| Acetate-based ionic liquids not only possess the inherent characteristics of conventional ionic liquids, such as higher solubility, negligible vapor pressure and so on, but also can act as a kind of absorbing material to be applied in the field of sour gases capture due to their alkalinity resulted from the weakly acidic groups. Nowadays most researches were focused on those imidazolium ionic liquids like 1-ethyl-3-methylimidazolium acetate [Emim]Ac and 1-butyl-3-methylimidazolium acetate [Bmim]Ac. In our previous work the ether oxygen group was grafted onto imidazolium cation, thus constructing the functionalized ionic liquid, 1-methoxyethyl-3-methylimidazolium acetate ([C1OC2mim]Ac), which has been successfully used in CO2 capturing. It was confirmed from the experimental results that the chemical absorption occurred at the ratio 1:1 of [C1OC2mim]Ac to CO2 in the ionic liquid. This ionic liquid exhibited higher gas capacity and had a better performance than the common ionic liquids.As a further extension of our previous experimental work, the quantum chemistry calculations for [C1OC2mim]Ac and its mixed system with CO2 ([C1OC2mim]Ac-CO2) were carried out. The concerned studies for these two systems were concentrated on the theoretical analysis involving their optimized stable configurations, distribution of electrostatic potential, hydrogen bonding and the other weak interactions, which from the microscopic point of view further interpreted the internal interactions and the charge transferring trend in ionic liquids. Moreover, the quantum chemistry calculations and nuclear magnetic resonance were used to explore the interaction between [C1OC2mim]Ac and solvent molecules, which could provide a good insight into understanding and ascertaining the influence of diverse solvents on CO2 absorption process of ionic liquid. As a part of the project supported by the National Science Foundation of China (NO.21573061), the main contents are as follows:1.At B3LYP/6-311++G(d, p) level with Density Functional Theory (DFT), electrostatic potential analysis on their optimized stable configurations of anionic and cationic monomers of [C1OC2mim]Ac were conducted to determine the possible binding sites between anion and cation. Then, the most stable configuration of [C1OC2mim]Ac was selected, and thus its structural parameters, electrostatic potential and the bonded interaction between the two ion pairs were analyzed in detail, which interpreted microscopically the charge transfer trend and possible interaction between cation and anion. Besides, these studies laid the foundation for the following work.2. In order to further investigate the effect of molecular structures of ionic liquids on their properties,-three different ionic liquids, [C1OC2mim]BF4, [C1OC2mim]Ac and [Bmim]Ac were selected to make a quantum chemistry calculation separately. Through comparing their structures and interaction parameters between anion and cation of three selected ionic liquids, the relationships between structures and properties on anion and cation of ionic liquids were established. These studies provided theoretical basis for further designing and developing the novel ionic liquids.3. At B3LYP/6-311++G(d, p) level with DFT, CO2-[C1OC2mim]+and [C1OC2mim]Ac-CO2 systems were optimized structurally and then the relevant electrostatic potential and topological properties were studied, and thus the interaction mechanism of inter-molecules was proposed. In addition, a deep study of possible mechanism of chemical absorption of [C1OC2mim]Ac on CO2, can provide a valuable reference for studying CO2 absorption mechanism of other ionic liquids.4. By combining the quantum chemistry calculation with NMR spectroscopy, the interaction between [C1OC2mim]Ac and small-molecule solvents such as H2O and DMSO was investigated. Furthermore, the effect of physicochemical properties of solvents on the structure of [CiOC2mim]Ac and interaction was discussed in detail, which can provide a theoretical support for further application of [C1OC2mim]Ac. |
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