The Dynamic Process of Atmospheric Water Sorption in [BMIM][Ac]: Quantifying Bulk versus Surface Sorption and Utilizing Atmospheric Water as a Structure Probe

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• 作者：Yu Chen ; Yuanyuan Cao ; Chuanyu Yan ; Yuwei Zhang ; Tiancheng Mu
• 刊名：Journal of Physical Chemistry B
• 出版年：2014
• 出版时间：June 19, 2014
• 年：2014
• 卷：118
• 期：24
• 页码：6896-6907
• 全文大小：663K
• 年卷期：v.118,no.24(June 19, 2014)
• ISSN：1520-5207

文摘

The dynamic process of the atmospheric water absorbed in acetate-based ionic liquid 1-butyl-3-methyl-imidazolium acetate ([BMIM][Ac]) within 360 min could be described with three steps by using two-dimensional correlation infrared (IR) spectroscopy technique. In Step 1 (0鈥?20 min), only bulk sorption via hydrogen bonding interaction occurs. In Step 2 (120鈥?20 min), bulk and surface sorption takes place simultaneously via both hydrogen bonding interaction and van der Waals force. In Step 3, from 320 min to steady state, only surface sorption via van der Waals force occurs. Specifically, Step 2 could be divided into three substeps. Most bulk sorption with little surface sorption takes place in Step 2a (120鈥?80 min), comparative bulk and surface sorption happens in Step 2b (180鈥?60 min), and most surface sorption while little bulk sorption occurs in Step 2c (260鈥?20 min). Interestingly, atmospheric water is found for the first time to be able to be used as a probe to detect the chemical structure of [BMIM][Ac]. Results show that one anion is surrounded by three C4,5H molecules and two anions are surrounded by five C2H molecules via hydrogen bonds, which are very susceptible to moisture water especially for the former one. The remaining five anions form a multimer (equilibrating with one dimer and one trimer) via a strong hydrogen bonding interaction, which is not easily affected by the introduction of atmospheric water. The alkyl of the [BMIM][Ac] cation aggregates to some extent by van der Walls force, which is moderately susceptible to the water attack. Furthermore, the proportion of bulk sorption vs surface sorption is quantified as about 70% and 30% within 320 min, 63% and 37% within 360 min, and 11% and 89% until steady-state, respectively.