A series of natural, environmentally friendly and low-cost menthol-based hydrophobic deep eutectic solvents (DES) were synthesized to extract and concentrate solutes from dilute aqueous solutions, especially triphenylmethane (TPM) dye micropollutants. The system has excellent extraction performance for TPM. Density functional theory (DFT) and molecular dynamics (MD) simulation were used to quantitatively analyze the effect of the DES composition and TPM structure on the distribution of target molecules in two phases. The solvation free energy of ethyl violet (EV) in DES (−17.128 to −21.681 kcal mol⁻¹) is much larger than that in water (−0.411 kcal mol⁻¹), and increases with the increase of the HBD chain length, which is proportional to the extraction rate, indicating that the TPM molecules are more inclined to the DES environment, especially long-chain DES, than aqueous solution. For the same C₁₂DES, the extraction efficiency of the TPM dyes follows the order: ethyl violet (EV) (99.9%) > crystal violet (CV) (99.6%) > methyl violet (MV) (98.8%). EV has the smallest positive charge and the smallest dipole moment (9.109 D), and the Flory–Huggins parameters of EV (χ_EV–C12DES 0.053) relative to MV and CV are the smallest in C₁₂DES, and are also the largest in water (χ_EV–H2O 0.053), indicating that EV has the largest polarity difference with H₂O and is more easily detached from water and compatible with the long-chain DES phase. The motion of EV and MV on the phase interface of DES and water was calculated to further analyze from the molecular level. At the same time, EV tends to move into the DES phase. In summary, the excellent extraction ability of DES for TPM is verified through experiments and simulations, providing solid theoretical support in terms of separation in other fields.

中文翻译：

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薄荷醇基疏水性低共熔溶剂的制备用于三苯甲烷染料的萃取：定量性质和萃取机理

合成了一系列天然，环保和低成本的基于薄荷醇的疏水性深共熔溶剂（DES），以从稀水溶液中提取和浓缩溶质，尤其是三苯甲烷（TPM）染料微污染物。该系统具有出色的TPM提取性能。用密度泛函理论（DFT）和分子动力学（MD）模拟定量分析了DES组成和TPM结构对目标分子在两相中分布的影响。在DES乙基紫（EV）的溶剂化自由能（-17.128到-21.681千卡摩尔^-1）是在水中比大得多（-0.411千卡摩尔^-1），并且随着HBD链长的增加而增加，而HBD链长与提取速率成正比，表明TPM分子比水溶液更倾向于DES环境，尤其是长链DES。对于相同的C ₁₂ DES，TPM染料的提取效率遵循以下顺序：乙基紫（EV）（99.9％）>结晶紫（CV）（99.6％）>甲基紫（MV）（98.8％）。EV具有最小的正电荷和最小的偶极矩（9.109 D），相对于MV和CV而言，EV的Flory-Huggins参数（χEV _{–C 12 DES} 0.053）在C ₁₂ DES中最小，并且也是水中最大（χEV _{–H 2 O}0.053），表明EV与H ₂ O具有最大的极性差异，并且更容易从水中脱离并与长链DES相兼容。计算了DES和水相界面上EV和MV的运动，以从分子水平进一步分析。同时，EV倾向于进入DES阶段。总之，通过实验和模拟验证了DES对TPM的优异提取能力，为其他领域的分离提供了坚实的理论支持。