Glucose-Induced Formation of Oxygen Vacancy and Bi-Metal

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Glucose Induced Formation of Oxygen Vacancy and Bi-Metal Comodified Bi5O7Br Nanotubes for efficient Performance Photocatalysis Huimin Xu, Yuwen Hu, Duan Huang, Ying Lin, Wenxia Zhao, Yongchao Huang, Shanqing Zhang, and Yexiang Tong ACS Sustainable Chem. Eng., Just Accepted Manuscript • DOI: 10.1021/ acssuschemeng.8b05336 • Publication Date (Web): 05 Feb 2019 Downloaded from http://pubs.acs.org on February 10, 2019

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ACS Sustainable Chemistry & Engineering

Glucose Induced Formation of Oxygen Vacancy and Bi-Metal Co-modified Bi5O7Br Nanotubes for efficient Performance Photocatalysis Huimin Xu†, Yuwen Hu†, Duan Huang†, Ying Lin†, Wenxia Zhao#, Yongchao Huang‡*, Shanqing Zhang§*, and Yexiang Tong†* †

MOE Laboratory of Bioinorganic and Synthetic Chemistry, the Key Lab of Low-Carbon

Chemistry and Energy Conservation of Guangdong Province, School of Chemistry, Sun Yat-sen University, No.135, Xinggangxi Road, Guangzhou, 510275, China ‡

Key Laboratory for Water Quality and Conservation of the Pearl River Delta, Ministry of

Education, Institute of Environmental Research at Greater Bay, Guangzhou University, Guangzhou Higher Education Mega Center, Outer Ring Road No. 230, Guangzhou 510006, China §

Centre for Clean Environment and Energy, Gold Coast Campus, Griffith University, Australia

#

Instrument Analysis and Research Centre, Sun Yat-sen University, No.135, Xinggangxi Road,

Guangzhou, 510275, China

*E-mail: [email protected] (Y.C. Huang); *E-mail: [email protected] (S.Q. Zhang); *E-mail: [email protected] (Y.X. Tong) ABSTRACT Here,

we

prepared

Bi

metal

modified

defective-Bi5O7Br

nanotubes

(Bi/Bi5O7Br-OV) by hydrothermal synthesis to be an efficient photocatalyst. The density function theory (DFT) revealed that oxygen vacancies in Bi5O7Br could form an intermediate level, which could allow electron transfer to new intermediate level, and finally move to the conduction band. The Bi/Bi5O7Br-OV nanotubes demonstrate superior photocatalytic degradation of phenol, showing 3 times higher than that of pristine Bi5O7Br. The defects and Bi endow Bi5O7Br nanotubes with abundant active sites and improve the solar absorption. The increased and more dispersed charge density allow enhanced electronic conductivity and the separation of photogenerated carriers. Furthermore, more ·OH radicals are generated during photochemical reaction, which is beneficial in improving the photocatalytic performance. This work will play significant roles and create opportunities in modifying Bi-based materials for 1

ACS Paragon Plus Environment

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promoting photocatalysis. KEYWORDS: bismuth oxybromide, photodegradation, visible light irradiation, water treatment. INTRODUCTION Organic pollutants in wastewater such as azo dyes and phenol have caused serious environmental pollution by reason of their general toxicity and excellent chemical stability.1-4 It is harmful to the eco-environment when the organic pollutants are released to the lakes or rivers without pretreatment. Many technological systems have been recently exploited to remove these organic pollutants.5-8 Photocatalytic oxidation is widely used as a novel economically and environmentally friendly technology to decompose the soluble organic pollutants in wastewater.9-13 In recent times, much attention has been focused on catalysts that could absorb visible light near-infrared light.14 As impressive visible-light-driven photocatalysts, bismuth oxybromide was broadly investigated in applications of water splitting, dye degradation and CO2 reduction due to the special unique structure.15-19 However, the photocatalytic efficiency is still unsatisfactory, limiting its practical application. Until now, defective photocatalysts could availably separate the photoinduced charges, where the photogenerated electrons-holes transfer into CBM and VBM of semiconductors, respectively.20-23 Defects have been confirmed to act as electron trap centers and could reduce O2 gases into reactive oxygen. Recently, we demonstrated that Bi2O2CO3 with oxygen vacancies displayed good photocatalytic performance of HCHO gases degradation, which results from the separation of photogenerated charge carriers.24 Xie’s group prepared defective K4Nb6O17 through controllable reduction in K4Nb6O17, promoting the generation of electron and hole, contributing to high photocatalytic performance.25 Based on those results, introducing vacancies should be highly desirable for enhancing the photocatalytic performance. However, oxygen vacancies are usually introduced into the semiconductors via thermal treatment in a reductive atmosphere, electrochemical reduction,26 chemical reagent reduction27 and so on.28,

29

Unfortunately, these methods always involved high temperature or 2


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producing hydrogen that is dangerous in application. Therefore, it is required to search a simple and safety way to introduce oxygen vacancy into photocatalytic materials. Bismuth (Bi) was deposited on the bismuth oxybromide to boost the photocatalytic performance of degradation organic pollutions,30-32 Such as Bi/Bi2O3,33 Bi/BiOCl0.5I0.527. The existence of Bi metal enhances light absorption and charge separation efficiency for improving the photocatalytic activity. Meanwhile, constructing special nanostructures could reduce the distance of electron migration, such as nanowires, nanotubes and nanosheets.34,

