Molecular Understanding of the Solid Interface-Induced Microstructures of 1-Hexyl-3-methylimidazolium Bis(trifluoromethylsulfonyl)imide in Gas Absorption

The abnormal intensification of gas absorption in nanoconfined ionic liquid (IL) systems has been receiving ever-increasing attention. In this work, grand canonical Monte Carlo and molecular dynamics simulations were performed for the systematic investigation of CO2 and H2S absorption by 1-hexyl-3-methylimidazolium bis(trifluoromethylsulfonyl)imide nanoconfined within different slits [graphene and rutile(110)]. The absorption mechanisms within different slits were greatly dependent on the solid interface-induced microstructures (spatial distribution and molecular orientation) of ILs. Within graphene slits, imidazole rings were mainly oriented parallel to the solid substrate, and IL stacking tightened such that gas absorption was dominated by the effect of the anions of ILs. By contrast, within rutile slits, the imidazole rings of ILs were mainly tilted on the solid surface because of the interfacial interaction. This orientation accounted for the large free volume that dominated the intensification of the absorption of both gases.