Activation of Persulfate by Quinones: Free Radical Reactions and Implication for the Degradation of PCBs

TLDR

Persulfate is widely studied for in situ chemical oxidation of organic contaminants, and humic acid quinones are suspected to influence its activation in environmental matrices. The study aims to determine how humic acid quinones affect persulfate‑mediated PCB degradation and sulfate radical production to guide remediation. Quenching and EPR experiments, together with concentration studies, revealed that quinones activate persulfate via a semiquinone radical pathway. Quinones and humic acid efficiently activate persulfate, generating sulfate radicals through a semiquinone radical mechanism, offering an effective route for degrading contaminants like PCB28.

Abstract

There has been considerable interest in the use of persulfate for in situ chemical oxidation of organic contaminants in soils, sediments, and groundwater. Since humic acid (HA) exists ubiquitously in these environmental compartments, its redox active functional moieties, such as quinones, may play an important role in the oxidation processes of persulfate treatments. Understanding the effects of HA, especially the quinone functional groups on the degradation of pollutants by persulfate and the production of sulfate radicals (SO4(•-)) from persulfate, is beneficial for devising effective and economically feasible remediation strategies. In this study, the effects of model quinone compounds and HA on the degradation of 2,4,4'-trichlorobiphenyl (PCB28) by persulfate and the production of SO4(•-) from persulfate were investigated. It was found that quinones and HA can efficiently activate persulfate for the degradation of PCB28. The mechanism of persulfate activation was elucidated by quenching and electron paramagnetic resonance (EPR) studies. The results indicated that production of SO4(•-) from persulfate and quinones was semiquinone radical-dependent. The effects of quinone concentrations were also studied. The findings of this study elucidated a new pathway of persulfate activation, which could degrade environmental contaminants efficiently and provide useful information for the remediation of contaminated soil and water by persulfate.