35

Such features inspired us to

introduce oxygen vacancy and Bi metal into Bi5O7Br nanotubes to increase the photocatalytic activity. In this work, we prepare novel defective Bi/Bi5O7Br nanotubes via two hydrothermal processes. The obtained defective Bi/Bi5O7Br nanotubes have suitable absorption edge and large surface area (45.5 m2 g-1). The existence of defects and Bi metal could availably prevent the recombination of photogenerated electron-hole pairs. As a result, defective Bi/Bi5O7Br nanotubes demonstrate a superior visible light-responded photocatalytic degradation of phenol. The degradation rate of defective Bi/Bi5O7Br nanotubes is much higher than that of pristine Bi5O7Br. Furthermore, the mechanism of oxygen vacancies and Bi metals co-modified photocatalytic activity on defective Bi/Bi5O7Br was proposed.

EXPERIMENTAL METHODS Preparation of Bi5O7Br nanotubes and defective Bi/Bi5O7Br nanotubes: Typically, 1.18 g Bi(NO3)3·H2O were put in 50 mL oleylamine to get transparent solution with vigorous stirring. 0.071 g KBr was then put into the solution. The solution was stirred for 10 days and kept at 25 oC. Adding 5 mL deionized water slowly into it and continue stirring. Bi5O7Br nanotubes was separated by a centrifuge (18000 r·min-1), washed with n-hexane and absolute ethanol many times, finally put the Bi5O7Br nanotubes into the oven at 60 oC for 12 h. 0.1g Bi5O7Br were added into 40 mL water contain different content glucose (0.01, 0.05 and 0.1 mol) and stirred for 3



1 h. The solution was poured into a 45 mL Teflon-lined stainless steel autoclave, heating at 180 oC (3 h). The samples were gathered by centrifugation, washing with ethanol and distilled water. Finally, the samples were marked Bi/Bi5O7Br-OV0.01, Bi/Bi5O7Br-OV0.05 and Bi/Bi5O7Br-OV0.1, respectively. Photocatalytic performance of degradation phenol: Adding catalyst (0.01 g) into the phenol solution (100 m, 10 mg·L-1) and stirring for 60 min to make sure absorption-desorption equilibrium. After turning on the light, a 300 W Xe lamp (with a 420 nm UV light cut filter), a certain amount of reactive solution (3.0 mL) was suck out at a regular times. UV-vis spectrophotometer is used to detect the concentrations of the residual dyes. Then, the removal efficiency (%) could be counted by C/Co × 100 (C is the concentration of the phenol and Co is the initial concentration of phenol).

RESULTS AND DISCUSSION Preparation, Characterization of Catalysts. X-ray diffraction (XRD) pattern were first performed to research the crystal structure and phase of all the catalysts. As shown in Figure 1, the peaks generated from Bi5O7Br corresponded to orthorhombic phase of Bi5O7Br (JCPDS No. 38-0493)36 and the crystal structure schematic is shown as well. After reaction with glucose, except for the diffraction peaks coming from Bi5O7Br, new peaks that could be ascribed to rhombohedral Bi (JCPDS No. 44-1246) appeared for Bi/Bi5O7Br-OV. The higher the concentration of glucose, the higher the content of Bi produced. All the samples possess strong diffraction peaks and no other peaks appeared in the XRD pattern, suggesting good crystallinity and high purity.

4


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Figure 1. XRD pattern of all the catalysts and the side view of Bi5O7Br. The morphology of the Bi/Bi5O7Br-OV0.05 is confirmed by typical transmission electron microscopy (TEM). Figure 2a-b displays TEM images of Bi/Bi5O7Br-OV0.05. The morphology of Bi/Bi5O7Br-OV0.05 is confirmed to be nanotubes and the corresponding selected-area electron diffraction (SAED) (a large area containing many nanotubes) suggested Bi/Bi5O7Br-OV0.05 is ploy crystal structure. Furthermore, the 0.313 nm and 0.326 nm lattice spacing are assigned to the (312) plane of the orthorhombic phase Bi5O7Br and (012) plane of rhombohedral Bi, respectively (Figure 2c). High-resolution TEM image of Bi/Bi5O7Br-OV0.05 in Figure 2d suggests that Bi nanoparticles existed on the surface of nanotubes. The selected area in square is the Bi nanoparticles and the 0.326 nm lattice spacing is assigned to the (012) plane of rhombohedral Bi. The corresponding FFT is also showed, suggesting Bi is single crystal structure. Additionally, elemental mapping demonstrated that Bi, O, Br is distributed uniformly in the Bi/Bi5O7Br-OV0.05 nanotubes, suggesting the high purity of Bi/Bi5O7Br-OV0.05 nanotubes (Figure 2e).

5



Figure 2. (a, b) TEM images (SAED pattern is inserted), (c, d) HRTEM image of Bi/Bi5O7Br-OV0.05 (Inset is the FFT pattern). (e) EDS elemental mappings of Bi/Bi5O7Br-OV0.05.

