Degradation of UV328 by ozone/peroxymonosulfate system: Performance and mechanisms

2-(2H-benzotriazol-2-yl)-4,6-di-tert-pentylphenol (UV328) is an emerging persistent organic pollutant ubiquitously found in environmental matrices. Though some advanced oxidation processes have been tested to degrade UV328 in waste streams, the degradation mechanisms are largely unknown. In this study, the degradation of UV328 by ozone (O₃) and peroxymonosulfate (PMS) was systemically investigated. At neutral pH, 97.0% UV328 was removed in 5 min with 6.4 mg/min O₃ and 2 mM PMS, and the degradation rate was positively correlated with the concentration of oxidants. Hydroxyl radical (•OH), sulfate radical (SO₄^•-) and singlet oxygen (¹O₂) participated in the degradation of UV328, in which ¹O₂ played a key role. Based on the identified transformation intermediates and density functional theory simulations, three degradation pathways of dehydrogenation, cycloaddition and hydroxylation were proposed. •OH and SO₄^•- radicals could attack UV328 through hydrogen atom abstraction channel. ¹O₂-mediated cycloaddition reaction is favorable, and •OH could react with UV328 via radical adduct formation pathway. Toxicity assessment indicated that O₃/PMS treatment mitigated the ecological risks of UV328.