Bi4NbO8Cl Heterojunction for Enhanced

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Z-Scheme g-C3N4/Bi4NbO8Cl Heterojunction for Enhanced Photocatalytic Hydrogen Production Yong you, Shuobo Wang, Ke Xiao, Tianyi Ma, Yihe Zhang, and Hongwei Huang ACS Sustainable Chem. Eng., Just Accepted Manuscript • DOI: 10.1021/ acssuschemeng.8b03075 • Publication Date (Web): 19 Oct 2018 Downloaded from http://pubs.acs.org on October 21, 2018

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ACS Sustainable Chemistry & Engineering

Z-Scheme g-C3N4/Bi4NbO8Cl Heterojunction for Enhanced Photocatalytic Hydrogen Production Yong You†, Shuobo Wang†, Ke Xiao†, Tianyi Ma‡, Yihe Zhang†, Hongwei Huang*,† †Beijing

Key Laboratory of Materials Utilization of Nonmetallic Minerals and Solid

Wastes, National Laboratory of Mineral Materials, School of Materials Science and Technology, China University of Geosciences, Beijing 100083, China ‡School

of Environmental & Life Sciences, The University of Newcastle (UON),

Callaghan, NSW 2308 Australia

*Corresponding author. E-mail: [email protected] (Hongwei Huang)

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ABSTRACT Photocatalytic water splitting is promising for sustainable energy development, but severely challenged by the low charge separation efficiency and slashing redox potentials requirement. Fabricating a Z-scheme heterojunction as an effective strategy for solving the aforementioned troubles gains enormous efforts. In this work, we develop a high-efficiency Z-scheme catalyst g-C3N4/Bi4NbO8Cl based on a facile high-energy ball milling method to form an intimate interface between the two phases. It exhibits an enormously promoted photocatalytic activity for H2 production with visible light illumination (λ > 420 nm), and the H2 evolution rate is 6.9 and 67.2 times higher than that of bare g-C3N4 and Bi4NbO8Cl, respectively. The stronger photoabsorption of g-C3N4/Bi4NbO8Cl (beyond 500 nm) allows generation of more photons than g-C3N4. More importantly, the separation and transfer of photoexcited charge carriers were greatly

improved

between

g-C3N4

and

Bi4NbO8Cl,

as

revealed

by

the

photoelectrochemical and time-resolved photoluminescence decay results. The Z-scheme charge transfer mechanism of g-C3N4/Bi4NbO8Cl was also manifested by electron spin resonance (ESR). The work furnishes a new solution to fabrication of high-efficiency Z-scheme catalysts for countering energy issues. KEYWORDS: Photocatalytic, g-C3N4, Bi4NbO8Cl, Z-scheme, hydrogen production 2 ACS Paragon Plus Environment

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INTRODUCTION It is a hot topic nowadays to design and develop highly efficient photocatalytic materials which can split water into hydrogen under visible light illumination. In the past few decades, a variety of semiconductors have been reported for photocatalytic hydrogen generation.1-4 Nevertheless, most of them have some blemishes, such as low efficiency, toxicity or high-cost.5-8 In particular, the weak light harvesting for long-wavelength and high recombination of photogenerated electrons and holes severely restrict the catalytic activity.9-12 A number of strategies have thus been proposed for settling these issues, such as band-gap engineering via doping of metal or nonmetal elements, enhancing the charge separation efficiency by depositing noble metal or constructing heterojunction, etc.13-15 Graphitic carbon nitride (g-C3N4) as a metal-free polymer semiconductor photocatalyst for efficient hydrogen evolution was first reported by Wang et al. in 2009.16-17 It has a moderate band gap of 2.7 eV and a visible-light absorption onset at around 450 nm, and it is nontoxic and chemically stable.18-19 However, the photocatalytic efficiency of bulk g-C3N4 is still hindered by several obstacles, like insufficient photoabsorption, small specific surface area and low-efficiency charge separation.20-23 In addition to nanostructure fabrication and electronic structure modulation,24-25 construction of a Z-scheme junction is regarded as one of the most effective strategies to 3 ACS Paragon Plus Environment


solve the low photoabsorption and charge separation efficiency as well as reserving the strong reduction and oxidation abilities.26-31 Recently, Bi4NbO8Cl has been demonstrated to be a stable and efficient visible-light driven photocatalyst for oxygen evolution from water splitting, and it is also promising for overall water splitting under visible-light irradiation.32 The relatively narrow band gap (2.4 eV) and proper valence band (VB) positions endow Bi4NbO8Cl with sufficient absorption in visible-light region and excellent water oxidation capability. Besides, the layered structure composed of typical components of [Bi2O2] layers and NbO6 perovskite blocks allows the fast migration of charge carriers of Bi4NbO8Cl.33 In view of the strong oxygen evolution ability of Bi4NbO8Cl, it may be very desirable to construct a Z-Scheme photocatalyst g-C3N4/Bi4NbO8Cl for high-performance water splitting. Herein, we for the first time prepare the Z-scheme heterojunction photocatalyst g-C3N4/Bi4NbO8Cl by a simple high-energy ball-milling method to construct a tight interface between the two phases. The light-responsive range of g-C3N4/Bi4NbO8Cl is extended to over 500 nm, obviously larger than that of pristine g-C3N4. In comparison with pure g-C3N4 and Bi4NbO8Cl, g-C3N4/Bi4NbO8Cl exhibits significantly enhanced photocatalytic water splitting performance, and the H2 production rate is 6.9 and 67.2 times higher than that of pure g-C3N4 and Bi4NbO8Cl under visible-light irradiation (λ > 420 nm), respectively. The great enhancement in H2 production activity should be due to the formation of Z-scheme heterojunction, which results in the high charge separation 4 ACS Paragon Plus Environment

