(454b) Fluorine-Free, Chemically Modular Polymer Adsorbents for PFAS Capture

Polymer adsorbents offer a versatile solution for PFAS removal from disparate water resources. Unfortunately, conventional “one size fits all” adsorbents such as activated carbon or ion exchange resins are insufficient for removing PFAS from water due to their poor specificity, weak binding affinities, and slow uptake kinetics. Recent developments in PFAS-selective polymers have primarily sought to leverage fluorine-fluorine and electrostatic interactions between PFAS and adsorbent matrices to improve separation. However, a limited fundamental understanding of how specific PFAS-ligand interactions govern underlying mass transfer phenomena in polymer adsorbents has hindered development of more efficient materials for PFAS capture.

In this study, we developed two modular synthetic strategies for patterning polymer adsorbents with Lewis base ligands which we hypothesize can interact with anionic PFAS via acid-base interactions. Notably, these materials are all fluorine-free which reduces reliance on fluorinated manufacturing precursors and reduces risk of leaching new fluorinated compounds into the environment. The first strategy uses active ester click chemistry to incorporate different Lewis bases at controlled grafting densities into PEG diacrylate copolymer networks. PFAS sorption experiments were performed via targeted analysis using Liquid Chromatography Tandem Mass Spectrometry (LC-MS/MS) at UF’s Mass Spectrometry Research and Education Center (MSREC) using a Bruker Impact II QTOF Mass Spectrometer. Combining strong Lewis bases and hydrophobic alkyl co-monomers enabled these polymers to adsorb >98% PFOA from 10 ng/mL (ppb) aqueous solutions at ligand grafting densities as low as 0.6 mol%. PFOA sorption was observed to be affected by both ligand density and basicity (pK_b), the latter of which controls their extent of protonation. These sorbents can be quantitatively regenerated using light alcohols such as methanol.

The second strategy incorporates similar ligands into macroporous polymer monoliths with controlled morphologies. Monoliths with continuous liquid pathways were formed by free radical copolymerization and crosslinking in the presence of a porogen solvent. Lewis base ligands were grafted onto the surfaces of monolith channels via epoxide ring opening reactions. Ligand-patterned monoliths showed no PFOA elution after >1,000 bed volumes whereas ligand-free analogues showed PFOA breakthrough in less than 40 bed volumes. Ongoing studies are investigating separation of other PFAS including short chain compounds and the effects of co-occurring solutes on separation efficiency.