Preparation Of Bismuth Tungstate Based Composite Material And Study On Its Photocatalytic Degradation Performance

With the rapid development of economy and industry,environment and energy issue must be faced and valued in the 21st century.Semiconductor photocatalytic degradation technology,using the inexhaustible and clean solar energy,is one of the core means to solve the environmental and energy problems.Especially in recent years,the development of semiconductor photocatalytic degradation technology has been very rapid.On the one hand,the mechanism of semiconductor photocatalysis has been explored from a theoretical point of view.On the other hand,many semiconductor photocatalytic products have been used in practical applications.However,traditional semiconductor photocatalysts such as Ti O₂ have some shortcomings,for example wide band gap and only response to the ultraviolet part of sunlight.Therefore,new semiconductor photocatalysts with excellent properties are the focus of current research.Bismuth tungstate(Bi₂WO₆)is considered to be the most promising semiconductor photocatalyst among Bi-based oxides because of the narrow band gap,visible light response and simple preparation method.However,the performance of the single semiconductor photocatalyst is still insufficient,and the most conventional semiconductor modification method is semiconductor compounding,combined with element doping,morphology control and other techniques to obtain a highly active semiconductor photocatalyst.Therefore,the bismuth tungstate composite material was prepared in this thesis based on bismuth tungstate.In this thesis,firstly,the Bi₂WO₆ and Cl doped g-C₃N₄（Cl CN）were synthesized.And the Cl CN/Bi₂WO₆ heterojunction with Bi₂WO₆ as the substrate was prepared by ultrasonic mechanical mixing strategy.The physical-chemical properties of the heterojunction were characterized by XRD,SEM,TEM,HR-TEM,EDS,FT-IR,XPS,UV-vis,PL,time-photocurrent,EIS,Mott-Schottky and Tafel measurements.The photocatalytic activity had been evaluated with methyl orange as the pollutant.The Cl CN/Bi₂WO₆ heterojunction exhibited the highest photocatalytic performance when the proportion of Cl CN was 10%.Besides,the degradation rate of 10%Cl CN/Bi₂WO₆(500 mg L^-1)to 15 mg L^-1 methyl orange reached more than 99%within 60 min under visible light irradiation.As a contrast,the photodegradation efficiency of Bi₂WO₆ was only 38%at the same conditions.It found that the heterojunction material coupled by Bi₂WO₆ and Cl CN could greatly improve the photocatalytic degradation efficiency.Finally,a free radical trap was added into the reaction system to explore the effective free radicals in the photocatalytic reaction process and build a photocatalytic mechanism model.Owing to the unique properties of three-dimensional（3D）ordered macroporous materials as photocatalysts,the 3D-Bi₂O₃/Bi₂WO₆ p-n heterojunction was prepared through the colloidal crystal template method.And the properties of the heterojunction were characterized using Laser particle sizer,XRD,SEM,EDS,TEM,HR-TEM,FTIR,XPS,BET,UV-vis,PL,time-photocurrent,EIS,Mott-Schottky and Tafel measurements.The photocatalytic activity of the p-n heterojunction has been evaluated with methyl orange as the pollutant.The 3D-Bi₂O₃/Bi₂WO₆ heterojunction exhibited the highest photocatalytic performance when the proportion of Bi₂O₃ was20%.Besides,the degradation rate of 3D-20%Bi₂O₃/Bi₂WO₆(500 mg L^-1)to 15 mg L^-1 methyl orange reached more than 96%within 40 min under visible light irradiation.However,the photodegradation efficiency of Bi₂WO₆ was only 24%under the same conditions.It could be seen that the Bi₂O₃/Bi₂WO₆ heterojunction material with 3DOM structure could greatly improve its photocatalytic degradation efficiency.Finally,a free radical trap was used to explore the effective free radicals in the photocatalytic reaction process and build a photocatalytic mechanism model.