Preparation And Photocatalytic Properties Of Phosphotungstate/Ag/ZnO Composite

Heteropoly acid is a typical polyoxometalate.Because of its special acidity,controllable structure,reversible redox and diverse composition,it has been widely used in catalytic degradation of organic pollutants in water.In this paper,PW₁₂/Ag/ZnO nanocomposites were successfully prepared,and their photocatalytic performance and photocatalytic mechanism were tested under simulated visible light conditions.The main research work is as follows:Firstly,saturated Keggin phosphotungstate PW₁₂heteropoly acid precursor was successfully prepared by hydrothermal synthesis.The structure of heteropoly acid was characterized by FT-IR,SEM and UV-vis.The absorption range is in ultraviolet region,and the band gap width is 3.02eV.Secondly,Ag nitrate was reduced by photoinduced transformation method with sodium citrate and sodium borohydride as reducing agents.Ag nanoparticles with different absorption ranges were prepared by using polyvinylpyrrolidone（PVP）as template under the irradiation of tungsten lamp.Combined with SEM,UV-vis and other characterization techniques,the relationship between the morphology and size of silver nanomaterials and the light absorption range was systematically discussed.Finally,cubic nano-silver material synthesized by 24 h illumination was selected,with a particle size of about 70 nm and a light absorption range of near infrared light.Then we used sol-gel method to reduce zinc acetate with sodium hydroxide,and successfully synthesized nano ZnO material.The structure of ZnO was systematically detected by XRD,IR,UV and other characterization methods.The absorption range is near visible light,and the band gap width is 3.25 e V.The PW₁₂/Ag composite was successfully prepared by compounding heteropoly acid precursor with silver by in situ growth method.The structure of composite materials was detected by infrared,ultraviolet,XRD and other characterization techniques.With the prepared composite material as photocatalyst,the photocatalytic experiment of rhodamine B（Rh B）dye was carried out under the simulated sunlight condition.The results of photocatalytic degradation experiments show that the optimum conditions for photocatalytic degradation of composite PW₁₂/Ag are p H=6,catalyst dosage 0.2 g/L,dye concentration 50 mg/L,and the decolorization rate reaches 97.72%.According to the mechanism test and cyclic voltammetry test,the catalytic mechanism of the composite was preliminarily discussed.The heteropoly acid/zinc oxide composite was prepared by compounding heteropoly acid with nano zinc oxide by chemical synthesis.The structure of the composite was detected and analyzed by infrared,ultraviolet and XRD.And explore the best compound ratio of zinc oxide.Finally,the heteropoly acid/silver/zinc oxide composite was prepared by chemical synthesis,and the structure of the composite was detected and analyzed by infrared,ultraviolet and XRD.Under the simulated visible light condition,the prepared heteropoly acid composite was used as photocatalyst to carry out photocatalytic experiments on rhodamine B（Rh B）dye.The results of photocatalytic degradation experiments show that the optimum conditions for photocatalytic degradation of composite PW₁₂/Ag/ZnO are p H=6,catalyst dosage 0.2 g/L,dye concentration 50mg/L,and the decolorization rate reaches 99.93%.The results of comparative photocatalytic experiments before and after composite photocatalyst showed that the prepared composite materials had good catalytic activity and stability,and the catalytic activity remained high after three photocatalytic cycle experiments.The relationship between the catalytic performance of photocatalyst and the microstructure of catalyst was obtained through analysis,and the catalytic mechanism of the heteropoly acid composite material was preliminarily discussed.