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efficiency. This work provides a new g-C3N4/Bi4NbO8Cl Z-scheme photocatalyst for water splitting. EXPERIMENTAL SECTION Preparation of the photocatalyst. All the chemicals were of analytical grade, and used as received without further purification. First, BiOCl was synthesized by co-precipitation method. During the preparation process of BiOCl, 5mmol of Bi(NO3)3·5H2O was dissolved in 30 mL of glycol, and 5 mmol of KCl was dissolved in 10 ml of deionized water. Then, the KCl solution was dropwise added into the Bi(NO3)3 glycol solution under magnetic stirring, and kept stirring for 1 h at room temperature. The resulting precipitate was washed with deionized water and collected after filtration, and dried at 353 K for 5 h. Bi4NbO8Cl was prepared by a solid-state-reaction method. Bi2O3, Nb2O5 and BiOCl with stoichiometric ratio were weighed and mixed thoroughly in an agate mortar. Then, the well-mixed powder was placed in a muffle furnace and heated in air at 1123 K for 8 h.32 g-C3N4 was prepared by a calcination procedure as follows: 10 g of melamine was calcined in a muffle furnace at 793 K for 4 h. When the muffle furnace was slowly cooled to room temperature, the yellow product was collected and ground to powder in a mortar. The g-C3N4/Bi4NbO8Cl composites were obtained by a facile high-energy ball-milling method. g-C3N4 and Bi4NbO8Cl with different molar ratios (1:1, 3:1, 6:1 and 5 ACS Paragon Plus Environment


10:1) were mixed in the ball-milling pots, respectively. And then, 10 mL of ethanol was added as grinding aid, and the mixture was rotated at 560 rpm for 5 h. The resulting composites were collected by washing with deionized water and filtration, and dried at 353 K. These samples with the molar ratios of g-C3N4 and Bi4NbO8Cl (1:1, 3:1, 6:1 and 10:1) are named as CNBN-1, CNBN-2, CNBN-3 and CNBN-4, respectively. Characterization. X-ray diffraction (XRD) data of samples were collected on a Bruker D8 focus Advance diffractometer (Cu-Kα radiation, 40kV/40mA). The X-ray photoelectron spectroscopy (XPS, Perkin-Elmer PHI 5000C) was used to test the surface element of sample. The general morphology of the photocatalysts were analyzed by scanning electron microscopy (SEM) on a Hitachi S-4800 instrument. Transmission electron microscopy (TEM) and high-resolution TEM (HRTEM; JEM-2100, Japan) were used to observe the morphology and microstructure of samples. UV-vis diffuse reflectance spectra (DRS) were obtained from the Varian Cary 5000 UV–vis spectrophotometer. The specific surface areas of photocatalysts were examined by nitrogen adsorption-desorption on Brunauer-Emmett-Teller (BET; Micromeritics ASAP 2460, USA). The photoluminescence (PL) spectra were measured by a Hitachi F-4600 fluorescence spectrophotometer made in Japan, using a 150W Xe lamp at 400V as the excitation lamp (λ ex = 260 nm). The electron spin resonance (ESR) signals, such as the superoxide radicals or hydroxyl radicals, were detected by a Bruker A300E spectrometer. Photocatalystic H2 evolution. Photocatalystic hydrogen production experiments were 6 ACS Paragon Plus Environment

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performed in a Pyrex glass photoreactor, which is a gas-closed circulation system. A 300W Xe lamp equipped with an optical filter (λ>420nm) as light source. In a typical photocatalystic experiment, 100 mg of powder was dispersed in 50 ml aqueous solution containing 40 mL of distilled water, 10 ml of lactic acid and 1%wt Pt as cocatalyst. Pt was loaded by photodeposition from H2PtCl6 solution with a 300 W high-pressure mercury lamp. Before starting the photocatalystic experiment, the dissolved oxygen in the above aqueous solution was removed by bubbling nitrogen for 15 min. Then, the above aqueous solution was irradiated under UV light for 30 min to load Pt cocatalyst. And then 50 mL distilled water was added into the photoreactor. Before irradiation, the photoreactor and the whole circulation system were pumped to attain a vacuum condition. The amount of products was in situ analyzed and recorded periodically by gas chromatography (Labsolar-III(AG)) with a high-purity nitrogen carrier gas. The apparent quantum efficiency (AQE) for hydrogen evolution was measured using the same experimental setup but with a series of band-pass filters (420 nm, 450 nm and 500 nm), the peak width of all above filters are 15 nm. The light intensity was measured by PLS-MV2000 photoradiometer. The equation of AQE was calculated by the following: AQY(%) 2ⅹ100ⅹnumber of evolved H2 molecules/number of incident photons. Photoelectrochemical measurements. The photoelectrochemical data, typically, the 7 ACS Paragon Plus Environment


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photocurrent (PC) and electrochemical impedance spectra (EIS) were measured in a standard three-electrode system (CHI-660E, China), using a saturated calomel electrode (SCE) as the reference electrode, a platinum wire as the counter electrode, and the g-C3N4, Bi4NbO8Cl, CNBN-1, CNBN-2, CNBN-3, and CNBN-4 sample films coated on ITO films (2 cm × 4 cm) as working electrode. The electrolyte solution was 0.1 M Na2SO4. The photoelectrochemical station was set at 0.0 V, and a 300 W Xe lamp with an optical filter (λ > 420 nm) was employed as light source, and the light intensity was about 1 mW/cm2. RESULTS AND DISCUSSION Structure, composition, and microstructure. The crystalline phase and structure of as-prepared samples were analyzed by XRD. The XRD patterns of g-C3N4, Bi4NbO8Cl and the g-C3N4/Bi4NbO8Cl composites with different molar ratios were shown in Fig.1. g-C3N4 shows broad diffraction peaks with low intensity. In contrast, Bi4NbO8Cl exhibits a set of sharp and narrow peaks, which indicates the good crystallinity. The diffraction peaks of pure g-C3N4 and Bi4NbO8Cl samples were ascribed to the standard cards of g-C3N4 (JCPDS 87-1526) and Bi4NbO8Cl (ICSD #93487), respectively.32,

34

There are

two main peaks in the pattern of g-C3N4. The strongest one at 27.4° can be assigned to the (002) diffraction plane and the other one at 13.09° belongs to the (100) crystal plane. The strongest peak in the XRD pattern of pristine Bi4NbO8Cl at 29.71° is attributed to the (116) crystal plane. As for the g-C3N4/Bi4NbO8Cl composites, the characteristic peaks of 8 ACS Paragon Plus Environment

