Role of inorganic anions in improving the oxidizing capacity of heat-activated peroxymonosulfate: Identification of primary degradative pathways

This study demonstrated a drastic improvement in the oxidizing capacity of heat-activated peroxymonosulfate (heat/PMS) upon the addition of bicarbonate (HCO3) and phosphate (PO4). Injecting the anions caused a 20- to 30-fold increase in the phenol degradation efficiency of heat/PMS at the temperature range of 40-50 celcius that was insufficient to thermally activate peroxydisulfate (PDS). The heat/PMS-PO4 outperformed heat/PDS in degrading benzoic acid, whereas heat/PMS-HCO3 marginally decomposed it. The reactivity of heat/PMS-PO4 did not vary sensitively depending on substrate type, which resulted from the increased yield of sulfate radical due to facile thermal cleavage of the peroxide bond loosened in the PMS-PO4 complex, based on the electron paramagnetic spectral features and quenching effects of radical scavengers. Degradation of phenols and furfuryl alcohol by heat/PMS-anion was highly accelerated under alkaline conditions through heat-promoted direct PMS oxidation and singlet oxygenation. Along with the similarity between the heat/PMS-anion systems in intermediate distribution (distinguished from that of heat/PDS) and chronoamperometric current response of the heated PMS solution upon the subsequent injection of anion and phenol, the extent of PMS consumption in the heated PMS-anion or PMS-organic-anion mixtures, which depended on substrate type and temperature, implied the role of heat-activated PMS-anion complexes as the non-radical oxidants.