Reaction of Fe aq II with Peroxymonosulfate and Peroxydisulfate in the Presence of Bicarbonate: Formation of Fe aq IV and Carbonate Radical Anions.

Many advanced oxidation processes (AOPs) use Fenton-like reactions to degrade organic pollutants by activating peroxymonosulfate (HSO 5 - , PMS) or peroxydisulfate (S 2 O 8 2- , PDS) with Fe(H 2 O) 6 2+ (Fe aq II ). This paper presents results on the kinetics and mechanisms of reactions between Fe aq II and PMS or PDS in the absence and presence of bicarbonate (HCO 3 - ) at different pH. In the absence of HCO 3 - , Fe aq IV , rather than the commonly assumed SO 4 •- , is the dominant oxidizing species. Multianalytical methods verified the selective conversion of dimethyl sulfoxide (DMSO) and phenyl methyl sulfoxide (PMSO) to dimethyl sulfone (DMSO 2 ) and phenyl methyl sulfone (PMSO 2 ), respectively, confirming the generation of Fe aq IV by the Fe aq II -PMS/PDS systems without HCO 3 - . Significantly, in the presence of environmentally relevant concentrations of HCO 3 - , a carbonate radical anion (CO 3 •- ) becomes the dominant reactive species as confirmed by the electron paramagnetic resonance (EPR) analysis. The new findings suggest that the mechanisms of the persulfate-based Fenton-like reactions in natural environments might differ remarkably from those obtained in ideal conditions. Using sulfonamide antibiotics (sulfamethoxazole (SMX) and sulfadimethoxine (SDM)) as model contaminants, our study further demonstrated the different reactivities of Fe aq IV and CO 3 •- in the Fe aq II -PMS/PDS systems. The results shed significant light on advancing the persulfate-based AOPs to oxidize pollutants in natural water.