Construction And Photocatalytic Properties Of Zn_xCd_1-xS And Its Heterojunction

With the development of industrialization,the problem of water pollution has become increasingly prominent.Photocatalytic degradation of pollutants by semiconductors is one of the widely used green and pollution-free methods.CdS is widely used in the field of photocatalysis because of its moderate band gap,but it has the phenomenon of photochemical corrosion,high recombination efficiency of photogenerated carriers and poor photocatalytic performance.In order to improve the shortcomings of CdS materials,Zn²⁺was doped to improve the photo corrosion phenomenon and stability of CdS,and then the materials with heterojunction structure were constructed with Ti O₂,WS₂ and Mo S₂.The composition of the material was characterized by XRD,the morphology and size of the photocatalyst were observed by SEM and TEM,the absorption band edge,photogenerated carrier recombination efficiency and interfacial electron migration rate of the composite were studied by UV-Vis DRS,PL and EIS methods,and the degradation of methylene blue（MB）by the photocatalyst was observed by degradation experiment.Finally,the photocatalytic mechanism was studied by radical quenching.Zn_xCd_1-xS photocatalyst was prepared by coprecipitation-hydrothermal method.The crystal structure was consistent with that of CdS with cubic zinc blende structure.After doping Zn²⁺,the recombination efficiency of photogenerated carriers of CdS was reduced and the electron transfer rate was improved.The prepared Zn_0.5Cd_0.5S has good degradation effects on different dyes（MB,methyl orange,rhodamine B,malachite green and crystal violet）.At 240 min,Zn_0.5Cd_0.5S has the best photocatalytic degradation effect on 10 mg/L MB,reaching to 77.45%,and the reaction rate constant is 0.007 min^-1,4.38 and 5.38 times that of CdS and Zn S,respectively.The active group in the degradation process is superoxide radical（O₂^-·）.After doping Zn²⁺,the stability of CdS has also been greatly improved,and the photocatalytic effect is 60.18%after four cycles.TiO₂/Zn_0.5Cd_0.5S,WS₂/Zn_0.5Cd_0.5S and Mo S₂/Zn_0.5Cd_0.5S photocatalysts were prepared by coprecipitation-hydrothermal method.After the heterojunction structure was formed,the band gap of the materials decreased in varying levels.Mo S₂/Zn_0.5Cd_0.5S photocatalyst has the best absorption of visible light,and its electron-hole pairs recombination efficiency is very low.The photocatalytic degradation performance of MB is improved by the three photocatalytic materials.At 240 min,the decolorization rate of MB with 90%-Ti O₂/Zn_0.5Cd_0.5S reaches to94.2%,and the reaction rate constant is 0.0142 min^-1,which is 2.1 times and 11.9times that of Zn_0.5Cd_0.5S and Ti O₂,respectively.The free radical in the degradation process is O₂^-·.At 240 min,the decolorization rate of WS₂/Zn_0.5Cd_0.5S composite reaches to 92.6%,and the reaction rate constant is 0.013 min^-1,which is 1.86 times and 5.4 times that of Zn_0.5Cd_0.5S and WS₂,respectively.The free radicals in the degradation process are O₂^-·and hydroxyl radical（·OH）.In the process of photocatalytic degradation of 100 mg/L MB,the degradation effect of 97%-Mo S₂/Zn_0.5Cd_0.5S reaches to 98.46%,and the degradation rate is 0.0243 min^-1.Compared with the two substrates,the adsorption effect is greatly improved,the adsorption effect reaches to 24.98%within 60 minutes of dark adsorption,and the free radical in the degradation process is O₂^-·.