Hefei National Laboratory for Physical Sciences at the Microscale, University of Science and Technology of China, Hefei, Anhui 230026, China.
J Chem Phys. 2012 Jul 21;137(3):034501. doi: 10.1063/1.4732313.
The systems of open-ended carbon nanotubes (CNTs) immersed in methanol-water solution are studied by molecular dynamics simulations. For the (6,6) CNT, nearly pure methanol is found to preferentially occupy interior space of the CNT. Even when the mass fraction (MF) of methanol in bulk solution is as low as 1%, the methanol MF within the CNT is still more than 90%. For CNTs with larger diameters, the methanol concentrations within CNTs are also much higher than those outside CNTs. The methanol selectivity decreases with increasing CNT diameter, but not monotonically. From microscopic structural analyses, we find that the primary reason for the high selectivity of methanol by CNTs lies on high preference of methanol in the first solvation shell near the inner wall of CNT, which stems from a synergy effect of the van der Waals interaction between CNT and the methyl groups of methanol, together with the hydrogen bonding interaction among the liquid molecules. This synergy effect may be of general significance and extended to other systems, such as ethanol aqueous solution and methanol/ethanol mixture. The selective adsorption of methanol over water in CNTs may find applications in separation of water and methanol, detection of methanol, and preservation of methanol purity in fuel cells.
通过分子动力学模拟研究了甲醇-水溶液中开口碳纳米管（CNT）的体系。对于（6,6）CNT，几乎纯甲醇被发现优先占据 CNT 的内部空间。即使在本体溶液中甲醇的质量分数（MF）低至 1%，CNT 内的甲醇 MF 仍高于 90%。对于直径较大的 CNT，CNT 内的甲醇浓度也远高于 CNT 外的甲醇浓度。甲醇的选择性随 CNT 直径的增加而降低，但并非单调递减。通过微观结构分析，我们发现 CNT 对甲醇具有高选择性的主要原因在于甲醇在 CNT 内壁附近的第一溶剂化壳层中具有很高的优先性，这源于 CNT 与甲醇的甲基之间的范德华相互作用以及液体分子之间的氢键相互作用的协同效应。这种协同效应可能具有普遍意义，并扩展到其他体系，如乙醇水溶液和甲醇/乙醇混合物。CNT 中甲醇对水的选择性吸附可能在水和甲醇的分离、甲醇的检测以及燃料电池中甲醇纯度的保持方面得到应用。
