Coupled oxidative and reductive pathways govern nitrogen fate during ionizing radiation degradation of sulfonamide antibiotics

Oxidative–reductive coupling governs nitrogen fate in ionizing radiation. • e aq − promoted reductive cleavage of sulfonamide groups and NH 4 + formation. • Electron-deficient moieties capture e aq − and suppress NO 3 − formation. • Reactive species and electron competition regulate nitrogen transformation. Ionizing radiation (IR) is an emerging advanced oxidation and reduction technology for micropollutant removal; however, the mechanisms governing nitrogen fate during contaminant degradation remain poorly understood. Here, five representative sulfonamide antibiotics were systematically investigated to elucidate how coupled oxidative and reductive pathways regulate nitrogen transformation during IR treatment. Results demonstrated that hydroxyl radicals (•OH) dominated parent compounds degradation, achieving complete degradation of all five sulfonamides at 2–5 kGy, whereas hydrated electrons (e aq − ) primarily promoted reductive cleavage of sulfonamide groups and NH 4 + formation. The highest mineralization efficiency reached 41.7% under intermittent irradiation at 5 kGy. The subsequent formation of NO 2 − and NO 3 − strongly depended on pH-regulated radical speciation and secondary oxidation of reduced nitrogen intermediates under alkaline conditions. Importantly, molecular structure influenced nitrogen transformation through intramolecular electron competition. Electron-deficient moieties, including N O and azo groups, preferentially captured e aq − , thereby redistributing reducing equivalents and suppressing oxidative nitrogen conversion to NO 3 − . Furthermore, environmentally relevant water constituents altered nitrogen partitioning through secondary radical chemistry but exerted comparatively limited influence on the overall nitrogen fate. Furthermore, toxicity evolution of degradation products was evaluated to assess the environmental safety of the treatment process. These findings demonstrate that nitrogen transformation during IR is jointly governed by oxidative–reductive pathway coupling and molecular electron-transfer characteristics. This study provides new mechanistic insight into nitrogen cycling during advanced oxidation and reduction processes and highlights the potential for controllable nitrogen management in IR-based water treatment technologies. Download: Download high-res image (205KB) Download: Download full-size image