Influence of Electrolytes on the Air–Water Interfacial Properties of Perfluoroalkyl Acids (PFAAs)

Perfluoroalkyl acids (PFAAs), a subclass of per- and polyfluoroalkyl substances (PFAS), are widely used but pose significant environmental concerns due to their toxicity and bioaccumulation. Foam fractionation, utilizing the amphiphilic nature of PFAS, offers a promising remediation method by exploiting their migration to air-water interfaces. The effectiveness of this technique is highly dependent on the air-water interfacial properties and the adsorption capacity of PFAS at the interface. This study investigates the impact of electrolytes prevalent in PFAS-contaminated water on the air-water interfacial properties of PFAAs, focusing on surface tension and diffusion behavior. Our results show that electrolytes reduced surface tension for both long- and short-chain PFAAs, with divalent ions (Ca²⁺) exhibiting stronger effects than monovalent ions (Na⁺). Surface tension modeling using Gibbs and Extended Langmuir isotherms revealed enhanced adsorption and increased surface excess concentrations in the presence of electrolytes, while dynamic surface tension analysis highlighted the influence of electrolytes on molecular diffusion and adsorption kinetics at short time scales.