Heterogeneous Electro-Fenton System Degradation Of Tetracycline In Water By Novel Iron/Cerium Bimetal Oxide

Tetracycline（TC）,as one of the most abused antibiotics,has been detected in a large amount of residues in various water environments,which directly or indirectly affects human health and life.Electro-Fenton（EF）,a well-studied electrochemical advanced oxidation process.Among them,heterogeneous EF system,which uses solid catalysts（e.g.,iron oxide）to supersede dissolved Fe²⁺,can effectively remove refractory organic pollutants.So far,developing efficient heterogeneous electro-Fenton catalysts for degradation of organic pollutants remains a challenge.The composite of Fe/Ce oxides has presented outstanding catalytic（especially photocatalytic）performance towards degradation of organic pollutants due to the synergistic effects of Fe-Ce and accelerated redox cycle between iron(Fe²⁺/Fe³⁺)and cerium(Ce³⁺/Ce⁴⁺),however,the EF catalytic activity of Fe/Ce bimetallic oxides has been rarely reported.In this study,the Fe@Fe₂O₃-CeO₂ composite was synthesized by one-step reduction method,and characterized by HRTEM,TEM-EDS,XRD,XPS and BET,which proved that the mesoporous Fe@Fe₂O₃-CeO₂ composite with core-shell structure was successfully synthesized.The heterogeneous electro-Fenton system with Fe@Fe₂O₃-CeO₂ was constructed with tetracycline as the target,and the catalytic performance of Fe@Fe₂O₃-CeO₂ was investigated.The Fe@Fe₂O₃-CeO₂ catalyst with 2:1 Fe/Ce molar ratio exhibited higher catalytic activity,which can effectively degrade the pollutant TC in the heterogeneous EF process.Under the conditions of 0.08 g L^-1 catalyst,50 mA applied current,p H without adjustment（p H 3.8±0.1）and 0.1 L min^-1 aeration rate,the removal efficiency of TC within 1 h was 90.7%,and the corresponding mineralization efficiency within 6 h was 86.9%,which attributed to the high utilization efficiency of H₂O₂ and the synergistic effects between Ce⁴⁺/Ce³⁺and Fe³⁺/Fe²⁺.Moreover,this catalyst exhibited good recyclability and stability in successive cycles with low metal iron and cerium leaching.Furthermore,the heterogeneous EF process showed satisfactory catalytic activity towards degradation of other organic pollutants（e.g.,metronidazole（MTZ）,diclofenac sodium（DFS）,and chloramphenicol（CAP））,the removal efficiency of contaminants after 1-h reaction（TOC after 6-h reaction）was found to be 100%（66.8%）for MTZ,86%（55.4%）for DFS and 84%（55.3%）for CAP.Then,based on the experimental results and analysis,combined with the identification of active species,the reaction mechanism for TC degradation of the heterogeneous EF process with Fe@Fe₂O₃-CeO₂catalyst was proposed,which could be summarized as the synergistic effect of Fe@Fe₂O₃-CeO₂catalyst surface adsorption,anodic oxidation,heterogeneous EF reaction between Fe²⁺and H₂O₂,Fenton-like oxidation between Ce³⁺and H₂O₂,and homogeneous EF reaction involving a small amount of Fe²⁺and Ce³⁺leaching.Finally,four possible degradation pathways were proposed based on the analysis of degradation intermediates.