To in-depth study the chemical states of Bi5O7Br and Bi/Bi5O7Br-OV, we conducted X-ray photoelectron spectroscopy (XPS) analyses. The full survey XPS spectra displayed that peaks of O, Br and Bi could be seen in Figure S1. As displayed in Figure 3a, O 1s XPS peaks could be de-convoluted into three peaks centered at 529.1 eV, 529.8 eV, and 532.0 eV, respectively. They could be ascribed to lattice oxygen, hydroxyl groups in the oxygen deficient region and water molecules, respectively.24, 37 The relative intensity of Bi/Bi5O7Br-OV at 529.8 and 532.0 eV is increased, revealing the generation of oxygen vacancies.38 The Bi 4f spectra display the symmetrical peaks (159.2 and 164.3 eV), revealing that Bi atoms in Bi5O7Br are Bi3+ (Figure 3b). Comparing with pristine Bi5O7Br, the Bi 4f peaks of Bi/Bi5O7Br-OV0.1 exhibit a 0.5 eV displacement toward lower binding energy. This result suggests that Bi3+ ions are reduced to low-charge Bi ions via glucose 6


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reduction.2, 26 A small peak at 162 eV could be observed, suggesting the existence of metallic Bi. Obviously, the Br 3d XPS peaks of Bi5O7Br is at about 68.2 eV, while the peak of Bi/Bi5O7Br-OV0.1 also moves 0.5 eV toward lower binding energy. All the catalysts display similar C 1s spectra, which attributes to carbon species from instrument,24 revealing that there is no other carbon materials generated during the hydrothermal process (Figure S2). The density of states (DOS) of pristine BiOBr and Bi/Bi5O7Br-OV are subsequently calculated, which is displayed in Figure 3d.31 The formation of defect level was due to the contribution of the p state and the p state formation is attributed to the Bi and O, which is shown in Figure S3. The defect level could availably reduce the photo energy requiring for electron excitation, electron transfer and separation. These results demonstrated Bi and oxygen vacancy were formed over Bi5O7Br via hydrothermal process.

Figure 3. XPS spectra for: (a) O 1s; (b) Bi 4f; (c) Br 3d of all the samples. (d) Calculated density of states (DOS) of Bi5O7Br and Bi/Bi5O7Br-OV. The existence of oxygen vacancies are also confirmed by the electron paramagnetic resonance (EPR) test (Figure 4a). For pristine Bi5O7Br, no peak was observed in the 7



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EPR spectra. The obvious oxygen vacancies signal existed at g=2.001 for the Bi/Bi5O7Br-OV suggested the existence of oxygen vacancies in the samples.39 The intensity of Bi/Bi5O7Br-OV0.1 is higher than those of other samples, suggesting more oxygen vacancies in Bi/Bi5O7Br-OV0.1 sample. Furthermore, auxiliary evidence could be identified by thermogravimetry analysis (TGA) of the samples (Figure 4b). The TGA spectra of pristine Bi5O7Br displayed the reaction stage below 339 oC. Beyond 339 oC, Bi2O3 is the final product. The Bi/Bi5O7Br-OV samples react with the O2 gas up to 413 oC before changing to Bi2O3. Compared with the pristine Bi5O7Br, Bi/Bi5O7Br-OV samples demonstrate drastic weight loss below 339 oC. This is because oxygen vacancies are re-filled with oxygen. Moreover, the DOS of Bi5O7Br and Bi/Bi5O7Br-OV are subsequently calculated utilizing the hybrid DFT method (Figure 3d). The valence and conduction band of Bi/Bi5O7Br-OV both transfer to lower energy level comparison with that of Bi5O7Br.31 Clearly, the existence of oxygen vacancies formed a defect energy level. So, the Bi/Bi5O7Br-OV has a higher hole oxidation capacity and the defect level reduces the photo energy for photogenerated

electron

migration.

All

these

results

demonstrated

that

Bi/Bi5O7Br-OV have more oxygen vacancies in the catalysts’ surface.

Figure 4. (a) EPR spectra and (b) TG spectra of all the samples. Optical properties of Catalysts. Figure 5 shows the UV-vis absorption spectra of the pristine Bi5O7Br and Bi/Bi5O7Br-OV catalysts. It can be observed that Bi5O7Br displays absorption in the visible light region. The bandgap of the pristine Bi5O7Br was estimated to be 2.17 eV, 8


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which is determined by αhν = A(hν-Eg)n/2.26, 27, 29 However, the band gap of Bi5O7Br is smaller than other literature (2.84 eV),40 which can be ascribed to the nanostructure influencing the ability of absorption. The VBM value of Bi5O7Br is 2.57 eV based on the XPS and the CBM value is 0.19 eV (Figure S4). According to our previous reports, the existence of oxygen vacancies in photocatalysts could indirectly enhance the absorption properties. As expected, the absorption band edge of Bi/Bi5O7Br-OV changed substantially compared to the pristine Bi5O7Br, which could absorb visible light and the absorption edge is at 800 nm. This suggested that OVs and Bi could enhance the absorption of Bi5O7Br and improve its photocatalytic activity.

