Sulfur-functionalized CoMn₂O₄ as a Fenton-like catalyst for the efficient rhodamine B degradation

Spinel-type bimetallic oxides have several potential applications in the catalytic degradation of organic wastewater due to their high catalytic activity and slow ion release rate caused by bimetallic synergy. In this study, sulfur-functionalized CoMn₂O₄ (S-CoMn₂O₄) was prepared as a Fenton-like catalyst by the sol–gel process, followed by calcination and sulfurization. The catalytic activity of CoMn₂O₄ was significantly increased by the incorporation of sulfur. The S-CoMn₂O₄(5.00%) catalyst modified with 5.00% sulfur in atomic percentage exhibited the best catalytic performance. Typically, 30 mg/L of rhodamine B was removed in 18 min by using 0.20 g/L S-CoMn₂O₄(5.00%) and 0.16 g/L peroxymonosulfate. Singlet oxygen and sulfate radicals are the primary active species, according to the trapping agent experiments and EPR measurements. The incorporation of sulfur leads to the formation of abundant oxygen vacancies in CoMn₂O₄ and sulfate groups bound on the surface of CoMn₂O₄, which promotes producing more active species. A synergism of Co and Mn ions in CoMn₂O₄ and high electron transfer mobility are also responsible for the enhanced degradation performance of S-CoMn₂O₄(5.00%). This study provides a feasible solution for improving cobalt manganese oxide as a more effective and long-lasting Fenton-like catalyst for the degradation of organic contaminants.