Microscopic Study on the Performance Optimization of Porous Ionic Liquids for CO2 Capture by Selection of Crown Ether Solvents

As a new type of porous material, porous ionic liquids (PILs) composed of cage-based molecules dissolved in crown ether molecules have attracted a lot of attention in recent years for the high potential in CO2 capture. Understanding the mechanisms on the molecular level is crucial and highly needed to further explore novel systems, optimize the performance, and promote the utilization process. In this work, density functional theory and molecular dynamics simulations are combined to investigate the micro-structure and molecular behaviors of PILs formed by a cage molecule anionic covalent cage (ACC) combined with K+ (KACC) in different crown ether solvents. The ability to adsorb CO2 and the effect of 10 kinds of crown ethers as solvents on the performance of PILs are systematically studied. It is found that the PILs can maintain certain fluidity and sufficient pores by using 18-crown-6 as the solvent with a specific molar ratio with the KACC and exhibit excellent CO2 adsorption capacity by intramolecular adsorption, intermolecular adsorption, interfacial layer adsorption, and strong van der Waals interaction. The adsorption capacity is higher at low temperatures and high pressure showing a better possibility of sustainable utilization than that of the existing systems. This study identifies the potential for PILs in CO2 capturing and the path of improving the performance by selecting favorable crown ether solvents, which will also provide a meaningful theoretical basis for the application of PILs in this field.