Cu/Cu cycle promoted PMS decomposition with the assistance of Mo for the degradation of organic pollutant.

The limited production of Cu in the Cu/PMS processes constrained its large-scan application for the elimination of organic pollutants. In this study, molybdenum powder (Mo) was applied as the co-catalyst to improve the degradation of 2,4-dichlorophenol (2,4-DCP) in Cu/PMS system at pH 5.6. By the assistance of Mo, Cu was rapidly reduced to Cu which exhibited super activity for the peroxymonosulfate (PMS) activation. Compared with Cu/PMS processes, the PMS decomposition rate and 2,4-DCP degradation efficiency respectively increased by 62.1% and 83.6% in the Mo co-catalytic Cu/PMS system after reaction for 20 min. The degradation of 2,4-DCP was completed via both the free radical and non-radical pathways and the free radicals rather than Cu contributed most to the reaction. In contrast to fresh Mo, the ratio of Mo increased and Mo decreased in the used Mo powder, due to the oxidation of Mo by Cu and/or ∙OH and the reduction of Mo by O∙. Additionally, the coexistence of Cl and humic acid with low concentrations showed little effects on the Mo/Cu/PMS system while HCO presented an obvious depression for 2,4-DCP degradation. During five cycling runs, all the degradation rates were higher than 92.8%, indicating the good stability of Mo/Cu/PMS system.