Article pubs.acs.org/JPCC
Bi2S3‑Nanowire-Sensitized BiVO4 Sheets for Enhanced Visible-Light Photoelectrochemical Activities Wuyou Wang,† Xuewen Wang,*,† Chengxi Zhou,† Biao Du,† Jianxin Cai,‡ Gang Feng,† and Rongbin Zhang*,† †
The Institute of Applied Chemistry, The College of Chemistry, Nanchang University, 999# Xuefu Road, Nanchang 330031, P. R. China ‡ School of Resources Environmental & Chemical Engineering, Nanchang University, 999# Xuefu Road, Nanchang 330031, P. R. China S Supporting Information *
ABSTRACT: BiVO4 is widely used for photoelectrochemistry and photocatalytic oxygen evolution under visible-light irradiation. To extend the range of visible-light absorption and reduce the recombination rate of photoexcited electrons and holes, a BiVO4 sheet−Bi2S3 nanowire heterostructure was fabricated through an easy in situ hydrothermal method. In this method, Bi2S3 nanowires were uniformly coated onto the surface of BiVO4 sheets. The heterostructure exhibits a wide visible-light absorption band ranging from 525 to 900 nm after coupling with Bi2S3 nanowires. The BiVO4 sheet−Bi2S3 nanowire heterostructures were used for photoelectrochemical measurements and exhibited higher photocurrent intensity than those of BiVO4 sheets and BiVO4 particle−Bi2S3 under visible-light irradiation. The optimized amount of Bi2S3 in the heterostructure was approximately 2.4 at. %. The remarkable enhancements in the photoelectrochemical property were attributed mainly to the solid sensitization of Bi2S3 nanowires providing a number of photoexcited electrons, shortening transport distance in BiVO4 sheets, smoothening migration along Bi2S3 nanowires, and enhancing the synergistic effect between BiVO4 and Bi2S3.
1. INTRODUCTION Photocatalysis is attracting considerable attention for its applications in energy conversion and environmental protection using solar energy.1,2 Numerous semiconductor materials with high stability and low cost are widely developed and used in the photocatalytic field. In recent years, Bi-based semiconductor photocatalysts, such as BiVO4,3 Bi2WO6,4 BiFeO3,5 and CaBi2O46 have attracted considerable attention because of the potential visible-light photocatalytic activity. BiVO4 with high oxidation potential is widely used for photocatalytic oxygen evolution, photoelectrochemical water splitting, and photodegradation. Among different phases of monoclinic scheelite (m-s), tetragonal scheelite (t-s), and tetragonal zircon (t-z), the m-s BiVO4 with a narrow bandgap of 2.4 eV and excellent stability was considered to be a promising efficient photocatalytic semiconductor material because of its intrinsic crystal structure.7−15 However, the photocatalytic activity of BiVO4 is limited by the high recombination rate of photoexcited electrons and holes16 and the low absorption capacity of visible-light (less than 520 nm).17 Various morphological structures of BiVO4, such as facet-controlled particles,18 nanoparticles,19 sheets,20,21 and rods,22 and element-doped BiVO4, such as S-doping,23 N-doping,24 Co-doping,25 and Modoping,26 have been widely developed to extend the visiblelight absorption range and improve the photocatalytic perform© 2017 American Chemical Society
