Research On The Preparation And Catalytic Property Of Zn_0.5Cd_0.5S/WO₃ Artificial Photosynthesized S-scheme Photocatalyst

Semiconductor photocatalytic technology can realize high-efficient solar energy conversion,it is of great significance for human development to solve the energy shortage and water environmental pollution issues.In this thesis,based on the design idea of artificial photosynthesized S-scheme photocatalyst,Zn_0.5Cd_0.5S/WO₃composite was constructed by using two narrow-gap semiconductors with different dimensions,and the synthesis methods of material was optimized.By First-Principles calculation,component adaptation of composites was predicted and heterojunction electron transfer mechanism was revealed.Combined with the experimental characterization and photocatalytic performance measurements,the dynamic behavior of photogenerated carriers and the photocatalytic mechanism was discussed.In this work,Zn_0.5Cd_0.5S with the best photocatalytic activity was selected as the reduction photocatalyst in a series of Zn_1-xCd_xS solid solution nanorods.Based on the results of First-Principles calculation,WO₃ nanosheets with large specific surface area were selected as the oxidation photocatalyst to construct S-scheme photocatalyst.The Zn_0.5Cd_0.5S/WO₃·H₂O photocatalyst was prepared by one-step hydrothermal method.The electron transfer mechanism of Zn_0.5Cd_0.5S/WO₃·H₂O was investigated by spectroscopic analysis,photoelectron spectroscopy and electrochemical testing.30 m L potassium dichromate solution with a concentration of 40 mg/L and Rhodamine B with a concentration of 5 mg/L were used as contaminant indicators.48 wt%Zn_0.5Cd_0.5S/WO₃·H₂O(ZCSW48 means the mass of WO₃·H₂O accounted for 48 wt%Zn_0.5Cd_0.5S/WO₃·H₂O)was the best high-efficiency S-scheme photocatalyst with the Cr（VI）photoreduction rate of 2.27μmol·s^-1·g_cat.^-1and the Rh B photooxidation rate of 0.38μmol·s^-1·g_cat.^-1,respectively.Although the preparation process of the one-step hydrothermal synthesis was simple,the existence of bound water in WO₃ affected the lattice integrity,causing the scattering effect in the process of photogenerated charge migration to some extent.Therefore,the thesis also designed and proposed a new composite synthesis method,namely the Zn_0.5Cd_0.5S nanorods and WO₃·H₂O nanocrystals were prepared by hydrothermal method,and then the surface electrostatic adsorption strategy was used to make Zn_0.5Cd_0.5S and WO₃·H₂O directional combination by adjusted the p H value of the two aqueous mixtures according to their isoelectric point.The Zn_0.5Cd_0.5S/WO₃ composites with high-quality hetero-interface connection were obtained by heat treatment at 380℃for 2 h in nitrogen atmosphere.Physical properties of the composites showed that the growth quality was high-quality and the number of interfacial heterojunction was considerable.For photocatalytic activity,the mass of WO₃ accounted for Zn_0.5Cd_0.5S 40 wt%（ZCSW40）has the best photocatalytic reduction property with the Cr（VI）photoreduction degradation rate of20.4μmol·min^-1·g_cat.^-1.The degradation rate of Cr（VI）was nearly 3 times higher than that of pure Zn_0.5Cd_0.5S solid solution,and the performance was much better than others.Its excellent photocatalytic performance was attributed to the synergistic effect on three aspects of photocatalytic efficiencies,including wide solar spectral absorption,high-efficient electron-hole separation and transfer,and fast surface chemical reactions.In this thesis,a novel preparation strategy of heterojunction composites was proposed,which provides a valuable reference for the design and development of high-efficient and high-quality artificial photosynthesized S-scheme photocatalysts.