Department of Chemistry and Material Science, Langfang Normal University, Langfang 065000, Hebei, P. R. China.
Phys Chem Chem Phys. 2019 Jan 30;21(5):2601-2610. doi: 10.1039/c8cp07383j.
Deep eutectic solvents (DESs) are one type of green solvents. Most of the DESs could absorb water from air. However, even a trace amount of water can affect the chemical structure and physical properties of DESs. To date, no study has been reported on the hygroscopicity of DESs. Consequently, in this study, a comprehensive investigation was performed on the capacity, kinetics, mechanism, and furthermore the dynamic process (by PCMW2D-COS IR spectra) of atmospheric water absorption from air by DESs. The results show that most DESs are highly hygroscopic. Surface absorption enhances the overall water absorption capacity by DESs in spite of decreasing the initial water absorption rate. In the beginning, the water absorption increases with an increase in the number of hydrophilic groups in DESs due to the retained DES nanostructure during this period. Therefore, DESs with more hydrophilic groups (ChCl:glucose than ChCl:xylitol) possess a higher water absorption initial rate. However, when the water absorption capacity is high, the hindrance from the H-bond strength from inner DESs needs to be overcome for the absorption of more water. In this case, DESs with stronger H-bonds (ChCl:glucose than ChCl:xylitol) have a lower steady-state water absorption capacity and an easier equilibrium.
深共晶溶剂 (DESs) 是一种绿色溶剂。大多数 DESs 可以从空气中吸收水分。然而，即使是微量的水也会影响 DESs 的化学结构和物理性质。迄今为止，尚未有关于 DESs 吸湿性的研究报道。因此，在本研究中，全面研究了 DESs 从空气中吸收水分的能力、动力学、机制，以及通过 PCMW2D-COS IR 光谱研究了动态过程。结果表明，大多数 DESs 具有很强的吸湿性。尽管表面吸收会降低 DESs 的初始吸水速率，但会增强 DESs 的整体吸水能力。在开始时，由于在这段时间内保留了 DES 纳米结构，DESs 中亲水性基团的数量增加，导致吸水增加。因此，具有更多亲水性基团的 DESs（ChCl:glucose 比 ChCl:xylitol）具有更高的初始吸水速率。然而，当吸水能力较高时，需要克服来自内部 DESs 的氢键强度的阻碍才能吸收更多的水。在这种情况下，氢键更强的 DESs（ChCl:glucose 比 ChCl:xylitol）具有较低的稳态吸水能力和更容易达到平衡。