ance to solve the previously mentioned problems. As another important method to improve photocatalytic property, BiVO4based heterostructures, such as BiVO4−ZnO,27 BiVO4−BiOI,28 BiVO4−Co3O4,29 and BiVO4−Bi2O3,30 were also synthesized to facilitate the separation of photoexcited electrons and holes and improve the visible-light absorption capability. However, the recombination rate of photoexcited charge carriers would increase due to a long transport distance in bulk materials and would restrict the promotion of photocatalytic activity. Two-dimensional (2D) structures have recently been attracting considerable attention due to their thinness, which helps shorten the transport distance of charge carriers in the BiVO4 sheet and improve photocatalytic activity. Bi2S3, as a narrow bandgap (approximately 1.3 eV) material, exhibits a wide range of visible-light absorption reaching 800 nm, which is widely used to sensitize wide bandgap materials and increase the number of photoexcited carriers under visible-light irradiation.31,32 Gao et al. recently reported that the BiVO4− Bi2S3 heterojunction photocatalyst exhibited an enlarged visible-light responsive range and improved the separation of photoexcited electrons and holes.33 Liu et al. also synthesized Received: July 12, 2017 Revised: August 14, 2017 Published: August 17, 2017 19104
DOI: 10.1021/acs.jpcc.7b06838 J. Phys. Chem. C 2017, 121, 19104−19111
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The Journal of Physical Chemistry C the BiVO4−Bi2S3 heterojunction to enhance its photoelectrochemical performance.34 Given the suitable band structures and band potentials of BiVO4 and Bi2S3,35 a BiVO4−Bi2S3 heterostructure with 2D or 1D structure can be fabricated to shorten the charge carrier transport distance. Meanwhile, the visible-light photocatalytic activity can be improved by sensitizing Bi2S3. In this work, an easy in situ hydrothermal method was developed to synthesize BiVO4 sheet−Bi2S3 nanowire heterostructure using thioacetamide (TAA) and BiVO4 sheets as precursors. Given that Bi2S3 is one of the Bi-based semiconductor photocatalysts, Bi2S3 nanowires were easily loaded on the surface of BiVO4 sheets. In this study, Bi2S3, with a wide visible-light absorption band, was introduced to enhance the visible-light photocatalytic activity of BiVO4. The BiVO4 sheet− Bi2S3 nanowire heterostructures were applied in the photoelectrochemical measurements and exhibited higher photocurrent intensity than that of BiVO4. The photocatalytic capability was further improved after optimizing the amount of Bi2S3 nanowires in the heterostructures. The possible photocatalytic mechanism for the enhanced visible-light absorption and photoelectrochemical performance was extensively discussed.
M (Micrometritics). The UV−visible (UV−vis) absorption spectra were measured by a UV−vis spectrophotometer (HITACHI U-4100). The chemical compositions of the samples were analyzed by using a monochromatic Al Kα Xray photoelectron spectroscopy (XPS) source (Thermo Escalab 250). All binding energies were referenced to the C 1s peak (284.6 eV) produced by adventitious carbon. The fluorescence spectra were tested by a fluorescence spectrophotometer (HITACHI F-7000). The content of sulfur in the BiVO4 sheet−Bi2S3 nanowire heterostructure was tested by an Element Analyzer (Elementar VARIO EL cube). 2.3. Photocatalytic Activity Measurement. A slurry consisted of 50 mg of resultant photocatalysts, 1 mL of deionized water, 2 drops of Triton X-100, and 2 drops of acetylacetone. The slurry was deposited on a FTO glass substrate by a doctor-blading method with adhesive type as a spacer. Then the film was dried at 180 °C for 2 h in an oven. Photoelectrochemical measurements were carried out in a quartz cell with a conventional three-electrode system. The samples loaded on FTO glass, Pt foil, and Ag/AgCl electrode served as the working electrode, counter electrode, and reference electrode, respectively. The electrolyte was 0.1 M of Na2SO4 aqueous solution. A solar simulator of 300 W Xe lamp was used as the excitation light source. Long-pass filters were utilized to cut off the light. The photoanode surface area illuminated was 1 cm2, and the scanning rate was 5 mV/s.
