Metal-Organic Framework-Enabled Mixed Matrix Membranes: Recent Breakthroughs, Limitations, and Interfacial Engineering for Gas Separation

• MOF-based mixed matrix membranes enable performance beyond polymer limits • Interfacial morphology governs permeability, selectivity, and defect formation • Surface functionalization and polymer grafting mitigate non-selective voids • Structure–property relationships guide rational MMM design for gas separations • Defect suppression strategies improve selectivity under realistic conditions. Mixed matrix membranes (MMMs) incorporating metal-organic frameworks (MOFs) have emerged as a compelling strategy to overcome the intrinsic permeability-selectivity trade-off that constrains conventional polymeric gas separation membranes. Owing to their crystalline porosity, modular chemistry, and structural diversity, MOFs provide unprecedented opportunities to tailor sorption and diffusion pathways when integrated within polymer matrices. Recent advances in MOF chemistry, including two-dimensional, core–shell, hierarchical, and surface-functionalized frameworks, have significantly expanded the design space for MMMs, enabling separation performances that increasingly exceed established Robeson upper bounds (2008 and 2017). This review critically surveys progress in MOF-based MMMs over the past decade, with a particular focus on the interplay between MOF structure, polymer–filler interfacial morphology, and gas transport behavior. Key parameters governing membrane performance, including MOF particle size, morphology, surface chemistry, dispersion, and loading, are examined in the context of defect formation, pore accessibility, and interfacial compatibility. Strategies to mitigate non-selective voids, pore blockage, and polymer rigidification, such as surface functionalization, polymer grafting, and in situ MOF growth, are discussed and evaluated across representative gas separation systems. This review outlines fundamental design principles and research directions necessary to advance MOF-enabled MMMs toward practical implementation in carbon capture, hydrogen purification, and natural gas upgrading.