Photodegradation Mechanism of UV-328 in Natural Organic Matter Contexts Under Simulated Solar Irradiation

2-(Benzotriazol-2-yl)-4,6-bis(2-methylbutan-2-yl)phenol (UV-328), a widely utilized UV absorber in plastics and diverse products, has been frequently detected in the environment; yet, research on its photochemical degradation is scarce. Dissolved organic matter (DOM) and particulate organic matter (POM), as important components of natural organic matter, can produce photosensitization by absorbing photons. This study examined the influence of DOM from various sources on the photodegradation of UV-328 under simulated daylight conditions. Experiments revealed that excited triplet DOM (³DOM*) is the primary factor enhancing the photodegradation of UV-328. Utilizing excitation–emission matrix spectroscopy combined with parallel factor analysis (EEMs-PARAFAC) and seawater ultrafiltration experiments, it was demonstrated that high molecular weight DOM, particularly autochthonous DOM produced in seawater, could more rapidly photodegrade UV-328. Additionally, the photodegradation of UV-328 in suspended particulate matter (SPM) was influenced by DOM, inorganic ions, and organic acids, with DOM contributing to a positive feedback effect on the degradation process. The degradation pathways and products of UV-328 were first elucidated using ultraperformance liquid chromatography-quadrupole time-of-flight mass spectrometry (UPLC-Q-TOF-MS), supplemented by density functional theory (DFT) calculations. This study provides novel insights into the photodegradation mechanisms of UV-328 by combining DOM and POM for the first time.