New Insights into the Activation of Peracetic Acid by Co(II): Role of Co(II)-Peracetic Acid Complex as the Dominant Intermediate Oxidant

The combination of Co(II) and peracetic acid (PAA) is an important alternative advanced oxidation process (AOPs), in which R-O• radicals including acetyloxyl radicals (CH3C(O)O•) and acetylperoxyl radicals (CH3C(O)OO•) have been considered to be the primary reactive species for the oxidative degradation of contaminants. However, it is still unclear how the active Co species participates in this process. In this study, we conduct a series of experiments including chemical probing, radical quenching, electron paramagnetic resonance (EPR), and Co(III) oxidation to investigate the degradation mechanism of contaminants in the Co(II)/PAA process, using bisphenol A (BPA) as target pollutant. On the basis of these results, we propose a Co(II)-PAA complex (Co(II)-OO(O)CCH3) to be the primary reactive species, while R-O• radicals and Co(III) (available as dimeric Co-peroxide species) derived from the decomposition of Co(II)-PAA complex are the minor contributors for the oxidation of BPA. Factors, including PAA concentration, Co(II) concentration, solution pH, inorganic anions, and natural organic matters (NOM), that might affect the oxidation performance of the Co(II)/PAA process were also investigated systematically. This study sheds new light on the mechanistic understanding of the Co(II)/PAA process for the oxidation of contaminants in water.