Controlling Metal Ion Counter Diffusion in Confined Spaces for In Situ Growth of Mixed Metal MOF Membranes for Gas Separation

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.