Unveiling the directional dynamics: Hydrated electron driven defluorination in PFOA⁻ and PFOS⁻ through ab Initio molecular dynamics and quantum chemistry

Abstract

Hydrated electrons (e⁻(aq)) are recognized for their potent reducing capabilities, making them significant in environmental engineering, particularly in the degradation of persistent pollutants like perfluoroalkyl compounds (PFCs). This study investigates the influence of attack direction of e⁻(aq) on the degradation mechanisms of PFCs, addressing a critical gap in understanding due to experimental limitations. Utilizing ab initio molecular dynamics and quantum chemical calculations, we systematically simulated the attack direction of e⁻(aq) on PFCs, focusing on the formation of anionic radicals and their excited-state reactivity. Our results indicate that the attack direction is pivotal for C-F bond cleavage: e⁻(aq) targeting the carboxyl end promotes effective bond cleavage, while approaches from the carbon-fluorine chain are hindered by molecular orbital shielding effects. Furthermore, we demonstrate that employing micellar systems to maintain PFCs in an unsolvated anionic state significantly reduces excitation energy, enhances red-shifted absorption, and increases excitation probability. Importantly, the excited-state electronic structure of PFCs closely mirrors that of their anionic radicals. These findings provide a novel strategy for improving the degradation of PFCs, thereby advancing treatment processes for persistent environmental pollutants and contributing to the broader understanding of water quality management.