Plasma-Generated Free Electrons Induced Perfluorooctanoic Acid Efficient Degradation at the Gas–Liquid Interface

Abstract

Low-temperature plasma, generating both reductive electrons and diverse oxidative species, has demonstrated considerable potential for the degradation of perfluorooctanoic acid (PFOA). However, limited understanding of electron propagation mechanisms during discharge has led previous research to focus on hydrated electrons (e_aq^–) while neglecting free electrons (e^–). In this study, a consistent and modeled dielectric barrier discharge (DBD) plasma was employed to degrade PFOA. Contribution analysis indicated that reactions driven by e^– were dominant, with substantial contributions from hydroxyl radical (•OH)-mediated oxidation. By integrating a kinetic model with a streamer solver, a basic discharge unit model was developed. Simulation of e^– streamer propagation identified a high-intensity response electric field formed by the e^– memory effect, with a peak strength of 1.816 × 10⁶ V/m. This electric field facilitated a secondary acceleration of e^–, allowing e^– to penetrate the surface water layer and directly attack PFOA via chain-shortening mechanisms. The delocalized state of e^– restricted degradation primarily to the gas–liquid interface, minimizing interference from the surrounding medium. This study highlights the previously overlooked role of e^– and provides essential theoretical insights for the plasma-based treatment of PFOA-contaminated water.