Zero-valent cobalt and oxygen vacancy rich catalyst derived from Ni/Co metal-organic framework nanosheets for enhanced oxidation of aqueous contaminants via peroxymonosulfate activation

Transition metal oxides/hydroxides are emerging as highly promising catalysts for triggering the activation of peroxymonosulfate (PMS) to decompose organic pollutants. However, the roles of metal species with different valence states and defects in the catalyst are worth further investigation. In this study, Ni/Co oxide-based catalysts were synthesized with plenty of zero-valent cobalt (Co0) and oxygen vacancies (Vo) through direct carbonization of Ni/Co metal-organic framework nanosheets. The prepared catalyst/PMS system facilitated almost complete removal of 4-nitrophenol (4-NP) at a concentration of 20 mg/L within 15 min, using 20 mg of catalyst and 0.8 g/L of PMS. Moreover, the catalyst was effective in decomposing different types of organic pollutants such as antibiotics and dyes, and exhibiting good stability and reusability. The study examined the impact of catalyst and PMS dosage, pH, temperature, and common anions on 4-NP degradation. Furthermore, scavenger experiments and Electron Paramagnetic Resonance (EPR) tests were utilized to investigate reactive oxygen species (ROS). It was uncovered that Co0 and Vo played a crucial role in the degradation process. Additionally, potential degradation mechanisms were proposed and degradation pathways for 4-NP were suggested based on the identified intermediate products. Finally, the toxicity level of the intermediate products was assessed.