Mechanistic Insights into Sulfamethazine Degradation by Defect-Rich MnO₂-Activated Peracetic Acid

Manganese (Mn)-based oxides, mainly MnO₂, have garnered significant attention in catalytic applications due to their superior redox properties and structural flexibility. However, their saturated coordination structure presents challenges in achieving an enhanced performance. Herein, a defective MnO₂ catalyst (MnO₂-D) was constructed, and for the first time, it was proven to effectively activate peracetic acid (PAA) for the complete degradation of sulfamethazine (SMT). Compared to MnO₂ with a saturated coordination structure (i.e., the perfect MnO₂ structure, MnO₂-P), the MnO₂-D catalyst exhibited a higher surface electron density and abundant surface oxygen vacancies (OVs), significantly improving its catalytic activity. Experimental evidence revealed that the OVs and Mn³⁺ on the surface of MnO₂-D were considered as the primary active sites and that the MnO₂-D/PAA system followed a singlet oxygen (¹O₂)-dominated nonradical pathway. The MnO₂-D catalyst can maintain its activity with minimal interference from inorganic anions, humic acid, varying pH levels, and real water environments. In addition, the MnO₂-D/PAA system was efficient in mitigating the toxicity of SMT and eliminating diverse micropollutants. This work presents an enhancement strategy for constructing defect-rich metal oxide catalysts to advance future water treatment technologies.