The Enhanced Photocatalytic Properties for Water Oxidation over Bi

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The Enhanced Photocatalytic Properties for Water Oxidation Over Bi/Bivo/VO Composite 4

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Xiaofeng Xu, Shufang Kou, Xia Guo, Xiaotong Li, Xiaojian Ma, and Hongzhi Mao J. Phys. Chem. C, Just Accepted Manuscript • DOI: 10.1021/acs.jpcc.7b03119 • Publication Date (Web): 11 Jul 2017 Downloaded from http://pubs.acs.org on July 12, 2017

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The Journal of Physical Chemistry

The Enhanced Photocatalytic Properties for Water Oxidation over Bi/BiVO4/V2O5 Composite Xiaofeng Xu,† Shufang Kou,† Xia Guo,†* Xiaotong Li,† Xiaojian Ma,† Hongzhi Mao† †

Key Laboratory of Colloid and Interface Chemistry, Ministry of Education, School of Chemistry

and Chemical Engineering, Shandong University, Jinan, Shandong 250100, China.

ABSTRACT: Bi/BiVO4/V2O5 has been successfully synthesized by a simple annealing of BiVO4 in Ar/H2. The obtained Bi/BiVO4/V2O5 was characterized by X-ray diffraction (XRD), Raman spectroscopy, X-ray photoelectron spectroscopy (XPS) and transmission electron microscopy (TEM). The photocatalytic activities are examined by oxygen evolution reaction. Compared with the products annealing in other atmospheres, BiO/BiVO4/V2O5 in air and Bi2VO5.5/ BiVO4/V2O5 in vacuum, Bi/BiVO4/V2O5 exhibited the best performances (2413 µmol·g-1·h-1), which could be attributed to the synergistic combination of Bi, BiVO4 and V2O5. This study may open up a new avenue for the development of efficient composite photocatalyst.

INTRODUCTION Solar light is an abundant, decentralized and inexhaustible natural resource which can be used for clean energy with minimal environmental impact.1,2 In recent years, the photocatalytic

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splitting of water into hydrogen and oxygen by semiconductor has been regarded as a promising strategy because of its renewable energy production without reliance on fossil fuels and no carbon dioxide emission.1,3 Water oxidation is the key step for water splitting. However, the conversion efficiency from solar energy to chemical energy is very low because oxygen evolution reaction (OER) is an endergonic reaction involving simultaneous transfer of four electrons.4,5 Thus, the discovery and design of high efficient photocatalytic materials for OER are demanding, yet challenging. Many photocatalysts for water oxidation have been reported, but most of them have very low photocatalytic activities under solar light.6 The monoclinic phase of BiVO4 has attracted wide attention due to its special crystal, electronic and optical properties.7 Furthermore, because of the overlapping between Bi 6s and O 2p orbitals, as well as the Bi3+ lone-pair contribution, the bandgap of BiVO4 is very narrow.7,8 With the relatively small bandgap energy , the monoclinic BiVO4 can effectively absorb visible light.7-9 In addition, BiVO4 is an ideal photocatalytic material for its low cost, nontoxic and favorable stability.2 However, the conversion efficiency from solar energy to chemical energy of BiVO4 is still quite low because it suffers from many drawbacks, such as low charge-separation efficiency and slow kinetics for oxygen evolution.7-10 Fortunately, in recent years, many significant breakthroughs have been made for BiVO4-based photocatalytic materials. Combination with semiconductor and deposition with metal are two predominant methods. Firstly, the combination with semiconductor which has different band gap energy can improve the absorption ability of solar light.11-18 Vanadium pentoxide (V2O5) is a good choice to improve the absorption ability due to its unique energy band gap (2.3 eV).19-24 For example, Sun et al.18 synthesized a novel V2O5/ BiVO4/TiO2 composite photocatalyst using a sequentially hydrothermal and adhering method, which shows that the multiple interfaces among


