Efficient Production of HO• and 3DOM* via Far-UVC Photolysis of Dissolved Organic Matter in Water

HO^• and ³DOM* that are photochemically produced from dissolved organic matter (DOM) affect the performance of UV-driven processes in water treatment. This study developed and applied a method to quantify the yields for HO^• and ³DOM* (expressed as ⌀_HO^• and f_TMP, respectively) from far-UVC (UV₂₂₂) photolysis of DOM. ⌀_HO^• at 222 nm (0.64-0.82%) is 13-34 times higher than at 254 nm and 136-213 times higher than at >290 nm. f_TMP at 222 nm (293-1011 M^-1) is 3.6-8.4 times and 1.8-19 times greater than at 254 nm and >290 nm, respectively. Electron-accepting moieties (e.g., carbonyl-containing compounds) are likely the major precursors of ³DOM* under UV₂₂₂ irradiation. Despite DOM's light-screening and radical-scavenging effects, the high ⌀_HO^• at 222 nm ensures that DOM has a negligible impact on HO^• concentrations in the absence of other radical precursors (e.g., NO₃^-). Concurrently, enhanced ³DOM* generation accelerates the photosensitized activation of NH₂Cl by 3-fold under UV₂₂₂ irradiation compared to UV₂₅₄. Given the critical roles of HO^• and ³DOM* in micropollutant degradation, oxidant activation, and reactive species transformation, this work advances both the fundamental photochemistry and the practical application of far-UVC-driven water treatment technologies.