Preparation And Characterization Of A Composite Photocatalyst For Bismuth/Bismuth/Mn-Zn Ferrite

The spread of diseases caused by water pollution,the lack of water resources,and the destruction of ecological environment have seriously affected people's lives.Therefore,the water pollution control is the primary task of environmental safety.Photocatalytic technololgy has excellent application prospects in controlling water pollution problems due to its low energy consumption,good performance and no hazard.Bi₂O₃ is a new type of photocatalyt with excellent performance.But,the shortcoming is that the recombination of electron-hole pairs is easy to occur and can not be recycled after use.BiVO₄ is a photocatalyst that can degrade organic matter in water,but its adsorption is poor,photo-generated electrons and holes are easily recombined.Mn-Zn ferrite has the advantages of high saturation magnetization,low magnetic loss and low coercivity.Therefore,in this thesis,Mn-Zn ferrite prepared by hydrothermal method is used as a magnetic matrix,and sensitizes?-Bi₂O₃ and BiVO₄ to prepare composite magnetic photocatalysts to improve their photocatalytic effect and facilitate recovery.The mechanism of photocatalytic activity of Mn-Zn ferrite for strengthening?-Bi₂O₃ and BiVO₄ was analyzed by characterization of structure and properties.Mn-Zn ferrite was prepared by hydrothermal method,and different ratios of?-Bi₂O₃/Mn_xZn_1-xFe₂O₄ composite magnetic photocatalysts(Bi/F_MnZn)were prepared by hydrothermal-coprecipitation-baking method.Its structure and properties were tested by using XRD,XPS,BET and SEM,etc.When the mass ratio of Mn_xZn_1-xFe₂O₄ and?-Bi₂O₃was 10%,the saturation magnetization of Bi₂O₃/Mn_xZn_1-xFe₂O₄ was 9.22 emu/g,the catalytic degradation rate of 0.1g composite to 100mL RhB of 10mg/L was 96.81%,and the average recovery rate of the composite was 89.7%under the action of an external magnetic field.The specific surface area of Bi₂O₃/Mn_xZn_1-xFe₂O₄ was 17.87 m²?g^-1.?-Bi₂O₃ is loaded on the outer layer of Mn-Zn ferrite particle in?-Bi₂O₃/Mn_xZn_1-xFe₂O₄,and it improved the agglomeration between particles.Addition of the magnetic source(Mn_xZn_1-xFe₂O₄)was modified?-Bi₂O₃ very well,and improved the photocatalytic activity of?-Bi₂O₃/Mn_xZn_1-xFe₂O₄.The composite photocatalyst?-Bi₂O₃/BiVO₄ was prepared by step-wise co-precipitation-baking method.In?-Bi₂O₃/BiVO₄,The p-n heterojunction was formed between?-Bi₂O₃ and BiVO₄,which prevented the combination between electron-empty pairs in?-Bi₂O₃ and BiVO₄ single substances.The visible light response range of the composite was enhanced,and the photocatalytic activity improved.When the mass ratio of?-Bi₂O₃and BiVO₄ is 1:1,the 100mL RhB solution of 10mg/L can be completely degraded at 130 min under the irradiation of simulated sunlight.The BET specific surface area of?-Bi₂O₃/BiVO₄ is 16.45 m²?g^-1,which is larger than the specific surface area of a single?-Bi₂O₃ or BiVO₄.The ternary composite magnetic photocatalyst?-Bi₂O₃/BiVO₄/Mn_xZn_1-xFe₂O₄ was prepared by hydrothermal-coprecipitation-baking method in the light of the above mass ratio of?-Bi₂O₃,BiVO₄ and Mn_xZn_1-xFe₂O₄.The addition of magnetic source Mn-Zn ferrite didn't damaged the p-n heterojunction formed between?-Bi₂O₃ and BiVO₄,and modified?-Bi₂O₃/BiVO₄,and enhanced the photocatalytic activity and the magnetic response capability.The structure and photocatalytic propeerties were analyzed and characterized.Uv-vis shows that?-Bi₂O₃/BiVO₄/Mn_xZn_1-xFe₂O₄ has stronger light absorption capacity.The saturation magnetization of the composite was 2.67 emu/g,which is enough to ensure the recovery of the composite under the action of magnetic field.Under simulated sunlight,the degradation rate of RhB by?-Bi₂O₃/BiVO₄/Mn_xZn_1-xFe₂O₄ was 92.8%,and that of the three recovered samples was still 84.9%,indicating that the prepared three-phase composite has excellent photocatalytic degradation efficiencies and recyclability.