Cu-doped ZnFe2O4 activating peroxymonosulfate for the degradation of organic contaminants: reaction kinetics, molecular structure- and pH-dependent reaction mechanisms

This study prepared Cu-doped ZnFe₂O₄ (Cu-ZFO) for peroxymonosulfate (PMS) activation, achieving 94% primidone (PMD) removal in 30   min, much higher than ZnFe₂O₄ (20%) due to the introduction of oxygen vacancies and Cu-enhanced Fe catalytic activity. Kinetic analysis revealed reaction orders of 1.25, 1.2, and 0.22 with respect to Cu-ZFO, PMS, and PMD, respectively. Electron transfer pathway (ETP) and free radical oxidation were believed to be involved in the degradation of various organic contaminants in Cu-ZFO/PMS system under neutral conditions through radicals quenching experiments, EPR measurements, electrochemical measurements, and Density functional theory (DFT) calculations. The dominant oxidation pathway for organic contaminants is dependent on their molecular structure and the solution pH. This study provides new insights into PMS activation mechanisms and signals attention to researchers and engineers about the potential influence of molecular structure and pH on oxidation pathways of organics during wastewater treatment using metal oxide-activated PMS.