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different semiconductors enhance the separation efficiency of the photo-induced charge carriers and improve the photocatalytic performance. However, the application of amorphous V2O5 in the photocatalytic area has yet to be reported. Secondly, metal nanoparticles, such as Au, Ag, Pt and Bi can enhance the separation efficiency and electron transfer rate of semiconductor photocatalysts by forming surface plutonic metallic nanostructures.25-33 Feng et al.33 fabricated a novel p-n heterojunctions of BiOCl/BiVO4 nanosheets deposited with metallic Bi via a one-step method, which illustrates that Bi plays a crucial role in enhancing the photocatalytic performance of BiVO4. Up to now, many related studies have been performed to improve the photocatalytic properties of BiVO4, but few have combined these two effective methods in one system. In this study, a Bi/BiVO4/V2O5 composite system was constructed by a facile method to overcome the poor charge-separation yield. More importantly, the as-prepared Bi/BiVO4/V2O5 composite exhibits superior photocatalytic and photoelectrochemical properties, in comparison to the other as-prepared materials (BiVO4, Bi2VO5.5/BiVO4/V2O5 and BiO/BiVO4/V2O5). Our results demonstrate that the metallic Bi improves the quantity and transfer rate of the photoinduced charge carriers, enhancing the photocatalytic activity of Bi/BiVO4/V2O5. In addition, for BiVO4 catalyst, combination with V2O5 enhances the separation of electron-hole pairs. EXPERIMENTAL SECTION Materials. Bismuth(III) nitrate pentahydrate (Bi(NO)3·5H2O, 99.0%), ammonium metavanadate (NH4VO3, 99.0%), and N,N-Dimethylformamide (C3H7NO, 99.5%) were purchased from Sinopharm Chemical Reagent Co. Ltd (Shanghai, China). Crystalline V2O5 used in Raman measurement was also purchased from Sinopharm Chemical Reagent Co. Ltd. All reagents were used without any further purification.


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Synthesis of BiVO4 photocatalyst. A total of 1 mmol NH4VO3 was dispersed into 10 mL deionized (DI) water, and then the suspension was added dropwise into a 30 mL DMF solution containing 1 mmol of Bi(NO3)·5H2O. An orange-colored solution was obtained after being vigorously stirred for 30 min. The final solution was then transferred into a 50 mL Teflon-lined autoclave and maintained at 120 °C for 10 h. The resultant mixture was separated by centrifugation, and the precipitate was washed with DI water and ethanol for several times to remove undesirable ions. The obtained product was dried at 60 °C for 12 h, and denoted as BiVO4. Annealing treatment. The annealing procedures of BiVO4 were carried out by a simple treatment in a tube furnace. BiVO4 was annealed in an argon-hydrogen atmosphere (Ar-H2, 5% of H2) for 10 min in a range of temperatures between 300 and 500 °C. All the samples were heated to the desired temperatures at a rate of 10 oC/min. After 10 min, they were cooled to room temperature at another rate of 7 oC/min. These samples were denoted as H-t, where t stands for the temperature in the corresponding annealing treatment. For example, H-450 was obtained by annealing BiVO4 in Ar-H2 at 450 °C for 10 minutes. For the sake of brevity, the products of BiVO4 annealed at 450 °C for 10 min in vacuum and air atmosphere were denoted as V-450 and A-450, respectively. Characterization. The XRD patterns of BiVO4 were obtained on an X-ray powder diffractometer (Bruker D8 Advance, German) equipped with a rotating anode, using the monochromatic Cu Kα as the radiation source. The working voltage and current of the diffractometer were kept at 40 kV and 40 mA, respectively. The Raman spectra were measured by a microscopic confocal Raman spectrometer (Renishaw plc, UK). The X-ray photoelectron spectroscopy (XPS) analysis was performed with an ESCALAB 250 spectrometer


