; Yang, Z.; Gu, L.; Zhang, X.; Sun, L. Enhanced Photocatalytic Activity Induced by Sp3 to Sp2 Transition of Carbon Dopants in Biocl Crystals. Appl. Catal. B-Environ 2018, 221, 467-472. 47. Furukawa, S.; Shishido, T.; Teramura, K.; Tanaka, T. Photocatalytic Oxidation of Alcohols over Tio2 Covered with Nb2o5. ACS Catalysis 2012, 2, 175-179. 48. Fan, X.; Zhang, L.; Cheng, R.; Wang, M.; Li, M.; Zhou, Y.; Shi, J. Construction of Graphitic C3n4-Based Intramolecular Donor–Acceptor Conjugated Copolymers for Photocatalytic Hydrogen Evolution. ACS Catalysis 2015, 5, 5008-5015.


Page 20 of 39

Page 21 of 39 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60


49. Yan, M.; Hua, Y.; Zhu, F.; Sun, L.; Gu, W.; Shi, W. Constructing Nitrogen Doped Graphene Quantum Dots-Znnb2o6/G-C3n4 Catalysts for Hydrogen Production Under Visible Light. Appl. Catal. B-Environ 2017, 206, 531-537. 50. Wang, W.; An, T.; Li, G.; Xia, D.; Zhao, H.; Yu, J. C.; Wong, P. K. Earth-Abundant Ni2p/G-C3n4 Lamellar Nanohydrids for Enhanced Photocatalytic Hydrogen Evolution and Bacterial Inactivation under Visible Light Irradiation. Appl. Catal. B-Environ 2017, 217, 570580. 51. Adhikari, S. P.; Hood, Z. D.; Wang, H.; Peng, R.; Krall, A.; Li, H.; Chen, V. W.; More, K. L.; Wu, Z.; Geyer, S. et al. Enhanced Visible Light Photocatalytic Water Reduction from a G-C3n4/Srta2o6 Heterojunction. Appl. Catal. B-Environ 2017, 217, 448-458. 52. Fu, J.; Bie, C.; Cheng, B.; Jiang, C.; Yu, J. Hollow Cosx Polyhedrons Act as HighEfficiency Cocatalyst for Enhancing the Photocatalytic Hydrogen Generation of G-C3n4. ACS Sustainable Chemistry & Engineering 2018, 6, 2767-2779. 53. Ding, N.; Zhang, L.; Zhang, H.; Shi, J.; Wu, H.; Luo, Y.; Li, D.; Meng, Q. MicrowaveAssisted Synthesis of Znin2s4/G-C3n4 Heterojunction Photocatalysts for Efficient Visible Light Photocatalytic Hydrogen Evolution. Catal. Commun. 2017, 100, 173-177. 54. Tan, Y.; Shu, Z.; Zhou, J.; Li, T.; Wang, W.; Zhao, Z. One-Step Synthesis of Nanostructured G-C3n4/Tio2 Composite for Highly Enhanced Visible-Light Photocatalytic H2 Evolution. Appl. Catal. B-Environ 2018, 230, 260-268. 55. Yu, J.; Chen, Z.; Wang, Y.; Ma, Y.; Feng, Z.; Lin, H.; Wu, Y.; Zhao, L.; He, Y. Synthesis of Knbo3/G-C3n4 Composite and Its New Application in Photocatalytic H2 Generation Under Visible Light Irradiation. J. Mater. Sci. 2018, 53, 7453-7465. 56. Hong, Y.; Fang, Z.; Yin, B.; Luo, B.; Zhao, Y.; Shi, W.; Li, C. A Visible-Light-Driven Heterojunction for Enhanced Photocatalytic Water Splitting over Ta2o5 Modified G-C3n4 Photocatalyst. Int. J. Hydrogen Energy 2017, 42, 6738-6745. 57. Cheng, C.; Shi, J. W.; Hu, Y. C.; Guo, L. J. Wo3/G-C3n4 Composites: One-Pot Preparation and Enhanced Photocatalytic H-2 Production UnderVisible-Light Irradiation. Nanotechnology 2017, 28, 9. 58. Hao, X.; Zhou, J.; Cui, Z.; Wang, Y.; Wang, Y.; Zou, Z. Zn-Vacancy Mediated Electron-Hole Separation in Zns/G-C3n4 Heterojunction for Efficient Visible-Light Photocatalytic Hydrogen Production. Appl. Catal. B-Environ 2018, 229, 41-51. 59. Lin, Z.; Li, L.; Yu, L.; Li, W.; Yang, G. Modifying Photocatalysts for Solar Hydrogen Evolution Based on the Electron Behavior. J. Mater. Chem. A 2017, 5, 5235-5259. 60. Liu, J.; Cheng, B.; Yu, J. A New Understanding of the Photocatalytic Mechanism of the Direct Z-Scheme G-C3n4/Tio2 Heterostructure. PCCP 2016, 18, 31175-31183. 61. Xu, C. M.; Qiu, P. X.; Li, L. Y.; Chen, H.; Jiang, F.; Wang, X. Bismuth Subcarbonate with Designer Defects for Broad-Spectrum Photocatalytic Nitrogen Fixation. ACS Appl. Mater. Interfaces 2018, 10, 25321-25328. 62. Huang, Y. C.; Li, K. S.; Lin, Y.; Tong, Y. X.; Liu, H. Enhanced Efficiency of ElectronHole Separation in Bi2o2co3 for Photocatalysis Via Acid Treatment. ChemCatChem 2018, 10, 1982-1987. 63. Jin, R. B.; Jiang, X. J.; Zhou, Y. Y.; Zhao, J. F. Microspheres of Graphene Oxide Coupled to N-Doped Bi2o2co3 for Visible Light Photocatalysis. Chin. J. Catal. 2016, 37, 760768. 64. Chen, M. J.; Huang, Y.; Yao, J.; Cao, J. J.; Liu, Y. Visible-Light-Driven N(Bio)(2)Co3/Graphene Oxide Composites with Improved Photocatalytic Activity and Selectivity for Nox Removal. Appl. Surf. Sci. 2018, 430, 137-144. 65. Liu, S. Q.; Tu, Y. Q.; Dai, G. P. The Effects of Citrate Ion on Morphology and Photocatalytic Activity of Flower-Like Bi2o2co3. Ceram. Int. 2014, 40, 2343-2348. 66. Madhusudan, P.; Zhang, J.; Cheng, B.; Liu, G. Photocatalytic Degradation of Organic



