Anchoring CoFe2O4 nanoparticles on ZnO for enhanced peroxymonosulfate activation in tetracycline degradation: Performance, mechanism and degradation pathway

The development of a catalyst with high efficiency and low metal leaching is highly essential for transition metal-based peroxymonosulfate (PMS) activators. In this study, a composite catalyst of CoFe 2 O 4 nanoparticles anchored on ZnO (CoFe 2 O 4 @ZnO) was successfully synthesized through coprecipitation coupled with calcination. Given that CoFe 2 O 4 and ZnO have opposing zeta potentials, their combination was strengthened by electrostatic forces. Moreover, the pH buffering environment provided by the ZnO carrier considerably reduced the degree of metal leaching; furthermore, the degree of aggregation of the CoFe 2 O 4 nanoparticles greatly decreased in the presence of ZnO, exposing more active sites for PMS activation. Consequently, a tetracycline (TC) removal rate of 96.5 % was achieved by CoFe 2 O 4 @ZnO within 10 min, with less than 0.5 % metal leaching, and the removal rates reached over 90 % over a wide range of pH values (3.0 11.0). Through the detection of reactive species, electrochemical analysis and comparison of catalyst components before and after the reaction, an activation mechanism for PMS mediated by CoFe 2 O 4 @ZnO was proposed, and SO 4 •− , 1 O 2 , and electron transfer played a dominant role in PMS activation for TC removal. HPLC MS analysis and density functional theory (DFT) calculations revealed three main pathways for TC degradation, and the results of software prediction and hydroponic experiments with peas indicated a general reduction in the toxicity of intermediate products. This work provides valuable theoretical and technical insights into metal-based catalysts for PMS activation.