New Insights into the Combination of Permanganate and Bisulfite as a Novel Advanced Oxidation Process: Importance of High Valent Manganese-Oxo Species and Sulfate Radical.

Recently, it has been reported that the combination of permanganate (Mn(VII)) and bisulfite can lead to a rapid degradation of organic contaminants, where soluble Mn(III) is proposed to be responsible. Interestingly, in this work, we demonstrated the involvement of high-valent Mn-oxo species (possibly Mn(V)) as well as sulfate radical in the Mn(VII)/bisulfite system, by using methyl phenyl sulfoxide (PMSO) as a chemical probe. It was found that the combination of Mn(VII) and bisulfite resulted in appreciable degradation of PMSO under various conditions, while negligible PMSO was degraded by manganese dioxide (MnO) in the presence of bisulfite under similar conditions. This result indicated that Mn(III) intermediate formed in situ in both Mn(VII)/bisulfite and MnO/bisulfite systems as proposed in literature exhibited sluggish reactivity toward PMSO. In parallel, the formation of methyl phenyl sulfone (PMSO) product in the Mn(VII)/bisulfite system was observed, suggesting the role of high-valent Mn-oxo species as an oxygen-atom donor in conversion of PMSO to PMSO. Moreover, the yield of PMSO (i.e., mole of PMSO produced per mole of PMSO degraded) was quantified to be 20-100%, strongly depending on the [Mn(VII)]/[bisulfite] ratio as well as solution pH. The competitive contribution of sulfate radical, which oxidized PMSO to hydroxylated and/or polymeric products but not to PMSO, accounted for the yield of PMSO less than 100%. This work advances the fundamental understanding of a novel class of oxidation technology based on the combination of Mn(VII) and bisulfite for environmental decontamination.