Revealing the Role of Varied Quaternary Ammonium Groups for Capturing Per- and Polyfluoroalkyl Substances

Per- and polyfluoroalkyl substances (PFAS) are synthetic chemicals that are challenging to remove from contaminated sources. Ion-exchange (IEX) resins that contain ammonium groups are commonly used for PFAS removal, relying on electrostatic interactions to capture anionic PFAS. Commercially available IEX products contain a variety of substituents on the ammonium cations, but little is known regarding the structure–property relationships of cation identification and PFAS removal. In this study, we prepared a series of IEX resins that have different charged segments to investigate their role in PFAS removal efficiency and capacity. To be more specific, polystyrene-based IEX resins were prepared using pentafluorostyrene, vinylbenzene chloride, and divinylbenzene [poly(FVD)], followed by quaternization with trimethylamine (TMA), tributylamine, triethylamine, or dimethylaminoethanol. Among all resins, the TMA+-containing IEX resins demonstrated the highest PFAS removal capacity, rapid sorption kinetics, and good regeneration capability. We hypothesize that the superior performance of poly(FVD)-TMA+ resin is due to the more efficient quaternization using TMA as well as its low dissociation energy with Cl^– and high exposure of cationic groups, leading to easier replacement by PFAS molecules. In addition, poly(FVD)-TMA+ performs significantly better for PFAS removal from landfill leachate and effluent lagoon natural water masteries compared to commercially available IEX resins like PFA694E and PSR2+. Overall, this study provides crucial design criteria for charged groups for preparing efficient PFAS sorbents with enhanced removal performance.