2. EXPERIMENTAL SECTIONS 2.1. Synthesis of BiVO 4 Sheet−Bi 2 S 3 Nanowire Heterostructures. The BiVO4 sheets were synthesized by a hydrothermal method.7 In a typical synthesis process, 0.57 mmol of sodium dodecyl benzenesulfonate (SDBS) and 2.0 mmol of Bi(NO3)3·5H2O were dissolved in 10 mL of 4 M HNO3 aqueous solution under stirring for 1 h. 2.0 mmol of NH4VO3 was dispersed in 10 mL of 2 M NaOH aqueous solution and then dropped in the Bi(NO3)3·5H2O solution with continuous stirring for 0.5 h. After that, 13 mL of 2 M NaOH was added to the above mixed solution to adjust the pH under stirring for 0.5 h. The mixed solution was transferred into a 100 mL Teflon-lined stainless-steel autoclave and thermally treated at 200 °C for 2 h. The yellow deposits were washed with deionized water for three times and then dried at 80 °C for 8 h. BiVO4 sheet−Bi2S3 nanowire heterostructures were prepared by an in situ hydrothermal method using BiVO4 sheets and TAA as precursors. In a typical process, 100 mg of as-prepared BiVO4 sheets were dispersed in 30 mL of deionized water under ultrasonication for 20 min. Then, 0.069 mol of TAA was dissolved in 20 mL of deionized water, which was dropped into the above solution under vigorous stirring for 20 min. Then, the resulting mixture solution was transferred into a 100 mL Teflon-lined stainless-steel autoclave and thermally treated at 150 °C for 10 h. The products were collected and washed with deionized water for four times. Then, the products were dried at 100 °C for 8 h. The different amounts of TAA (0.046, 0.069, 0.092, and 0.37 mol) were used to control the proportion of Bi2S3 in BiVO4−Bi2S3 heterostructures. 2.2. Characterization of Catalyst. X-ray diffraction (XRD) patterns were recorded by a Rigaku diffractometer using Cu Kα irradiation where the scanning rate is 2° min−1 in the 2θ from 10° to 70°. Scanning electron microscopy (SEM) images and energy dispersive X-ray (EDX) spectroscopy profiles were obtained on a Nova SEM 200. Transmission electron microscope (TEM) images were obtained by a JEOL2100. The Brunauer−Emmett−Teller (BET) specific surface areas and pore size distribution were analyzed on ASAP-2010
3. RESULT AND DISCUSSION The crystalline structures of the as-prepared BiVO4 sheets and BiVO4 sheet−Bi2S3 nanowire heterostructures with different amounts of Bi2S3 were determined by XRD patterns shown in Figure 1. All of the diffraction peaks are indexed to m-s BiVO4
Figure 1. XRD patterns of as-prepared BiVO4 sheets and BiVO4− Bi2S3 heterostructures prepared using different amounts of TAA.
(JCPDS: 14-0688). In contrast to BiVO4 sheets, no obvious diffraction peaks of Bi2S3 were observed in the heterostructures when using TAA amounts less than 25%. A possible reason is that the content of Bi2S3 was below the detection range of the XRD instrument. BiVO4−Bi2S3 heterostructures with different amounts of Bi2S3 were synthesized by varying the amounts of TAA added to explore the effect of the Bi2S3 amount. With the increase in TAA concentration, the diffraction peaks of Bi2S3 (JCPDS: 84-0279) began to appear in the XRD patterns (Figure 1). When the amount of TAA reached 50%, the obvious diffraction peaks of Bi2S3 were detected in the range from 15° to 35° in the XRD patterns of the BiVO4−Bi2S3−50% heterostructure. The XRD results confirm that Bi2S3 can be 19105
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The Journal of Physical Chemistry C formed on the surface of BiVO4 in an aqueous solution containing TAA during the hydrothermal process. SEM images of the BiVO4 and BiVO4−Bi2S3 heterostructure are shown in Figure 2 to assess the morphology and structure
Figure 3. TEM images of (a) the BiVO4−Bi2S3 heterostructure and (b) Bi2S3 nanowires on the surface of BiVO4 sheets; (c) highresolution TEM image of a Bi2S3 nanowire; and (d) TEM image of the interface between BiVO4 and Bi2S3, the inset is the high-resolution TEM image of BiVO4.
Figure 2. SEM images of (a) BiVO4 sheets and (b) BiVO4 sheet−Bi2S3 nanowire heterostructure (15%) and (c) the corresponding EDX spectrum.
