National Energy Technology Laboratory, U.S. Department of Energy, Pittsburgh, Pennsylvania 15236, USA.
J Phys Chem B. 2010 Nov 25;114(46):15029-41. doi: 10.1021/jp106500p. Epub 2010 Nov 3.
Atomistic simulations are used to study the ionic liquid (IL) 1-n-hexyl-3-methylimidazolium bis(trifluoromethylsulfonyl)amide ([hmim][Tf(2)N]) confined into (20,20) and (9,9) carbon nanotubes (CNTs) and the effect of confinement upon gas sorption. The cations and the anions exhibit highly ordered structures in the CNT. There are more cations adsorbed close to the (20,20) tube wall while more anions adsorb in the tube center at high IL loadings. The IL molecules in the CNT exhibit self-diffusivity coefficients about 1-2 orders of magnitude larger than the corresponding bulk IL molecules. Sorption of CO(2) and H(2) gases in the composite material consisting of CNT and IL indicates that H(2) molecules diffuse about 1.5 times faster than the CO(2). In contrast, H(2) diffuses about 10 times faster than CO(2) in both the CNT and in bulk IL. The CNT exhibits the largest amount of sorption for both CO(2) and H(2), followed by the composite material, and the IL exhibits the least gas sorption. When the temperature is increased, the amount of sorbed CO(2) decreases in all three types of systems (IL, CNT, and the composite material) while the H(2) sorption increases in [hmim][Tf(2)N], decreases in the CNT, and does not change significantly in the composite material. The composite material exhibits higher sorption selectivity for CO(2)/H(2) than both the IL and the CNT. It is very interesting to note that the IL molecules can be dissolved in the CO(2) molecules under confinement due to a favorable negative transferring energy. However, in the absence of confinement the IL molecules will not dissolve in the CO(2) due to a very large unfavorable positive transferring energy.
利用原子模拟方法研究了离子液体 1-己基-3-甲基咪唑双（三氟甲烷磺酰基）酰胺 ([hmim][Tf2N]) 在（20,20）和（9,9）碳纳米管 (CNT) 中的受限情况及其对气体吸附的影响。在 CNT 中，阳离子和阴离子呈现出高度有序的结构。在高离子液体负载下，更多的阳离子靠近（20,20）管壁吸附，而更多的阴离子吸附在管中心。CNT 中的离子液体分子的自扩散系数比相应的本体离子液体分子大约大 1-2 个数量级。在 CNT 和离子液体复合材料中 CO2 和 H2 气体的吸附表明，H2 分子的扩散速度比 CO2 快约 1.5 倍。相反，在 CNT 和本体离子液体中，H2 的扩散速度比 CO2 快约 10 倍。对于 CO2 和 H2，CNT 的吸附量最大，其次是复合材料，而离子液体的吸附量最小。当温度升高时，三种体系（离子液体、CNT 和复合材料）中吸附的 CO2 量均减少，而 [hmim][Tf2N] 中的 H2 吸附量增加，CNT 中的 H2 吸附量减少，复合材料中的 H2 吸附量变化不大。复合材料对 CO2/H2 的吸附选择性高于离子液体和 CNT。值得注意的是，由于负传递能有利，离子液体分子在受限条件下可以溶解在 CO2 分子中。然而，在没有限制的情况下，由于非常大的正传递能不利，离子液体分子不会溶解在 CO2 中。