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(ThermoFisher SCIENTIFIC, USA), using the radiation of Al KR line as the excitation source. The binding energy was calibrated using the C 1s photoelectron peak at 284.6 eV as the reference.The photoluminescence (PL) spectra were achieved from an LS-55 fluorescence spectrophotometer (PerkiElmer, USA) nm at a rate of 10-1500 nm/min. The PL spectra were recorded in the range of 380-700 nm at room temperature at the excitation wavelength of 310 nm. The TEM images were recorded by a transmission electron microscope (JEM-1011, Japan) at an accelerating voltage of 100 kV. The elemental maps and high-resolution TEM (HRTEM) image were obtained by a JEM 2100F analytical transmission electron microscope equipped with an energy dispersive spectrometer (EDS) at 200 kV. The UV-Vis DRS was recorded on a Shimadzu UV-2450 spectrophotometer in the range of 850-220 nm at room temperature, using BaSO4 as the reference. The resistivity was measured using the RTS-8 four-point probes instrument by preparing samples as tablets with a thickness of 0.3 mm and a diameter of 12.90 mm. The test current was controlled at 0.1293 µA. Photocatalytic activity measurements. Photocatalytic O2 evolution tests were carried out in a solution of AgNO3 (100 mM, 15mL), which was used as the sacrificial reagent for electrons. Typically, 40 mg of the as-prepared sample as a photocatalyst was added to the AgNO3 solution in a 50 mL bottle with rubber stopper. The reaction system was vacuumed, flushed with argon by a Schlenk line to remove the residual gas. Then the solution was stirred for 3 h in dark to reach absorption-desorption equilibrium. The reactor was illuminated with a xenon lamp (Perfect Light Solaredge 700) equipped with a UV cut-off filter (λ>400 nm). The irradiance of the lamp used for photocatalytic activity measurement of the sample is 200 W. Using Ar as the carrier gas, the amount of O2 was determined by a gas chromatograph (FULI9790II, molecular sieve 5 Å column) equipped with a thermal conductivity detector (TCD).


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Photoelectrochemical measurements. Photocurrent measurements were performed on a CHI760E electrochemical station using a standard three-electrode system. The Pt plate was used as the counter electrode and Ag/AgCl as the reference electrode. A mixed solution of naphthol and ethanol containing 40 mg of the sample was dispersed on ITO glass, which was used as the working electrode. The electrolyte was a mixture of 0.25 M Na2SO4 and 0.25 M Na2SO3. A 200 W Xe lamp equipped with a cut-off filter at 400 nm was used as the light source. A shutter was used to record transient photocurrent decay at 20 s intervals, and the photoelectric responses of the photocatalysts when the light was on and off were measured at +0.8 V vs. Ag/AgCl electrode. RESULTS AND DISCUSSION


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Figure 1. XRD patterns of as-prepared (a) BiVO4, (b) H-450, (c) A-450 and (d) V-450. Raman spectra of BiVO4, H-450, A-450, V-450 and V2O5 in a range of (e) 50-1200 cm-1 and (f) 50-500 cm-1. The products were examined by XRD patterns to identify their crystal structure. As shown in Figure 1a, the product obtained by the solvothermal reaction could be indexed as monoclinic-


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phase BiVO4 (JCPDS Card No. 14-0688). No impurities are observed in this XRD pattern. After the calcination at 450 oC in Ar/H2, new diffraction peaks at 27.2o, 38.0o and 39.6o appear in the pattern (Figure 1b), besides those from BiVO4. These peaks could be attributed to those from metallic Bi (JCPDS Card, No. 44-1246). It is believed that reducing atmosphere and high calcination temperature lead to the reduction of BiVO4 to metallic Bi. Along with this change, there must be VOx in the product. But the absence of the diffraction peaks of VOx indicates that they are probably amorphous. For the sake of clarity, this product obtained in Ar/H2, which is composed of BiVO4, Bi and VOx, is denoted as H-450. If the calcination atmosphere was switched to air, BiO (JCPDS Card, No. 27-0654) rather than metallic Bi, is observed in the pattern (Figure 1c). Similar to the case of H-450, the formation of BiO indicates the decomposition of BiVO4 that definitely produces some sort of VOx, although it is likely amorphous. The product composed of BiVO4, BiO and VOx, is labelled as A-450. If BiVO4 was calcinated in vacuum, the diffraction peaks belonging to Bi2VO5.5 (JCPDS Card, No. 41-0575) are detected (Figure 1d). So, the product composed of BiVO4, Bi2VO5.5 and VOx, is denoted as V-450. These results confirm the influences of calcination atmosphere to the product, thereby greatly altering the photocatalytic activity in OER. Raman spectra were used to clarify the potential species of VOx. As shown in Figure 1e, the Raman peaks at 208, 329, 365, 710 and 826 cm-1 are in good agreement with those reported for BiVO4.2,34,35 The Raman band at 208 cm-1 comes from the external rotation mode. The peaks at 329 and 365 cm-1 originate from symmetric bending mode and asymmetric bending mode of VO4 tetrahedron. The peaks at 710 and 826 cm-1 can be assigned to the stretching modes of V-O bonds. After high-temperature calcination, the main peaks of BiVO4 are kept for all three samples (H-450, A-450 and V-450). It indicates the dominance of BiVO4 in the samples.


