NiCo-MOF-derived spinel NiCo₂O₄ for peroxymonosulfate activation: Efficient degradation, mechanism and toxicity assessment of norfloxacin

A NiCo bimetallic metal-Organic Framework served as a precursor for direct carbonization, yielding a spinel metal oxide with a central control skeleton structure (NiCo₂O₄). The NiCo₂O₄ catalyst demonstrated outstanding efficiency in activating peroxymonosulfate (PMS) to degrade norfloxacin (NOR), with 92.77 % removal within 60 min—outperforming the Co₃O₄/PMS system, which achieved 82 % NOR removal. Surface metal oxide particles enhanced electron transfer rates. A consistent degradation efficiency of NOR was observed across varying conditions, including varying levels of PMS concentration, initial pollutant levels, catalyst dosage, inorganic anions, humic acid (HA) and pH. Mechanistic inquiries including EPR testing, batch experiment, and electrochemical analysis revealed that NOR degradation proceeded mainly through a non-radical pathway involving singlet oxygen (¹O₂), enabled by a NiCo₂O₄-PMS* mediated electron transfer process. LC-MS testing identified degradation intermediates and proposed potential pathways for NOR breakdown. The Eco-toxicity of NOR and its degradation products was evaluated using the T.E.S.T. method. The results indicate that the degradation process of NOR represents a detoxification mechanism, and the overall toxicity of the degradation products is significantly lower than that of the original compound. This study presents a highly effective NiCo₂O₄ metal oxide catalyst for advanced oxidation processes driven by peroxymonosulfate, providing an effective solution for antibiotic removal and environmental remediation.