Tunable macromolecular-based materials for the adsorption of perfluorooctanoic and octanoic acid anions

Abstract

The sorption properties of tunable urethane-based copolymer materials containing β-cyclodextrin (β-CD) were evaluated with perfluorooctanoic acid (PFOA) and octanoic acid (OA) anions in aqueous solutions, respectively. The copolymer materials are herein referred to as macromolecular imprinted materials (MIMs) since their design strategy incorporates a porogen macromolecule (β-CD) within a cross-linked hexamethylene diisocyanate (HDI) framework. We report the tunable uptake of OA and PFOA anions from aqueous solution with variable adsorption modes, in accordance with the composition of the MIMs. The sorption results with granular activated carbon (GAC) were compared at 295K and pH values exceeding the pKa values of each adsorbate. The BET and Sips models provided estimates of the monolayer sorption capacity (Qm) and related equilibrium sorption parameters. The Qm value for GAC with PFOA was ∼1.4mmol/g; whereas, a greater Qm value for PFOA (up to 2.6mmol/g) was observed with the MIMs. GAC displays greater sorption capacity toward PFOA at relatively low Ce values and saturation of the monolayer occurs at Ce∼0.5mM. The MIMs/PFOA system displays monolayer completion at values of Ce∼1mM and multilayer sorption when Ce>1mM. Equilibrium sorption of PFOA onto MIMs occurs at the inclusion sites of β-CD and interstitial binding sites of the polymeric framework. Surface adsorption of the PFOA anion occurs between the PFOA carboxylate head group and dipolar interstitial domains of the cross-linker framework. The MIMs sorbents display tunable and favorable binding with PFOA and OA anions where the uptake (per mg MIMs) with PFOA was ∼5–33% (5μM–5mM) and with OA was ∼0.5–5% (1–20mM). The overall sorptive uptake of OA and PFOA anions by the MIMs sorbents meets or exceeds those observed for GAC.