0.36 nm were assigned to the (130) crystal plane of Bi2S3. TEM images of the interface structure of BiVO4 and Bi2S3 shown in Figure 3d suggested that a Bi2S3 nanowire was firmly coated on the surface of the BiVO4 sheet. In the interface of BiVO4 sheets and Bi2S3 nanowires, the crystal spacing of 0.47 and 0.36 nm can be well assigned to the (011) plane of the monoclinic BiVO4 phase33 and the (130) plane of the orthorhombic Bi2S3 phase. From the results of XRD, SEM, and TEM, Bi2S3 nanowires can be well loaded on the surface of BiVO4 sheets and can form the BiVO4 sheet−Bi2S3 nanowire heterostructure during the hydrothermal process involving TAA. According to the preparation process, the SEM and TEM results, and previous reports,33−35 the proposed growth mechanism of the BiVO4 sheet−Bi2S3 nanowire heterostructure is shown in Figure 4. The heterostructure was synthesized by an easy in situ anion exchange course during the hydrothermal process including the BiVO4 sheets as precursor and TAA as sulfur source. TAA can release S2− at high temperature, and the anion exchange reaction can smoothly occur at 150 °C in an
of the BiVO4−Bi2S3 heterostructure. The SEM image (Figure 2a) of BiVO4 used as the precursor shows that the BiVO4 has a sheet-like structure which will shorten the photoexcited carrier transport distance in the bulk and increase the surface reaction sites. Figure 2b clearly shows that Bi2S3 nanowires are uniformly coated onto the surface of BiVO4 sheets. The EDX spectrum of BiVO4−Bi2S3−15% is shown in Figure 2c. The elemental composition of BiVO4−Bi2S3−15% from the EDX spectrum confirms the existence of Bi, V, O, and S elements. The 2D-projected element mapping analysis of the BiVO4− Bi2S3 heterostructure shown in Figure S1 indicated that Bi, V, O, and S elements were homogeneously distributed in the heterostructure, which in turn indicated that Bi2S3 nanowires uniformly grew on the surface of BiVO4 sheets. When the amounts of TAA used in the preparation process were 10%, 15%, and 25%, the BET surface areas, adsorption− desorption isotherms, and pore size distribution of the heterostructure were tested. The results are shown in Table S1 and Figure S3. The BET surface area of the BiVO4 sheet− Bi2S3 nanowire heterostructure (15%) is 5.4 m2 g−1, and the pore size distribution is centered at approximately 28 nm. Compared with that of the BiVO4 sheets, the surface areas of BiVO4 sheet−Bi2S3 nanowire heterostructures only slightly increased after loading Bi2S3 nanowires. A possible reason is that Bi2S3 nanowires preferably formed on the defect centers of BiVO4 sheets, which will reduce the extent of the increased surface area of the heterostructures introduced by the Bi2S3 nanowires. Furthermore, the morphology and microstructure of the BiVO4−Bi2S3 heterostructure were investigated in more detail using TEM, as shown in Figure 3. The TEM images shown in Figure 3a indicated that Bi2S3 nanowires uniformly grew on the surface of BiVO4 sheets. The TEM images shown in Figure 3b indicated that the diameter of Bi2S3 nanowires was less than 30 nm. The high-resolution TEM image of Bi2S3 nanowires shown in Figure 3c indicated that the lattice fringes with a d-spacing of
