Gallic acid enhanced sulfamethoxazole degradation in Cu(II)/peracetic acid system: Key roles of HO• and Cu(III)

The Cu(II)-activated peracetic acid (PAA) process shows promise in eliminating emerging organic contaminants (EOCs), yet it encounters difficulties stemming from the sluggish reduction of Cu(II) to Cu(I). Herein, gallic acid (GA), a representative plant-derived polyphenol, was introduced to enhance the oxidative potential of the Cu(II)/ PAA system by facilitating the Cu(II)/Cu(I) redox cycle. The results demonstrated that the GA/Cu(II)/PAA process achieved 90.2 % degradation of sulfamethoxazole (SMX) within 60 minutes under neutral conditions, which is 2.4 times higher than the degradation achieved by the Cu(II)/PAA process alone. Multiple reactive species, including HO center dot, center dot CH3, CH3O2 center dot, CH3CO2 center dot, 1O2, and Cu(III), were involved in GA/Cu(II)/PAA system, among which HO center dot and Cu(III) were identified as the primary contributors to SMX oxidation, while Cu(III) played a dominant role. SMX transformation predominantly occurred through hydroxyl substitution, side chain oxidation, and polymerization pathways, significantly reducing the biotoxicity of the SMX solution posttreatment. Additionally, SMX degradation in GA/Cu(II)/PAA system was significantly enhanced in the presence of high Cl-concentrations, but slightly inhibited by CO32- /HCO3- and humic acid. This study introduces a robust strategy for enhancing the Cu(II)/PAA process and underscores its promising applications, particularly in the remediation of SMX-contaminated wastewater.