Sustainable Oxidation of Azoles: Structure-Reactivity Controls and Reactive Species Dynamics in UV-Activated...

Despite the increasing use of azoles, comparative studies on their degradation and mineralization across oxidative systems remain limited. This study systematically examined the degradation and mineralization behaviors of four representative azoles, benzotriazole (BTA), 5-methylbenzotriazole (5MBTA), triazole (TA), and pyrazole (PR), in UV-activated persulfate processes. Although all azoles were rapidly degraded, mineralization efficiencies differed markedly between peroxymonosulfate (PMS) and peroxydisulfate (PDS) and were strongly influenced by molecular structure. PR and TA achieved near-complete mineralization within 30 min, whereas BTA and 5MBTA showed limited total organic carbon removal, particularly in UV/PMS. Scavenger and probe tests indicated that BTA degradation was dominated by singlet oxygen, while 5MBTA proceeded through both singlet oxygen and electron-transfer pathways. Electrochemical analysis confirmed that PMS facilitated electron transfer more effectively than PDS, explaining differences in oxidation behavior. pH tests showed that alkalinity reduced mineralization in UV/PDS but enhanced it in UV/PMS through SO₅ ^2--mediated electron transfer. Both systems maintained strong performance under varying pollutant levels, oxidant dosages, and realistic water matrices. Overall, degradation followed PR > TA > 5MBTA > BTA. These findings clarify structure-reactivity relationships in azole oxidation and highlight UV/PMS and UV/PDS as promising and sustainable advanced treatment technologies for azole-contaminated wastewater.