(360ae) Insights of Phenolic Compounds Extraction from an Aqueous Environment Using Natural Deep Eutectic Solvents: Quantum Chemical and Molecular Dynamics Simulation

The phenolic compounds can be found in fruit, coffee, or tea and industrial wastewater from various industries and processes. The World Health Organization (WHO) has designated some of these phenolic compounds as priority pollutants because of their toxicity, so they must be removed before wastewater discharge. There has been a recent surge in interest in water-immiscible hydrophobic deep eutectic solvents (DESs). However, the hydrophobicity of these DESs has only been measured in a small number of studies. The stability of different DESs-water systems were studied to understand the stability of eutectic solvents to extract the phenolic compounds from aqueous environment. Based on relative stability screening, further molecular dynamics simulations studies of interfacial properties of DESs and water systems were performed, which plays critical role in application of liquid-liquid extraction(LLE). The considered DESs were DL-Menthol: Octanoic acid with a molar ratio of 1:1, DL-Menthol: Decanoic acid with a molar ratio of 1:1, Dodecanoic acid: Octanoic acid with a molar ratio of 1:3, and Dodecanoic acid: Decanoic acid with a molar ratio of 1:2. Thereafter, Non-bonded interactions, radial distribution function, combined distribution function, spatial distribution functions, and hydrogen bonding topology of various components were explored via MD simulations that highlighted the enhanced and favorable interactions of phenolic compounds (i.e., phenol and 2-chlorophenol) with hydrogen bond donor species of eutectic solvents. The charge-transfer (CT) process in quantum calculation confirmed the direction of CT from DESs to phenolic compounds, and the NBO analysis established the stability of DESs. The increase in bond distance between the HBA and HBD was confirmed with an increase in interaction between the DES and phenolic compounds. The atom-in-molecules (AIM) and noncovalent interaction (NCI) analysis suggest that strong noncovalent interactions are responsible for the higher extraction of phenolic compounds from water. The distribution coefficient (β), selectivity (S), and extraction efficiency (% EE) of phenolic compounds were calculated from the simulation and compared to the experimental LLE data. According to the MD simulation results, the extraction efficiency for the ternary DES-Water-Phenol or 2-chlorophenol systems was compared, which was in excellent agreement with experimental literature data with an RMSD of 1.7%.