Preparation And Photoelectrocatalytic Properties Of Zn₂SnO₄ Composite Electrode

Due to the development of industry and urbanization,a large amount of organic pollutant has been discharged,which has caused the environmental pollution problem to become more and more serious.It is difficult to be completely removed by conventional methods,therefore advanced oxidation processes are required.Among them,photoelectrocatalysis（PEC）uses an applied voltage to assist photocatalysis,which has the characteristics of photocatalysis and electrocatalysis,and is an effective method for environmental remediation.In the process of photoelectrocatalysis,the most important thing is to select a stable and efficient photocatalyst.Metal oxide semiconductors are usually used as photocatalysts.Among them,Zn₂SnO₄（ZTO）is a typical ternary n-type semiconductor with a band gap of 3.6 e V and is characterized by high conductivity,chemical stability,non-toxicity,and can be used in acids/alkali and organic solvents.Compare to traditional Ti O₂ semiconductors,the electron transfer rate of ZTO is higher.The large band gap of ZTO illustrates the powerful redox capability,however,it can barely absorb and utilize most of the energy in a visible light region that accounts for about 44%of the solar spectrum.Therefore,the construction and synthesis of ZTO-based photoelectro-catalyst which can utilize visible light have become a popular reseach direction.The modification of ZTO with composite narrow bandgap semiconductor materials and/or metal compounds is the most effective strategies to utilize visible light and reduce the combination rates of photo-exicted charge carriers.In this research,MoS₂ with flake structure,reduced graphene oxide（rGO）,plasma Ag/AgCl and Ag/AgBr are successively combined with ZTO to form ZTO/MoS₂/Ag/AgCl and ZTO/rGO/Ag/AgBr photocatalysts and prepare the electrodes by scrape coating method and then applied to the photoelectrocatalytic process.The sample was characterized by XRD,XPS,SEM,UV-Vis DRS,PL,transient photocurrents,and EPR.In this way,its phase composition,microscopic morphlogy,light absorption range,photoelectrochemical properties,photoelectrocatalytic performance and photoelectrocatalytic mechanism are systematically analyzed.According to the experimental results,the following conclusion can be drawn:（1）In the preparation and characterization of the ZTO/MoS₂/Ag/AgCl electrode,when the loading amount of MoS₂ is constant,and the loading amount of Ag/AgCl is 5%,the photoresponse range,carrier recombination and degradation efficiency of methylene blue by ZTO/MoS₂/Ag/AgCl electrode have reached the best results.The SPR effect of the Ag component in the plasma Ag/AgCl can effectively extend the light absorption range and suppress the recombination of carriers,while the MoS₂ component can adsorb a large number of pollutant molecules due to its flake-like structure,and it can also be functioned as an electron mediator in the ZTO/MoS₂/Ag/AgCl multi-component system to accelerate the transfer of electrons.The electrode can exhibit extraordinary photoelectrocatalytic activity by degrading Methylene Blue（MB）of 96.5%within 2 h.It also has good stability and can be used to cyclically degrade pollutants.（2）In the preparation and characterization of ZTO/rGO/Ag/AgBr electrodes,changes in hydrothermal temperature caused changes in the morphology of ZTO,so its band structure also changed,which is more conducive to the use of visible light energy by ZTO.In this study,when the loading of rGO is constant and the loading of Ag/AgBr is 2.5%,the photoresponse range,carrier recombination and degradation efficiency of methylene blue by the ZTO/rGO/Ag/AgBr electrode are all optimal.The SPR effect of Ag in Ag/AgBr can enhance the visible light absorption capacity of the electrode and effectively restrain the recombination of carriers.The rGO component can be used as an electron mediator in the ZTO/rGO/Ag/AgBr multi-component system and the electron transfer is accelerated.In addition,the introduction of rGO can produce·O₂^-during the photoelectrocatalytic degradation process,so the electrode has better photoelectrocatalytic activity for phenol than the ZTO/MoS₂/Ag/AgCl electrode.This research provides expectional insights for the use of zinc stannate-based materials for environmental remediation.