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 (•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 •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.

过一硫酸盐（Peroxymonosulfate, PMS）常作为硫酸根前驱体应用于高级氧化工艺，用于污水处理以及受污染地下介质的修复。本研究证实，未活化的过一硫酸盐可直接氧化天然有机质（natural organic matter, NOM），使其在紫外A波段（UV-A）辐照下，激发三重态天然有机质（excited triplet NOM, ³NOM*）、单线态氧（singlet oxygen, ¹O₂）与羟基自由基（hydroxyl radical, •OH）的生成量显著提升。通过紫外光谱表征与电子给体能力（electron-donating capacity, EDC）测定，发现经PMS氧化后，NOM的芳香性、分子量与电子给体能力均显著降低。³NOM*、¹O₂与•OH的量子产率与254 nm与365 nm处吸光度比值（E2/E3）呈正相关，而与254 nm处比紫外吸光度（specific UV absorbance at 254 nm, SUVA254）以及经PMS处理后的EDC呈负相关。傅里叶变换红外光谱分析与模型化合物研究表明，芳香酮类化合物的生成是PMS氧化后NOM光化学反应活性增强的关键原因。此外，傅里叶变换离子回旋共振质谱结果显示，PMS可与NOM中的烷基苯与酚官能团反应，生成芳香酮类与醌类化合物。本研究结果凸显了PMS对NOM分子的潜在氧化能力，而NOM特性的改变对光照地表水中微量污染物的降解具有重要意义。