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Meanwhile, the close check around 150 cm-1 discloses a weak but clear sign for V2O5 in all three samples, although the content of V2O5 might vary from one to another (Figure 1f).

Figure 2. High-resolution XPS spectra of (a) Bi 4f and (b) V 2p in BiVO4 and H-450. The high-resolution XPS spectra of Bi and V were obtained to further prove the existence of metallic Bi and V2O5 in H-450 sample. Figure 2a shows the Bi 4f spectra of BiVO4 and H-450. There are two new peaks at 156.7 and 162.3 eV in the Bi 4f spectrum of H-450, as compared with that of BiVO4. These peaks are well consistent with those reported for Bi 4f5/2 and Bi 4f7/2 of metallic Bi.31 The other double at 159.2 eV and 164.4 eV in the spectrum agrees well with Bi 4f5/2 and Bi 4f7/2 of BiVO4.15 On the basis of these peaks, the molar ratio of Bi(0) and Bi(III) is estimated as ~2.6 %, suggesting only a small quantity of metallic Bi on the surface. Figure 2b shows the V2p spectra of H-450 and BiVO4. There are two doublets in the high-resolution spectrum of V 2p in H-450. The doublet at 524.0 eV and 516.7 eV is in good accordance with the reported data for V2p1/2 and V2p3/2 in BiVO4.15,18 The other at 524.7 eV and 517.1 eV, slightly higher than those in BiVO4, is consistent with those in V2O5.15,18 This result strongly


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support the presence of V2O5 in H-450, although it was obtained by annealing in Ar/H2. Based on the evidence above, the reactions during the annealing treatments can be concluded as follows: H2:

2 BiVO4 +3 H2 → 2 Bi + V2O5 + 3 H2O

(1-1)

Air: 4 BiVO4 → 4 BiO + 2 V2O5 + O2

(1-2)

Vac: 4 BiVO4 → 2 Bi2VO5.5 + V2O5

(1-3)

Figure 3. TEM image (a) and HRTEM image (b) of H-450. TEM images of (c) A-450 and (d) V-450. Figure 3 shows the TEM results of H-450, A-450 and V-450. BiVO4 consists of highly aggregated nanoparticles with their overall size about 70-130 nm (Figure S1). This size is smaller than many of the reported ones.36-39 After treated in Ar/H2, the aggregated nanoparticles fuse together, producing solid nanoparticles with a similar size for H-450 (Figure 3a). The morphology change of H-450 could be attributed to the low melting point of Bi (271.3 oC) in H450, which makes Bi an effective binder to bridge BiVO4 and V2O5. HRTEM image (Figure 3b)


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of H-450 shows clear lattice fringes, corresponding to (012) of Bi, (121) of BiVO4 and (001) of V2O5. As shown in Figure 3b, BiVO4 is the main component and Bi and V2O5 are uniformly distributed throughout the particles. The few crystalline V2O5 is the transformation of amorphous V2O5 under high temperature. In addition, these parts without clear lattice fringes are the amorphous V2O5, which uniformly distributed throughout the particles. This result confirms that Bi and V2O5 are well mixed with BiVO4. This structure benefits the charge transfer from the bulk to the surface, thereby improving the photocatalytic activity of H-450. Different from H450, A-450 and V-450 basically inherit the morphology from BiVO4 (Figure 3c-3d), although they are different in components.

Figure 4. (a) Diffuse reflection spectra and (b) real-color photographs of BiVO4, H-450, A-450 and V-450. Optical properties of BiVO4, H-450, A-450 and V-450 are investigated by diffuse reflection spectra, which is important to their photocatalytic performances. As shown in Figure 4a, BiVO4 gives an absorption edge at 500 nm without any tails beyond this wavelength, consistent with the reported bandgap.7,8 The similar case happens to A-450, although the absorption edge slightly


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moves to the red (~ 535 nm). V-450 and H-450 exhibit an apparent absorption over the range of 500-730 nm, which makes them unique colors (Figure 4b). This absorption to visible light likely originates from Bi in H-450 or Bi2VO5.5 in V-450. In spite of different origins, the energy levels reflected by this absorption could promote the charge separation and prolong the lifetime, thus enhancing the photocatalytic activity.

