(453d) ZIF?14 Membrane Supported on ZnO Nanorods for Gas Permeation and Separation

Zeolitic imidazolate frameworks (ZIFs) area subclass of metal organic frameworks (MOFs) consisting of tetrahedral transition metal ions (zinc/cobalt) bridged by imidazole-type linkers. ZIF-14 is one of the promising ZIFs for gas separation. It features a ANA type zeolitic structure with Zn²⁺ metal nodes and 2-ethylimidazole (2-EtIm) linkers. The pore aperture of ca. 2.2 Ã… is ideal for molecular sieving for small gas molecules such as H₂. However, it is difficult to prepare a pinhole-free continuous ZIF-14 membrane by direct in-situ growth method since the low heterogeneous nucleation rates on ceramic substrates.

Here, we have designed an interfacial layer of aligned ZnO nanorods (NRs) for inducing the nucleation and growth of ZIF-14 thin films on porous α-Al₂O₃ tube substrate. The ZnO NR seed layer significantly reduces the nucleation barrier for ZIF-14 due to the dissolution and surface reaction of ZnO with the 2-EtIm linker in the hydrothermal synthesis. Highly crystalline, pinhole-free ZIF-14 membranes obtained in this work exhibit high performance for gas separation. The H₂ permeance reaches 1.7×10^-8 mol·m^-2s^-1Pa^-1, while the ideal separation factors for H₂/CO₂, H₂/N₂ and H₂/CH₄ are 20.2, 27.1 and 30.2, respectively. The high selectivity combined with its excellent hydrothermal stability indicates the reported ZIF-14 membrane as a promising candidate for gas separation. In addition, this preparation strategy has high reproducibility scalability and also is possible to extend the same principle to the preparation of other ZIF and MOF membranes.