Figure 5. UV-vis spectra of all the catalysts. The photogenerated charge separation in materials is evaluated by the photoelectrochemical performance. Firstly, the transient photocurrent responses of all the catalysts are detected over several on-off cycles with irradiating (visible light), which is displayed in Figure 6a. All catalysts display good photocurrent responses during four cycles with on-off intermittent irradiation. Apparently, Bi/Bi5O7Br-OV0.05 sample (24 μA/cm-2) shows about 6 times higher photocurrent intensity than the value of pristine Bi5O7Br (4 μA/cm-2), suggesting good transportation efficiency of photogenerated carriers for Bi/Bi5O7Br-OV0.05 with visible light irradiating. Additionally, the photocurrent value of Bi/Bi5O7Br-OV0.1 decreases compared with Bi/Bi5O7Br-OV0.05. This result reveals that moderate oxygen vacancy could efficiently enhance the separation of photogenerated carriers. Besides, the charge transfer properties of all the catalysts is studied by the electrochemical impedance 9



spectroscopy.41 As shown in Figure 6b, the EIS Nyquist plot of Bi/Bi5O7Br-OV0.05 demonstrates a smaller arc radius than that of Bi5O7Br, suggesting the lower charge transfer resistance of Bi/Bi5O7Br-OV0.05 sample. Simultaneously, it is worth noting, with the visible light irradiation, the charge transfer resistance of all the catalysts is better than those in dark, indicating that lower photogenerated carrier recombination rate with the irradiation of visible light. The enhanced photoexcited electrons-holes separating can be also monitored by photoluminescence spectra (Figure 6c). It can be seen that Bi/Bi5O7Br-OV0.05 displays the lowest intensity among all the tested samples, indicating excellent charge transfer and migration. The photocurrent, EIS and PL results are well accordance, revealing Bi and oxygen vacancies could obviously improve the charge transfer and migration, therefore improving the photocatalytic performance of Bi5O7Br.

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Figure 6. (a) Photocurrent spectra, (b) Electrochemical impedance results and (c) photoluminescence results of Bi5O7Br, Bi/Bi5O7Br-OV0.01, Bi/Bi5O7Br-OV0.05 and Bi/Bi5O7Br-OV0.1. Photocatalytic activity of removing organic pollutants. Photocatalytic removal of organic pollutants in water was performed to reveal the role of defects in photocatalysis. Firstly, the entire catalysts were kept on stirring for 60 min without light to detect the adsorption capabilities. All the catalysts displayed almost the same adsorption capabilities and could reach 20% adsorption capabilities (Figure S5). The results are in accordance with the BET specific surface areas of the catalysts. The values of BET specific surface areas of the catalysts are about 45.4 mg m-3, suggesting that they have the similar adsorption capabilities (Figure S6). Secondly, after turning on the light, the Bi/Bi5O7Br-OV samples have better photocatalytic performance compared to the pristine Bi5O7Br. Figure 7a demonstrates the photocatalytic activity of degradation of phenol toward all the catalysts. No obvious degradation of phenol can be seen without the catalysts, suggesting that phenol is stable with the irradiation of visible light. In the existence of Bi/Bi5O7Br-OV0.01, Bi/Bi5O7Br-OV0.05 and Bi/Bi5O7Br-OV0.1, the removal ratios of phenol attained after 2 h irradiation are 56%, 80% and 99%, respectively. This result suggests that the existence of Bi and oxygen vacancies could effectively boost the photocatalytic activity of Bi5O7Br. The performance of the Bi/Bi5O7Br-OV0.05 nanotubes is compared with the Bi-based photocatalysts reported in the literature and the commercially available photocatalysts as shown in Table S1. It is worth noting that the usage amount of Bi/Bi5O7Br-OV (10 mg) in photocatalysis is smaller than these reported BiOX samples, verifying the excellent performance of Bi/Bi5O7Br-OV. It should be pointed out that more oxygen vacancies will decreased the photocatalytic activity because too much defects could act as the sites for recombination of photoelectron and hole pairs. Furthermore, in the light of Langmuir-Hinshelwood model, the kinetic behaviors for degradation of phenol with all the catalysts are studied. It could be seen that the degradation process complied with the 11



pseudo-first-order kinetics42 As displayed in Figure 7b, Bi/Bi5O7Br-OV0.05 demonstrates the best reaction rate constant, about 10 times higher that of pristine Bi5O7Br, 3 times that of Bi/Bi5O7Br-OV0.01. Interestingly, after 5 continuous cycles, the photodegradation rate of Bi/Bi5O7Br-OV0.05 did not changed, suggesting its outstanding stability (Figure 7c). All these results demonstrate that Bi/Bi5O7Br-OV0.05 is an excellent photocatalyst. Possible photocatalytic mechanism. The active species trapping experiments are systematically performed to disclose the roles of h+, superoxide radical and hydroxyl radical during the photocatalytic reacted process.43, 44 According to our previous literatures, three scavengers are used in the photocatalysis (triethanolamine for h+, detect hydroxyl radical with tert-butylalcohol and benzoquinone with superoxide radical).45 Figure 7d shows the photocatalytic efficiencies of degradation phenol by adding scavengers over the Bi/Bi5O7Br-OV0.05. In the presence of BQ, the phenol degradation efficiency has not decreased comparing with the efficiency without sacrificial reagents, suggesting no ·O2- production during the photocatalysis. Additionally, the degradation efficiency decreased obviously to 30% and 40% by adding TBA and TEOA, respectively, indicating that h+ and ·OH active species play an important role in photocatalysis. To further confirm these results, the ESR measurements are carried out with adding the 5, 5-dimethyl-1-pyrroline N-oxide (DMPO).46 Figure 7e displays the DMPO-·OH for Bi/Bi5O7Br-OV0.05 under the visible light irradiation. Four typical signals are detected with visible light irradiating, revealing that ·OH played a very important role in photocatalysis. The intensity of the peaks in 10 min was higher than that of 5 min, revealing that much ·OH species generated in the process. The ESR spectra of ·O2- for Bi/Bi5O7Br-OV0.05 is shown in Figure S7. No signals are observed with visible light irradiating for 10 min. The ESR results correlate with the trapping experiments results, demonstrating that ·OH and h+ radical are the important reactive species in the photocatalytic process. Therefore, we propose a photocatalytic mechanism of Bi/Bi5O7Br-OV0.05, which is shown in Figure 7f. After the light irradiating Bi5O7Br, electrons on the valence band are directly excited and moved to the conduction band. 12


