Fundamental insight on how carbon chain length affects per-and polyfluoroalkyl substances adsorption onto hydrophobic deep eutectic solvents

In this study, our focus lies on hydrophobic deep eutectic solvents (HDES) as we explore their potential for the adsorption of short -chain perand polyfluoroalkyl substances (PFAS) from water. This investigation utilizes Conductor -like Screening MOdel for Real Solvents (COSMO-RS) to fundamentally evaluate HDES for the adsorption of perfluorobutanesulfonic acid (PFBS), perfluorobutanoic acid (PFBA), perfluorohexanesulfonic acid (PFHxS), and perfluorohexanoic acid (PFHxA). By analyzing sigma surfaces, sigma profiles, and sigma potentials, it was observed that the PFAS compounds possess sufficiently strong nonpolar and hydrogen bond donating sites, having affinity towards hydrogen bond acceptor surfaces. According to the thermodynamic adsorption studies, short -chain PFAS exhibit higher affinity towards 5 main HBAs (trioctylphosphine oxide, tetrabutylammonium bromide, tetraoctylammonium chloride, tetraoctylammonium bromide, trihexyltetradecylphosphonium chloride) and 2 HBDs (camphor and L-arginine), with activity coefficients being as low as -13.07. Excess enthalpy analysis reveals that nonpolar interactions play a dominant role in the exchanges between HDES and PFAS compounds, suppressing hydrogen bonding interactions by an order of magnitude. TOPO: L-arginine (1:1) showed the lowest excess enthalpy of mixing for PFBS at -13.43 kJ/mol. The same HDES showed values of -10.60 kJ/mol, -15.14 kJ/mol, and -12.27 kJ/mol for PFBA, PFHxS, and PFHxA, respectively. Lastly, the bestperforming solvent combinations underwent virtual models for property evaluation of chemicals within a global architecture (VEGA) analysis to assess their impact on human and environmental toxicity aspects such as mutagenicity, carcinogenicity, bioaccumulation, and acute toxicity. The outcome reveals that the best performing HDES components listed above present minimal toxicity and pose negligible environmental risks.