Enhanced Photochemical Reactivity of Natural Organic Matter Post-Peroxymonosulfate Oxidation

Peroxymonosulfate (PMS) is commonly used as sulfate radical precursor in advanced oxidation processes, employed for wastewater treatment and remediating polluted subsurface. Here, we demonstrated that unactivated PMS can directly oxidize natural organic matter (NOM), resulting in the enhanced formation of excited triplet NOM (3NOM*), singlet oxygen (1O2), and hydroxyl radical (center dot OH) upon exposure to ultraviolet (UV)-A irradiation. UV spectroscopic characterization and electron-donating capacity (EDC) measurement unveiled a notable decrease in aromaticity, molecular weight, and EDC. The quantum yields of 3NOM*, 1O2, and center dot OH exhibited positive correlations with E2/E3 (ratio of absorbance at 254 to 365 nm), while displaying negative correlations with specific UV absorbance at 254 nm (SUVA254) and EDC after PMS treatment. Fourier transform infrared spectroscopic analysis and a model compound study suggested that the rise in aromatic ketone compounds contributed to the heightened photochemical reactivity following PMS oxidation. Furthermore, Fourier transform ion cyclotron resonance mass spectrometry results revealed that aromatic ketones and quinones can be formed by PMS reactions with alkylbenzene and phenol moieties in NOM. These findings highlight the potential oxidizing capacities of PMS on NOM molecules. The alterations in NOM characteristics bear significance for the degradation of micropollutants in sunlit surface waters.