Gas Separation With COF Membranes: Crystalline Design Meets Selective Transport

Covalent organic frameworks (COFs) are emerging crystalline porous materials with precisely defined architectures and tunable chemistry, offering strong potential for next-generation gas separation membranes. This review provides a material-centric perspective on COF-based membranes, emphasizing how framework design governs molecular transport behavior. We discuss key structure-property relationships in COF synthesis, highlighting the roles of crystallinity and chemical functionality in regulating selective transport. Recent advances in synthetic methods are compared in terms of framework order, pore alignment, and scalability. The evolution of COF membrane fabrication is then reviewed, from mixed-matrix systems to in situ grown and freestanding membranes, with attention to interfacial engineering, mechanical stability, and orientation control. Fundamental transport mechanisms are summarized to connect pore chemistry with separation performance. Application-focused progress in CO₂ and H₂ separations is highlighted, where COF membranes have achieved ultrahigh permeance and selectivity exceeding the Robeson upper bound. Finally, we identify key challenges, including defect control, mechanical robustness, scalable manufacturing, and long-term stability under realistic conditions, and outline future directions toward industrial deployment. By integrating framework chemistry, membrane architecture, and transport mechanisms, this review establishes COFs as a versatile platform for energy-efficient gas separations and provides general design principles for crystalline membrane materials.