Figure 4. Scheme of the formation process of the BiVO4 sheet−Bi2S3 nanowire heterostructure prepared by a hydrothermal process. 19106
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nm due to their intrinsic bandgap. After the Bi2S3 nanowires were introduced into the BiVO4 sheets, all of the BiVO4−Bi2S3 heterostructures exhibited wide bands of visible-light absorption of more than 900 nm due to the narrow bandgap Bi2S3 with a wide range of visible-light absorption. The visible-light absorbance of the heterostructures gradually increased with the increase in the amounts of Bi2S3 nanowires. Therefore, Bi2S3nanowire-sensitized BiVO4 sheets within a wide visible-light absorption range can ensure good visible-light photocatalytic performance of the heterostructures. The high-resolution XPS spectra of BiVO4−Bi2S3 and BiVO4 and Bi2S3 shown in Figure 6 are used to explore the surface chemical compositions and chemical states of the BiVO4 sheet−Bi2S3 nanowire heterostructure. The XPS spectra show that the heterostructure includes Bi, V, O, and S elements, which indicates that Bi2S3 formed on the surface of BiVO4 sheets in an aqueous solution containing TAA. The highresolution XPS spectra of Bi 4f and S 2p of BiVO4, Bi2S3, and BiVO4−Bi2S3 heterostructures are shown in Figure 6a. The peaks of S 2p3/2, S 2p1/2, Bi 4f7/2, and Bi 4f5/2 of the BiVO4 sheet−Bi2S3 nanowire heterostructure, appear at 160.7, 162.2, 159.1, and 164.4 eV, respectively. Compared with those of Bi2S3, the binding energies of S 2p3/2 of the BiVO4−Bi2S3 heterostructure shift to a high-energy direction. By contrast, the binding energies of Bi 4f and S 2p1/2 exhibit a low energy shift. The XPS results indicate that a new chemical bond, i.e., O−Bi− S, was formed at the interface between Bi2S3 and BiVO4 in the BiVO4−Bi2S3 heterostructure, which favors the smooth transport of photoexcited carriers. The peaks centered at 159.1 and
aqueous solution. Thus, BiVO4 can transfer to Bi2S3 due to the low solubility of Bi2S3 (Ksp = 1 × 10−97). In the growth process, Bi3+ that dissociated from BiVO4 can react with S2− ions and then form Bi2S3 nanowires that are uniformly distributed on the surface of the BiVO4 sheets in an aqueous solution. The UV−vis light absorption spectra of BiVO4 sheets and BiVO4−Bi2S3 heterostructures with different amounts of Bi2S3 loading are shown in Figure 5 to investigate the range of visible-
Figure 5. UV−vis light absorption spectra of the BiVO4 sheets and the BiVO4 sheet−Bi2S3 nanowire heterostructure prepared using different amounts of TAA concentrations.
light response of the heterostructures. The BiVO4 sheets exhibited a weak visible-light absorption range of less than 525
Figure 6. High-resolution XPS spectra of Bi 4f and S 2p (a), V 2p (b), and O 1s (c) of the BiVO4−Bi2S3 heterostructure, Bi2S3, and BiVO4 sheets. 19107
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Figure 7. Photocurrent curves vs Ag/AgCl of (a) BiVO4 sheets and BiVO4−Bi2S3 heterostructures with different amounts of Bi2S3 under visible-light (λ ≥ 420 nm) irradiation; (b) BiVO4 sheet−Bi2S3 nanowire and BiVO4 particle−Bi2S3 nanowire under visible-light (λ ≥ 420 nm) irradiation; and (c) BiVO4 sheets and BiVO4−Bi2S3 heterostructure under visible-light (λ ≥ 510 nm) irradiation.
