Adsorption of per- and polyfluoroalkyl substances (PFAS) by quaternary ammonium and fluorine-functionalized...

Per- and polyfluoroalkyl substances (PFAS) are globally pervasive contaminants in aquatic environments. Their structural diversity and complex chemistries present significant challenges for adsorption-based remediation technologies. Traditional sorbents, which typically rely on a single dominant interaction mechanism, often fail to effectively capture the broad spectrum of PFAS present in aqueous film-forming foam (AFFF) matrices. This study integrates experimental and computational approaches to investigate the synergistic roles of host-guest inclusion, hydrophobic, fluorophilic, and electrostatic interactions in PFAS adsorption. The sorbents examined were cyclodextrin-based polymers engineered with varying proportions of fluorinated, amine, and quaternary ammonium functional groups to promote these interactions. Among the tested materials, the fluorinated, quaternary ammonium-modified cationic sorbent exhibited superior performance in adsorbing short-chain anionic PFAS. We directly treated a diluted AFFF sample with this sorbent, with 95 distinct identified PFAS at total concentration up to 1.3 mg·L^-1, including 55 anionic, 33 zwitterionic, and 7 nonionic PFAS-making this one of the most complex but extremely environmentally-relevant PFAS matrices studied to date in the context of novel sorbents. 48 of the PFAS have not, to our knowledge, been included in prior studies. Our sorbent demonstrated exceptional performance under these challenging conditions, achieving 96.6 % total PFAS mass removal. This included 88.5 % removal of zwitterionic PFAS, which accounted for 24.3 % of the total PFAS mass. These zwitterionic PFAS serve as long-term sources for more mobile PFAS and are particularly environmentally relevant in the context of remediation of AFFF-impacted environmental aqueous media. These findings underscore the critical roles of hydrophobic, fluorophilic and electrostatic interactions in enhancing sorbent performance. While cyclodextrin's host-guest chemistry was not the dominant adsorption mechanism, it contributed to stabilizing PFAS orientation and improving overall uptake. This study provides valuable insights and a theoretical foundation for the rational design of next-generation sorbent technologies aimed at efficient PFAS remediation in complex aqueous environments.