Studies on an Ionic Liquid Confined in Silica Nanopores: Change in Tg and Evidence of Organic–Inorganic Linkage at the Pore Wall Surface

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• 作者：Abhishek Kumar Gupta ; Yogendra Lal Verma ; Rajendra Kumar Singh ; Suresh Chandra
• 刊名：Journal of Physical Chemistry C
• 出版年：2014
• 出版时间：January 23, 2014
• 年：2014
• 卷：118
• 期：3
• 页码：1530-1539
• 全文大小：613K
• ISSN：1932-7455

文摘

Ionic liquid (IL) 1-ethyl-3-methylimidazolium ethyl sulfate [EMIM][EtSO₄] has been immobilized in silica matrix by using nonhydrolytic one-pot sol鈥揼el method, with tetraethyl orthosilicate (TEOS) used as precursor and formic acid as a reagent. The glass transition temperature (T_g) of the confined IL was 20 掳C higher than the bulk IL. The thermal stability of IL also increased upon confinement. These changes are explained on the basis of interactions between the inorganic SiO₂ pore wall surface and the organic cation [EMIM]⁺ and anion [EtSO₄]^{鈭?/sup> of the ionic liquid. Quantum mechanical calculation based on DFT has been used to show that the oxygen of SiO₂ interacts with the C鈥揌 of the imidazolium ring of [EMIM]+ cation and the surface Si atoms interact with S鈥揙 of the [EtSO₄]鈭?/sup> anion. The latter has led to Si鈥揙鈥揝 linkages, which have been experimentally confirmed by FTIR studies. The silanol OH group is also likely to interact but less dominantly as compared to the earlier discussed interaction. These interactions have also led to changes in the fluorescence spectra of the confined IL.}