Laser mineralization of per- and polyfluoroalkyl substances on laser-induced graphene

Abstract

Per- and polyfluoroalkyl substances (PFAS) are persistent and toxic water pollutants that pose significant environmental and health risks. Various methods exist for PFAS treatment, most of which rely on adsorption. However, these methods often produce byproducts that require additional treatment before disposal. Here we show a facile method for degrading model pollutants perfluorooctanoic acid (PFOA) and trifluoroacetic acid (TFA) using a low energy IR CO₂ laser on a laser-induced graphene (LIG) substrate, with NaOH serving as a mineralizing reagent. Laser treatment achieved up to 68% mineralization and the conversion of strong CF bonds present in PFOA into inorganic fluoride (NaF) was observed depending on the laser power, with optimum performance at 8% power. The fluorine mineralization efficiency increased with a larger Na-to-F molar ratio, up to a ratio of 4.5. Additionally, the LIG substrate was reusable for up to five treatment cycles under the optimal laser power. The method was also applied to a more volatile short chain perfluoroalkyl carboxylate TFA, and up to ∼27% of the organic fluorine was converted to NaF as quantified by ion chromatography. Contact angle measurements for both PFOA- and TFA-treated LIG showed decreased wettability after laser irradiation compared to deionized water (DI)-treated controls, possibly indicating incorporation of fluorine (CF) into the LIG chemical structure surface during degradation. The low cost of the methodology and reuse of the substrate offers a sustainable alternative for PFAS degradation and mineralization that might be incorporated into advanced water purification technologies.