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Concurrent regulation of crystallographic orientation and thickness of zirconium metal–organic framework (Zr‐MOF) membranes is challenging but promising for their performance enhancement. In this study, we pioneered the fabrication of uniform triangular‐shaped, 40 nm thick UiO‐66 nanosheet (NS) seeds by employing an anisotropic etching strategy. Through innovating confined counter‐diffusion‐assisted epitaxial growth, highly (111)‐oriented 165 nm‐thick UiO‐66 membrane was prepared. The significant reduction in thickness and diffusion barrier in the framework endowed the membrane with unprecedented CO2 permeance (2070 GPU) as well as high CO2/N2 selectivity (35.4), which surpassed the performance limits of state‐of‐the‐art polycrystalline MOF membranes. In addition, highly (111)‐oriented 180 nm‐thick NH2‐UiO‐66 membrane showing superb H2/CO2 separation performance with H2 permeance of 1230 GPU and H2/CO2 selectivity of 41.3, was prepared with the above synthetic procedure. [ABSTRACT FROM AUTHOR]

Concurrent manipulation of orientation and thickness of MOF membranes has become a reliable approach for improving their separation performances. In terms of oriented seeded growth, oriented deposition of MOF nanosheets during seeding process and sealing all intergranular gaps with no discernible increase in membrane thickness during secondary growth have become indispensable. In this study, we pioneered the fabrication of uniform hexagonal-shaped, 20–40 nm thick MIL-96 nanosheets through solvent composition optimization (V H2O /V FA = 1/2). Subsequently, spin coating was employed for c -oriented deposition of uniform MIL-96 seed layer, during which the addition of PVP in the suspension was found to be critical for obtaining qualified seed layer. Finally, well-intergrown, highly c -oriented ultrathin MIL-96 membrane was prepared upon employing NMF as the solvent during secondary growth. Gas permeation results implied that prepared MIL-96 membrane exhibited superior gas separation performance compared with that of a -& b -oriented counterpart. [Display omitted] • Uniform 20–40 nm thick MIL-96 nanosheets were synthesized via solvent optimization. • Solvent type affected preferred orientation and thickness of the MIL-96 membrane. • c -Oriented ultrathin MIL-96 membrane showed superior H 2 /CO 2 separation performance. [ABSTRACT FROM AUTHOR]