Efficient extraction of phenolics from coal gasification wastewater by hydrophobic deep eutectic solvents: Experimental and mechanistic study

Phenolic pollutants, particularly polyphenolic compounds, present a significant challenge in wastewater treatment due to their refractory nature, which leads to excessive emissions and substantial ecological risks. This study designed and synthesized a novel hydrophobic deep eutectic solvent (HDES) and systematically elucidated the microscopic mechanism of its highly efficient phenol extraction. Initially, three HDES systems were screened based on the Conductor-like Screening Model for Real Solvents (COSMO-RS) model. Molecular dynamics (MD) simulations demonstrated that HDES3 exhibited the best performance. MD simulations further revealed that electrostatic interactions (E elec ) dominate the phenol extraction process, while radial distribution function (RDF) and spatial distribution function (SDF) analyses indicated that a 1:1 hydrogen bond donor-acceptor (HBA-HBD) ratio creates stronger interaction sites. Experimental results showed that the extraction efficiencies for phenol and hydroquinone reached 99.9 % and 97.7 %, respectively, with the total phenol concentration in wastewater reduced from 6300 mg/L to 57.6 mg/L. The extraction mechanism was also elucidated. Electrostatic potential (ESP) and independent gradient model based on Hirshfeld partition (IGMH) analyses demonstrated that the oxygen atoms on the hydroxyl groups in HDES3 (1:1) form additional interaction sites with the O atoms of phenolic compounds, where hydrogen bonding plays a dominant role, synergistically enhanced by van der Waals (vdW) forces to significantly increase interaction strength. This study proposes an efficient phenolic pollutant extraction technology based on an HDES system, providing a green and high-performance solution for coal gasification wastewater treatment.