164.4 eV are assigned to the binding energies of Bi 4f in BiVO4. As shown in Figure 6b, c, the characteristic peaks of V 2p3/2 and V 2p1/2 (516.4 and 524.2 eV) and O 1s (529.9 and 531.1 eV) in the BiVO4−Bi2S3 heterostructure shift to a low-energy direction compared with those in BiVO4 and Bi2S3 due to the formation of new chemical bonds at the interfaces. The BiVO4 sheets and BiVO4−Bi2S3 heterostructures loaded on FTO glass were used to estimate their photoelectrochemical behaviors in a conventional three-electrode system. As shown in Figure 7a, all of the Bi2S3-nanowire-sensitized BiVO4 sheets exhibited a higher photocurrent intensity than that of the BiVO4 sheets under visible-light irradiation (λ ≥ 420 nm). The results indicate that the Bi2S3 nanowires contributed to a number of photoexcited electrons and improved visible-light photoelectrochemical activity of the heterostructures. Notably, the quantity of Bi2S3 nanowire loading has an evident influence on the photocatalytic activity of BiVO4−Bi2S3 heterostructures. The photocurrent intensity of the heterostructures was gradually enhanced with the increase in the amounts of Bi2S3, which is attributed to the photoexcited electrons from Bi2S3 transfer to the surface of BiVO4. However, the photoelectrochemical behavior became weak when the content of TAA used reached 25% in the heterostructure. A possible reason is that the excess Bi2S3 nanowires covered the surface of BiVO4 sheets and reduced the photochemical reaction sites although the Bi2S3 nanowires provided photoexcited electrons. Therefore, the appropriate amount of Bi2S3 nanowire loading should be employed to achieve a good photoelectrochemical performance. When the amount of TAA was 15% in the precursor solution, the corresponding amount of Bi2 S 3
nanowires coated onto the BiVO4 sheets was approximately 2.4 at. % based on the element analysis results. The BiVO4 sheet−Bi2S3 nanowire heterostructure exhibited the highest photocurrent intensity, which is 17 times that of BiVO4 sheets at the potential of 0.4 V under visible-light irradiation. BiVO4 particle−Bi2S3 nanowire was synthesized and used to compare with the BiVO4 sheet−Bi2S3 nanowire heterostructure to explore the effect of BiVO4 structures on the photocatalytic activity of the heterostructures further. The corresponding SEM image and XRD patterns are shown in the Figure S2. Bi2S3 nanowires were uniformly coated onto the surface of BiVO4 particles. Their corresponding photoelectrochemical activities are shown in Figure 7b. The BiVO4 sheet−Bi2S3 nanowire heterostructure shows a better photoelectrochemical performance than that of BiVO4 particle−Bi2S3, and its photocurrent intensity is approximately 3.5 times that of BiVO4 particle− Bi2S3. The higher photocurrent intensity of the BiVO4 sheet− Bi2S3 nanowire heterostructure is attributed to the sheet-like structure that resulted from the shortened transport distance of photoexcited carriers in the BiVO4 sheets. The photoelectrochemical behaviors of BiVO4 sheets and BiVO4−Bi2S3 irradiated by visible-light (λ ≥ 510 nm) shown in Figure 7c is used to verify the source of photoexcited electrons in the heterostructures. A low photocurrent intensity was generated by BiVO4 sheets. By contrast, the photocurrent intensity (λ ≥ 510 nm) of the BiVO4−Bi2S3 heterostructure showed only a slight degradation compared with that under visible-light (λ ≥ 420 nm) irradiation. Most of light spectra utilized by the BiVO4 sheets were filtered under visible-light (λ ≥ 510 nm) irradiation. However, the Bi2S3 nanowires in the 19108
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The Journal of Physical Chemistry C heterostructure still utilized the visible-light range from 510 to 900 nm. Thus, the photoexcited carriers in the heterostructure are mainly provided by Bi2S3 nanowires under visible-light irradiation based on the classic carrier transport mechanism,36 in which photoexcited electrons from a narrow bandgap semiconductor transfer to a wide bandgap semiconductor. Bi2S3 nanowires are introduced into the BiVO4 sheets and used to construct the BiVO4 sheet−Bi2S3 heterostructure in an aqueous solution containing BiVO4 sheets and TAA as precursors. The improved visible-light photoelectrochemical activity likely occurs because of the following reasons. (1) The synergistic effect between BiVO4 and Bi2S3 is the main reason for the improved photocatalytic activity. Based on previous reports35 and the light absorption spectra results, the top of the valence band (VB) and the bottom of the conduction band (CB) are estimated to be 0.35 and 2.71 eV for BiVO4 and are 0.12 and 1.42 eV for Bi2S3, respectively. The possible sensitization mechanism, which improves the charge carrier transport process in the heterostructure, is shown in Figure 8.
Figure 9. Fluorescence spectra of BiVO4 sheets and the BiVO4−Bi2S3 heterostructure (15%) excited at 320 nm at room temperature.
