Degradation Of Tetracycline In Wastewater By Perovskite-based Heterogeneous Fenton-like System

Tetracycline antibiotic wastewater,as a refractory organic wastewater with high biological toxicity and low biodegradability,is regarded as one of the difficulties in the field of sewage treatment.Heterogeneous Fenton-like technology is an advanced oxidation process,which is based on Fenton technology and use solid-phase catalysts,so it can effectively treat refractory organic wastewater.In the research of high-efficiency heterogeneous Fenton-like catalysts,perovskite is regarded as the heterogeneous Fenton-like catalysts with potential and great value because of its good catalytic ability and stability.In this study,the sol-gel method was used to synthesize the perovskite-type oxides Ca_1-xFe O_3-σ（x=0,0.1,0.2）with different A site defects and the perovskite-type oxides CaFe_1-xCo_xO_3-σ（x=1/3,1/2,2/3,1）with different cobalt substitution,and the morphology,structure,catalytic performance and other aspects were studied.In this study,a variety of characterizations were used to analyze the basic properties of Ca_1-xFe O_3-σ,and it was confirmed that all of them were irregular small-sized particles with a perovskite crystal structure.The heterogeneous Fenton-like system with Ca_1-xFe O_3-σwas constructed,and the performance of Ca_1-xFe O_3-σwas investigated with tetracycline as the target.The results showed that Ca_1-xFe O_3-σwas better than the conventional heterogeneous Fenton-like catalysts.Among the Ca_1-xFe O_3-σ,Ca_0.9Fe O_3-σhad the best catalytic performance and could degrade 88.3%of the tetracycline in the system when the initial p H was 3.However,the Ca_0.9Fe O_3-σ’s catalytic ability was greatly affected by the p H,H₂O₂ concentration and catalysts dosage.Ca_0.9Fe O_3-σhad good stability,and the removal rate of tetracycline was more than 70%after repeated use for 3 times.It was determined that·OH was the main active free radical in the Ca_0.9Fe O_3-σ/H₂O₂ system.Both the Fe（Ⅱ）/Fe（Ⅲ）components and oxygen vacancies on Ca_0.9Fe O_3-σwere the active sites for the reaction.In addition,the possible decomposition pathways of tetracycline in the system were deduced.In order to broaden the applicable p H range of the catalysts,CaFe_1-xCo_xO_3-σwas prepared and analyzed by various methods.The characterization results showed that the B-site doping with Co did not change the original crystal structure,and could also increase the oxygen vacancy concentration of the perovskite-type oxides.The heterogeneous Fenton-like system with CaFe_1-xCo_xO_3-σwas constructed,the tetracycline was used as the research object,and the catalytic activity of the material was investigated.Among the cobalt-doped perovskites,CaFe_0.5Co_0.5O_3-σhad the best catalytic performance.More than 79%of tetracycline could be oxidized when the initial p H was 3 to 11.However,the CaFe_0.5Co_0.5O_3-σ’s performance was greatly affected by the catalysts dosages and the concentration of H₂O₂.The stability of CaFe_1-xCo_xO_3-σwas good,and it could keep the removal rate of tetracycline above75%after 4 cycles of use.It was determined that O₂^-was the free radical that degraded pollutants in the CaFe_1-xCo_xO_3-σ/H₂O₂ system.The Fe（Ⅱ）/Fe（Ⅲ）components,the Co（Ⅱ）/Co（Ⅲ）components and oxygen vacancies were the active sites on CaFe_1-xCo_xO_3-σ.In addition,the possible degradation pathways of tetracycline in the system were deduced.