Hanhan Chen,Xiaobin Wang,Yi Liu,Tengfei Yang,Naitao Yang,Bo Meng,Xiaoyao Tan,Shaomin Liu
Despite many methods available to synthesize MOF membrane, the cost-effective synthesis with high reproducibility and scalability is still a challenge. We present here a homologous support-induced approach for the growth of ZIF membrane supported on the dual-layer ZnO–Al2O3 hollow fibers, which has the potential for applications at larger scales. The developed unique dual-layer hollow fibers consisting of a thin outer ZnO layer firmly attached onto an inner porous alumina substrate were realized through one-step co-extrusion/sintering technique. During the MOF membrane synthesis, ZnO can be used not only as the support, but also as the nucleation sites and growth centers for the ZIF-8 membrane formation. More importantly, ZnO can act as a transitional bridge to direct the membrane growth outward along the support and inward embedded into the support, which significantly improving the binding force between the support and MOF, thus bringing in the outstanding membrane stability. Permeation of single gas and separation of binary mixtures revealed that the prepared membranes were free of defects. The resultant ZIF-8 composite membrane exhibits good hydrogen separation performance and excellent reproducibility. This protocol can achieve an easy and large-scale synthesis. In addition to ZIF-8 membrane, ZIF-67 membrane was also successfully synthesized via this method, which may provide some general guidelines for the preparation of other MOF membranes.
Graphical Counter diffusion has been used to drive the in situ formation of mixed metal MOF membranes in a confined space with nanostructure arrays under hydrothermal conditions. Through this approach, a variety of mixed metal ZIF membranes can be synthesized on different kinds of porous substrates. The development of facile, versatile strategies for the fabrication of mixed component metal-organic framework (MOF) membranes is highly desired, but still very challenging due to the difficulty in controlling crystal growth rates of every single component in a specific confined space. It is difficult to adjust the formation of multicomponent MOF membrane in a controlled manner using conventional approaches such as secondary growth methods. Herein, we present a facile strategy that prepares the mixed metal zeolitic imidazolate framework (ZIF) membranes in situ in a confined space with nanostructure arrays under hydrothermal conditions using the counter diffusion mechanism. The counter diffusion of different metal ions from both the homogeneous bulk solution and the solid metal oxide nanostructure grown on substrate leads to the specific effective reaction zone by encountering with linker molecules at the interface. Subsequently, nucleation and crystal growth generate the continuous mixed metal MOF membranes. With this approach, a variety of mixed metal ZIF membranes were synthesized on different kinds of substrates. The prepared membranes exhibited good sieving effect to H 2 and heavier gas molecules during both single and mixed gas permeation tests. This work opens a fresh avenue for the synthesis of mixed component MOF membranes, and the counter diffusion effect can be intentionally adopted to the design and fabrication of selective mixed metal MOF membrane on various supports.
An original synthesis strategy for tubular zeolitic imidazolate framework (ZIF) membranes was developed by the deposition of a novel porous amorphous hybrid material prepared by 3-isocyanatopropyltrimethoxysilane (IPTMS) and ZIF-8 crystals onto a coarse macroporous α-Al2O3 tubular support. This porous amorphous hybrid material (ZIF-8-IPTMS) not only strongly adhered to the support but also repaired the defects to make the support surface smooth due to the abundant hydroxyl groups and the appropriate particle size. Using this synthesis strategy, we successfully prepared a high-quality ZIF-8 membrane on an inorganic α-Al2O3 tubular support via the sufficient heterogeneous nucleation sites provided by the amino groups of ZIF-8-IPTMS. This ZIF-8 membrane with an ultrathin thickness of approximately 0.9 μm was prepared, and its ideal H2/CO2 selectivity increased as the temperature increased. The membrane exhibited a competitive selectivity of 13.8 with a remarkably high H2 permeance of 1.46 × 10–5 mol·m–2·s–1·Pa–1 at 90 °C and 0.1 MPa. H2/CO2 binary gas permeation measurements indicated a separation factor of 9.2, and the H2 permeance was maintained at 0.83 × 10–5 mol·m–2·s–1·Pa–1 at 90 °C and 0.1 MPa. This synthesis strategy was also suitable to fabricate ZIF-67 membranes. The ZIF-67 membrane with a thickness of approximately 1.2 μm exhibited a H2/CO2 ideal selectivity of 5.3 and maintained a high H2 permeance of 1.06 × 10–5 mol·m–2·s–1·Pa–1 at 35 °C and 0.1 MPa.
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