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

Abstract

The slow electron transfer rate, insufficient active sites and sluggish Mn(Ⅳ)/Mn(Ⅲ) redox cycling of MnO2 in peroxymonosulfate (PMS) activation severely hinder its application in wastewater treatment. Herein, Co doped MnO2 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 Co0.07-MnO2/NF exhibited superior norfloxacin (NOX) degradation efficiency, achieving 98.2 % removal and 56.4 % total organic carbon (TOC) mineralization within 60 min. The Co0.07-MnO2/NF/PMS system possessed prominent tolerance to inorganic anions (Cl–, NO3– and H2PO4–) 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 SO4•–, •OH, •O2–, 1O2 and high-valent Co(IV)/Mn(V)-oxo species in Co0.07-MnO2/NF/PMS system, among which SO4•– and 1O2 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 MnO2 and can provide valuable guidance for rational design of highly efficient and stable PMS activators through defect engineering for wastewater remediation.