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Bi4NbO8Cl are observed. There are no obvious diffraction peaks of the g-C3N4, which is due to the low diffraction intensity of the g-C3N4. Besides, no impurity peaks can be found in the g-C3N4/Bi4NbO8Cl composites. The surface chemical state and elements were measured by XPS. From Fig. 2a, one can see that CNBN-3 contains the elements of C, N, Bi, Nb and O, suggesting the successful fabrication of g-C3N4/Bi4NbO8Cl composite. Fig. 2b shows the Bi 4f high-resolution XPS spectrum. The two peaks at 159.1 and 164.5 eV are attributed to the Bi 4f7/2 and Bi 4f5/2 of Bi3+ ions, respectively. The Nb 3d spectrum of CNBN-3 is shown in Fig. 2c. Two peaks at 209.9 and 206.4 eV can be observed, which correspond to Nb 3d3/2 and Nb 3d5/2, respectively. Fig. 2d shows three peaks at 398.95, 399.75 and 401.15 eV, which represent the sp2-hybridized N in C=N-C, the incomplete polymerization in C-N-H, N-(C)3 and structure defects, and π excitation, respectively. The morphology and element distribution of g-C3N4, Bi4NbO8Cl and the g-C3N4/Bi4NbO8Cl composites are investigated by SEM, TEM, HRTEM and EDX mapping. Fig. 3a shows that g-C3N4 samples are irregular blocks in micron sizes. Bi4NbO8Cl products are composed of micro-particles with smooth surface, as seen from Fig. 3b. After ball-milling treatment, the Bi4NbO8Cl particles were crushed and attached on the surface of g-C3N4 (Fig. 3c). The SEM result suggests formation of the g-C3N4/Bi4NbO8Cl heterostructure. Fig. 3d-e display the TEM and HRTEM images of CNBN-3. The dark Bi4NbO8Cl particles are found attaching on the surface of g-C3N4, 9 ACS Paragon Plus Environment


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which clearly illustrate the distribution of g-C3N4 and Bi4NbO8Cl (Fig. 3d). HRTEM image (Fig. 3e) displays a set of lattice fringes with a spacing of 0.385 nm, corresponding well to the (111) plane of Bi4NbO8Cl. The HRTEM image also reveals the clear phase interface

between

g-C3N4

and

Bi4NbO8Cl,

demonstrating

formation

of

the

g-C3N4/Bi4NbO8Cl heterojunction. EDX-mapping image of CNBN-3 sample manifests the distribution of Bi, Nb, C and N, which further verifies the construction of g-C3N4/Bi4NbO8Cl heterojunction. UV-vis

DRS

analysis.

The

optical

absorption

of

g-C3N4,

Bi4NbO8Cl

and

g-C3N4/Bi4NbO8Cl composites are investigated by DRS. As shown in Fig. 4a, the absorption edges of g-C3N4 and Bi4NbO8Cl are about 460 and 530 nm, respectively. With the increase of Bi4NbO8Cl content, the absorption edge of g-C3N4/Bi4NbO8Cl composites gradually red-shifts, all beyond 500 nm. Thus, the light response of g-C3N4 can be effectively enhanced by combining Bi4NbO8Cl. In semiconductors, the absorption edge is connected with band gap. The band gaps of g-C3N4 and Bi4NbO8Cl are obtained by the following equation: αhv = A(hv - Eg)n/2

(1)

where A, h, α, v and Eg are the proportionality constant, Plank constant, optical absorption coefficient, photonic frequency and band gap, respectively.35-37 In this formula, the value of n is determined by the transition type of semiconductor (n = 1 for 10 ACS Paragon Plus Environment

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direct transition and n = 4 for indirect transition), and both g-C3N4 and Bi4NbO8Cl are indirect transition semiconductors. From Fig. 4b, the band gaps of the g-C3N4 and Bi4NbO8Cl are estimated to be 2.78 and 2.48 eV respectively. These values are well consistent with that from our previous work38 and that from Hironori et al32. Tian et al. and Hironori et al. determined the ECB of g-C3N4 and Bi4NbO8Cl to be -1.13 and -0.28 eV, respectively, by Mott-Schottky method. According to the band gap from DRS, the EVB of g-C3N4 and Bi4NbO8Cl are estimated to be 1.65 and 2.20 eV, respectively. Photocatalytic H2 evolution. Photocatalytic H2 evolution from water splitting was conducted to survey the photocatalytic activity of g-C3N4, Bi4NbO8Cl and a series of g-C3N4/Bi4NbO8Cl composites with illumination of visible light (λ > 420 nm). The experiments for all the samples are carried out under the same condition. As illustrated by Fig. 5a, the hydrogen production amount of all the g-C3N4/Bi4NbO8Cl composites are higher than that of pure g-C3N4 and Bi4NbO8Cl. With increasing the content of g-C3N4 (from CNBN-1 to CNBN-4), the hydrogen generation of g-C3N4/Bi4NbO8Cl composites first increases and then decreases, and CNBN-3 with the g-C3N4:Bi4NbO8Cl ratio of 6:1 shows the best photocatalytic performance. As shown in Fig. 5b, CNBN-3 exhibits the highest hydrogen evolution rate (287.7 μmol g-1 h-1), which is nearly 6.9 and 67.2 times that of pristine g-C3N4 (42.01 μmol g-1 h-1) and Bi4NbO8Cl (4.28 μmol g-1 h-1), respectively. XRD of CNBN-3 after 4 h light irradiation was shown in Fig. 5c, and not any obvious change was seen for the diffraction pattern. It indicates that the prepared 11 ACS Paragon Plus Environment


