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Metal–organic frameworks (MOFs) are one of the most promising membrane materials for olefin/paraffin separations. However, most of MOF membranes have a thickness over 1 µm, which greatly compromises the permeation flux. While previous studies are focused on increasing crystal nucleus density on the substrates, achieving ultrathin membrane via modulation of the crystal growth is lacking. Herein, an inhibited Ostwald ripening (IOR) strategy is proposed to fabricate ultrathin ZIF‐8 membranes, through incorporating polymer‐based inhibitors into the membrane formula to inhibit the growth process of ZIF‐8 crystals via the metal–organic coordination. The IOR process can be readily tuned by varying the functional groups, molecular weights, and concentrations of the inhibitors, enabling a facile control over the IOR degree and thus the membrane thickness. Consequently, the thickness of ZIF‐8 membranes can be dramatically reduced to 180 nm. The resulting membranes exhibit ultrahigh C3H6/C3H8 separation performance with C3H6 permeance of 386 GPU and C3H6/C3H8 separation factor of 120. It is anticipated that this straightforward and efficient IOR strategy can open a new avenue for the fabrication of ultrathin MOF membranes to tackle many critical molecular separations. [ABSTRACT FROM AUTHOR]

Covalent organic framework (COF) membranes with tunable ordered channels and free organic groups hold great promise in molecular separations owing to the synergy of physical and chemical microenvironments. Herein, we develop a defect engineering strategy to fabricate COF membranes for efficient CO2 separation. Abundant amino groups are in situ generated on the COF nanosheets arising from the missing‐linker defects during the reactive assembly of amine monomer and mixed aldehyde monomers. The COF nanosheets are assembled to fabricate COF membranes. Amino groups, as the CO2 facilitated transport carriers, along with ordered channels endow COF membrane with high CO2 permeances exceeding 300 GPU and excellent separation selectivity of 80 for CO2/N2, and 54 for CO2/CH4 mixed gas under humidified state. Our defect engineering strategy offers a facile approach to generating free organic functional groups in COF membranes and other organic framework membranes for diverse chemical separations. [ABSTRACT FROM AUTHOR]