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Some of the electrons will transfer to the defect energy level, and portion electrons transport to Bi metal (Bi metal with high electrical conductivity). Subsequently, electrons on Bi metal will transfer to the CBM of Bi5O7Br. The electrons in CBM could not react with the O2 because the CBM potential (0.19 eV) is not negative than the potential of O2/ · O2- (-0.33 eV).47 The holes existed in the valence band of Bi5O7Br can oxidize H2O into ·OH species. It is because that VBM of Bi5O7Br (2.57 eV) is much higher than the redox potential of OH-/·OH (1.99 eV).48 Finally, h+ and ·OH could finally oxidize the pollutants into CO2 and H2O.

Figure 7. (a) The degradation curve of phenol with different catalysts. (b) Reaction 13



kinetic of different samples based on the Figure 7a. (c) Activity of photocatalytic degradation of phenol over Bi5O7Br-OV0.05 with 5 cycles. (d) Activity of degradation phenol in the present of Bi/Bi5O7Br-OV0.05 with adding different scavengers. (e) EPR measurements of DMPO-·OH for Bi/Bi5O7Br-OV0.05 with irradiating (≥420 nm). (f) Proposed photocatalysis mechanism of Bi/Bi5O7Br-OV0.05. Conclusions In summary, we prepared novel defective Bi/Bi5O7Br nanotubes as photocatalysts for degradation of phenol. As a result, defective Bi/Bi5O7Br nanotubes demonstrate a superior photocatalytic degradation of phenol, which improves 3 times higher performance comparing with pristine Bi5O7Br. Such excellent performance could be ascribed to the enhancement of surface area and suitable absorption edge, therefore improving the segregating of photogenerated electron – hole pairs. This current study may develop a novel path to construct active catalysts, removing harmful organic pollutants in wastewater through light irradiating. ASSOCIATED CONTENT Supporting Information. XPS dates, Calculated density of states, Phenol adsorption capacity, N2 adsorption–desorption isotherms, EPR spectra. AUTHOR INFORMATION Corresponding Author *E-mail: [email protected] (Y.C. Huang); *E-mail: [email protected] (S.Q. Zhang); *E-mail: [email protected] (Y.X. Tong)

Acknowledgements We are grateful for the support of various funds. The Natural Science Foundation of 14


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China (21706295, 21773315, 41273039), Natural Science Foundation of Guangdong Province (2017A030313055), the Fundamental Research Funds for the Central Universities (17lgjc36), Innovative School Project (2823010936) and the Science Starting Foundation of Guangzhou University (69-18ZX10301), National Key Science

and

Technology

Special

Foreign

Talents

Introduction

Program

(ZD20180029). Guangdong Provincial Key Platform and Major Scientific Research Projects for Colleges and Universities (2015KCXTD029), Special Funds for the Cultivation of Guangdong College Students' Scientific and Technological Innovation (pdjh2018a0004). Reference (1) Wang, T.; Li, C.; Ji, J.; Wei, Y.; Zhang, P.; Wang, S.; Fan, X.; Gong, J., Reduced Graphene Oxide (rGO)/BiVO4 Composites with Maximized Interfacial Coupling for Visible Light Photocatalysis. ACS Sustainable. Chem. Eng. 2014, 2, 2253-2258, DOI 10.1021/sc5004665. (2) Dong, F.; Li, Q.; Sun, Y.; Ho, W.-K., Noble Metal-Like Behavior of Plasmonic Bi Particles as a Cocatalyst Deposited on (BiO)2CO3 Microspheres for Efficient Visible

Light

Photocatalysis.

ACS

Catal.

2014,

4,

4341-4350,

DOI

10.1021/cs501038q. (3) Martin, D. J.; Liu, G.; Moniz, S. J. A.; Bi, Y.; Beale, A. M.; Ye, J.; Tang, J., Efficient Visible Driven Photocatalyst, Silver Phosphate: Performance, Understanding and

Perspective.

Chem.

Soc.

Rev.

2015,

44,

7808-7828,

DOI

10.1002/chin.201550189. (4) Ranjith, K. S.; Uyar, T., Conscientious Design of Zn-S/Ti-N Layer by Transformation of ZnTiO3 on Electrospun ZnTiO3@TiO2 Nanofibers: Stability and Reusable Photocatalytic Performance under Visible Irradiation. ACS Sustainable. Chem. Eng. 2018, 6, 12980-12992, DOI 10.1021/acssuschemeng.8b02455. (5) Cao, B.; Li, G.; Li, H., Hollow Spherical RuO2@TiO2@Pt Bifunctional Photocatalyst for Coupled H2 Production and Pollutant Degradation. Appl. Catal., B 2016, 194, 42-49, DOI 10.1016/j.apcatb.2016.04.033. 15



Page 16 of 21

(6) Hu, J.; Zhai, C.; Yu, C.; Zeng, L.; Liu, Z.; Zhu, M., Visible Light-Enhanced Electrocatalytic Alcohol Oxidation Based on Two Dimensional Pt-BiOBr Nanocomposite.

