Degradation of antibiotics in aqueous media using manganese nanocatalyst-activated peroxymonosulfate

Abstract

ε-MnO2 effectively activates peroxymonosulfate (PMS) for the efficient degradation of emerging pollutants. ε-MnO2 was synthesized by a facile thermal-treatment method and its long-term stability and efficiency for the elimination of emerging pollutants, including sulfamethoxazole (SMX), sulfachloropyridazine (SCP), sulfamethazine (SMT), ciprofloxacin (CIP), and azithromycin (AZI), from aqueous media were evaluated. ε-MnO2 was found to activate PMS more efficiently than α-MnO2, β-MnO2, or δ-MnO2, owing to its high − OH-group content, unique structure, and high surface area. Sulfate (SO4•−), hydroxyl (•OH), and superoxide (O2•−) radicals, as well as singlet oxygen (1O2) were generated, with O2•− acting as the 1O2 precursor. The ε-MnO2/PMS system proved to be effective in the pH range of 3.5–9.0 and the rate of SMX degradation was not significantly affected by the presence of inorganic anions or natural organic matter. The proposed pathway for the activation of PMS by ε-MnO2 includes inner-sphere interactions between ε-MnO2 and PMS, and electron transfer to PMS via the MnIII ↔ MnIV redox cycle, which generates reactive oxygen species. These findings provide new insight into PMS activation by less-toxic metal oxides as catalysts and demonstrate that Mn-based materials can be used to effectively treat water matrices containing emerging pollutants.