Endowing deep eutectic solvent with neutral and ionizable perfluoroalkyl substances extracting capability: experimental study and ab initio molecular dynamics simulation

Abstract

The simultaneous separation of neutral and ionizable perfluoroalkyl substances (PFASs) is challenging. The traditional solvents used for this purpose are toxic and harmful. Deep eutectic solvents (DESs) as sustainable alternatives to toxic reagents have received considerable attention in current research. In this work, an array of complementary experimental (liquid–liquid equilibrium experiments) and computational (ab initio molecular dynamics, AIMD) techniques were utilized to explore the distinct distribution behaviors, complicated interaction network, and corresponding mechanisms from multidimensional temporal and spatial perspectives. The proposed bromophenylcyanide-based eutectic solvent systems exhibited good separation and extraction performance for both neutral and ionizable PFASs. The presence of a cyano group adjacent to bromine leads to increased polarization of the C–Br bond, resulting in increased strength of the Br···F contact, which provides selectivity to some extent. For fatty acids, their disruptive effect on eutectic systems is greater because of the relatively strong aggregation that affects DES structuring. For PFASs, different categories of target monomers are confined in the DES cavities and interact with the surrounding solvent through abundant interaction sites (such as electrostatic attraction, N-H···F-C, O-H···F-C, O-H···O-H, and C≡N···O-H hydrogen bonds) without significantly disrupting the solvent structural properties by reducing the molecular mobility.