Rapid and highly efficient removal of aqueous perfluorooctanoic acid using deep eutectic solvents for sustainable water remediation: An integrated experimental-modeling approach

This work reports on the first use of deep eutectic solvents (DESs) as an environmentally sustainable solution for the extractive removal of perfluorooctanoic acid (PFOA), one of the most prevalent and persistent emerging contaminants, from aqueous media. The design framework of the DESs was based on multiple metrics, including the extraction performance, density, viscosity, environmental impact, and hydrophobicity. Through the multi-criteria evaluation of ten candidate DESs, trioctylphosphine oxide and lauric acid (TOPO:LauA, 1:1) demonstrated exceptional single-stage extraction efficiency (99.74 %), far outperforming the toluene benchmark (82.26 %), and showing favorable characteristics across all other assessed criteria. Remarkably, the exceptional extraction efficiency (>98 %) of TOPO:LauA was sustained across diverse operational conditions. The latter included a broad pH and temperature spectrum (3–9 pH; 15–100 °C), solvent-to-feed ratios down to 1:7 (w/w), contaminant concentrations as low as 0.100 mg/L, rapid equilibration within 1 min, and reusability throughout seven cycles without any observable degradation, as verified by spectroscopic analysis. TOPO:LauA also demonstrated exceptional selectivity for PFOA, in the presence of other per- and polyfluoroalkyl substances (PFAS) or in a synthetic wastewater matrix simulating municipal wastewater. Moreover, computational quantum chemistry modeling using density functional theory (DFT) and COSMO-RS, implemented in Materials Studio and COSMOtherm software, was employed. This provided insights into the molecular mechanism of extraction and demonstrated strong agreement with the experimental findings. The development of this new DES for the extraction of aqueous PFOA is a critical breakthrough in water treatment that surpasses the efficacy, sustainability, and scalability of traditional PFAS extraction solvents and other conventional removal methods of PFAS, such as adsorption and membrane separation.