Screening Of La FeO₃B-Site Doped Catalysts And Its Photo-Fenton Catalytic Mechanism

Perovskite is a compound with ABO₃-type structure.The ions located at A and B sites of the crystal can be completely or partially replaced by other metal ions with similar radius to maintain the crystal structure basically unchanged,but the properties have changed.Studies have shown that La Fe O₃perovskite with A-site La has a narrow band gap and high stability,which is not only an ideal photocatalytic material but also a catalyst for Fenton reaction to catalyze the degradation of organic pollutants by hydrogen peroxide.However,the photocatalytic effect of La Fe O3 is still limited,and further modification research is needed to improve its photocatalytic performance.In this paper,the B-site perovskite oxides doped with Cu,Mn and Co in La Fe O₃were prepared by sol-gel method.The catalytic performance of the catalyst in H₂O₂and Na₂S₂O₈systems was investigated by using azo dye Orange II as the target pollutant.The experimental results show that La Fe_0.5Co_0.5O₃catalyst exhibits the best catalytic performance in H₂O₂system.Then the effect of B-site doping ratio of cobalt ions on the structure and catalytic performance of the catalyst was studied.The results showed that with the increase of the doping ratio of cobalt ions,the perovskite cell volume decreased,resulting in the red shift of XRD diffraction peak to the high angle direction,and the peak height and peak area decreased gradually.The degradation experiment of Orange II showed that the decolorization rate of Orange II increased first and then decreased with the increase of Co doping ratio in lanthanum ferrite catalyst.The degradation rate of Orange II on La Fe_0.5Co_0.5O₃catalyst in UV+H₂O₂system was the fastest,and the kinetic fitting K value reached 0.0762 min^-1,which was 1.75 times of that of La Fe O₃catalyst before doping.After 180 min reaction,the TOC removal rate in the system was 81.60%.The cyclic experiments showed that the La Fe_0.5Co_0.5O₃catalyst remained stable catalytic performance after three cycles.Physicochemical characterization results such as FTIR,XRD and XPS before and after cycling showed that the catalyst had good structural stability.Through the free radical quenching experiment and the analysis of total iron ion,ferrous ion,hydroxyl radical and hydrogen peroxide concentration changes,it is proved that the La Fe_0.5Co_0.5O₃photo-assisted Fenton catalytic process includes photoexcitation,hole oxidation,superoxide radical oxidation,photogenerated electron reduction iron ion,ferrous ion release,homogeneous Fenton reaction,iron ion readsorption process.The degradation of Orange II in the system is completed by Fenton reaction and photocatalytic reaction.