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Efficient Heterojunctions via the In-Situ Self-Assembly of BiVO4 Quantum Dots on SiC Facets for Enhanced Photocatalysis Da Wang, Lin Huang, Zhongnan Guo, Shifeng Jin, chun jun liu, Wenjun Wang, and Wenxia Yuan ACS Appl. Nano Mater., Just Accepted Manuscript • DOI: 10.1021/acsanm.8b00907 • Publication Date (Web): 16 Aug 2018 Downloaded from http://pubs.acs.org on August 17, 2018
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ACS Applied Nano Materials
Efficient Heterojunctions via the In-Situ Self-Assembly of BiVO4 Quantum Dots on SiC Facets for Enhanced Photocatalysis Da Wanga,b, Lin Huanga, Zhongnan Guoa, Shifeng Jinb, Chunjun Liuc, Wenjun Wangb*, Wenxia Yuana*
a
Department of Chemistry, School of Chemistry and Biological Engineering, University of
Science and Technology Beijing, Beijing, 100083, China. b
Research & Development Center for Functional Crystals, Beijing National Laboratory for
Condensed Matter Physics, Institute of Physics, Chinese Academy of Sciences, Beijing 100190, China. c
TankeBlue CO., LTD., Shinong Building, No.9 Tianrong Street, Daxing District, Beijing 102600,
China
*E-mail addresses:
[email protected] (W. X. Yuan). *E-mail addresses:
[email protected] (W. J. Wang).
Abstract Constructing
highly-efficient
heterojunction
for
photogenerated
charges
separation is essential to photocatalysis for solar energy conversion. In this work, we prepare an efficient photocatalyst, SiC/QD-BiVO4 composite, through in-situ self-assemble method. This effective heterojunction is constructed by controlling QD-BiVO4 orientated deposition on certain facets of SiC. Efficient electron-hole separation is achieved by this heterojunction resulted from the following two effects. One is that the selective distribution of QD-BiVO4 on SiC facets, rather than random deposition, reduces the transfer path-length of photoexcited carriers. The other one is
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that the negative shift of conduction band of BiVO4 quantum dots increases the electric potential difference in built-in field, which accelerates the carriers transfer rate at the interface. Consequently, the O2 production is enhanced to 2096 µmol h-1 g-1 in SiC/QD-BiVO4 photocatalyst. Moreover, the degradation rate of RhB is doubled. Our work exhibits a rational route to prepare environmental-friendly photocatalytic material with potential applications.
Keywords: quantum BiVO4; SiC; Z-scheme system; photocatalysis, self-assembly; orientated deposition
1. Introduction Semiconductor-based photocatalytic process, a clean way for converting the solar energy, is considered as an economic and environment-friendly technology to solve energy crisis for global sustainable development.1-3 Developing an economical and highly active catalyst to replace the toxic metal-included materials is still in urgent need.4-6 SiC, based on its suitable band gap, is one of potential metal-free materials for photocatalytic reactions.7-14 Unfortunately, the activity is unsatisfied because of the large surface charge recombination. Therefore, it is desired to promote the efficient charges separation for improving the photocatalytic reactions. Considerable progresses have been made to solve this issue. Noble metal (such as Pt and Au), reduced graphene and suitable semiconductors are introduced to modify SiC for enhancing electron-hole separation.15-17 In these strategies, forming a heterojunction is proved to be effective for promoting this separation. In this regard,
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materials (TiO2, SnO2) have been successfully utilized for efficient photocatalysis.18,19 Different from the traditional heterojunction, the Z-Scheme heterojunction exhibits spatial charge-separation and redox ability of the excited charges.20 C3N4, CdS, and BiVO4 have been introduced on SiC to establish the Z-scheme heterojunction.21-23 However, the surface charges separation in these composites is still not enough. In this system, the surface charges separation could be achieved by inducing the fast charges transfer at the interface. Some conducting materials (such as Ag in AgPO3/Ag/SiC) were introduced to accelerate the electrons migration at the interface.24,25
Unfortunately,
these
inserted
mediator
usually
became
the
recombination centers of the surface functional charges, which thus inhibited the surface reaction. Recently, quantum-sized semiconductors have attracted wide attentions due to their special properties.26-31 It is reported that the conduction band would be negative shift when the grain of material is decreased to nano-scale.32 That is a potential route by introducing quantum dot (such as BiVO4) on SiC to construct strong electric field heterojunctions, in which the increased band position at the interface that can facilitate the electrons migration without introducing conducting materials. However, this tactic is a neglected investigation as far as we know. Mostly, the quantum dot is randomly distributed on semiconductor surface. The direct Z-scheme in heterojunctions is not functional fully because the excited charges are area-selectively distributed on certain facets in some semiconductors.33,34 Hexagonal SiC have both the polar and non-polar facets. The recent work has reported that the photogenerated holes are preferred to assemble on non-polar {10-10}
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facets while the electrons in polar Si-{0001} facets.35 Prospectively, it is feasible to control quantum dots (BiVO4) distribution on such facets using the anisotropic structure of SiC. In this situation, the excited electrons in QD-BiVO4 will directly recombine with holes in SiC through the Z-scheme system. This would be another favorable process to improve the charges spatial separation that attributed to the reduced transfer path length in Z-scheme system. In this paper, QD-BiVO4 is used to modify the micro-SiC for heterojunction formation. We report a new strategy that is described as in situ self-assembly method, through which the efficient photocatalyst of SiC/QD-BiVO4 composite with orientated deposition can be synthesized. The QD-BiVO4 is orientated deposited on the SiC surface rather than the randomly deposited. Efficient charges separation is achieved based on the effective heterojunction resulted from the particular deposition and thereby leads to a high photocatalysis. The O2 production from water splitting (by 3.5 times (compared to SiC/nano-BiVO4)) and degradation of RhB (two times) based on this composite can be greatly enhanced.
2. Experimental Section 2.1 Preparation of SiC/QD-BiVO4 photocatalysts The composites were synthesized by using in situ hydrothermal method. Typically, 1.3 mmol sodium oleate combined with 0.4 mmol Bi(NO3)3·5H2O were dissolved in 50 mL de-ionized water, named solution A. Meanwhile, 0.4 mmol NH4VO3 combined with SiC was dissolved in 50 mL de-ionized water by mechanically mixing for 15 min, named solution B. And then the solution B and A are
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mixing and stirring for 2 h. It was transferred to a 150 mL autoclave, heated at 100 °C for 12 h and then cool down. The obtained powder were washed by n-hexane and ethanol many times, and then freeze-dried for final production. These SiC/QD-BiVO4 composites were denoted as SiC/QD-BiVO4 (1:x, 0
