Polychlorinated naphthalenes (PCNs) are a new type of persistent organic pollutant (POP) characterized by persistence, bioaccumulation, dioxin-like toxicity, and long-range atmospheric transport. Focusing on one type of PCN, monochlorinated naphthalenes (CN‒1, CN‒2), this study aimed to examine their photodegradation in the environment. In this work, CN‒1 and CN‒2 were employed as the model pollutants to investigate their photodegradation process under UV-C irradiation. Factors like the pH, initial concentrations of CN‒1, and inorganic anions were investigated. Next, the roles of hydroxyl radicals (·OH), superoxide anion radicals (O2•‒), and singlet oxygen (1O2) in the photodegradation process were discussed and proposed via theory computation. The results show that the photodegradation of CN‒1 and CN‒2 follows pseudo-first-order kinetics. Acidic conditions promote the photodegradation of CN‒1, while the effects of pH on the photodegradation of CN‒2 are not remarkable. Cl−, NO3−, and SO32− accelerate the photodegradation of CN‒1, whereas the effect of SO42‒ and CO32‒ is not significant. Additionally, the contributions of ·OH and O2•‒ to the photodegradation of CN‒1 are 20.47% and 38.80%, while, for CN‒2, the contribution is 16.40% and 16.80%, respectively. Moreover, the contribution of 1O2 is 15.7%. Based on DFT calculations, C4 and C6 of the CN‒1 benzene ring are prioritized attack sites for ·OH, while C2 and C9 of CN‒2 are prioritized attack sites.
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