Investigation On Preparation And Photocatalytic Properties Of Zn_xCdi_1-xS Solid Solution-based Heterojunctions

Photocatalytic degradation of pollutants and hydrogen production by utilizing solar energy is an important way to solve the environmental pollution and energy crisis.As a novel photocatalytic material,Zn_x Cd_1-x-x S solid solution has attracted more and more attention in recent years due to its unique band potential.However,the photocatalytic activity and photocatalytic stability of most sulfides are still poor.In this paper,Zn_x Cd_1-x-x S?x=0,0.1,0.3,0.5,0.7,0.9,1?was prepared by hydrothermal method,and then combined with other semiconductors?g-C₃N₄,BiOBr?to construct a semiconductor heterojunction.Accelerate the transfer of photogenerated carriers,reduce the photogenerated electron-hole combination,and increase the photocatalytic activity and photostability.Finally,methylene?MB?was used as the degradation pollutant to study the photocatalytic properties of Zn_x Cd_1-x-x S solid solution,g-C₃N₄/Zn_0.5Cd_0.5S and Zn_0.5Cd_0.5S/BiOBr heterojunction.First of all,the Zn_x Cd_1-x-x S solid solution was synthesized by changing the stoichiometric ratio of Zn²⁺to Cd²⁺and using a coprecipitation-hydrothermal method.The results show that the structure of Zn_x Cd_1-x-x S is cubic sphalerite solid solution,which is not only a simple mixture of CdS and ZnS.With the increase of the stoichiometric ratio of Zn²⁺,the light absorption wavelength shifts blue,the band gap width increases gradually,and the photogenerated carrier separation and mobility decrease.When the hydrothermal temperature is 120°C,Zn_0.5Cd_0.5S has the highest efficiency for photocatalytic degradation of MB,reaching 85.54%.And the photocatalytic degradation process accorded with the first-order kinetic model,and the degradation rate was 0.00922 min^-1.Second,the g-C₃N₄/Zn_0.5Cd_0.5S heterojunction photocatalyst was fabricated by in-situ growth technique using the solid solution of Zn_0.5Cd_0.5S with the highest photocatalytic efficiency.The results show that when the mass ratio of g-C₃N₄ reaches 50%,Zn_0.5Cd_0.5S wrapped on the surface of g-C₃N₄ forms core-shell heterojunction structure.The test results show that when the mass ratio of g-C₃N₄ reaches 50%,Zn_0.5Cd_0.5S is coated on the surface of g-C₃N₄ to form a core-shell heterojunction structure,This structure enhances the light absorption of the material while enhancing the separation and migration of photogenerated carriers.As the mass ratio of g-C₃N₄ increases,the forbidden band width of the composite material gradually becomes smaller.The photocatalytic degradation efficiency of 50-CN/ZCS core-shell heterojunction was the highest.The decolorization rate of MB reached 99%at 240 min,and the degradation rate was15.7 times and 3.7 times that of g-C₃N₄ and Zn_0.5Cd_0.5S,respectively.The photocatalytic activity did not decrease significantly after four cycles,and the main active substances involved in the degradation process were h⁺and O₂^-·.Finally,Zn_0.5Cd_0.5S/BiOBr composite photocatalyst was constructed by in-situ growth technique.The test results show that the Zn_0.5Cd_0.5S particles are supported on the surface of BiOBr to form a well-formed heterojunction structure.This structure enhances the light absorption of the material while enhancing the separation and migration of photogenerated carriers.With the increase of Zn_0.5Cd_0.5S content,the light absorption band edge of the composite material first increases or decreases,and the forbidden band width also changes.The photocatalytic degradation efficiency of MB was the highest in 70-ZCS/BiOBr heterojunction and the decolorization rate of MB reached 99.52%at 240 min.The degradation rates were 2.52 and 5 times that of Zn_0.5Cd_0.5S and BiOBr,respectively.After 4 cycles,there was no significant decrease in photocatalytic activity;the main active substances involved in the degradation process were h⁺and·OH.