g-C3N4/Bi4NbO8Cl composite is stable during the photocatalytic reaction. Fig. 5d shows the apparent quantum yield (AQY) of CNBN-3 at different wavelength, and the AQY reaches 2.02% at λ = 420 ± 15 nm. The H2 production comparison with other similar photocatalysts is listed in Table S1. It can be seen that CNBN-3 has excellent photocatalytic performance compared to other similar materials. Mechanism investigation on photocatalytic performance improvement. It is well known that the particle size and specific surface area of photocatalyst have large effects on the photocatalytic activity.39-44 To reveal the reason for photocatalytic performance improvement, specific surface area was firstly investigated. The N2 adsorption-desorption isotherms of g-C3N4, Bi4NbO8Cl and CNBN-3 were displayed in Fig. 6. The adsorption-desorption of g-C3N4 and CNBN-3 is specified as type Ⅳ in BDDT (Brunauer, Deming, Deming and Teller divided the large number of isotherms into five categories: Micropores, Nonporous, Weak Substrate, Mesopores Capillary Condensation, Weak Substrate. and then Sing added a sixth type of Layering isotherms),45-47 which indicated the presence of mesopores. The hysteresis loop belongs to type H3 according to IUPAC classification, which manifests that the pores were caused by agglomeration of the particles. Bi4NbO8Cl exhibits type Ⅱ adsorption-desorption isotherm, which demonstrates the characteristic of nonporous or macroporous sample. Fig. 6b shows the pore size distribution curves corresponding to the N2 adsorption-desorption isotherms, confirming the nonporous feature of Bi4NbO8Cl. The pores sizes of g-C3N4 and CNBN-3 12 ACS Paragon Plus Environment

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are mainly in the range of 10-40 nm. It is seen from Fig. 3 and Fig. 6b that g-C3N4 has more pores, smaller pore size and smaller particles size than others. The specific surface areas of g-C3N4, Bi4NbO8Cl and g-C3N4/Bi4NbO8Cl composites were provided in Fig. 6c. The specific surface area of Bi4NbO8Cl is 5.23 m2/g, and that of g-C3N4 is 17.27 m2/g. With raising the g-C3N4 content, the specific surface area of the g-C3N4/Bi4NbO8Cl composites increases, but they are all smaller than that of g-C3N4. It revealed that the specific surface area of composites did not increase compared to pure g-C3N4 after ball milling. In the other words, specific surface area is not the reason for the enhanced photocatalytic H2 evolution of g-C3N4/Bi4NbO8Cl composites. The generation, transfer and recombination rate of the photoexcited charge carriers are detected by a sequence of photoelectrochemical characterizations. The comparison for transient photocurrent response of different samples with light on and off is illustrated in Fig. 7a. Obviously, Bi4NbO8Cl shows the weakest photocurrent response and the photocurrent response increases as g-C3N4 content increases in the g-C3N4/Bi4NbO8Cl composites. The charge separation efficiency of CNBN-3 and CNBN-4 are higher than that of g-C3N4, which indicates that formation of g-C3N4/Bi4NbO8Cl heterojunction promotes the separation efficiency of photogenerated electrons and holes, contributing to the improved photocatalytic H2 production activity. Electrochemical impedance spectra (EIS) is used to disclose the photoinduced charges’ interfacial transfer efficiency of the composites.48 Fig. 7b reveals EIS Nyquist plots of g-C3N4, Bi4NbO8Cl and CNBN-3. It 13 ACS Paragon Plus Environment


can be seen that the arc radius of CNBN-3 is much smaller than that of Bi4NbO8Cl and is very close to g-C3N4. It indicates that the interface charge transfer of CNBN-3 is much higher than that of Bi4NbO8Cl and similar to that of g-C3N4. Photoluminescence (PL) spectra are herein utilized to indicate the recombination rate of photoexcited electrons and holes, and the fluorescence intensity is positively correlated to the recombination degree. As displayed in Fig. 7c, Bi4NbO8Cl exhibits the lowest the emission intensity, which may be due to that few photoexcited electrons and holes are generated from it, as reflected by Fig. 7a. Though g-C3N4 has a slightly higher charge transfer efficiency, all the composites show much lower fluorescence emission intensity than g-C3N4. It indicated that introduction of Bi4NbO8Cl indeed depresses the charge recombination of g-C3N4. CNBN-1 shows the lowest PL emission intensity among all the composites, which indicates that it has the lowest recombination rate of photogenerated electrons and holes. But meanwhile, CNBN-1 shows the weakest photocurrent response among all the composites, which means production of the smallest amount of photogenerated charge carriers. Thus, CNBN-1 exhibits a moderate photocatalytic activity. Due to the both relatively high photocurrent density and low fluorescence emission intensity of CNBN-3, they may contribute to the highest photocatalytic H2 generation performance. Fluorescence decay lifetime curve can better illustrate the separation, transfer and recombination of the photoexcited electrons and holes. The longer the decay time of the fluorescence lifetime is, the weaker the recombination of photoexcited electrons and 14 ACS Paragon Plus Environment

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holes are. As can be seen in Fig. 7d, the Bi4NbO8Cl exhibits the shortest radiative lifetime and the average time is 7.33 ns. The radiative lifetime of g-C3N4 and CNBN-3 are similar, which are 39.60 and 32.03 ns, respectively. Unexpectedly, CNBN-3 does not show a longer fluorescence lifetime, but a relatively smaller one than g-C3N4. It should be owing to the recombination of electrons located on CB of Bi4NbO8Cl and holes from the VB of g-C3N4. Based on these results, it is speculated that Z-scheme charge transfer mechanism is formed in the g-C3N4/Bi4NbO8Cl heterojunction.49 To verify the Z-scheme charge transfer mechanism of g-C3N4/Bi4NbO8Cl heterojunction, electron spin resonance (ESR) spectra of g-C3N4, Bi4NbO8Cl and CNBN-3 were measured. Fig. 8 shows the ESR signals of DMPO-assisted superoxide radicals (·O2-) and hydroxyl radicals (·OH) adducts. Without light, no signals of DMPO−·O2- and DMPO−·OH can be observed. Under visible light irradiation, only four identical peaks that are assigned to the signal of DMPO−·O2- were detected over g-C3N4, and the signal of DMPO−·OH was not observed, as shown in the Fig. 8a and b. In contrast to g-C3N4, Bi4NbO8Cl can only produce DMPO−·OH (four peaks with intensities of 1:2:2:1) without DMPO−·O2- (Fig. 8c and d). For CNBN-3, it is evident that both DMPO−·O2- and DMPO−·OH signals are generated (Fig. 8e and f). It provides a direct evidence to corroborate the construction of Z-scheme heterojunction of g-C3N4/Bi4NbO8Cl, as portrayed by Fig. 9.50 CONCLUSION 15 ACS Paragon Plus Environment


