Thin-film composite (TFC) membranes containing various fillers and additives present an effective alternative to conventional dense polymer membranes, which often suffer from low permeance (flux) and the permeability–selectivity tradeoff. Alongside the development and utilization of numerous new polymers over the past few decades, diverse additives such as metal–organic frameworks (MOFs), graphene oxides (GOs), and ionic liquids (ILs) have been integrated into the polymer matrix to enhance performance. However, achieving desirable interfacial compatibility between these additives and the host polymer matrix, particularly in TFC structures, remains a significant challenge. This review discusses recent advancements in TFC membranes for CO₂/N₂ separation, focusing on material structure, polymer–additive interaction, interface and separation properties. Specifically, we examine membranes operating under dry conditions to clearly assess the impact of additives on membrane properties and performance. Additionally, we provide a perspective on future research directions for designing high-performance membrane materials.

Crosslinked poly(ethylene oxide) (PEO)-based membranes are known for their excellent CO2 separation performance and mechanical robustness; however, their application has largely been confined to free-standing membranes with thicknesses of several tens of micrometers. Herein, we report a mechanically robust and CO2-selective thin-film composite (TFC) membrane (~300 nm selective layer) based on a semi-interpenetrating polymer network (semi-IPN) formed via in situ UV-induced crosslinking of a polymerized poly(oxyethylene methacrylate) (PPOEM) comb polymer and poly(ethylene glycol) diacrylate (PEGDA). The strong chemical affinity between PPOEM and PEGDA resulted in a highly miscible system, in which low-molecular-weight PEGDA was effectively confined within the entangled PPOEM matrix, enabling efficient crosslinking without pore infiltration. The high gel fractions (75–90%) further confirmed successful network formation along with physical immobilization of PPOEM chains. The crosslinked PEGDA phase provided dual benefits by enhancing mechanical stability while maintaining favorable CO2-philic characteristics. The optimized PPOEM/c-PEGDA-50 membrane demonstrated outstanding performance, achieving a tensile modulus of 2.46 MPa, a CO2 permeance of 1192 GPU and a CO2/N2 selectivity of 44. Molecular dynamics simulations revealed that the enhanced separation performance originates from optimized free-volume connectivity and preferential polymer–gas interactions within the PEO-rich semi-IPN matrix. This work demonstrates a scalable strategy for integrating crosslinked PEO materials into TFC architectures and provides a practical pathway toward mechanically durable and high-performance membranes for industrial CO2 separation.

Crosslinked poly(ethylene oxide) (PEO)-based membranes are known for their excellent CO2 separation performance and mechanical robustness; however, their application has largely been confined to free-standing membranes with thicknesses of several tens of micrometers. Herein, we report a mechanically robust and CO2-selective thin-film composite (TFC) membrane (~300 nm selective layer) based on a semi-interpenetrating polymer network (semi-IPN) formed via in situ UV-induced crosslinking of a polymerized poly(oxyethylene methacrylate) (PPOEM) comb polymer and poly(ethylene glycol) diacrylate (PEGDA). The strong chemical affinity between PPOEM and PEGDA resulted in a highly miscible system, where low-molecular-weight PEGDA was effectively confined within the entangled PPOEM matrix, enabling efficient crosslinking while suppressing polymer infiltration into the porous support. The high gel fractions (75–90%) further confirmed successful network formation along with physical immobilization of PPOEM chains. The crosslinked PEGDA phase provided dual benefits by enhancing mechanical stability while maintaining favorable CO2-philic characteristics. The optimized PPOEM/c-PEGDA-50 membrane demonstrated outstanding performance, achieving a tensile modulus of 2.46 MPa, a CO2 permeance of 1192 GPU and a CO2/N2 selectivity of 44. Molecular dynamics simulations revealed that the enhanced separation performance originates from optimized free-volume connectivity and preferential polymer–gas interactions within the PEO-rich semi-IPN matrix. This work demonstrates a scalable strategy for integrating crosslinked PEO materials into TFC architectures and provides a practical pathway toward mechanically durable and high-performance membranes for industrial CO2 separation.