Study On Preparation Of BiFeO₃-based Composites Catalysts And Their Photocatalytic Performance For Tetracycline Degradation

BiFeO₃ with visible light response as a photocatalyst has a narrow band gap and can effectively utilize 50%of the visible light from sunlight,but still suffers from defects such as low electron-hole pair separation efficiency.Therefore,in this study,three heterojunction composites with high catalytic activity and stability were designed and synthesized by combining them with other semiconductor materials to construct heterojunctions,and the photocatalytic degradation of tetracycline（TC）was investigated.The main research and results of this thesis are as follows:（1）A core-shell structured Z Scheme heterojunction composite catalyst,In₂O₃@BiFeO₃,was prepared by wrapping BiFeO₃ nanoparticles on the surface of In₂O₃ cubes by a simple hydrothermal method.The prepared catalyst was characterised by various means,and the photocatalytic activity of In₂O₃@BiFeO₃ for TC was evaluated,and the charge transfer mechanism at the interface of the heterojunction was explored.The charge transfer mechanism at the heterojunction interface was investigated.The results showed that the photocatalytic activity of In₂O₃@BiFeO₃ was significantly higher compared with that of pure BiFeO₃ and In₂O₃,and the photocatalytic degradation efficiency of TC by 30%In₂O₃@BiFeO₃ reached 83%,with a degradation rate constant of 0.0117 min^-1,which was2.9 and 14.6 times higher than that of BiFeO₃ and In₂O₃,respectively.The reasons for the significantly higher photocatalytic activity of In₂O₃@BiFeO₃ are mainly twofold:firstly,the core-shell structure coupled with the photosensitization of In₂O₃ by BiFeO₃ makes In₂O₃@BiFeO₃ exhibit excellent visible light collection ability;secondly,the charge migration at the heterojunction interface follows the Z-Scheme charge transfer mechanism,which promotes both the effective separation of photogenerated carriers and The strong redox ability of photogenerated electrons and holes is preserved.（2）BiFeO₃/Bi₂O₄ heterojunctions were prepared by attaching BiFeO₃ nanoparticles to the surface of Bi₂O₄ micrometer rods using a simple hydrothermal method.The prepared catalysts were characterized by X-ray diffraction（XRD）,scanning electron microscopy（SEM）,high transmission electron microscopy（HRTEM）,X-ray electron spectroscopy（XPS）,ultraviolet-visible diffuse reflectance（UV-Vis）and photoluminescence（PL）spectroscopy,and the photocatalytic performance of the heterojunctions was evaluated by photocatalytic degradation of tetracycline（TC）,and the heterojunctions were explored The migration mechanisms of photogenerated electrons and holes at the interface were investigated.The results showed that the BiFeO₃/Bi₂O₄ composite photocatalysts showed stronger visible light response,significantly lower complexation rate of photogenerated electron-hole pairs and significantly enhanced photocatalytic activity compared with pure BiFeO₃ and Bi₂O₄,with the highest photocatalytic activity of BB10 with a BiFeO₃ mass ratio of 10%and a photocatalytic degradation efficiency of TC of up to 92.0%within 120min.The interfacial charge transfer mechanism of the BB10 complex followed the Z-Scheme heterojunction charge transfer pathway,and the main active species in the photocatalytic reaction were·O^2-and·OH.（3）The type II BiFeO₃/CaSnO₃ heterojunction photocatalyst was synthesized by a simple hydrothermal method,and its photocatalytic degradation performance against TC was investigated using various characterization tools to explore the photocatalytic mechanism.The results showed that the BiFeO₃/Ca Sn O₃ heterojunction photocatalysts exhibited excellent photocatalytic performance compared to pure BiFeO₃ and Ca Sn O₃,and the highest photocatalytic activity was achieved for the BCa10 complex with a 10%mass ratio of BiFeO₃,with a photocatalytic degradation efficiency of 82.0%for TC within 120min under visible light irradiation.The degradation rate constant of 0.0096 min^-1 for the complex BCa10 was 4.2 and 3.2 times higher than that of BiFeO₃ and Ca Sn O₃,respectively.This is mainly attributed to the formation of heterojunctions resulting in a smaller rate of complexation of photogenerated electron-hole pairs.