Computational investigation of the performance of ZIF-8 with encapsulated ionic liquids towards CO2 capture

The effect of Ionic Liquid (IL) encapsulation in Metal Organic Frameworks (MOFs) is extensively studied towards the enhancement of the MOFs as CO2-selective materials. The influence of the IL anion-cation pair type is investigated through the combination of two different cations, namely 1-butyl-3-methylimidazolium [bmim+] and 1-octyl-3-methylimidazolium [omim+] and three distinct anions, namely bis-trifluoromethylsulfonyl-imide [Tf2N−], tricyanomethanide [TCM−], and tertracyanoborate [B(CN)4−], that can be encapsulated in ZIF-8, resulting in a series of ZIF hybrids (IL@ZIF-8). The study investigates the impact of the anion and the cation on the separation of CO2 from mixtures with CH4 and N2. Monte Carlo simulations of adsorption of the three gases in both the pristine ZIF-8 and in ILs@ZIF-8 reveal that CO2 capacity increases dramatically for the case of ILs@ZIF-8. Moreover, analysis of the simulations and additional density functional theory calculations show that CO2/CH4 (related to natural gas purification) and CO2/N2 (related to post-combustion CO2 capture) mixture selectivity is affected by the distribution, composition and type of the IL pair. Moreover, the sorbent selection parameter, S, and the regenerability factor, R, are used to evaluate the performance of all IL@ZIF-8 analogues along with other known CO2-selective materials.