Selective degradation of phenols/nonphenols via biochar-mediated persulfate activation: Influence of redox potential on dominant reactive oxygen species formation

Abstract

This study highlights that pollutant redox potential significantly influences persulfate activation, affecting both degradation efficiency and decomposition pathways more than operational parameters. The degradation performance of the SP-biochar/persulfate system was evaluated, and the influence of the physicochemical properties of pollutants was assessed. In the SP-600/persulfate system ([Con.] = 50 μM, [dose] = 0.15 g L−1, [persulfate] = 0.25 mM), phenol and 4-chlorophenol were completely degraded within 10 min, whereas benzoic acid and nitrobenzene exhibited maximum degradation of approximately 40 %. The difference in degradation rates was attributed to variations in the pollutant characteristics, particularly redox potential, as demonstrated by the strong correlation between half-wave potential and the degradation rate, analyzed by cyclic voltammetry. Open-circuit potential measurements further confirmed that compounds with lower redox potential experience more efficient degradation because of enhanced electron transfer, highlighting that the intrinsic properties of pollutants have a greater impact on degradation behavior. In addition, variations in redox potential lead to the formation of distinct reactive species, as confirmed by scavenger experiments. O2•- primarily degrades phenolic compounds, whereas 1O2 is primarily responsible for the removal of nonphenolic compounds, reflecting differences in the decomposition pathways and the generation of reactive species driven by redox behavior. Although the impact of catalyst dosage, persulfate concentration, and pH on the degradation rate was analyzed, none accounted for the observed differences in the decomposition of phenols and nonphenols. Therefore, targeting appropriate redox conditions is a critical strategy for effective pollutant degradation.