Molecular and Supramolecular Pathways for CO₂ Separation Membranes: Amine-Functionalized Silica and Hydrogen-Bonded...

Efficient CO₂ capture from flue gas is fundamentally limited by the trade-off between permeability, selectivity, and chemical stability. Amine-functionalized sorbents (AFS) achieve high selectivity via strong chemisorption, but suffer from kinetic limitations, pore blocking, and degradation under humid, high-temperature. Hydrogen-bonded organic frameworks (HOFs), enabling rapid and selective transport through ordered supramolecular pores without strong binding, although their weak intermolecular interactions and structural fragility pose challenges. Our review, critically compare AFS and HOF-based membranes, elucidating how chemical functionality, pore architecture, and framework stability govern CO₂ transport. AFS deliver CO₂/N₂ selectivities up to ∼800 at low partial pressures but exhibit limited permeance and durability. In contrast, HOF-based mixed-matrix membranes decouple selectivity from chemisorption, achieving permeabilities exceeding 750 Barrer with CO₂/N₂ selectivity ∼60, and up to 7,000-8,400 Barrer with sustained performance over 400 h. Cross-linked HOF-derived carbon reach CO₂/CH₄ selectivity of 192 with significantly enhanced permeability. Emerging strategies, including hydrogen bonding, charge-assisted-interactions, and post-synthetic cross-linking, that overcome intrinsic limitations of HOFs. Hybrid AFS-HOF membranes, integrating strong binding sites with well-defined transport channels, are identified as a promising route toward scalable, defect-tolerant separations. Collectively, this review establishes molecular-level-design principles and outlines pathway for translating supramolecular membrane into industrially viable CO₂ capture technologies.