High-efficient degradation of oxytetracycline by visible photo-Fenton process using MnFe2O4/g-C3N4: Performance and mechanisms

Abstract

Oxytetracycline (OTC) is a broad-spectrum antibiotic that has strong persistence, bioaccumulation, and biodegradability, and poses great harm to human health. In this study, MnFe2O4/g-C3N4 heterojunction composite was successfully synthesized and its photo-Fenton catalytic activity for OTC degradation was tested. The MnFe2O4/g-C3N4 catalyst exhibited excellent photo-Fenton catalytic activity; approximately 80.5 %, 42.9 %, 5 %, and 3 % of OTC was decomposed after 10 min of treatment in the presence of MnFe2O4/g-C3N4, single MnFe2O4, single g-C3N4, and single H2O2, respectively. The OTC degradation was mainly initiated by h+ oxidation, and the roles of ·OH and O2·- were quite weak. Simultaneously, the Fe2+/Fe3+ and Mn2+/Mn3+ redox reactions promoted the production of reactive species. As a result, the conjugated double bond system, naphthol ring, and benzene ring in the OTC molecules were destroyed, accompanied by the removal of groups such as –OH, –NH2, –CH3, and –CONH2. Based on the analysis of degradation intermediates and characteristics of MnFe2O4 and g-C3N4, possible degradation pathways and mechanisms of OTC in the MnFe2O4/g-C3N4 photo-Fenton catalytic system were depicted. Furthermore, the stability and recycling of the MnFe2O4/g-C3N4 were evaluated.