Cation Radical Induced Photochlorination of Naphthalene in Saline Water under UV Light Irradiation

The phototransformation process of polycyclic aromatic hydrocarbons (PAHs) into chlorinated polycyclic aromatic hydrocarbons (Cl-PAHs) holds importance. Prior research indicated that Cl-PAHs are usually formed via the electrophilic chlorination of parent PAHs by chlorine radicals (Cl·). However, the contribution of nucleophilic photochlorination of PAHs that results in the generation of chlorinated products remains elusive. This work aims to explore the photochlorination mechanisms of naphthalene (NAP), with a focus on the active intermediates implicated in these reactions. We also evaluated the impact of natural factors such as pH, fulvic acid (FA), inorganic ions, and suspended particulate matter on the production of the chlorination products of NAP (1-chloronaphthalene, 1-ClNAP). The experimental results demonstrated that the maximum yield of 1-ClNAP reached 7.34%. In actual saline water, 1-ClNAP was also detected but with a lower yield of 0.71%. The quenching experiments revealed that the photochlorination of NAP was triggered by cationic radicals, which were generated after electron transfer from singlet state NAP (1NAP*) and triplet state NAP (3NAP*, T1) to O2 in saline water. Notably, Cl· was not involved in the photochlorination reaction. The objective of this study is to enhance our understanding and control of the photochlorination behaviors of PAHs in saline water.