J.

Colloid

Interf.

Sci.

2018,

524,

195-203,

DOI

10.1016/j.jcis.2018.03.104. (7) Li, J. F.; Chen, Y.; Wang, Z.; Liu, Z. Q., Self-Templating Synthesis of Hollow Copper Tungstate Spheres as Adsorbents for Dye Removal. J. Colloid Interf. Sci. 2018, 526,459-469, DOI 10.1016/j.jcis.2018.05.023. (8) Xia, P.; Zhu, B.; Cheng, B.; Yu, J.; Xu, J., 2D/2D g-C3N4/MnO2 Nanocomposite as a Direct Z-Scheme Photocatalyst for Enhanced Photocatalytic Activity. ACS Sustainable. Chem. Eng. 2017, 6, 965-973, DOI 10.1021/acssuschemeng.7b03289. (9) Peng, Z.; Wang, T.; Chang, X.; Gong, J., Effective Charge Carrier Utilization in Photocatalytic

Conversions.

Acc.

Chem.

Res.

2016,

49,

911-921,

DOI

10.1021/acs.accounts.6b00036. (10) Liu, G.; Wang, T.; Ouyang, S.; Liu, L.; Jiang, H.; Yu, Q.; Kako, T.; Ye, J., Band-Structure-Controlled BiO(ClBr)(1−x)/2Ix Solid Solutions for Visible-Light Photocatalysis. J. Mater. Chem. A 2015, 3, 8123-8132, DOI 10.1039/c4ta07128j. (11) Madhusudan, P.; Ran, J.; Zhang, J.; Yu, J.; Liu, G., Novel Urea Assisted Hydrothermal Synthesis of Hierarchical BiVO4/Bi2O2CO3 Nanocomposites with Enhanced Visible-Light Photocatalytic Activity. Appl. Catal., B 2011, 110, 286-295, DOI 10.1016/j.apcatb.2011.09.014. (12) Tong, H.; Ouyang, S.; Bi, Y.; Umezawa, N.; Oshikiri, M.; Ye, J., Nano-Photocatalytic Materials: Possibilities and Challenges. Adv. Mater. 2012, 24, 229-251, DOI 10.1002/chin.201210222. (13) Marschall, R., Photocatalysis: Semiconductor Composites: Strategies for Enhancing Charge Carrier Separation to Improve Photocatalytic Activity. Adv. Funct. Mater. 2014, 24, 2420-2420, DOI 10.1002/adfm.201470108. (14) Huang, Y.; Lu, Y.; Lin, Y.; Mao, Y.; Ouyang, G.; Liu, H.; Zhang, S.; Tong, Y., Cerium–Based Hybrid Nanorods for Synergetic Photo-Thermocatalytic Degradation of Organic Pollutants. J. Mater. Chem. A 2018, 6, 24740-24747, DOI 10.1039/C8TA06565A. 16


Page 17 of 21 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


(15) Huang, Y.; Xu, H.; Yang, H.; Lin, Y.; Liu, H.; Tong, Y., Efficient Charges Separation Using Advanced BiOI-Based Hollow Spheres Decorated with Palladium and Manganese Dioxide Nanoparticles. ACS Sustainable Chem. Eng. 2018, 6, 2751-2757, DOI 10.1021/acssuschemeng.7b04435. (16) Liu, Y.; Yao, W.; Liu, D.; Zong, R.; Zhang, M.; Ma, X.; Zhu, Y., Enhancement of Visible Light Mineralization Ability and Photocatalytic Activity of BiPO4/BiOI. Appl. Catal., B 2015, 163, 547-553, DOI 10.1016/j.apcatb.2014.08.039. (17) Dong, F.; Xiong, T.; Sun, Y.; Zhao, Z.; Zhou, Y.; Feng, X.; Wu, Z., A Semimetal Bismuth Element as a Direct Plasmonic Photocatalyst. Chem. Commun. 2014, 50, 10386-10389, DOI 10.1039/c4cc02724h. (18) He, R.; Xu, D.; Cheng, B.; Yu, J.; Ho, W., Review on Nanoscale Bi-Based Photocatalysts. Nanoscale Horiz. 2018, 3, 464-504, DOI 10.1039/C8NH00062J. (19) Huo, Y.; Hou, R.; Chen, X.; Yin, H.; Gao, Y.; Li, H., BiOBr Visible-Light Photocatalytic Films in a Rotating Disk Reactor for the Degradation of Organics. J. Mater. Chem. A 2015, 3, 14801-14808, DOI 10.1039/C5TA03279B. (20) Wu, J.; Li, X.; Shi, W.; Ling, P.; Sun, Y.; Jiao, X.; Gao, S.; Liang, L.; Xu, J.; Yan, W.; Wang, C.; Xie, Y., Efficient Visible-Light-Driven CO2 Reduction Mediated by Defect-Engineered BiOBr Atomic Layers. Angew. Chem. 2018, 130, 8855-8859, DOI 10.1002/anie.201803514. (21) Jun, L.; Xiaoyong, W.; Wenfeng, P.; Gaoke, Z.; Hong, C., Vacancy-Rich Monolayer BiO2−x as a Highly Efficient UV, Visible, and Near-Infrared Responsive Photocatalyst. Angew. Chem. 2018, 57, 491-495, DOI 10.1002/anie.201708709. (22) Trogadas, P.; Parrondo, J.; Ramani, V., CeO2 Surface Oxygen Vacancy Concentration Governs in Situ Free Radical Scavenging Efficacy in Polymer Electrolytes. ACS Appl. Mater. Inter. 2012, 4, 5098-5102, DOI 10.1021/am3016069. (23) Li, R.; Liu, J.; Zhang, X.; Wang, Y.; Wang, Y.; Zhang, C.; Zhang, X.; Fan, C., Iodide-Modified Bi4O5Br2 Photocatalyst with Tunable Conduction Band Position for Efficient Visible-Light Decontamination of Pollutants. Chem. Eng. J. 2018, 339, 42-50, DOI 10.1016/j.cej.2018.01.109. (24) Huang, Y.; Li, K.; Lin, Y.; Tong, Y.; Liu, H., Enhanced Efficiency of 17



