Spectroscopic Observation of Na Cations Entrapped in Small Cages of sII Propane Hydrate

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• 作者：Jiwoong Seol ; Woongchul Shin ; Dong-Yeun Koh ; Hyery Kang ; Boram Sung ; Huen Lee
• 刊名：The Journal of Physical Chemistry C
• 出版年：2012
• 出版时间：January 12, 2012
• 年：2012
• 卷：116
• 期：1
• 页码：1439-1444
• 全文大小：437K
• 年卷期：v.116,no.1(January 12, 2012)
• ISSN：1932-7455

文摘

Although numerous studies have been conducted on various ionic clathrate hydrates, in spite of its potential importance the inclusion of metal cations in continuous water-host frameworks has not yet been clearly identified by direct spectroscopic evidence. Here, a key question arises as to whether the small alkali metals such as Na⁺ can be entrapped because they are considered to be too small to be stabilized in the hydrate cages. In this study, we first suggested spectroscopic evidence for the enclathration of Na⁺ in a small cage of sII propane hydrate. First, we checked the overall structure of sII propane hydrate incorporated with NaSO₃CH₃ and NaSO₃NH₂ with powder XRD and ¹³C NMR. Next, we revealed the difference of chemical shift of ²³Na between Ih and sII hydrate phases with solid-state ²³Na MAS NMR as direct evidence of entrapped Na⁺ in 5¹² cages. In addition, we also checked ¹³C MAS NMR of the CH₃SO₃^{鈥?/sup> anion and found that Na+ cations in a small cage could be stabilized with an enclathrated CH₃SO₃鈥?/sup> anion in a large cage. To the best of our knowledge, it is the first discovery of small alkali cations stabilized in a continuous hydrate phase. Finally, we would like to emphasize that clathrate hydrate including small alkali metals can be designed and synthesized for its potential applications to various types of energy devices using its ionic mobility through the hydrate channel.}