Highly efficient catalyst of Crednerite CuMnO₂ for PMS activation: Synthesis, performance and mechanism

Exploring highly efficient and stable transition metal-based catalysts is significant for the heterogeneous catalysis of peroxymonosulfate (PMS) in contaminants removal during water purification. Herein, we developed a series of Crednerite CuMnO₂ catalysts by tuning the hydrothermal synthesis conditions and applied them to catalyze PMS to degrade Orange I (OI). Hydrothermal temperature, hydrothermal reaction time, and NaOH dosage had a great influence on the catalytic performance of catalysts, but different synthetic raw materials had little diversity. Amongst, CMO-160°C-110mmol-24h exhibited the optimal PMS activation effect due to the promoted surface oxygen mobility and electron conduction. Regardless of the wide pH range of 5-9, the coexistence of Inorganic anions and humic acid, the inhibition of OI removal was not significant. Additionally, CMO-160°C-110mmol-24h showed low metal ion leaching and noticeable reusability, implying a great potential application of the CMO-160°C-110mmol-24h/PMS system in practical wastewater engineering. Mechanism studies indicated that surface hydroxyl groups, Cu⁺/Cu²⁺ and Mn²⁺/Mn³⁺ redox couples were key active sites for PMS activation. Both free radical pathways (•OH, SO₄^•−, O₂^•−) and non-free radical pathways (¹O₂ and electron transfer) were detected in the oxidation reaction, with non-free radical pathways as major contributors. The possible degradation pathway of OI was proposed, and the toxicity of intermediates was assessed. Overall, this study provided an important strategy for the construction of efficient and stable PMS catalysts in wastewater treatment.