Mixed‐Linker‐Directed Seed‐Free Growth of CO ₂ ‐Selective MOF‐303 Membranes

Realizing metal‐organic framework (MOF) membranes for industrial gas separations hinges on scalable routes to dense, low‐defect layers. We report a mixed‐linker, seed‐layer‐free strategy for the one‐step growth of aluminum MOF‐303 membranes directly on porous α ‐alumina supports. Partial substitution of 3,5‐pyrazoledicarboxylic acid (H 3 PDC) with 2,5‐furandicarboxylic acid (FDCA) accelerates interfacial nucleation and promotes continuous membrane formation, obviating the conventional seeding step required for MOF‐303. Structural and spectroscopic analyses confirm uniform FDCA incorporation without perturbing the intrinsic framework chemistry. The resulting mixed‐linker membranes, exemplified by MOF‐303(P7F3) and MOF‐303(P6F4), deliver outstanding CO 2 separations: for MOF‐303(P6F4), CO 2 /N 2 separation factors reach 170 and 236 at 20% and 50% CO 2 feeds, respectively; CO 2 /CH 4 separation factors reach 431 and 393 under the same conditions, surpassing the 2019 polymeric‐membrane upper bound. Molecular simulations also indicate that FDCA incorporation leaves intrinsic adsorption and diffusivity largely unchanged, attributing the observed performance gains to improved membrane morphology and grain‐boundary suppression arising from the mixed‐linker‐directed growth. This simple, versatile route enables dense, high‐selectivity MOF‐303 membranes without seeding and is readily extendable to MOF systems where conventional in situ synthesis fails to yield defect‐minimized membranes.