Preparation And Properties Of Bismuth Tungstate Composite Photocatalyst

With the rapid development of economy,the increasingly serious problems of environmental pollution and energy shortage pose a great threat to the sustainable development of mankind.Photocatalytic technology has the advantages of high catalytic activity,energy saving,environmental protection and so on.It has outstanding advantages in energy conversion and environmental management.Bismuth-based photocatalysts have attracted much attention because of their unique photocatalytic activity,good thermal stability and narrow band gap.Among bismuth catalysts,Bi₂WO₆is considered as a promising visible light catalytic material due to its non-toxic and narrow band gap（～2.7 e V）.However,pure Bi₂WO₆has some problems,such as small specific surface area,low electron transport efficiency,low visible light utilization rate,and easy photogenic carrier recombination,which affect its photocatalytic activity.In this paper,Bi₂WO₆is taken as the research object and its modification is studied.The main research contents are as follows:（1）With Bi（NO₃）₃·5H₂O and Na₂WO₄·2H₂O as raw materials,a series of Bi₂WO₆samples were prepared by hydrothermal method and one-step precipitation method,and the photocatalytic activity of the synthesized samples under different solvent conditions was discussed.The photocatalytic activity of rhodamine B（Rh B）was studied to simulate the pollutant.The samples were characterized by XRD,SEM,BET and other methods.The results show that the photocatalytic activity of Bi₂WO₆prepared by hydrothermal method is better than that prepared by precipitation method.Among them,the sample prepared with glacial acetic acid as the solvent had the best photocatalytic effect.After 90 min of sunlight irradiation,the Rh B removal rate of 8 mg/L reached 98.27%.The catalyst maintained good stability after three cycles of use,which had practical application value.（2）Using Na₂WO₄·2H₂O,Bi（NO₃）₃·5H₂O,Ag NO₃and CTAB as raw materials,AgBr/Bi₂WO₆composite photocatalyst was synthesized by two-step precipitation method,and the effects of Ag/Bi ratio and stirring time on the photocatalytic activity of the sample were discussed.The AgBr/Bi₂WO₆composite powders were characterized by means of XRD,SEM,BET and UV-Vis,etc.The suitable addition amount of catalyst and the cyclic stability of photocatalytic degradation process were investigated.The active species which played a major role in the photocatalytic reaction process were determined by free radical capture experiment.The results showed that the catalyst had the best performance when the mixing time was 0.5 h and the mass percentage of Ag/Bi was 10%.The photocatalyst degradability of 8 mg/L Rh B solution reached 67.5%when the sunlight was irradiated for 20 min.The degradation rate was 80.3%after 40 min of illumination.The degradation rate reached 96.8%after 90 min of illumination,and the catalyst remained high activity after 4 times of recycling.（3）Using Na₂WO₄·2H₂O,Bi（NO₃）₃·5H₂O,Ag NO₃,Na₂CO₃and CTAB as raw materials,Ag₂CO₃/AgBr/Bi₂WO₆photocatalyst was prepared by two-step precipitation method.By means of XRD,SEM,BET,TEM,HRTEM and EDS,the characterization of Ag₂CO₃/AgBr/Bi₂WO₆was carried out to determine the composition,morphology and specific surface area of the sample.The effects of reaction time and solvent on the photocatalytic properties of synthetic products were studied.The degradation ability of photocatalyst to Rh B with different initial concentration and different pollutants was investigated.The main active species in photocatalytic degradation process were determined by free radical capture experiment,and the photocatalytic reaction mechanism was preliminarily inferred.The results showed that the synthesized Ag₂CO₃/AgBr/Bi₂WO₆composite photocatalyst had the best performance when the reaction solvent was 36%acetic acid,the precursor Bi₂WO₆stirred for 1.5 h and the composite stirred for 2.5 h.The degradation rate of 8 mg/L Rh B over the composite photocatalyst reached 71.9%after 20 min exposure to etheric sunlight.The degradation rate was 88.5%after 40 min of illumination.The degradation rate was 96.4%after 90 min of illumination.The composite photocatalyst has good cycling stability,and the degradation rate is still 62.1%after 4 cycles.