Fe3O4@S-doped ZnO: A magnetic, recoverable, and reusable Fenton-like catalyst for efficient degradation of ofloxacin under alkaline conditions.

In this study, an efficient and reusable heterogeneous Fenton catalyst Fe3O4@S-doped ZnO magnetic composite was synthesized for the degradation of ofloxacin (OFX) under alkaline conditions without external energy input. The Fe3O4@S-doped ZnO exhibited excellent catalytic activity toward ofloxacin degradation within 120 min. Using 0.25 g/L of catalyst and 5.0 mL/L of H2O2 under optimized conditions, the catalyst was effective in pH values ranging from 5.2 to 9.0. The catalytic performance at optimal conditions was in accordance with a pseudo-first-order kinetics model. The reaction constant of Fe3O4@S-doped ZnO (0.0354 min-1) was three times than that of Fe3O4@ZnO (0.0124 min-1) under alkaline conditions (pH 8.2). The reactive oxygen species were the ·OH and O2·-, with ·OH dominating in the degradation of OFX. It is proposed that the catalyst acts as a Lewis acid, creating an acidic microenvironment on the catalyst's surface and widening the pH range of the Fenton reaction to alkaline conditions. Additionally, the catalyst was stable and reusable after six cycles of use. The Fenton-like Fe3O4@S-doped ZnO catalyst overcomes the problem of the narrow pH of the reaction system, thus providing promising environmental applications.