Transport and Energetics of Carbon Dioxide in Ionic Liquids at Aqueous Interfaces

Nanoconfinement of Carbon Dioxide within Interfacial Aqueous/Ionic Liquid Systems

“…The RDFs shown here and those reported in the literature show strong associations between various imidazolium cation atoms and CO 2 atoms. , This observation poses a question as to how, under nanoconfinement, the CO 2 diffusion ratio is larger than that of the imidazolium cations with which they appear to be strongly interacting with. To elucidate this result, we examined the continuous dimer existence autocorrelation functions (DACFs) for the methyl carbon on the imidazolium cation and carbon in CO 2 shown in Figure .…”

“…The magnitude of Δ G is comparable for [EMIM] + (Δ G ∼ −4.62 kJ/mol) and [OMIM] + (Δ G ∼ −3.97 kJ/mol) solutions. These values are slightly less than the values found in bulk (−5.86 and −5.66 kJ/mol for the [EMIM] + and [OMIM] + systems) . This reduction could be a result of the hydroxyl groups in the hydrophilic region making the water phase more favorable and, by comparison, reducing the Δ G when transported from the aqueous to IL phases.…”

“…Interestingly, in the 3 nm pore system, the absolute diffusion coefficient of CO 2 is larger in the [OMIM] + system compared to that in the [EMIM] + system (albeit within the error of the MD simulations). This finding is surprising as bulk [OMIM]­[TFSI] is ∼3× more viscous than bulk [EMIM]­[TFSI] and we had previously found that CO 2 diffuses faster in bulk [EMIM]­[TFSI] relative to bulk [OMIM]­[TFSI]; however, the nanoconfinement effects of the 3 nm pore disrupt the liquid structure of [OMIM]­[TFSI]/CO 2 comparatively more than [EMIM]­[TFSI]/CO 2 , enough to reverse this trend. Moreover, CO 2 -[EMIM] + and CO 2 -[OMIM] + RDFs for bulk liquid and all three pore sizes are shown in Figure S6, allowing us to see the effect of pore size on the CO 2 /cation structure directly.…”

“…Bulk liquid IL/CO 2 simulation boxes were taken from our previous study and are available on GitHub . These simulation boxes contain 512 IL ion pairs and 100 CO 2 molecules.…”

“…Previously, we used both classical molecular dynamics (MD) and laboratory experiments to investigate the behavior of CO 2 in bulk, interfacial aqueous-[EMIM]­[TFSI] and aqueous-[OMIM]­[TFSI] systems, where [EMIM] + = 1-ethyl-3-methylimidazolium, [OMIM] + = 1-octyl-3-methylimidazolium, and [TFSI] − = bis­(trifluoromethanesulfonyl)­imide (Figure a). We observed that CO 2 will transport spontaneously from the aqueous phase to the IL phase and that the diffusion of CO 2 in the ILs does not follow the conventional Stokes–Einstein relation . To expand on this work, here we used MD simulations to investigate CO 2 dissolved in aqueous and IL systems when confined in cylindrical, silica nanopores (3, 5, and 8 nm diameters) with hydrophilic and hydrophobic pore surface termination (Figure b,c).…”