Per- and poly-fluorinated alkyl substances (PFAS) are composed of C-F bonds which impart high thermodynamic stability to these materials. Due to their attractive properties, PFAS have been widely utilized in industry and consumer products for a variety of applications including as firefighting foams and in various manufacturing environments, which has led to their release into the environment. Throughout the United States, PFAS contamination in drinking water has been a recurring issue, with concentrations exceeding 70 ng/L, necessitating implementation of treatment technologies. In recent years, PFAS remediation using filtration with sorbents such as granulated activated carbon, ion-exchange resins, and synthetic membranes have been studied. While these materials can remove PFAS from water, they are unable to selectively remove short-chain and long-chain PFAS at environmentally relevant concentrations. Macrocycle-based sorbents show promise in PFAS remediation due to their tunable cavities and their ability to incorporate functional groups that can modulate underlying interactions, including dispersion, hydrogen bonding, and sterics, thereby promoting selective PFAS uptake. Moreover, it stands to reason that the integration of macrocyclic molecules in porous polymer networks to develop cross-linked macrocyclic polymers may be an effective strategy to remove PFAS from water. In this work, we investigate cyclodextrin-based cross-linked polymers for PFAS removal. Using atomistic molecular dynamics (MD), we uncover molecular-scale mechanisms underlying PFAS adsorption, highlighting the roles of electrostatic and hydrophobic interactions on PFAS adsorption in cross-linked macrocyclic polymers. Our simulations reveal distinct PFAS adsorption patterns across regions within the cross-linked macrocyclic polymers which can be attributed to differences in hydrophobicity and ionic character. Guided by these insights, we propose modifications to our base cyclodextrin-based polymer structure and validate our computational predictions with experimental data. This integrated approach deepens our understanding of key PFAS-sorbent interactions and provides a framework for development of next-generation sorbent materials for effective PFAS removal from water.