(3) Photocatalytic activity is also significantly related to the structure of the photocatalyst. In the BiVO4 sheet−Bi2S3 nanowire heterostructures, the transport distance of photoexcited carriers is markedly shortened in the sheet-like BiVO4, which will directly reduce the recombination rate of photoexcited electrons and holes. The transport process of photoexcited electrons also become smoother along the growth direction of Bi2S3 nanowires.38
4. CONCLUSION The BiVO4 sheet−Bi2S3 nanowire heterostructures were synthesized by an anion exchange approach using BiVO4 sheets and TAA as precursors. The visible-light absorption range of the heterostructure was considerably extended from 525 to 900 nm after coupling with Bi2S3 nanowires. The heterostructures exhibited a higher photoelectrochemical property than BiVO4 sheets under visible-light irradiation. In particular, the optimized content of Bi2S3 nanowire loading is approximately 2.4 at. %. The enhanced photocurrent response under visible-light irradiation is attributed to the enhanced visible-light absorption, solid sensitization mechanism between BiVO4 and Bi2S3, the shortened transport distance of photoexcited carriers in the BiVO4, and the smooth carrier transport in the Bi2S3 nanowires. The Bi2S3-nanowire-sensitized BiVO4 sheets bearing visible-light photocatalytic activity promote the wide use of BiVO4 in the photocatalysis.
Figure 8. Scheme of the solid-sensitization mechanism in the BiVO4 sheet−Bi2S3 nanowire heterostructure.
Under visible-light irradiation, Bi2S3 nanowires generate a number of photoexcited electrons due to their narrow bandgap. Subsequently, the photoexcited electrons from Bi2S3 nanowires can easily transfer to BiVO4 and markedly increase the number of photoexcited electrons on BiVO4 because both the VB and CB positions of Bi2S3 are higher than those of BiVO4. Therefore, the heterostructure can utilize most of visible-light and exhibit improved photoelectrochemical performance. (2) The recombination rate of photoexcited electron−hole pairs, which is an important influencing factor on the catalytic activity, can be illustrated by the fluorescence spectra.37 The fluorescence spectra of BiVO4 sheets and the BiVO4 sheet− Bi2S3 nanowire heterostructure with an excitation wavelength of 320 nm are shown in Figure 9. The BiVO4 sheets generated a wide emission peak at approximately 530 nm, which resulted from the recombination of the photoexcited holes formed in the O 2p band and the photoexcited electrons in the V 3d band.35 After loading Bi2S3 on the surface of BiVO4 sheets, it is clearly found that the fluorescence emission intensity of the heterostructure was obviously reduced, indicating that Bi2S3 loading can restrain the recombination of electrons and holes due to the formation of the heterojunction.
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ASSOCIATED CONTENT
S Supporting Information *
The Supporting Information is available free of charge on the ACS Publications website at DOI: 10.1021/acs.jpcc.7b06838. Preparation of BiVO4 particle−Bi2S3 nanowire, SEM image of element mapping (Figure S1) of the BiVO4− Bi2S3 heterostructure, SEM image and XRD patterns of BiVO4 particle−Bi2S3 nanowire (Figure S2), BET surface areas (Table S1), and N2 adsorption−desorption isotherms and pore size distributions (Figure S3). (PDF)
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AUTHOR INFORMATION
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[email protected]. 19109
DOI: 10.1021/acs.jpcc.7b06838 J. Phys. Chem. C 2017, 121, 19104−19111
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The Journal of Physical Chemistry C ORCID
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Xuewen Wang: 0000-0001-6269-8086 Notes
The authors declare no competing financial interest.
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ACKNOWLEDGMENTS Financial support is from National Science Fund of China (Nos. 51662030 and 21366020) and the Natural Science Foundation of Jiangxi Province (Nos. 20151BAB216006 and 20171BAB206014). We also acknowledge great support from the Institute of Metal Research, Chinese Academy of Sciences.
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DOI: 10.1021/acs.jpcc.7b06838 J. Phys. Chem. C 2017, 121, 19104−19111
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DOI: 10.1021/acs.jpcc.7b06838 J. Phys. Chem. C 2017, 121, 19104−19111
