Defect Engineering in Fluorinated Metal-Organic Frameworks Within Mixed-Matrix Membranes for Enhanced CO₂ Separation

Developing highly permeable and selective membranes for energy-efficient CO₂/CH₄ separation remains challenging. Mixed-matrix membranes (MMMs) integrating polymer matrices with metal-organic frameworks (MOFs) offer significant potential. However, rational filler-matrix matching presents substantial difficulties, constraining separation performance. In this work, defects were engineered within fluorinated MOF ZU-61 through the partial replacement of 4,4'-bipyridine linkers with pyridine modulators, producing high-porosity HP-ZU-61 nanoparticles exhibiting a 267% BET surface area enhancement (992.9 m² g^-1) over low-porosity ZU-61 (LP-ZU-61) (372.2 m² g^-1). The HP-ZU-61/6FDA-DAM MMMs (30 wt.%) demonstrated homogeneous filler dispersion and pre-served crystallinity, achieving a CO₂ permeability of 1626 barrer and CO₂/CH₄ selectivity (33), surpassing the 2008 Robeson upper bound. Solution-diffusion modeling indicated ligand deficiencies generated accelerated diffusion pathways, while defect-induced unsaturated metal sites functioned as strong CO₂ adsorption centers that maintained solubility selectivity. This study establishes defect engineering in fluorinated MOF-based MMMs as a practical strategy to concurrently overcome the permeability-selectivity trade-off for efficient CO₂ capture.