Electron-Hole Separation in Bi2O2CO3 for Photocatalysis via Acid Treatment. ChemCatChem 2018, 10, 1982-1987, DOI 10.1002/cctc.201800101. (25) Bi, W.; Ye, C.; Xiao, C.; Tong, W.; Zhang, X.; Shao, W.; Xie, Y., Spatial Location Engineering of Oxygen Vacancies for Optimized Photocatalytic H2 Evolution Activity. Small 2014, 10, 2820-2825, DOI 10.1002/smll.201303548. (26) Huang, Y.; Li, H.; Balogun, M.-S.; Liu, W.; Tong, Y.; Lu, X.; Ji, H., Oxygen Vacancy Induced Bismuth Oxyiodide with Remarkably Increased Visible-Light Absorption and Superior Photocatalytic Performance. ACS Appl. Mater. Inter. 2014, 6, 22920-22927, DOI 10.1021/am507641k. (27) Huang, Y.; Long, B.; Li, H.; Balogun, M.-S.; Rui, Z.; Tong, Y.; Ji, H., Enhancing the Photocatalytic Performance of BiOClxI1−x by Introducing Surface Disorders and Bi Nanoparticles as Cocatalyst. Adv. Mater. Interfaces 2015, 2, 1500249-1500256, DOI 10.1002/admi.201500249. (28) Fan, W.; Li, H.; Zhao, F.; Xiao, X.; Huang, Y.; Ji, H.; Tong, Y., Boosting the Photocatalytic Performance of (001) BiOI: Enhancing Donor Density and Separation Efficiency of Photogenerated Electrons and Holes. Chem. Commun. 2016, 52, 5316-5319, DOI 10.1039/C6CC00903D. (29) Huang, Y.; Li, H.; Fan, W.; Zhao, F.; Qiu, W.; Ji, H.; Tong, Y., Defect Engineering of Bismuth Oxyiodide by IO3– Doping for Increasing Charge Transport in Photocatalysis. ACS Appl. Mater. Inter. 2016, 8, 27859-27867, DOI 10.1021/acsami.6b10653. (30) Jiao, Z.; Zhang, Y.; Ouyang, S.; Yu, H.; Lu, G.; Ye, J.; Bi, Y., BiAg Alloy Nanospheres: A New Photocatalyst for H2 Evolution from Water Splitting. ACS Appl. Mater. Inter. 2014, 6, 19488-19493, DOI 10.1021/am506030p. (31) Dong, X. A.; Zhang, W.; Sun, Y.; Li, J.; Cen, W.; Cui, Z.; Huang, H.; Dong, F., Visible-Light-Induced Charge Transfer Pathway and Photocatalysis Mechanism on Bi Semimetal@Defective BiOBr Hierarchical Microspheres. J. Catal. 2017, 357, 41-50, DOI 10.1016/j.jcat.2017.10.004. (32) Wang, H.; Zhang, W.; Li, X.; Li, J.; Cen, W.; Li, Q.; Dong, F., Highly Enhanced Visible Light Photocatalysis and in Situ FT-IR Studies on Bi 18


