Anion exchange beads for PFAS capture using a polymerization-induced microphase separation approach

Abstract

Per- and poly-fluoroalkyl substances (PFAS) are contained in various consumer products that include nonstick coatings, packaging materials, cosmetics, and firefighting foams due to their combined hydrophobic and oleophobic properties and chemical and thermal stability. These properties also result in human toxicity and have led to their accumulation in the environment. Several methods are being used to remove PFAS contaminants from the environment, and one common technique involves removal through ion exchange. Polymerization-induced microphase separation (PIMS) enables the synthesis of PFAS-capturing anion exchange beads featuring co-continuous morphology, tunable domain spacing, and high surface accessibility within a mechanically robust crosslinked network. Beads were synthesized using a poly(ε-caprolactone)-b-poly(4-vinylbenzyl chloride)-based macro chain transfer agent, styrene, and divinylbenzene. Anion exchange beads were obtained by etching the poly(ε-caprolactone) component and quaternizing the poly(4-vinylbenzyl chloride), and their ion exchange capacity was measured to be 1.00 ± 0.05 mmol g⁻¹. The rates of PFAS removal were evaluated using pseudo-second-order kinetic analysis for both short-chain (trifluoroacetic acid [TFA] and perfluorobutanoic acid [PFBA]) and long-chain (perfluorooctanoic acid [PFOA]) PFAS. The initial sorption rates of TFA and PFBA were 2.9 and 2.3 times higher, respectively, in quaternized beads (PB-Q) compared to Amberlite IRA 900 whole resin. In contrast, PFOA exhibited a 1.7 times higher initial sorption rate to IRA 900 whole resin than to PB-Q. Langmuir isotherm analysis indicated significantly stronger affinities of all PFAS for PB-Q than IRA 900, even though the IRA 900 had greater capacity, suggesting that PB-Q is more effective for removing PFAS at low concentrations. Treating the PFAS loaded PB-Q beads with a 1 : 1 v/v mixture of methanol and 1 M NaCl_(aq) resulted in 100% PFAS desorption.