In summary, the Z-scheme heterojunction photocatalyst g-C3N4/Bi4NbO8Cl was fabricated by a simple high-energy ball-milling process. Close interfacial interaction was formed between g-C3N4 and Bi4NbO8Cl, and the photoabsorption in visible region was consumedly extended (over 500 nm) compared with pure g-C3N4. Z-scheme g-C3N4/Bi4NbO8Cl revealed a significantly enhanced photocatalytic hydrogen production activity with the evolution rate of 6.9 and 67.2 folds increase in contrast to g-C3N4 and Bi4NbO8Cl, respectively. Photoelectrochemical, time-resolved photoluminescence decay and ESR measurements disclose that this enhancement is mainly due to formation of Z-scheme junction that promotes the migration and separation of photoexcited charges, and the recombination process was also efficaciously impeded. This study offers a new high-performance catalyst, and proposes a facile and effective strategy to construct Z-scheme heterojunction for photocatalytic water splitting.

■ ASSOCIATED CONTENT Supporting Information Comparison on H2 production rate and AQY of similar photocatalysts. This material is available free of charge via the Internet at

■ AUTHOR INFORMATION 16 ACS Paragon Plus Environment

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Corresponding Authors

*E-mail: [email protected]. Tel: +86-010-82332247.

ORCID

Hongwei Huang: 0000-0003-0271-1079

Notes

The authors declare no competing financial interest.

■ ACKNOWLEDGMENTS This work was jointly supported by the National Natural Science Foundations of China (No. 51572246 and No. 51672258), the Fundamental Research Funds for the Central Universities (2652015296).

REFERENCES 1.

Ong, W. J.; Tan, L. L.; Ng, Y. H.; Yong, S.-T.; Chai, S. P., Graphitic Carbon Nitride

(g-C3N4)-Based Photocatalysts for Artificial Photosynthesis and Environmental Remediation: Are We a Step Closer To Achieving Sustainability? Chem. Rev. 2016, 116 (12), 7159-7329. 2.

DOI: 10.1021/acs.chemrev.6b00075

Li, J.; Cai, L. J.; Shang, J.; Yu, Y.; Zhang, L. Z. Giant Enhancement of Internal 17 ACS Paragon Plus Environment


Page 18 of 36

Electric Field Boosting Bulk Charge Separation for Photocatalysis. Adv. Mater. 2016, 28 (21), 4059-4064.

DOI: 10.1002/adma.201600301

3. Shi, H. F.; Chen, G. Q.; Zhang, C. L.; Zou, Z. G. Polymeric g-C3N4 Coupled with NaNbO3 Nanowires toward Enhanced Photocatalytic Reduction of CO2 into Renewable Fuel. ACS Catal. 2014, 4 (10), 3637-3643. 4.

DOI: 10.1021/cs500848f

Huang, H. W.; Cao, R. R.; Yu, S. X.; Xu, K.; Hao, W. C.; Wang, Y. G.; Dong, F.;

Zhang, T. R.; Zhang, Y. H. Single-unit-cell layer established Bi2WO6 3D hierarchical architectures:

Efficient

photoelectrochemical

adsorption,

performance.

photocatalysis

Appl.

Catal.

B

and 2017,

dye-sensitized 219,

526-537.

DOI:10.1016/j.apcatb.2017.07.084 5.

Guo, S. E.; Deng, Z. P.; Li, M. X.; Jiang, B. J.; Tian, C. G.; Pan, Q. J.; Fu, H. G.

Phosphorus ‐ Doped Carbon Nitride Tubes with a Layered Micro ‐ nanostructure for Enhanced Visible ‐ Light Photocatalytic Hydrogen Evolution. Angew. Chem. Int. Ed. 2016, 55 (5), 1830-1834. 6.

DOI: 10.1002/anie.201508505

Li, K. X.; Zeng, Z. X.; Yan, L. S.; Luo, S. L.; Luo, X. B.; Huo, M. X.; Guo, Y. H.

Fabrication of platinum-deposited carbon nitride nanotubes by a one-step solvothermal treatment strategy and their efficient visible-light photocatalytic activity. Appl. Catal. B 2015, 165, 428-437. 7.

DOI: 10.1016/j.apcatb.2014.10.039

Huang, H. W.; He, Y.; Lin, Z. S.; Kang, L.; Zhang, Y. H. Two Novel Bi-Based

Borate Photocatalysts: Crystal Structure, Electronic Structure, Photoelectrochemical 18 ACS Paragon Plus Environment

Page 19 of 36 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


Properties, and Photocatalytic Activity under Simulated Solar Light Irradiation. J.phys.chem.c 2013, 117 (44), 22986-22994. 8.

DOI: 10.1021/jp4084184

Huang, H. W.; He, Y.; Li, X. W.; Li, M.; Zeng, C.; Dong, F.; Du, X.; Zhang, T. R.;

Zhang, Y. H. Non-Centrosymmetric Bi2O2(OH)(NO3) as a Desirable [Bi2O2]2+ Layered Photocatalyst: Strong Intrinsic Polarity, Rational Band Structure and {001} Active Exposing Facets Co-Benefiting for Robust Photooxidating Capability. J. Mater. Chem. A 2015, 3, 24547-24556. 9.

DOI: 10.1039/C5TA07655B

Gao, H. L.; Yan, S. C.; Wang, J. J.; Huang, Y. A.; Wang, P.; Li, Z. S.; Zou, Z. G.

Towards efficient solar hydrogen production by intercalated carbon nitride photocatalyst. PCCP 2013, 15 (41), 18077-18084.