Dyes with Hierarchical Bi2o2co3 Microstructures Under Visible-Light. Crystengcomm 2013, 15, 231-240. 67. Zhang, Y. F.; Zhu, G. Q.; Hojamberdiev, M.; Gao, J. Z.; Hao, J.; Zhou, J. P.; Liu, P. Synergistic Effect of Oxygen Vacancy and Nitrogen Doping on Enhancing the Photocatalytic Activity of Bi2o2co3 Nanosheets with Exposed {001} Facets for the Degradation of Organic Pollutants. Appl. Surf. Sci. 2016, 371, 231-241.


Page 22 of 39

Page 23 of 39 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60


Figure legends

Figure 1. (a) Diagrammatic sketch of the synthesis procedure of Bi2O2CO3/g-C3N4 heterojunction. Bi2O2CO3 nanoparticle is represented by BO. (b) SEM image of Bi2O2CO3/gC3N4 heterojunction. (c-e) TEM images of Bi2O2CO3/g-C3N4 heterojunction. Bi2O2CO3 nanoparticles not only locate at the surface and margin of g-C3N4 sheet, but also intercalate into the interlayer.



Figure 2. (a) High resolution TEM image and (b) selected area electron diffraction image of Bi2O2CO3/g-C3N4 heterojunction. (c) Bright-field (BF) image of Bi2O2CO3/g-C3N4 heterojunction for element mapping. Element mapping images of (d) carbon, (e) nitrogen, (f) bismuth and (g) oxygen.


Page 24 of 39

Page 25 of 39 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60


Figure 3. (a) The XRD patterns of pure g-C3N4 and all the Bi2O2CO3/g-C3N4 heterojunctions. (b) The FTIR spectra of Bi2O2CO3 (BO), g-C3N4 and Bi2O2CO3/g-C3N4 heterojunctions recorded in the region from 400 to 4000 cm-1. The high-resolution XPS spectra of (c) C1s and (d) N1s of g-C3N4 and Bi2O2CO3/g-C3N4 heterojunction detected with monochromatic Al Kα radiation (1486.6 eV). The binding energy was calibrated by C1s line at 248.6 eV.



Figure 4. The results of photocatalytic hydrogen evaluation measurements. (a) The photocatalytic activity of pristine g-C3N4 and Bi2O2CO3/g-C3N4 heterojunction during 5 hours under visible light illumination. (b) Cyclic photocatalytic experiment of CN and BC3 during 15 hours. (c) Comparison of photocatalytic activity for hydrogen production between this work and previous work reported in literature. (d) The amount of hydrogen of CN and BC3 under monochromatic light irradiation.


Page 26 of 39

Page 27 of 39 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60


Figure 5. (a) UV-VIS diffuse adsorption spectra and the inserted pictures of Bi2O2CO3 modified g-C3N4 materials together with pristine g-C3N4. (b) PL spectra of all the assynthesized samples measured under 325 nm emission wavelength.