Page 18 of 21

Page 19 of 21 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


Metal@Defective BiOCl Hierarchical Microspheres. Appl. Catal., B 2018, 225, 218-227, DOI 10.1016/j.apcatb.2017.11.079. (33) Liu, X.; Cao, H.; Yin, J., Generation and Photocatalytic Activities of Bi@Bi2O3 Microspheres. Nano Res. 2011, 4, 470-482, DOI 10.1007/s12274-011-0103-3. (34) Wang, S.; Hai, X.; Ding, X.; Chang, K..; Xiang, Y.; Meng, X.; Yang, Z.; Chen, H.; Ye, J., Light-Switchable Oxygen Vacancies in Ultrafine Bi5O7Br Nanotubes for Boosting Solar-Driven Nitrogen Fixation in Pure Water. Adv. Mater. 2017, 29, 1701774-1701781, DOI 10.1002/adma.201701774. (35) Huang, Y.; Li, K.; LI, S.; Lin, Y.; Liu, H.; Tong, Y., Ultrathin Bi2MoO6 Nanosheets for Photocatalysis: Performance Enhancement by Atomic Interfacial Engineering. ChemistrySelect 2018, 3, 7423-7428, DOI 10.1002/slct.201800908. (36) Ketterer, J.; Krämer, V., NOTIZEN. Darstellung und Kristalldaten der isotypen Wismut-Oxid -Halogenide Bi5O7I und Bi5O7Br/Preparation and Crystal Data of the Isotypic Bismuth Oxide Halides Bi5O7I and Bi5O7Br. Z. Naturforsch. B, 1984, 39, 105. (37) Wang, S.; Chen, P.; Bai, Y.; Yun, J. H.; Liu, G.; Wang, L., New BiVO4 Dual Photoanodes with Enriched Oxygen Vacancies for Efficient Solar-Driven Water Splitting. Adv. Mater. 2018, 30, 1800486-1800493, DOI 10.1002/adma.201800486. (38) Bao, J.; Zhang, X.; Fan, B.; Zhang, J; Zhou, M.; Yang, W.; Hu, W.; Wang, H.; Pan, B.; Xie, Y., Ultrathin Spinel‐Structured Nanosheets Rich in Oxygen Deficiencies for Enhanced Electrocatalytic Water Oxidation. Angew. Chem. 2015, 54, 7399-7404, DOI 10.1002/ange.201502226. (39) Xiong, J.; Di, J.; Xia, J.; Zhu, W.; Li, H., Surface Defect Engineering in 2D Nanomaterials for Photocatalysis. Adv. Funct. Mater. 2018, 28, 1801983-1801202, DOI 10.1002/adfm.201801983. (40) Su, Y.; Ding, C.; Dang, Y.; Wang, H.; Ye, L.; Jin, X.; Xie, H.; Liu, C., First Hydrothermal Synthesis of Bi5O7Br and Its Photocatalytic Properties for Molecular Oxygen Activation and RhB Degradation. Appl. Surf. Sci. 2015, 346, 311-316, DOI 10.1016/j.apsusc.2015.04.021. (41) Yan, T.; Tian, J.; Guan, W.; Qiao, Z.; Li, W.; You, J.; Huang, B., Ultra-Low 19



Page 20 of 21

Loading of Ag3PO4 on Hierarchical In2S3 Microspheres to Improve the Photocatalytic Performance: The Cocatalytic Effect of Ag and Ag3PO4. Appl. Catal., B 2017, 202, 84-94, DOI 10.1016/j.apcatb.2016.09.017. (42) Li, A.; Chang, X.; Huang, Z.; Li, C.; Wei, Y.; Zhang, L.; Wang, T.; Gong, J., Thin Heterojunctions and Spatially Separated Cocatalysts To Simultaneously Reduce Bulk and Surface Recombination in Photocatalysts. Angew. Chem. 2016, 128, 13938-13942, DOI 10.1002/anie.201607765. (43) Li, Z.; Qu, Y.; Hu, K.; Humayun, M.; Chen, S.; Jing, L., Improved Photoelectrocatalytic Activities of BiOCl with High Stability for Water Oxidation and MO Degradation by Coupling RGO and Modifying Phosphate Groups to Prolong Carrier

Lifetime.

Appl.

Catal.,

B

2017,

203,

355-362,

DOI

10.1016/j.apcatb.2016.10.045. (44) Xie, Y.-S.; Yuan, L.; Zhang, N.; Xu, Y.-J., Light-Tuned Switching of Charge Transfer Channel for Simultaneously Boosted Photoactivity and Stability. Appl. Catal., B 2018, 238, 19-26, DOI 10.1016/j.apcatb.2018.07.006. (45) Di, J.; Xia, J.; Ji, M.; Wang, B.; Sheng, Y.; Qi, Z.; Chen, Z.; Li, H., Advanced Photocatalytic Performance of Graphene-like BN Modified BiOBr Flower-Like Materials for the Removal of Pollutants and Mechanism Insight. Appl. Catal., B 2016, 183, 254-262, DOI 10.1016/j.apcatb.2015.10.036. (46) Huang, H.; Li, X.; Wang, J.; Dong, F.; Chu, P. K.; Zhang, T.; Zhang, Y., 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. (47) Tilocca, A.; Selloni, A., O2 and Vacancy Diffusion on Rutile(110): Pathways and

Electronic

Properties.

ChemPhysChem

2005,

6,

1911-1916,

DOI

10.1002/cphc.200400570. (48) Wang, K.; Zhang, G.; Li, J.; Li, Y.; Wu, X., 0D/2D Z-Scheme Heterojunctions of Bismuth Tantalate Quantum Dots/Ultrathin g-C3N4 Nanosheets for Highly Efficient Visible Light Photocatalytic Degradation of Antibiotics. ACS Appl. Mater. Inter. 2017, 9, 43704-43715, DOI 10.1021/acsami.7b14275. 20


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TOC

The novel defective Bi/Bi5O7Br nanotubes demonstrated high efficiency for photocatalytic oxidation of phenol.

21


Glucose-Induced Formation of Oxygen Vacancy and Bi-Metal

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