DOI: 10.1039/c3cp53774a

10. Liu, G.J.; Shi, J. Y.; Zhang, F. X.; Chen, Z.; Han, J. F.; Ding, C. M.; Chen, S. S.; Wang, Z. L.; Han, H. X.; Li, C. A Tantalum Nitride Photoanode Modified with a Hole-Storage Layer for Highly Stable Solar Water Splitting. Angew. Chem. Int. Ed. 2014, 53 (28), 7295-7299.

DOI: 10.1002/anie.201404697

11. Zheng, D. D.; Cao, X. N.; Wang, X. C. Precise Formation of a Hollow Carbon Nitride Structure with a Janus Surface To Promote Water Splitting by Photoredox Catalysis. Angew. Chem. Int. Ed. 2016, 55 (38), 11512-11516.

DOI:

10.1002/anie.201606102 12. Huang, H. W.; Xiao, K.; Tian, N.; Dong, F.; Zhang, T. R.; Du, X.; Zhang, Y. H. Template-free precursor-surface-etching route to porous, thin g-C3N4 nanosheets for 19 ACS Paragon Plus Environment


Page 20 of 36

enhancing photocatalytic reduction and oxidation activity. J. Mater. Chem. A 2017, 5, 17452-17463.

DOI: 10.1039/C7TA04639A

13. Zhang, J. S.; Zhang, M. W.; Yang, C.; Wang, X. C. Nanospherical Carbon Nitride Frameworks with Sharp Edges Accelerating Charge Collection and Separation at a Soft Photocatalytic Interface. Adv. Mater. 2014, 26 (24), 4121-4126.

DOI:

10.1002/adma.201400573 14. Yang, P. J.; Ou, H. H.; Fang, Y. X.; Wang, X. C. A Facile Steam Reforming Strategy to Delaminate Layered Carbon Nitride Semiconductors for Photoredox Catalysis. Angew. Chem. Int. Ed. 2017, 56 (14), 3992-3996.

DOI: 10.1002/ange.201700286

15. Zheng, Y.; Lin, L. H.; Ye, X. J.; Guo, F. S.; Wang, X. C. Helical Graphitic Carbon Nitrides with Photocatalytic and Optical Activities. Angew. Chem. Int. Ed. 2014, 53 (44), 11926-11930.

DOI: 10.1002/anie.201407319

16. Wang, X. C.; Maeda, K.; Thomas, A.; Takanabe, K.; Xin, G.; Carlsson, J. M.; Domen, K.; Antonietti, M. A metal-free polymeric photocatalyst for hydrogen production from water under visible light. Nat. Mater. 2008, 8, 76.

DOI:10.1038/NMAT2317

17. Chen, Z. P.; Pronkin, S.; Fellinger, T.-P.; Kailasam, K.; Vilé, G.; Albani, D.; Krumeich, F.; Leary, R.; Barnard, J.; Thomas, J. M.; Pérez-Ramírez, J.; Antonietti, M.; Dontsova, D. Merging Single-Atom-Dispersed Silver and Carbon Nitride to a Joint Electronic System via Copolymerization with Silver Tricyanomethanide. ACS Nano 2016, 10 (3), 3166-3175.

DOI: 10.1021/acsnano.5b04210 20 ACS Paragon Plus Environment

Page 21 of 36 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


18. Shan, W. J.; Hu, Y.; Bai, Z. G.; Zheng, M. M.; Wei, C. H., In situ preparation of g-C3N4/bismuth-based oxide nanocomposites with enhanced photocatalytic activity. Appl. Catal. B 2016, 188, 1-12.

DOI: 10.1016/j.apcatb.2016.01.058

19. Zhang, X. D.; Wang, H. X.; Wang, H.; Zhang, Q.; Xie, J. F.; Tian, Y. P.; Wang, J.; Xie, Y. Single-Layered Graphitic-C3N4 Quantum Dots for Two-Photon Fluorescence Imaging of Cellular Nucleus. Adv. Mater. 2014, 26 (26), 4438-4443.

DOI:

10.1002/adma.201400111 20. Gao, J.; Zhou, Y.; Li, Z. S.; Yan, S. C.; Wang, N. Y.; Zou, Z. G. High-yield synthesis of

millimetre-long,

semiconducting

carbon

nitride

nanotubes

with

intense

photoluminescence emission and reproducible photoconductivity. Nanoscale 2012, 4 (12), 3687-3692.

DOI: 10.1039/c2nr30777d

21. Shalom, M.; Gimenez, S.; Schipper, F.; Isaac, H. C.; Bisquert, J.; Antonietti, M. Controlled Carbon Nitride Growth on Surfaces for Hydrogen Evolution Electrodes. Angew. Chem. Int. Ed. 2014, 53 (14), 3654-3658.

DOI: 10.1002/ange.201309415

22. Liu, C. Y.; Zhang, Y. H.; Dong, F.; Reshak, A. H.; Ye, L.; Pinna, N.; Zeng, C.; Zhang, T. R.; Huang, H. W. Chlorine intercalation in graphitic carbon nitride for efficient photocatalysis. Appl. Catal. B 2017, 203, 465-474.

DOI: 10.1016/j.apcatb.2016.10.002

23. Lan, Z. A.; Zhang, G. G.; Wang, X.C. A facile synthesis of Br-modified g-C3N4 semiconductors for photoredox water splitting. Appl. Catal. B 2016, 192, 116-125. DOI: 10.1016/j.apcatb.2016.03.062 21 ACS Paragon Plus Environment


Page 22 of 36

24. Huang, H. W.; Li, X. W.; Wang, J. J.; Dong, F.; Chu, P. K.; Zhang, T. R.; Zhang, Y. H. Anionic Group Self-Doping as a Promising Strategy: Band-Gap Engineering and Multi-Functional Applications of High-Performance CO32–-Doped Bi2O2CO3. ACS Catal. 2015, 5, 4094-4103.

