Molecular-Level Understanding of Solvation Structures and Vibrational Spectra of an Ethylammonium Nitrate Ionic Liquid around Single-Walled Carbon Nanotubes

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• 作者：Guobing Zhou ; Zhen Yang ; Fangjia Fu ; Yiping Huang ; Xiangshu Chen ; Zhanghui Lu ; Na Hu
• 刊名：Industrial & Engineering Chemistry Research
• 出版年：2015
• 出版时间：August 26, 2015
• 年：2015
• 卷：54
• 期：33
• 页码：8166-8174
• 全文大小：656K
• ISSN：1520-5045

文摘

Molecular dynamics simulations have been performed to explore the solvation structures and vibrational spectra of an ethylammonium nitrate (EAN) ionic liquid (IL) around various single-walled carbon nanotubes (SWNTs). Our simulation results demonstrate that both cations and anions show a cylindrical double-shell solvation structure around the SWNTs regardless of the nanotube diameter. In the first solvation shell, the CH₃ groups of cations are found to be closer to the SWNT surface than the NH₃⁺ groups because of the solvophobic nature of the CH₃ groups, while the NO₃^{鈥?/sup> anions tend to lean on the nanotube surface, with three O atoms facing the bulk EAN. On the other hand, the intensities of both C鈥揌 (the CH₃ group of the cation) and N鈥揙 (anion) asymmetric stretching bands at the EAN/SWNT interface are found to be slightly higher than the corresponding bulk values owing to the accumulation and orientation of cations and anions in the first solvation shell. More interestingly, the N鈥揙 stretching band exhibits a red shift of around 10 cm鈥? with respect to the bulk value, which is quite contrary to the blue shift of the O鈥揌 stretching band of water molecules at the hydrophobic interfaces. Such a red shift of the N鈥揙 stretching mode can be attributed to the enhanced hydrogen bonds (HBs) of the NO₃鈥?/sup> anions in the first solvation shell. Our simulation results provide a molecular-level understanding of the interfacial vibrational spectra of an EAN IL on the SWNT surface and their connection with the relevant solvation structures and interfacial HBs.}