Selective elimination of aniline contaminants induced by semiquinone radicals during peracetic acid oxidation of dihydroxybenzenes.

This study investigated the reaction mechanisms of peracetic acid (PAA) with dihydroxybenzenes (HBs) to generate reactive species for degradation of micropollutants containing aniline(-like) structures, including 7 sulfonamide antibiotics, 17 (non-)substituted anilines, and 3 nucleobases. Three of the studied HBs significantly enhanced aniline degradation kinetics by PAA, with degrees following the order of catechol (CA) > protocatechuic acid > hydroquinone. The PAA/CA process at the optimal condition (initial pH 7, 100-μM PAA, 50-μM CA) achieved 90% removal efficiency of sulfadiazine in 40 min with minimal interference by anions (Cl-, SO42-, and HCO3-), humic acid, and real (waste)waters. Results of scavenging experiments, electron paramagnetic resonance analyses, and transformation product profiles collectively support that semiquinone radical (SQ•-), originated from oxidation of CA by PAA, dominated aniline degradation through nucleophilic addition toward the amino groups on aniline moieties, resulting in formation of C-N coupling products and detoxication of anilines. The critical role of o-SQ•- is further highlighted by the linear correlation between ln-scale observed pseudo-first-order rate constant (kobs) with the Hammett constant (σ) for sulfonamides and (non-)substituted anilines (r = -0.77). Besides, a non-radical pathway driven by singlet oxygen (1O2) made important while non-dominant contribution to aniline degradation. Overall, this work sheds light on reactive species formation during oxidation of phenolic compounds by PAA and proposes a novel strategy for selective elimination of aniline-containing contaminants in wastewater treatment.