DOI: 10.1021/acscatal.5b00444

25. Huang, H. W.; Xiao, K.; He, Y.; Zhang, T. R.; Dong, F.; Du, X.; Zhang, Y. H. In situ assembly of BiOI@Bi12O17Cl2 p - n junction: charge induced unique front-lateral surfaces coupling heterostructure with high exposure of BiOI {001} active facets for robust and nonselective

photocatalysis.

Appl.

Catal.

B

2016,

199,

75-86.

DOI:

10.1016/j.apcatb.2016.06.020 26. Yan, M.; Zhu, F. F.; Gu, W.; Sun, L.; Shi, W. D.; Hua, Y. Q. Construction of nitrogen-doped graphene quantum dots-BiVO4/g-C3N4 Z-scheme photocatalyst and enhanced photocatalytic degradation of antibiotics under visible light. Rsc Adv. 2016, 6, 60996-61000.

DOI: 10.1039/c6ra07589d

27. Su, Y. H.; Chen, P.; Wang, F. L.; Zhang, Q. X.; Chen, T. S.; Wang, Y. F.; Yao, K.; Lv, W. X.; Liu, G. G. Decoration of TiO2/g-C3N4 Z-scheme by carbon dots as a novel photocatalyst with improved visible-light photocatalytic performance for the degradation of enrofloxacin. Rsc Adv. 2017, 7 (54), 34096-34103.

DOI: 10.1039/c7ra05485h

28. She, X. J.; Wu, J. J.; Xu, H.; Zhong, J.; Wang, Y.; Song, Y. H.; Nie, K. Q.; Liu, Y.; Yang, Y. C.; Rodrigues, M. T. F. High Efficiency Photocatalytic Water Splitting Using 2D α-Fe2O3/g-C3N4 Z-Scheme Catalysts. Adv. Energy Mater. 2017, 7, 1-7. 22 ACS Paragon Plus Environment

DOI:

Page 23 of 36 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


10.1002/aenm.201700025 29. Li, X.; Xing, J. L.; Zhang, C. L.; Han, B.; Zhang, Y. H.; Wen, T.; Leng, R.; Jiang, Z. H.; Ai, Y. J.; Wang, X. K., Adsorption of Lead on Sulfur-doped Graphitic Carbon Nitride Nanosheets: Experimental and Theoretical Calculation Study. Acs Sustainable Chem. Eng. 2018, 6, 10606-10615.

DOI: 10.1021/acssuschemeng.8b01934

30. Fu, J. W.; Yu, J. G.; Jiang, C. J.; Cheng, B., g-C3N4-Based Heterostructured Photocatalysts. Adv. Energy Mater. 2018, 8, 1701503.

DOI: 10.1002/aenm.201701503

31. Adhikari, S. P.; Hood, Z. D.; More, K. L.; Chen, V. W.; Lachgar, A., A Visible-Light-Active

Heterojunction

with

Enhanced

Generation. Chemsuschem 2016, 9 (14), 1869-1879.

Photocatalytic

Hydrogen

DOI: 10.1002/cssc.201600424

32. Fujito, H.; Kunioku, H.; Kato, D.; Suzuki, H.; Higashi, M.; Kageyama, H.; Abe, R. Layered Perovskite Oxychloride Bi4NbO8Cl: A Stable Visible Light Responsive Photocatalyst for Water Splitting. J. Am. Chem. Soc. 2016, 47 (26), 2082-2085.

DOI:

10.1021/jacs.5b11191 33. Lin, X. P.; Huang, T.; Huang, F. Q.; Wang, W. D.; Shi, J. L. Photocatalytic activity of a Bi-based oxychloride Bi3O4Cl. Cheminform 2006, 110 (48), 24629. 34. She, X. J.; Wu, J. J.; Zhong, J.; Xu, H.; Yang, Y. C.; Vajtai, R.; Lou, J.; Liu, Y.; Du, D. L.; Li, H. M.; Ajayan, P. M. Oxygenated monolayer carbon nitride for excellent photocatalytic hydrogen evolution and external quantum efficiency. Nano Energy 2016, 27, 138-146.

DOI: 10.1039/b615903f 23 ACS Paragon Plus Environment


Page 24 of 36

35. Niu, P.; Zhang, L. Z.; Liu, G.; Cheng, H. M. Graphene-Like Carbon Nitride Nanosheets for Improved Photocatalytic Activities. Adv. Funct. Mater. 2012, 22 (22), 4763-4770.

DOI: 10.1002/adfm.201200922

36. Shi, L.; Liang, L.; Wang, F. X.; Ma, J.; Sun, J. M. Polycondensation of guanidine hydrochloride into a graphitic carbon nitride semiconductor with a large surface area as a visible light photocatalyst. Catal. Sci. & Technol. 2014, 4 (9), 3235-3243.

DOI:

10.1039/c4cy00411f 37. Huang, H. W.; Han, X.; Li, X. W.; Wang, S. C.; Chu, P. K.; Zhang, Y. H. Multiple Heterojunctions Fabrication with Tunable Visible-Light-Active Photocatalytic Reactivity in the BiOBr-BiOI Full Range Composites Based on Microstructure Modulation and Band Structures. ACS Appl. Mater. Interfaces 2015, 7 (1), 482-92.

DOI:

10.1021/am5065409 38. Tian, N.; Huang, H. W.; He, Y.; Guo, Y. X.; Zhang, Y. H. Novel g-C3N4/BiIO4 heterojunction

photocatalysts:

synthesis,

characterization

and

enhanced

visible-light-responsive photocatalytic activity. Rsc Adv. 2014, 4 (80), 42716-42722. DOI: 10.1039/c4ra05917d 39. Xu, N.P.; Shi, Z. F.; Fan, Y. Q.; Dong, J. H.; Shi, J.; Hu, Z. C., Effects of Particle Size of TiO2 on Photocatalytic Degradation of Methylene Blue in Aqueous Suspensions. Ind. Eng. Chem. Res. 1999, 38 (2), 373-379.