Figure 5. (a) Photocatalytic performances of BiVO4, H-450, A-450 and V-450 in OER. (b) Electrical resistivities and (c) Photocurrent responses of BiVO4, H-450, A-450 and V-450. (d) Recycling performance of H-450. Figure 5a shows photocatalytic activities of BiVO4, H-450, V-450 and A-450 in OER under visible light. Although all the samples generate oxygen over time, they are quite different in


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terms of photocatalytic activity. As compared to BiVO4, V-450 and A-450, H-450 exhibits the highest activity, although the rate of oxygen generation gradually slows down after 20 min. This result might be attributed to the consumption of the self-sacrificial agent (AgNO3), the deposition of silver on the surface. This result is supported by the XRD pattern (Figure S2b) and elemental maps (Figure S3) of H-450 after OER. Figure S4 shows the OER test of H-450 with Na2S2O8 as sacrificial reagent. Compared with reaction in AgNO3 solution, the oxygen evolution rate of H450 keeps unchanged with reaction time, illustrating the inhibition effect of the consumption of the self-sacrificial agent (AgNO3) for the photocatalytic performance of H-450. The similar phenomenon has been reported in previous reports.2,9,34 In spite of this, H-450 could be still regarded as the best photocatalyst. At 20 min, the oxygen- generation rate of H-450 for OER is 2413 µmol·g-1·h-1, ~3.6 times higher than that of V-450 (662 µmol·g-1·h-1), ~6.4 times for BiVO4 (375 µmol·g-1·h-1), or ~29.4 times for A-450 (82 µmol·g-1·h-1), which is much higher than that of the other BiVO4-based catalysts using AgNO3 as electron capture agent have been reported so far (~750 µmol·g-1·h-1).40 To understand the excellent performance, electrical resistance and photocurrent responses were measured for all the samples. As shown in Figure 5b, H-450 shows the lowest electrical resistance, due to metallic Bi in the composite. This result indicates fast charge transfer from the bulk to the surface, which could reduce the recombination of photogenerated charges and then promote the catalytic reaction on the surface. V-450 and A-450 are worse than H-450, but better than BiVO4, due to abundant crystal boundaries.33,41 Photocurrent responses of photocatalysts under irradiation is a powerful tool to identify their charge-separation efficiencies. Here, photocurrent responses of BiVO4, V-450, A-450 and H-450 were measured at 0.8 V by depositing them on ITO glasses. As displayed in Figure 5c, H-450 shows the largest photocurrent response under visible light, which could be ascribed to its small


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resistance, enhanced adsorption tail between 500-700 nm, as well as abundant crystal boundaries. The response follows the order of V-450, BiVO4, and A-450, which is in good agreement with their photocatalytic activities. This result is also supported by PL. As shown in Figure S5, the PL intensities of these samples are in the following order: H-450 < V-450 < A450 < BiVO4, which is consistent with the trend from photocatalytic performance. The cycling performance of used H-450 was also examined as shown in Figure 5d. It is found that the photocatalyst show little degradation after five cycles, suggesting its good stability.

Figure 6. A proposed mechanism for photo-induced processes on H-450. Figure 6 shows the schematic illustration on photogenerated charges transfer on H-450. The conduction band (CB) and valance band (VB) potentials of BiVO4 and V2O5 can be calculated by related equations.15,42 For amorphous semiconductor, there are two tail states at the top of valance band and at the bottom of conduction band due to the localized states compared to crystalline semiconductor.43 So, the band structure of amorphous V2O5 is illustrated as the


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thickened localized states of CB and VB as shown in Figure 6. Both V2O5 and Bi have positive effects for promoting the charge separation and prolong the lifetime. Firstly, the photogenerated electrons on BiVO4 could transfer to the CB of V2O5, which increases the separation efficiency of photo-excited electron-hole pairs.15 Secondly and most importantly, the interfacial transfer of electrons from CB of BiVO4 and V2O5 to metallic Bi enhances the separation of electron-hole pairs and increases the lifetime of charge carriers in BiVO4 and V2O5, enhancing the photocatalytic activity of OER. Hence, the special band gap structure and superior conductivity of Bi determine the high separation efficiency, intensity and transfer rate of photo-induced charge carriers, and these elements facilitate the superior photocatalytic performance of Bi/BiVO4/V2O5 composite.


