Dynamic characteristics of two alkoxy radicals towards emerging pollutants with different molecular structures in peracetic acid activation systems

The distinct roles of the two dominant organic radicals produced in peracetic acid (PAA)-based advanced oxidation processes, acetyloxy radicals (CH₃COO•) and peroxyacetyl radicals (CH₃COOO•), in degrading emerging pollutants with different molecular structures remain unclear. In this study, a Co(II)/PAA system that generates organic radicals was constructed, and the degradation behaviors and mechanisms of seven emerging contaminants were investigated by combining experimental kinetics with density functional theory (DFT) calculations. Organic radicals were identified as the dominant reactive species, and the degradation efficiencies of the seven pollutants varied markedly depending on their molecular structures. The results reveal that the reaction preferences of CH₃COO• and CH₃COOO• are jointly governed by the electronic properties of the radicals and the structural features of the pollutants: electron-rich compounds tend to undergo radical adduct formation (RAF) with CH₃COOO•, whereas electron-deficient compounds preferentially react through pathways involving the more electrophilic CH₃COO•. The intrinsic structural differences of both radicals and pollutant molecules dictate the dominant degradation pathway, including single electron transfer (SET), hydrogen atom abstraction (HAA), and RAF. These findings reveal the selectivity rules of CH₃COO• and CH₃COOO• toward emerging contaminants, providing a mechanistic basis for designing radical-specific treatment strategies in PAA-based water decontamination.