Abstract
We have carried out an ab initio molecular dynamics study on the sulfur dioxide (SO2) solvation in 1-ethyl-3-methylimidazolium thiocyanate for which we have observed that both cations and anions play an essential role in the solvation of SO2. Whereas, the anions tend to form a thiocyanate- and much less often an isothiocyanate-SO2 adduct, the cations create a “cage” around SO2 with those groups of atoms that donate weak interactions like the alkyl hydrogen atoms as well as the heavy atoms of the pi -system. Despite these similarities between the solvation of SO2 and CO2 in ionic liquids, an essential difference was observed with respect to the acidic protons. Whereas CO2 avoids accepting hydrogen bonds form the acidic hydrogen atoms of the cations, SO2 can from O(SO2)–H(cation) hydrogen bonds and thus together with the strong anion-adduct it actively integrates in the hydrogen bond network of this particular ionic liquid. The fact that SO2 acts in this way was termed a linker effect by us, because the SO2 can be situated between cation and anion operating as a linker between them. The particular contacts are the H(cation)cdots O(SO2) hydrogen bond and a S(anion)–S(SO2) sulfur bridge. Clearly, this observation provides a possible explanation for the question of why the SO2 solubility in these ionic liquids is so high.Electronic supplementary materialThe online version of this article (doi:10.1007/s10953-015-0321-5) contains supplementary material, which is available to authorized users.
Highlights
The capture of sulfur dioxide (SO2) has drawn significant attention because SO2 is one of the most harmful air pollutants, mainly originating from the combustion of fossil fuels [1]
We have carried out an ab initio molecular dynamics study on the sulfur dioxide (SO2) solvation in 1-ethyl-3-methylimidazolium thiocyanate for which we have observed that both cations and anions play an essential role in the solvation of SO2
In this article we have provided a detailed investigation of SO2 solvation in the [C2C1im][SCN] ionic liquid from ab initio molecular dynamics (AIMD)
Summary
The capture of sulfur dioxide (SO2) has drawn significant attention because SO2 is one of the most harmful air pollutants, mainly originating from the combustion of fossil fuels [1]. The physical absorption of SO2 in ILs is almost independent of the type of anion and cation [8], whereas in case of the chemical absorption the dependence on the type of IL becomes more pronounced with the nature of the anion playing the crucial role [8,9,10] Such a principle difference in the behavior on the microscopic scale might be better understood when theoretical methods are used. The structural properties of pure [C2C1Im][SCN] [20, 21] and its mixtures with another ionic liquid [22], as well as carbon dioxide (CO2) absorption in imidazolium and ethylammonium ionic liquids [23,24,25], have been studied from AIMD, providing a solid background for the current investigation.
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