Enhanced Interfacial Plasma Degradation of Per- and Polyfluoroalkyl Substances (PFAS) via Ultrasonically Generated...

The exceptional stability of C-F bonds renders PFAS highly persistent in aqueous environments, posing significant challenges for conventional treatment technologies. While plasma-based technologies show promise, their efficiency is often limited by poor gas-liquid mass transfer in bulk liquid. Here, an in-house constructed ultrasonic atomization-dielectric barrier discharge (UEN-DBD) system was developed to promote PFAS degradation under non-thermal plasma conditions. Ultrasonic atomization generated microdroplets, which promoted PFAS enrichment at the surface of microdroplets and facilitate interactions with plasma-generated reactive species. Using perfluorooctanoic acid (PFOA) and perfluorooctanesulfonate (PFOS) as model compounds, degradation behavior was evaluated over an initial concentration range of 0.01-1.0 ppm. At 0.01 ppm, degradation efficiencies of 96.06% for PFOA and 94.86% for PFOS were achieved within 5 min. Electron paramagnetic resonance (EPR) spectroscopy confirmed the formation of oxidative radicals (·OH) and suggested a mixed redox environment involving reactive species, potentially including superoxide (O₂·^-) or hydrated electrons (e_aq^-), in the discharge-treated system. High-resolution mass spectrometry results are consistent with a stepwise chain-shortening pathway dominated by successive -CF₂- scission, while fluoride-release measurements provided supporting evidence for partial defluorination. These findings advance the understanding of plasma-assisted PFAS degradation at the gas-liquid interface and provide a basis for the further development of plasma-assisted PFAS treatment strategies.