Heterogeneous Activation Of Persulfate By Ag Doped BiFeO₃ Composites For Tetracycline Degradation

The advanced oxidation technology based on sulfate radicals(SO ₄^·-)has attracted the attention of many researchers due to its high efficiency in removing refractory pollutants and its wide range of applications.Catalysts activating persulfate（PS）to produce free radicals with high oxidation activity are one of them.However,a catalyst with high reactive and convenient recovery for PS activation still remains to be developed,bismuth ferrite materials have attracted attention because of their unique perovskite structure,magnetic properties,and acid and alkali resistance.In this work,the silver-doped bismuth ferrite（Ag_x-BiFeO₃,x=0.1,0.2,0.3 and 0.4）catalysts with variable Ag content were synthesized via a facile sol-gel method and applied as heterogeneous catalyst in PS activation for tetracycline（TC）degradation.This research first systematically studied the physicochemical properties of the synthesized catalyst,using a series of characterization metho ds,including X-ray diffraction（XRD）test,scanning electron microscope（SEM）test,etc.The results show ed that the synthesized catalysts possess a hexagonal rhombohedral structure（R3c）,and Ag doping is beneficial to inhibit the formation of impurities during the synthesis process.In addition,XPS results show that there are four elements Bi,Ag,Fe and O in the catalyst.After the reaction,part of the catalyst Fe²⁺will be completely oxidized to Fe³⁺,and Ag will also be completely oxidized to AgO.After conducting catalytic degradation experiments,it was found that Ag_0.4-BiFeO₃ presented the best catalytic activity compared with other Ag doped BiFeO ₃composites,91%TC could be efficiently removed within 60 min under optimized conditions and the reaction rate constant was 0.0338 min^-1.On the basis of the characterization analysis and catalytic test results,both Fe and Ag could be the effective active site in PS activation,and Ag active site had a more significant effect on PS.Moreover,single factor influence experiments found that the dose of catalyst,the dose of PS,and the initial TC concentration all have a certain effect on the system,but the initial p H has negligible effect on the catalytic performance,indicating that Ag_0.4-BiFeO₃/PS system could work in a wide p H range.The results of electron spin-resonance spectroscopy（ESR）and radical quenching tests suggested that both SO ₄^·-and^·OH radicals were involved in the reaction.The possible mechanism of Ag_0.4-BiFeO₃ activating PS and the major degradation pathway of TC degradation were proposed.At last,the reusability experiment results proved that Ag _0.4-BiFeO₃ catalyst still has a high catalytic performance after 4 times used.