Alcohol-induced drying of carbon nanotubes and its implications for alcohol/water separation: a molecular dynamics study.
Alcohol-induced drying of carbon nanotubes and its implications for alcohol/water separation: a molecular dynamics study.
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DOI：
10.1063/1.4807484
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发表时间：
2013-05
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通讯作者：
Xingling Tian;Zaixing Yang;Bo Zhou;P. Xiu;Y. Tu
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文献类型：
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作者：
Xingling Tian;Zaixing Yang;Bo Zhou;P. Xiu;Y. Tu
醇类化合物是化学工业中的重要产物，但由于醇类化合物的亲水性，从其水溶液中分离出醇类化合物是非常困难的。基于分子动力学模拟，我们观察到一个惊人的纳米级干燥现象，并提出了一种节能和高效的方法，即使用单壁碳纳米管（SWNTs）来分离酒精/水。我们使用各种常见的线性醇，包括C1-C6 - 1醇和甘油来演示（苯酚也用作比较）。我们的模拟结果表明，当单壁碳纳米管浸泡在醇水溶液中时，尽管醇的浓度很低（1 M），但各种醇都会导致纳米管脱水（干燥），并在宽[(13,13)]和窄[（6,6）或（7,7）]的单壁碳纳米管内部积累。特别是，在狭窄的单壁碳纳米管中，大多数醇形成了几乎均匀的一维分子线。详细的能量分析表明，纳米管内醇类比水更优先吸附是由于醇类与单壁碳纳米管的分散相互作用比水更强。有趣的是，我们发现对于宽SWNT， 1-醇的选择性随着醇的碳原子数（n碳）的增加而增加，并且C1-C5的1-醇的选择性与n碳呈指数规律；对于窄碳纳米管，甲醇、乙醇和丙醇对1-醇的选择性非常高，并在Ncarbon = 3时达到最大值。讨论了潜在的物理机制和这些观察结果对醇/水分离的影响。我们的发现提供了利用SWNT束∕膜有效脱水水性醇（和其他亲水性有机分子）的可能性。
Alcohols are important products in chemical industry, but separating them from their aqueous solutions is very difficult due to the hydrophilic nature of alcohols. Based on molecular dynamics simulations, we observe a striking nanoscale drying phenomenon and suggest an energy-saving and efficient approach toward alcohol∕water separation by using single-walled carbon nanotubes (SWNTs). We use various common linear alcohols including C1-C6 1-alcohols and glycerol for demonstration (the phenol is also used as comparison). Our simulations show that when SWNTs are immersed in aqueous alcohols solutions, although the alcohols concentration is low (1 M), all kinds of alcohols can induce dehydration (drying) of nanotubes and accumulate inside wide [(13, 13)] and narrow [(6, 6) or (7, 7)] SWNTs. In particular, most kinds of alcohols inside the narrow SWNTs form nearly uniform 1D molecular wires. Detailed energetic analyses reveal that the preferential adsorption of alcohols over water inside nanotubes is attributed to the stronger dispersion interactions of alcohols with SWNTs than water. Interestingly, we find that for the wide SWNT, the selectivity for 1-alcohols increases with the number of alcohol's carbon atoms (Ncarbon) and exhibits an exponential law with respect to Ncarbon for C1-C5 1-alcohols; for narrow SWNTs, the selectivity for 1-alcohols is very high for methanol, ethanol, and propanol, and reaches a maximum when Ncarbon = 3. The underlying physical mechanisms and the implications of these observations for alcohol∕water separation are discussed. Our findings provide the possibility for efficient dehydration of aqueous alcohols (and other hydrophilic organic molecules) by using SWNT bundles∕membranes.