Design of Task-Specific Ionic Liquid-Incorporated IL/ZIF-8 Composites for High-Performance CO ₂ Separation

Rising atmospheric CO2 levels, primarily driven by fossil fuel combustion, necessitate the development of advanced carbon capture technologies. In this study, we investigate the incorporation of a task-specific ionic liquid (TSIL) into the zeolitic imidazolate framework ZIF-8, known for its high thermal stability and molecular sieving properties, to enhance CO2 separation performance. Among 35,476 screened ionic liquids, guanidinium iodide (GAI) was identified as an optimal candidate and incorporated into ZIF-8. The resulting composites exhibited significantly improved CO2 adsorption capacity and selectivity. This enhanced gas separation performance was attributed to the strong chemical interactions between CO2 and the amine-functionalized cation of GAI. Notably, GAI/ZIF-8 composites with 40 and 50 wt % loadings achieved CO2/N2 and CO2/CH4 selectivities of 32.3 and 18.7, respectively, at 1 bar and 25 °C. A trade-off value between selectivity and capacity (TSN) of 208 for CO2/CH4 separation was observed at 50 wt % GAI-loaded composite, while TSN values of 310 and 271 were obtained for CO2/N2 separation at 40 and 50 wt % loadings. Moreover, under dynamic mixed-gas breakthrough conditions, GAI/ZIF-8 composites also exhibit markedly enhanced CO2/N2 separation performance, with significantly delayed CO2 breakthrough and up to 8.4-fold higher selectivity than pristine ZIF-8. These results demonstrate the potential of TSIL-functionalized ZIF-8 composites for efficient CO2 separation and highlight the importance of tailoring host–guest interactions to optimize performance.