Preparation, Modification And Properties Of Bismuth Tungstate-based Heterojunction Photocatalysts

Photocatalytic technology is a kind of green and high-efficiency treatment of water pollutants,which shows a good application prospect in the degradation of organic pollutants.In recent years,Bi2WO6 has attracted much attention as a new type of photocatalytic material with bismuth-based layered perovskite structure,but due to its internal structure,photo-generated electron-hole pairs are liable to recombine.Therefore,the construction of high-efficiency semiconductor photocatalysts that can expand the photoresponse range,increase the photocarrier generation,and suppress photocarrier recombination is the main subject for further research and attention by researchers.In this paper,a binary heterojunction SiO2/Bi2WO6 photocatalyst was synthesized by using a wind band gap SiO2;a ternary heterojunction SiO2/Bi2WO6/TiO2 photocatalyst was jointly synthesized by using a wind band gap SiO2 and TiO2;and finally modified by metal Ag nanoparticles Bi2WO6-based heterojunction photocatalysts,Ag/Bi2WO6/TiO2,SiO2/Ag/Bi2WO6 and SiO2/Ag/Bi2WO6/TiO2 composites were hydrothermally synthesized.XRD,SEM,EDS,TEM,HRTEM,XPS,UV-vis and other testing methods were used to characterize and analyze the phase structure,micromorphology,and optical characteristics of the synthesized samples.With Rhodamine B as the target to degrade the pollutants,the photocatalytic performance of the synthesized samples was tested with a UV spectrophotometer under a xenon lamp(equipped with a 420 nm filter).The specific research contents of this thesis are as follows:(1)SiO2/Bi2WO6 and SiO2/Bi2WO6/TiO2 composite photocatalysts were synthesized by hydrothermal method and impregnation method,and then SiO2 was etched away with KOH to form a Bi2WO6 photocatalyst for comparison.XRD,SEM,TEM,HRTEM and XPS are used to characterize and analyze the phase structure,morphology and chemical composition of synthetic samples.XRD and SEM data show that the heterojunction structure does not affect the crystal structure and microstructure of Bi2WO6.appear.With rhodamine B as the degradation target,the effects of SiO2/Bi2WO6 binary heterojunction photocatalyst and SiO2/Bi2WO6/TiO2 ternary heterojunction photocatalyst on the photodegradation of organic pollutants were studied under the irradiation of xenon lamp.The results show that in the synthesized samples,the SiO2/Bi2WO6/TiO2 composite photocatalyst exhibits the best photocatalytic performance for RhB dyes.After 120 minutes of exposure,the degradation efficiency of RhB can reach 87.1%.Finally,we analyzed the reason for the enhanced activity of SiO2/Bi2WO6/TiO2 heterojunction photocatalysts due to the synergy between SiO2,TiO2 and Bi2WO6.The formation of a heterojunction between SiO2,TiO2 and Bi2WO6 can inhibit photo-generated electrons,the recombination of holes and the wind band gap characteristics of SiO2 form a unidirectional electron-hole pair transfer,thereby maintaining the reducibility and reducing the redox capacity.The reduction in the photocatalytic activity is improved.(2)In order to further improve the photocatalytic activity of the Bi2WO6 photocatalyst,Ag/Bi2WO65 Ag/Bi2WO6/TiO25 SiO2/Bi2WO6/TiO2 and SiO2/Ag/Bi2WO6/TiO2 composite materials were synthesized by hydrothermal and impregnation methods of Ag nanoparticle-modified Bi2WO6 based heterojunction photocatalyst.XRD,SEM,EDS,TEM,HRTEM,XPS were used to characterize and analyze the phase structure,morphology,and chemical composition of the synthesized samples.XRD and SEM data showed that the modification of Ag nanoparticles did not change the structural and morphological of original composite material.Under the irradiation of xenon lamp,with Rhodamine B as the target to degrade the pollutants,the effect of heterostructure modified by Ag nanoparticles on the photocatalytic activity of photocatalyst was investigated.The results show that the photocatalytic activity of heterojunction photocatalysts modified by Ag nanoparticles is significantly improved.Finally,we analyze that the photocatalytic activity of Ag/Bi2WO6/TiO2,SiO2/Bi2WO6/TiO2 and SiO2/Bi2WO6/TiO2 heterojunction photocatalysts is enhanced by the plasma effect of Ag nanoparticles.As an electron trap,it mainly collects Electron;The injection of hot electrons makes Ag and TiO2 build a built-in electric field inside Bi2WO6 to suppress the recombination of photo-generated carriers,resulting in enhanced photocatalysis activity.