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Figure 7. TEM images of (a) H-350, (b) H-400, (c) H-450 and (d) H-500. XRD patterns of BiVO4, H-350, H-400, H-450 and H-500 in a range of (e) 10o-70o and (f) 25o-32o. The H-t samples were produced to illustrate the influence of annealing temperature on the morphology and photocatalytic properties during the formation of Bi/BiVO4/V2O5 composite. As shown in Figure 7a-7d, the spherical morphology becomes irregular gradually with the increasing of annealing temperature in Ar-H2, which is attributed to higher temperature make more Bi produced on the surface of BiVO4. The increase of the amount of Bi with the rise of annealing temperature is supported by XRD (Figure 7e-7f). Bi is melted at high temperature and plays an important role in composite connection. The more Bi is produced, the more obvious the change of the morphology.

Figure 8. Photocurrent response (a) and photocatalytic performance (b) of BiVO4, H-350, H400, H-450 and H-500. Figure 8a and Figure 8b show the photocurrent response and photocatalytic oxygen evolution of the samples annealed at different temperatures, respectively. H-t samples show better photocurrent response and photocatalytic activity than pristine BiVO4. Among these samples, H450 had the highest photocatalytic oxygen evolution. Under the reducing atmosphere (Ar-H2),


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high temperature is beneficial to the production of Bi, which promotes the transfer and separation of photo-induced charge carriers. However, the consumption of BiVO4 catalyst with the production of Bi is adverse to the photocatalysis of OER. These parameters lead to the best photocatalytic oxidation activity of H-450. All results indicate that the Ar-H2 atmosphere and 450 oC of annealing temperature are the two necessary elements of the formation of Bi/BiVO4/V2O5 composite photocatalyst with excellent photocatalytic oxidation performance. CONCLUSION In summary, a Bi/BiVO4/V2O5 composite was successfully prepared by a facile annealing of BiVO4 in Ar/H2. Furthermore, BiO/BiVO4/V2O5 and Bi2VO5.5/BiVO4/V2O5 composite were synthesized by annealing BiVO4 in air and vacuum, respectively. The optical properties, photoelectrochemical properties and photocatalytic performance of different composites were explored, which demonstrate that Bi/BiVO4/V2O5 composite has outstanding photocatalytic properties. Our results indicate that Bi plays a more crucial role in the enhancement of photocatalytic performance of BiVO4. Bi deposition can enhance the intensity and the transfer rate of the photo-induced charge carriers. V2O5 component can improve the separation efficiency of the photo-induced electron-hole pairs due to its bandgap structure. Hence, the Bi/BiVO4/V2O5 composite is an outstanding photocatalyst for oxygen evolution reaction. Our findings may open up a new avenue for the development of efficient composite photocatalyst. AUTHOR INFORMATION Corresponding author *Fax: +86-531-88364489. Tel.: +86-88364489. E-mail: [email protected].


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Notes The authors declare no competing financial interest. SUPPORTING INFORMATION TEM image of BiVO4, XRD and elemental maps of samples before and after OER; Photocatalytic performance of H-450 sample with Na2S2O8 as sacrificial reagent and PL spectra of samples. ACKNOWLEDGEMENTS This study was financially supported by the Natural Science Foundation of China (21071055). REFERENCES (1) Walter, M. G.; Warren, E. L.; McKone, J. R.; Boettcher, S. W.; Mi, Q. X.; Santori, E. A.; Lewis, N. S. Solar Water Splitting Cells. Chem. Rev. 2010, 110, 6446-6473. (2) Thalluri, S. M.; Suarez, C. M.; Hussain, M.; Heranadez, S.; Virga, A.; Saracco, G.; Russo, N. Evaluation of The Parameters Affecting The Visible-Light-Induced Photocatalytic Activity of Monoclinic BiVO4 for Water Oxidation. Ind. Eng. Chem. Res. 2013, 52, 17414-17418. (3) Maeda, K.; Domen, K. Photocatalytic Water Splitting: Recent Progress and Future Challenges. J. Phys. Chem. Lett. 2010, 1, 2655-2661. (4) Wang, D.; Jiang, H.; Xu, Z.; Xu, Q.; Yi, M.; Li, G. L.; Li C. Crystal Facet Dependence of Water Oxidation on BiVO4 Sheets under Visible Light Irradiation. Chem. Eur. J. 2011, 17, 12751282.


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The Enhanced Photocatalytic Properties for Water Oxidation over Bi

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