Preparation Of Bi₂Fe₄O₉ Photocatalyst And Its Modification Research

With the progress of urbanization and the growing human survival needs,we have encountered a very serious energy crisis and environmental problems.Photocatalytic degradation of pollutants by semiconductor materials is considered as a promising method because of its green and fast degradation rate.Bismuth ferrite（Bi₂Fe₄O₉）,as an excellent photocatalyst with suitable bandgap,good chemical stability and no precious metals,so it has become a popular photocatalytic material in recent years.However,Bi₂Fe₄O₉ itself has some shortcomings,such as photogenic electrons and holes recombination efficiency is high,and its photocatalytic degradation ability is not very good.In this paper,on the basis of investigating the effects of concentration of mineralizer、precursor molar ratio、hydrothermal temperature and hydrothermal time on Bi₂Fe₄O₉ synthesis and performance,and in view of the deficiencies of Bi₂Fe₄O₉,Mn²⁺was doped,and the heterostructures were constructed with carbon nitride（g-C₃N₄）and bismuth chloride oxide（Bi OCl）.XRD was used to study the phase structure of the material.SEM and TEM were used to study the morphology and size of the sample.The absorption band edge was measured by UV-Vis DRS and the band gap was calculated by absorption band edge.PL was used to study the recombination efficiency of carrier in the conduction band and valence band,and EIS was used to study the migration rate of interfacial electrons.The degradation rate of Rhodamine B（Rh B）was studied by photocatalytic degradation experiment.Finally,the photocatalytic mechanism of the sample was analyzed by comprehensive study.Bi₂Fe₄O₉ photocatalyst was prepared by coprecipitation-hydrothermal method,the influence of precursor molar ratio、concentration of mineralizer、hydrothermal temperature and time on Bi₂Fe₄O₉ synthesis and performance were studied.According to the photocatalytic degradation experiment,when C（KOH）=7M,n（Fe）:n（Bi）=2:1,at 200℃for 6h,the synthetic Bi₂Fe₄O₉ had the best effect on dye degradation,reaching to 45.70%,and the reaction rate constant was 0.00305 min^-1,which was 1.26times and 1.36 times that of 18h and 30h,respectively.Hydroxyl radical（·OH）was the main active component in the degradation of dyes.Bi₂Fe_4（1-x）Mn_4xO₉ photocatalyst was prepared by coprecipitation-hydrothermal method.After doping Mn²⁺,the photogenerated carrier recombination efficiency of Bi₂Fe₄O₉ was reduced,the electron transfer efficiency was accelerated,and had good degradation effect for Rh B.When Mn²⁺doping was 6%,the degradation effect of organic dyes was very good,reaching to 82.29%,and the reaction rate constant was0.00606min^-1,which was 1.99 times that of Bi₂Fe₄O₉.The main active component of dye degradation process was·OH,which was consistent with that of Bi₂Fe₄O₉.G-C₃N₄/Bi₂Fe₄O₉ and Bi OCl/Bi₂Fe₄O₉ composite photocatalysts were prepared by mechanica mixing-calcination and coprecipitation-hydrothermal method,respectively.The heterojunction structure formed by the combination of the two materials reduces the recombination efficiency of photogenerated electron-hole pairs and improves the degradation efficiency of Rh B.At 240 min,25%-g-C₃N₄/Bi₂Fe₄O₉photocatalytic degradation efficiency of 10 mg/L Rh B was good,reaching to 87.59%.The reaction rate constant was 0.00674 min^-1,which was 2.21 times and 2.32 times that of Bi₂Fe₄O₉ and g-C₃N₄.Superoxide radical（O₂^-·）and·OH were the main active component in the dye degradation process.At 240 min,20%-Bi OCl/Bi₂Fe₄O₉ showed the best photocatalytic degradation of 10 mg/L Rh B,reaching to 99.56%.The reaction rate constant was 0.01463 min^-1,which was 4.79 times and 3.92 times that of Bi₂Fe₄O₉and Bi OCl,respectively.·OH was the main active component in the dye degradation process.