Singlet-Oxygen Generation in Alkaline Periodate Solution

A nonphotochemical generation of singlet oxygen (1O2) using potassium periodate (KIO4) in alkaline condition (pH > 8) was investigated for selective oxidation of aqueous organic pollutants. The generation of 1O2 was initiated by the spontaneous reaction between IO4– and hydroxyl ions, along with a stoichiometric conversion of IO4– to iodate (IO3–). The reactivity of in-situ-generated 1O2 was monitored by using furfuryl alcohol (FFA) as a model substrate. The formation of 1O2 in the KIO4/KOH system was experimentally confirmed using electron spin resonance (ESR) measurements in corroboration with quenching studies using azide as a selective 1O2 scavenger. The reaction in the KIO4/KOH solution in both oxic and anoxic conditions initiated the generation of superoxide ion as a precursor of the singlet oxygen (confirmed by using superoxide scavengers), and the presence of molecular oxygen was not required as a precursor of 1O2. Although hydrogen peroxide had no direct influence on the FFA oxidation process, the presence of natural organic matter, such as humic and fulvic acids, enhanced the oxidation efficiency. Using the oxidation of simple organic diols as model compounds, the enhanced 1O2 formation is attributed to periodate-mediated oxidation of vicinal hydroxyl groups present in humic and fulvic constituent moieties. The efficient and simple generation of 1O2 using the KIO4/KOH system without any light irradiation can be employed for the selective oxidation of aqueous organic compounds under neutral and near-alkaline conditions.