Carbon capture and sequestration (CCS) has become an increasingly important technology for environmental protection and resource utilization. In this work, four task-specific ionic liquids (TSILs), NH2-functionalized IL and three ether-functionalized ILs, were synthesized for CO2 absorption. CO2 absorption experiments of these task-specific ionic liquids (TSILs) showed that the absorption performance of NH2-functionalized IL was higher than that of ether-functionalized ILs. The recycling experiments of CO2 absorption demonstrated a good reusability of synthesized TSILs for CO2 absorption. Supported ionic liquid membranes (SILMs) with synthesized TSILs were prepared, and the CO2/CH4 and CO2/N-2 separation performance of SILMs was examined. Results indicated that the SILMs with ether-functionalized ILs have slightly lower permeability but much higher selectivity (up to 9.7) than the SILMs with NH2-functionalized IL. Poly(RTIL)-RTIL composite membranes were prepared using ether-functionalized ILs. The effect of cross-linking monomer content and nonpolymerizable IL ("free" IL) content in poly(RTIL)-RTIL membranes on the CO2/CH4 and CO2/N-2 separation performance was investigated. The composite membranes have higher gas permeability with little or no sacrifice in selectivity compared with SILMs. The stability evaluation and comparison of the SILMs and poly(RTIL)-RTIL membranes were conducted, the results of which verified the stronger structural stability of the poly(RTIL)-RTIL membranes. This suggests the potential of poly(RTIL)-RTIL membranes in future CO2-selective membrane separation.