Entropy driving highly selective CO2 separation in nanoconfined ionic liquids

Nowadays, the global greenhouse effect has led to the imminent development of CO2 capture, separation, and storage technologies. Hybrid membranes with nanoconfined ionic liquids (ILs) show great potential for CO2 separation, but the intrinsic mechanism is still obscure. Herein, the thermodynamical properties and solvating processes of CO2 and CH4 in ILs confined in graphene oxide were studied via performing massive molecular dynamics simulations. It was first identified that selectivity rises from 25.01 to 149.20 as the interlayer distance decreases from 3.00 to 1.50 nm, showing an ultrahigh separating selectivity. Interestingly, the solubility of CO2 in confined ILs increases by almost two orders of magnitude compared with that in bulk ILs, which is far larger than CH4 in confined ILs. The high solubility mainly originates from the fact that the confined ILs can induce the structure rearrangement and provide abundant CO2 adsorbing sites, raising the configurational entropy of CO2 in the confined ILs, and further driving the high separation selectivity of CO2 over CH4. Finally, quantitative relations between solubility, diffusion capacity, permeability, selectivity, and structural entropy of gas in confined ILs are constructed, which are meaningful for the theoretical understanding, rational design, and applications of highly efficient and low-cost separation of CO2.