Complementarity and action mechanisms of Fe2+-activated persulfate and H2O2 system

The Fe 2+ -activated persulfate and H 2 O 2 (Fe 2+ /persulfate/H 2 O 2 ) system achieved 94% removal of four mixed sulfonamides with 300-s treatment and possessed excellent complementarity and stability over a wide pH (3–11) and temperature (5–65°C) range. The quenching and electron spin resonance spectroscopy results confirmed the coexistence of sulfate radicals and hydroxyl radicals in the coupled system, which were responsible for the elimination of sulfonamides under ambient conditions. The reaction rate constants of sulfate radicals and hydroxyl radicals at possible reactive sites distinguished the difference in removal ratios of four sulfonamides, according to experimental determination and density functional theory calculations. The removal ratio of sulfathiazole was higher than others because its calculated reaction rate constants of sulfate radicals and hydroxyl radicals were higher than those of sulfamerazine, sulfamethoxazole, and sulfamethazine. The finding provided a reference for investigating the removal mechanism of mixed organic pollutants in the presence of multiple free radicals.