DOI: 10.1021/ie980378u

40. Almquist, C. B.; Biswas, P., Role of Synthesis Method and Particle Size of 24 ACS Paragon Plus Environment

Page 25 of 36 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


Nanostructured TiO2 on Its Photoactivity. J. Catal. 2002, 212 (2), 145-156.

DOI:

10.1006/jcat.2002.3783 41. Cozzoli, P. D.; Comparelli, R.; Fanizza, E.; Curri, M. L.; Agostiano, A., Photocatalytic activity of organic-capped anatase TiO2 nanocrystals in homogeneous organic solutions. Mater. Sci. Eng. C 2003, 23 (6), 707-713.

DOI:

10.1016/j.msec.2003.09.101 42. Adhikari, S. P.; Lachgar, A., Effect of particle size on the photocatalytic activity of BiNbO4 under visible light irradiation. J. Phys. Conf. Ser. 2016, 758 (1). 012017. DOI: 10.1088/1742-6596/758/1/012017 43. Amano, F.; Nogami, K.; Tanaka, M.; Ohtani, B., Correlation between Surface Area and Photocatalytic Activity for Acetaldehyde Decomposition over Bismuth Tungstate Particles with a Hierarchical Structure. Langmuir 2010, 26 (10), 7174-7180.

DOI:

10.1021/la904274c 44. Elze, H. T., Quantum features of natural cellular automata. J. Phys. Conf. Ser. 2016, 701 (1), 012017. 45. Kruk,

M.;

DOI: 10.1088/1742-6596/701/1/012017 Jaroniec,

M.,

Gas

Adsorption

Characterization

of

Ordered

Organic−Inorganic Nanocomposite Materials. Chem. Mater. 2001, 13 (10), 3169-3183. DOI: 10.1021/cm0101069 46. Oh, Y.; Le, V.-D.; Maiti, U. N.; Hwang, J. O.; Park, W. J.; Lim, J.; Lee, K. E.; Bae, Y.-S.; Kim, Y.-H.; Kim, S. O., Selective and Regenerative Carbon Dioxide Capture by 25 ACS Paragon Plus Environment


Highly Polarizing Porous Carbon Nitride. ACS Nano 2015, 9 (9), 9148-9157.

Page 26 of 36

DOI:

10.1021/acsnano.5b03400 47. Huang, Z. F.; Song, J. J.; Pan, L.; Wang, Z. M.; Zhang, X. Q.; Zou, J. J.; Mi, W. B.; Zhang, X. W.; Wang, L. Carbon nitride with simultaneous porous network and O-doping for efficient solar-energy-driven hydrogen evolution. Nano Energy 2015, 12, 646-656. DOI: 10.1016/j.nanoen.2015.01.043 48. Zhao, J.; Holmes, M. A.; Osterloh, F. E., Quantum Confinement Controls Photocatalysis: A Free Energy Analysis for Photocatalytic Proton Reduction at CdSe Nanocrystals. ACS Nano 2013, 7 (5), 4316-4325.

DOI: 10.1021/nn400826h

49. Zhu, M. S.; Sun, Z. C.; Fujitsuka, M.; Majima, T., Z-Scheme Photocatalytic Water Splitting on a 2D Heterostructure of Black Phosphorus/Bismuth Vanadate Using Visible Light. Angew. Chem. Int. Ed. Engl. 2018, 57, 1-6.

DOI: 10.1002/anie.201711357

50. Li, H. F.; Quan, X.; Chen, S.; Yu, H. T. Ferroelectric-enhanced Z-schematic electron transfer in BiVO4-BiFeO3-CuInS2 for efficient photocatalytic pollutant degradation. Appl. Catal. B 2017, 209, 591-599.

DOI: 10.1016/j.apcatb.2017.03.043


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Fig. 1 (a) XRD patterns of g-C3N4, Bi4NbO8Cl and the Bi4NbO8Cl/ g-C3N4 composites.



Fig. 2 (a) XPS survey spectra of CNBN-3 and high-resolution spectra of (b) Bi 4f, (c) Nb 3d, (d) and N 1s of CNBN-3.


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Fig. 3 SEM images of (a) g-C3N4, (b) Bi4NbO8Cl and (c) CNBN-3. (d) TEM, (e) HRTEM images and (f-j) EDX mapping of CNBN-3.



Fig. 4 (a) UV-vis diffuse reflectance spectra of g-C3N4, Bi4NbO8Cl and Bi4NbO8Cl/ g-C3N4 composites. (b) the absorbtion1/2 vs energy in the absorbtion edge region of g-C3N4 and Bi4NbO8Cl.


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Fig. 5 (a) Photocatalytic H2 evolution, (b) the rate of H2 production under visible light illumination, (c) XRD patterns before and after photoreaction of CNBN-3 and (d) wavelength-dependent AQY of CNBN-3.



Fig. 6 (a) N2 adsorption-desorption isotherms, and (b) the corresponding pore size distribution curves of g-C3N4, Bi4NbO8Cl and CNBN-3, (c) Specific surface area of g-C3N4, Bi4NbO8Cl and Bi4NbO8Cl/ g-C3N4 composites.


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Fig. 7 (a) Transient photocurrent response, (b) electrochemical impedance spectra (EIS), (c) photoluminescence (PL) spectra of g-C3N4, Bi4NbO8Cl and Bi4NbO8Cl/ g-C3N4 composites. (d) Time-resolved photoluminescence decay spectra of g-C3N4, Bi4NbO8Cl and CNBN-3.



Fig. 8 ESR signals of (a) (c) (e) DMPO-·O2- and (b) (d) (f) DMPO-·OH adducts in the presence of g-C3N4, Bi4NbO8Cl and CNBN-3 under visible light irradiation (λ ≥ 420 nm), respectively.


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Fig.9 Schematic illustration for Z-scheme photocatalytic water splitting over CNBN-3 under visible light irradiation.



For Table of Contents Use Only

Z-scheme photocatalyst g-C3N4/Bi4NbO8Cl was prepared via a facile high-energy ball-milling method, which exhibits an enormously promoted photocatalytic activity for H2 production with visible light illumination (λ > 420 nm).


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Bi4NbO8Cl Heterojunction for Enhanced

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