Fabrication And Photocatalytic Performance Of Zn-Sn Based Semiconductor Heterojunction Photocatalysts

Water pollution has become one of the most important issues to be addressed in today’s society.Zinc stannate（Zn₂SnO₄）photocatalysts are widely used for the degradation of organic pollutants in water.However,the wide band gap of Zn₂SnO₄ and the rapid compounding of photogenerated carriers limit its application in photocatalysis.To improve its performance of photocatalysis,two kinds of Zn₂SnO₄ and a derivative of Zn₂SnO₄heterojunction photocatalysts are constructed in this paper.And their morphology,structure,photoelectrochemical properties,degradation performance and mechanism of catalytic degradation are investigated.The details are as follows.（1）SnS/Zn₂SnO₄ photocatalyst（SZS-x）is synthesized by a one-step hydrothermal method.The results show that SnS is successfully attached to the surface of Zn₂SnO₄,and there is a Z-scheme heterojunction between SnS and Zn₂SnO₄.The optimized SZS-6sample exhibits good photocatalytic degradation activity and photogenerated carrier separation ability.It is demonstrated that the Z-scheme heterojunction is formed between SnS and Zn₂SnO₄,and the present of SnS effectively shortens the band gap of Zn₂SnO₄.And their synergistic effect enhances the light absorption capacity of SZS-6.Meanwhile,SZS-6 shows a stable photocatalytic activity under different pollutants,catalyst amounts,ion concentrations,p H and temperature environments.The degradation mechanism study demonstrates that the hole（h⁺）and superoxide free radical（?O₂^-）produced by this catalyst under light are the main active species for methylene blue（MB）degradation of SZS-6.（2）Zn-Sn-Mo trimetallic sulfides（ZSM-x）are fabricated by direct vulcanizing Zn₂SnO₄ by using ammonium molybdate as the molybdenum source.TEM analysis indicates that the lamellar Mo S₂ is uniformly loaded with Zn S/SnS nanoparticles,and their interfaces are tightly combined.Results demonstrate that the formation of Zn S/SnS/Mo S₂double heterojunctions within ZSM-x accelerates the charge separation and transfer of ZSM-x catalysts to increase the electron transfer rate.The degradation experiments shows that ZSM-x exhibits great degradation activity for MB under visible light.The ZSM-15 has the best performance.Its removal rate of MB achieves 99.5%within 50 min,corresponding to 0.0994 min^-1 of rate constant k.The mechanism study shows that the electrons（e^-）and hydroxyl radicals（·OH）dominate the degradation of MB.（3）Zn₂SnO₄/Ti₃C₂（ZTC-x）is prepared by electrostatic adsorption of positively charged Zn₂SnO₄ polyhedral nanoparticles and negatively charged Ti₃C₂ ultra-thin nanosheets via an ultrasound-assisted method.The degradation experiment displays that the degradation rate of ZTC-4 is 0.0537 min^-1 for MB,which is approximately 16.8 times that of Ti₃C₂ and 26.8 times that of Zn₂SnO₄.This is due to the good light response capacity and metal-like property of black Ti₃C₂ itself,which enhances the light trapping ability and electrical conductivity of ZTC-4.Meanwhile,the Schottky barrier between Ti₃C₂ and Zn₂SnO₄ effectively accumulates electrons,and enhances the carrier transfer rate of Zn₂SnO₄,inhibits the rapid recombination of photogenerated electron-hole and greatly improves the photocatalytic degradation activity of Zn₂SnO₄.