Insights into the mechanism of enhanced peroxymonosulfate activation for norfloxacin degradation by Co doping into MnO2 nanosheet

Co doped MnO 2 nanosheets with oxygen vacancies were hydrothermally prepared. • Co doped MnO 2 enabled 98.2 % NOX removal and 56.4 % TOC mineralization. • Co doping promoted PMS adsorption on catalyst and interfacial electron transfer. • SO 4 • – and 1 O 2 dominated NOX degradation in Co doped MnO 2 /PMS. • Three degradation pathways were proposed and ecotoxicity of intermediates was declined. The slow electron transfer rate, insufficient active sites and sluggish Mn(Ⅳ)/Mn(Ⅲ) redox cycling of MnO 2 in peroxymonosulfate (PMS) activation severely hinder its application in wastewater treatment. Herein, Co doped MnO 2 nanosheet with oxygen vacancy on nickel foam (NF) was fabricated via a simple hydrothermal method. Phase composition and microstructure of the as-prepared catalysts were systematically characterized. The optimized Co 0.07 -MnO 2 /NF exhibited superior norfloxacin (NOX) degradation efficiency, achieving 98.2 % removal and 56.4 % total organic carbon (TOC) mineralization within 60 min. The Co 0.07 -MnO 2 /NF/PMS system possessed prominent tolerance to inorganic anions (Cl – , NO 3 – and H 2 PO 4 – ) and universal degradation capability for typical organic contaminants as well as satisfactory cyclic stability. Electrochemical analysis, scavenger experiment and EPR analysis verified the generation of SO 4 • – , •OH, •O 2 – , 1 O 2 and high-valent Co(IV)/Mn(V)-oxo species in Co 0.07 -MnO 2 /NF/PMS system, among which SO 4 • – and 1 O 2 dominated NOX degradation. XPS analysis and density functional theory (DFT) calculation elucidated that Co/Mn active sites and oxygen vacancies boosted reactive oxygen species generation during PMS activation by enhancing PMS adsorption, accelerating interfacial electron transfer and promoting O-O bond cleavage in PMS. Finally, three plausible degradation pathways were proposed, and the overall ecotoxicity of the degradation solution can be reduced as the reaction progresses. This work clarifies the underlying mechanism of Co doping enhancing PMS activation capability of MnO 2 and can provide valuable guidance for rational design of highly efficient and stable PMS activators through defect engineering for wastewater remediation. Download: Download high-res image (67KB) Download: Download full-size image