Chemically Modular, Nonfluorinated Polymer Adsorbents for Capturing Per- and Polyfluoroalkyl Substances (PFAS)

Abstract

Recent design strategies for polymeric adsorbents which remove per- and polyfluoroalkyl substances (PFAS) from water have relied on coupling both electrostatic and fluorine–fluorine interactions with PFAS in polymer adsorbents. Nonfluorinated polymers are a desirable alternative to reduce cost and reliance on fluorinated precursors. Molecular design of new adsorbents requires development of chemically modular synthetic strategies to uncover new, useful structure–property relationships. We utilize a modular synthetic platform using active ester click chemistry to prepare a library of PFAS adsorbents containing a wide range of Lewis base ligands alongside both hydrophilic and hydrophobic co-monomers. Poly(ethylene glycol) diacrylate networks containing both aliphatic groups and strong bases such as piperazine and piperidine exhibit rapid removal of >98% perfluorooctanoic acid (PFOA) from dilute solutions and can be regenerated using light alcohols. PFOA binding capacities are as high as 750 mg g−1 despite these materials having lower effective fixed charge densities than commercial anion exchange polymers. Sorption behavior is strongly influenced by ligand basicity, ligand grafting density, and equilibrium pH in addition to the presence of aliphatic co-monomers. Notably, the highest sorption capacities are achieved at low pH where some sorbed PFOA is hypothesized to exist as neutral rather than anionic species, indicating a new potential route for optimizing PFAS capture. This systematic structure–property study lays the foundation for future mechanistic studies using click-functionalized polymeric PFAS adsorbents.