Figure 6. The results of photoelectrochemical (PEC) experiment of CN and BC3. (a) Transient photocurrent response results under intermittent visible light irradiation. (b) Mott-schottky plots (MS) of CN and BC3. The results of ultraviolet photoelectron spectra of (c) CN and (d) BC3, containing secondary electron cutoff (SEC) and valence band (VB).


Page 28 of 39

Page 29 of 39 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60


Figure 7. (a) Optimized geometric structures and total density of state (TDOS) of the g-C3N4 monolayer and Bi2O2CO3. (b) Planar-averaged electron density difference of Bi2O2CO3/g-C3N4 heterojunction material. (c) The projected density of state (PDOS) and TDOS of Bi2O2CO3/gC3N4 heterojunction. (d, e) The proposed heterojunction systems of Bi2O2CO3/g-C3N4 heterojunction material.



Figure 8. Rational photocatalytic mechanism for Bi2O2CO3/g-C3N4 heterojunction material.


Page 30 of 39

Page 31 of 39 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60


TOC Graphic



Figure 1. (a) Diagrammatic sketch of the synthesis procedure of Bi2O2CO3/g-C3N4 heterojunction. Bi2O2CO3 nanoparticle is represented by BO. (b) SEM image of Bi2O2CO3/g-C3N4 heterojunction. (c-e) TEM images of Bi2O2CO3/g-C3N4 heterojunction. Bi2O2CO3 nanoparticles not only locate at the surface and margin of g-C3N4 sheet, but also intercalate into the interlayer. 176x197mm (300 x 300 DPI)


Page 32 of 39

Page 33 of 39 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60


Figure 2. (a) High resolution TEM image and (b) selected area electron diffraction image of Bi2O2CO3/gC3N4 heterojunction. (c) Bright-field (BF) image of Bi2O2CO3/g-C3N4 heterojunction for element mapping. Element mapping images of (d) carbon, (e) nitrogen, (f) bismuth and (g) oxygen. 176x94mm (300 x 300 DPI)



Figure 3. (a) The XRD patterns of pure g-C3N4 and all the Bi2O2CO3/g-C3N4 heterojunctions. (b) The FTIR spectra of Bi2O2CO3 (BO), g-C3N4 and Bi2O2CO3/g-C3N4 heterojunctions recorded in the region from 400 to 4000 cm-1. The high-resolution XPS spectra of (c) C1s and (d) N1s of g-C3N4 and Bi2O2CO3/g-C3N4 heterojunction detected with monochromatic Al Kα radiation (1486.6 eV). The binding energy was calibrated by C1s line at 248.6 eV. 175x146mm (300 x 300 DPI)


Page 34 of 39

Page 35 of 39 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60


Figure 4. The results of photocatalytic hydrogen evaluation measurements. (a) The photocatalytic activity of pristine g-C3N4 and Bi2O2CO3/g-C3N4 heterojunction during 5 hours under visible light illumination. (b) Cyclic photocatalytic experiment of CN and BC3 during 15 hours. (c) Comparison of photocatalytic activity for hydrogen production between this work and previous work reported in literature. (d) The amount of hydrogen of CN and BC3 under monochromatic light irradiation. 175x125mm (300 x 300 DPI)



Figure 5. (a) UV-VIS diffuse adsorption spectra and the inserted pictures of Bi2O2CO3 modified g-C3N4 materials together with pristine g-C3N4. (b) PL spectra of all the as-synthesized samples measured under 325 nm emission wavelength. 175x70mm (300 x 300 DPI)


Page 36 of 39

Page 37 of 39 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60


Figure 6. The results of photoelectrochemical (PEC) experiment of CN and BC3. (a) Transient photocurrent response results under intermittent visible light irradiation. (b) Mott-schottky plots (MS) of CN and BC3. The results of ultraviolet photoelectron spectra of (c) CN and (d) BC3, containing secondary electron cutoff (SEC) and valence band (VB). 82x64mm (600 x 600 DPI)



Figure 7. (a) Optimized geometric structures and total density of state (TDOS) of the g-C3N4 monolayer and Bi2O2CO3. (b) Planar-averaged electron density difference of Bi2O2CO3/g-C3N4 heterojunction material. (c) The projected density of state (PDOS) and TDOS of Bi2O2CO3/g-C3N4 heterojunction. (d, e) The proposed heterojunction systems of Bi2O2CO3/g-C3N4 heterojunction material. 175x70mm (600 x 600 DPI)


Page 38 of 39

Page 39 of 39 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60


Figure 8. Rational photocatalytic mechanism for Bi2O2CO3/g-C3N4 heterojunction material. 82x39mm (600 x 600 DPI)


Visible-light Driven Photocatalytic H2 Generation and Mechanism

Recommend Documents