Advances of Ionic-Mediated Polymer Architectures for CO₂ Gas Separation Membranes: A Comprehensive Review of Design,...

Polymeric membrane-based gas separation is widely regarded as a promising strategy for CO₂ separation and capture due to its economic viability and energy efficiency compared with other conventional techniques. Emerging polymeric materials, especially those containing or derived from polar functional groups, particularly ionic liquids (ILs), have attracted considerable interest in separating CO₂ from various gas mixtures with distinct applications, mainly in postcombustion carbon capture (CO₂/N₂), natural gas/biogas sweetening (CO₂/CH₄), and hydrogen purification in fuel gas or syngas streams (CO₂/H₂). Despite the multifunctional benefits of ionic liquids in polymeric membrane systems, the ongoing quest for material selections that enhance the separation performance of CO₂ gas molecules remains a critical priority in industrial applications. Therefore, a comprehensive discussion of material design that conveys the structure-property relationships alongside the separation performance of ionic-liquid-derived polymeric membranes is always engaging. Unlike other review reports that focus on specific aspects of ionic liquids in membrane-based separation using typical polymeric ionic liquids (PILs), this review exclusively concentrates on thorough research exploring a diverse range of ionic-mediated polymeric membranes for CO₂ separation. Specifically, we examine all configurations of ionic-mediated polymeric architectures, including pure PILs, composite PIL/IL films, PIL-based mixed matrix membranes, ionomers or PIL copolymers, and, most importantly, the recently developed ionenes. Beginning with a general background on polymer-based gas separation, we discuss the key parameters and factors that influence the properties of membranes for selective CO₂ separation. We further investigate the material design of ionic-mediated polymers in contemporary state-of-the-art polymer membrane-based CO₂ separation, highlighting the promising advantages of ionic groups in macromolecular substructures. Later, empirical data reviewing the permeability/selectivity trade-off of ionic-mediated polymeric membranes were plotted against the 2008 and 2019 upper bounds, demonstrating the material performances toward CO₂ over light gases. Finally, we provide a concise comment on the challenges and future perspectives on encouraging material design of ionic-mediated polymeric membranes for CO₂ separation applications.