Institute of Advanced Materials, Physicochemical Processes, Nanotechnology and Microsystems-Division of Physical Chemistry, National Center for Scientific Research "Demokritos" , Aghia Paraskevi Attikis, 15310 Athens, Greece.
J Phys Chem B. 2013 Oct 10;117(40):12234-51. doi: 10.1021/jp407364e. Epub 2013 Oct 1.
Absorption of carbon dioxide and water in 1-butyl-3-methylimidazoliun tricyanomethanide ([C4C1im][TCM]) and 1-octyl-3-methylimidazolium tricyanomethanide ([C8C1im][TCM]) ionic liquids (ILs) was systematically investigated for the first time as a function of the H2O content by means of a gravimetric system together with in-situ Raman spectroscopy, excess molar volume (V(E)), and viscosity deviation measurements. Although CO2 absorption was marginally affected by water at low H2O molar fractions for both ILs, an increase of the H2O content resulted in a marked enhancement of both the CO2 solubility (ca. 4-fold) and diffusivity (ca. 10-fold) in the binary [C(n)C1im][TCM]/H2O systems, in contrast to the weak and/or detrimental influence of water in most physically and chemically CO2-absorbing ILs. In-situ Raman spectroscopy on the IL/CO2 systems verified that CO2 is physically absorbed in the dry ILs with no significant effect on their structural organization. A pronounced variation of distinct tricyanomethanide Raman modes was disclosed in the [C(n)C1im][TCM]/H2O mixtures, attesting to the gradual disruption of the anion-cation coupling by the hydrogen-bonded water molecules to the TCM anions, in accordance with the positive excess molar volumes and negative viscosity deviations for the binary systems. Most importantly, CO2 absorption in the ILs/H2O mixtures at high water concentrations revealed that the TCM Raman modes tend to restore their original state for the heavily hydrated ILs, in qualitative agreement with the intriguing nonmonotonous transients of CO2 absorption kinetics unveiled by the gravimetric measurements for the hybrid solvents. A molecular exchange mechanism between CO2 in the gas phase and H2O in the liquid phase was thereby proposed to explain the enhanced CO2 absorption in the hybrid [C(n)C1im][TCM]//H2O solvents based on the subtle competition between the TCM-H2O and TCM-CO2 interactions, which renders these ILs very promising for CO2 separation applications.
首次系统研究了 1-丁基-3-甲基咪唑三氰胺([C4C1im][TCM])和 1-辛基-3-甲基咪唑三氰胺([C8C1im][TCM])离子液体(ILs)中二氧化碳和水的吸收情况，作为功能随 H2O 含量的变化通过重量系统与原位拉曼光谱、过量摩尔体积(V(E))和粘度偏差测量一起进行。尽管在两种 ILs 中，低 H2O 摩尔分数对 CO2 吸收的影响很小，但随着 H2O 含量的增加，二元[C(n)C1im][TCM]/H2O 体系中 CO2 的溶解度(约 4 倍)和扩散系数(约 10 倍)显著增强，与大多数物理和化学 CO2 吸收 ILs 中较弱和/或有害的水影响形成对比。对 IL/CO2 体系的原位拉曼光谱证实，CO2 在干燥的 IL 中被物理吸收，对其结构组织没有显著影响。在[C(n)C1im][TCM]/H2O 混合物中，明显改变了独特的三氰胺拉曼模式，证明随着氢键水分子逐渐破坏阴离子-阳离子偶联，TCM阴离子与TCM阴离子的偶联，符合二元体系的正过量摩尔体积和负粘度偏差。最重要的是，在高水浓度下 ILs/H2O 混合物中 CO2 的吸收表明，对于高度水合的 ILs，TCM拉曼模式趋于恢复其原始状态，这与重量测量为混合溶剂揭示的 CO2 吸收动力学的奇特非单调瞬态定性一致。因此，提出了一种气相 CO2 和液相 H2O 之间的分子交换机制，以解释在混合[C(n)C1im][TCM]//H2O 溶剂中增强的 CO2 吸收，这基于 TCM-H2O 和 TCM-CO2 相互作用之间的微妙竞争，这使得这些 ILs 非常有前途用于 CO2 分离应用。
