Unraveling PFAS adsorption mechanisms on amine-functionalized mesoporous silica by ¹ ⁹F NMR

The removal of per- and polyfluoroalkyl substances (PFAS) is a rapidly growing research area, yet key knowledge gaps remain in understanding adsorption mechanisms. To advance adsorbent design, the adsorption of a mixture of 22 PFAS species on pristine SBA-15 silica were examined, aminoethyl-grafted SBA (SBA-NH), and diethylenetriamine-terminated SBA (SBA-TA). Adsorption pathways were investigated using liquid-state ¹ ⁹F NMR and LC-MS/MS. SBA-TA achieved the highest PFAS removal (79% in methanol:water (50:50) and 93% in 3% aqueous film-forming foam), followed by SBA-NH (78% and 69%) and pristine SBA (36% and 66%). Pristine SBA showed notable adsorption in methanol:water (∼70 mg/g dry weight), attributed to its linear micropores matching PFAS cross-sectional dimensions. Functionalization with ammonium groups greatly enhanced capacity (∼150 mg/g), with SBA-TA outperforming SBA-NH, underscoring the role of ion–ion interactions in PFAS retention. These results were validated using groundwater from the Hovgården landfill site in Sweden.