Oriented Zeolitic Imidazolate Framework (ZIF) Nanocrystal Films for Molecular Separation Membranes

Abstract

The direct synthesis of oriented, defect-free nanocrystal metal–organic framework (MOF) films is a challenging step toward their applications in advanced technologies, such as optics, sensing, and membrane-based separations. Here, we propose a one-step, in-situ growth approach to synthesize oriented zeolitic imidazolate framework-L (ZIF-L) membranes by using an isoporous film as the support. The high metal-binding efficiency, as well as the ordered pore structure, given by the polymeric isoporous support, promote the preferred nucleation and rapid growth of vertically aligned ZIF-L nanocrystals to construct dense membranes. Vertically aligned nanochannels between the inter-lattice of ZIF-L are therefore formed through the polycrystalline membrane. The membrane exhibited a high H2 permeance, 1635 GPU (1 GPU= 1 × 10−6 cm3 (STP)/cm2 s cmHg), and H2/C3H8 selectivity of 516, when targeting hydrogen separation from hydrocarbon in a steam reforming process. The membrane can be further used in organic solvents nanofiltrations, with a methanol permeance of 38.7 L m−2 h−1 bar−1, and >90% rejection of organic dye molecules. Furthermore, by taking advantage of the anisotropic pore structure, the ZIF-L membrane could be further hydrolyzed to produce ultrathin ZIF-L nanosheets with a thickness ~5 nm, which provides a facile platform to synthesize two-dimensional MOFs nanosheets