Carbonate-induced enhancement of phenols degradation in CuS/peroxymonosulfate system: A clear correlation between this enhancement and electronic effects of phenols substituents

This study investigated the enhancement effects of dissolved carbonates on the peroxymonosulfate-based advanced oxidation process with CuS as a catalyst. It was found that the added CO32- increased both the catalytic activity and the stability of the catalyst. Under optimized reaction conditions in the presence of CO32-, the degradation removal of 4-methylphenol (4-MP) within 2 min reached 100%, and this was maintained in consecutive multi-cycle experiments. The degradation rate constant of 4-MP was 2.159 min-1, being 685% greater than that in the absence of CO32- (0.315 min-1). The comparison of dominated active species and 4-MP degradation pathways in both CO32--free and CO32--containing systems suggested that more CO3•-/1O2 was produced in the case of CO32-deducing an electron transfer medium, which tending to react with electron-rich moieties. Meanwhile, Characterization by X-ray photoelectron spectroscopic and cyclic voltammetry measurement verified CO32- enabled the effective reduction of Cu2+ to Cu+. By investigating the degradation of 11 phenolics with different substituents, the dependence of degradation kinetic rate constant of the phenolics on their chemical structures indicated that there was a good linear relationship between the Hammett constants σp of the aromatic phenolics and the logarithm of k in the CO32--containing system. This work provides a new strategy for efficient removal of electron-rich moieties under the driving of carbonate being widely present in actual water bodies.