Peroxymonosulfate (HSO5-, PMS) is an alternative bulk oxidant in advanced oxidation processes (AOPs), where it is normally activated by the input of energy or reducing agents to generate the reactive oxygen species, sulfate and hydroxyl radicals. This study finds that PMS undergoes direct reaction with a variety of compounds, including antibiotics (sulfamethoxazole, trimethoprim, ampicillin), pharmaceuticals (ranitidine, cimetidine), phenolics (2,4,6-trichlorophenol, 4-chlorophenol), and singlet oxygen (1O2) scavengers (furfuryl alcohol (FFA), histidine, azide) over timescales ranging from minutes to a few hours. For a test compound with intermediate reactivity (FFA), involvement of hydroxyl and/or sulfate radicals was ruled out by scavenging experiments and EPR spectroscopy. While self-decomposition of PMS generates 1O2 quantitatively, as shown spectroscopically, kinetically, and in trapping experiments, we show conclusively that 1O2 plays only a minor role in the transformation of FFA—and by inference the other compounds— due to efficient quenching of 1O2 by water. The pH-rate constant profile for FFA transformation was consistent with electrophilic attack by PMS or its deprotonated form on the diene group of FFA or its conjugate base. Direct electrophilic oxidation of the other compounds is similarly proposed. The direct oxidation of FFA by PMS is accelerated by (bi)carbonate, borate, and pyrophosphate ions. This study indicates that direct reaction of PMS must be taken into account in AOPs and other applications of PMS, and also signals caution to researchers about the choice of buffering agent and 1O2 trapping/scavenging agent used in PMS studies.

Oxidation of organic contaminants by unactivated peroxymonosulfate: Roles of reactive species and direct oxidation

256th National Meeting (2018)

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