Progress, Challenges, and Opportunities in Ionic Liquid-Modified Polymer Membranes for CO₂ Separation

Driven by the critical challenge of mitigating anthropogenic CO₂ emissions, the field of carbon capture and utilization (CCU) has undergone rapid development. Among these, membrane-based CO₂ separation stands out for its energy efficiency and ease of industrial implementation. However, challenges such as the selectivity-permeability trade-off and plasticization limit its effectiveness. Functionalizing membranes with ionic liquids (ILs) has emerged as a promising strategy that takes advantage of the ILs' high CO₂ solubility, stability, and tunability to enhance separation performance. Beyond CO₂ capture, ILs also serve as key promoters in CO₂ conversion by facilitating various reactions. This Review summarizes recent progress in IL-functionalized polymer membranes, highlighting advances in polymerized ILs, mixed matrix membranes, and hollow fiber configurations. Representative studies are discussed to illustrate how IL incorporation can improve gas transport, selectivity, and stability and enable integrated systems for simultaneous CO₂ capture and catalytic transformation. Remaining technical challenges, including IL leaching, polymer compatibility, and thermal constraints, are identified, providing guidance for future design and optimization of next-generation IL-membrane platforms for CO₂ separation and conversion.