Evaluation of Regenerability of Ionic Liquid-Impregnated Activated Carbon Adsorbed with PFAS via Chemical and Sonochemical Extraction

This study evaluates the extraction efficiency of per- and polyfluoroalkyl substances (PFAS) from ionic liquid (IL)-impregnated activated carbon (AC) that has adsorbed PFAS, compares chemical and sonochemical extraction methods, and assesses adsorbent reusability. PFAS-laden IL-impregnated AC was subjected to chemical or sonochemical extraction using deionized water, methanol, and ethanol. Chemical extraction with deionized water showed recovery efficiencies below 1% across all durations, whereas organic solvents achieved > 90% for perfluoropentanoic acid (PFPeA) and perfluorobutane sulfonic acid (PFBS), and 38.09%-95.09% for perfluorononanoic acid (PFNA) and perfluorooctane sulfonic acid (PFOS) over 4 days. Sonochemical extraction with methanol removed PFAS much more rapidly, achieving recovery efficiencies from 16.95% (PFOS) to 81.30% (PFBS) within 1 hour. Detection of fluoride and PFAS degradation by-products through targeted and non-targeted analysis confirmed that sonochemical extraction partially degraded and defluorinated PFAS originally adsorbed to IL-impregnated AC. Elemental, thermogravimetric, and BET surface analyses of sonochemically treated IL-impregnated AC showed that both adsorbed PFAS and impregnated IL were largely removed, leaving a material with physicochemical properties similar to unmodified AC. Re-impregnation of IL into the recovered material yielded PFAS removal efficiencies comparable to pristine IL-impregnated AC, with no statistically significant decrease. These results demonstrate that sonochemical extraction of spent IL-impregnated AC enables rapid PFAS release, partial defluorination, and AC recovery. This regeneration technique supports the practical application of IL-impregnated AC and strengthens its competitiveness against conventional PFAS adsorbents.