Effect of Hydrophobic Cross-Linkers in Strong Base Gel-Type Resins on the Adsorption Kinetics and Capacity for Perfluoroalkyl Substances

The persistence and water mobility of per- and polyfluoroalkyl substances (PFAS) have led authorities worldwide to lower regulatory limits to prevent adverse health effects. Removal via adsorption on activated carbon can be inefficient due to the unspecific surface interaction, while ion exchange resins with positive charges and hydrophobic chains can offer faster kinetics and improved removal. In here, novel cationic resins were synthesized by cross-linking polyethylenimine, followed by methylation. To obtain cross-linked particles and introduce hydrophobic interacting moieties in one single synthetic step, aliphatic, fluorous, and silicone-based oligoethers were used as cross-linkers. These cationic adsorbents were compared with two state-of-the-art strong base gel-type ion exchange resins and granular activated carbon in isotherm and kinetic studies. The newly developed adsorbents showed significantly faster removals of all tested long- and short-chain PFAS. The fluorous cationic adsorbent achieved equilibrium loadings that were comparable to those of the state-of-the-art adsorbents for all PFAS with five or more perfluorinated carbon atoms.