Investigation of the Adsorption Processes of Fluorocarbon and Hydrocarbon Anions at the Solid–Solution Interface of Macromolecular Imprinted Polymer Materials

This study details the isotherm adsorption properties of cross-linked polymers containing β-cyclodextrin (β-CD), hereafter referred to as macromolecular imprinted materials (MIMs). The isotherm sorption parameters of the MIMs are reported with perfluorooctanoic acid (PFOA), octanoic acid (OA), and perfluorooctanesulfonate (PFOS) anions. The Sips and BET models describe variable solid--solution interfacial interactions for the MIMs with perfluorocarbon (PFC) and hydrocarbon (HC) anions, respectively. Typical monolayer adsorption occurs for the MIMs/OA system via the hydrocarbon alkyl tail of OA. Atypical adsorption is observed for PFOA and is driven via interactions between the MIMs surface with the carboxylate headgroup, as evidenced by the formation of multilayer adsorption and aggregation of the PFC alkyl chain at elevated levels. Molecular level support for the unique interfacial adsorption phenomenon is provided by several complementary methods: contact angle, infrared (IR) spectral shifts and intensity variations, differential scanning calorimetry (DSC), and isothermal titration calorimetry (ITC). Isotherm studies reveal the formation of monolayers of a hydrocarbon surfactant anion (OA) vs self-assembled multilayer aggregates for PFC anion species (PFOA and PFOS) at the MIMs solid–solution interface. The surface interactions are interpreted as a balance between headgroup electrostatic interactions and hydrophobic effects of the amphiphile chain at the adsorbent–solution interface.