NMR Study of Preferential Endohedral Adsorption of Methanol in Multiwalled Carbon Nanotubes

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• 作者：Xin Liu ; Xiulian Pan ; Wanling Shen ; Pengju Ren ; Xiuwen Han ; Xinhe Bao
• 刊名：The Journal of Physical Chemistry C
• 出版年：2012
• 出版时间：April 12, 2012
• 年：2012
• 卷：116
• 期：14
• 页码：7803-7809
• 全文大小：373K
• 年卷期：v.116,no.14(April 12, 2012)
• ISSN：1932-7455

文摘

Adsorption of ¹³C-enriched methanol in multiwalled carbon nanotubes (MWNTs) was systematically studied under well-controlled environment by ¹³C MAS NMR. The results of variable-pressure experiments indicate that the endohedral adsorption of methanol in carbon nanotubes (CNTs) is preferential over the exohedral adsorption. The exohedral adsorption does not occur until the endohedral adsorption saturates. The ¹³C chemical shift of endohedral methanol exhibits a large upfield shift due to the strong spatial diamagnetic shielding effect induced by the delocalized electrons of nanotubes under the influence of external magnetic field. The exohedral methanol is also shielded, but to a lesser extent. DFT calculations support these experimental results. The ¹³C spin鈥搇attice relaxation times, T₁, of endohedral and exohedral methanol were also measured, and they have different vapor pressure dependence at room temperature. Furthermore, variable-temperature experiments suggest that methanol molecules inside CNTs may form a layered structure at low temperature with one layer close to the wall and the second layer near the center of the nanotubes.