Photodegradation of polychlorinated Biphenyls (PCBs) in surfactant solutions: experimental and theoretical Insights into dechlorination pathways

Polychlorinated biphenyls (PCBs) are persistent organic pollutants with low aqueous solubility, which limits their photodegradation and hinders environmental remediation. This study hypothesizes that micellar environments formed by anionic surfactants can enhance PCB photodegradation by improving their aqueous solubility and altering dechlorination pathways. To test this, three representative PCB congeners were exposed to UV irradiation in sodium dodecyl sulfate (SDS) micellar solutions. Experimental results showed that SDS micelles facilitate stepwise PCBs dechlorination under UV light, with ortho-chlorine atoms removed preferentially, followed by para-chlorine removal. Photodegradation efficiency was enhanced under alkaline conditions, at lower initial concentrations, and in the relatively nonpolar microenvironment of the SDS micelles. Complementary DFT and TD-DFT calculations were performed to investigate the electronic structure and bond dissociation behavior of the selected congeners. The results revealed that ortho-chlorine atoms possess lower C-Cl bond dissociation energies, more localized HOMO distribution, and lower electrostatic potential than para-chlorines. TD-DFT results further suggested that photodechlorination is initiated from the singlet excited state. These theoretical insights are consistent with the experimentally observed positional selectivity and provide a molecular-level basis for understanding PCB reactivity in surfactant-rich systems. Overall, this study offers mechanistic insight into surfactant-assisted PCB photodegradation and supports its potential as a practical strategy for treating PCB-contaminated environments.