Balancing the Grain Boundary Structure and the Framework Flexibility through Bimetallic Metal–Organic Framework (MOF) Membranes for Gas Separation

Separation is one of the most energy-intensive processes in the chemical industry, and membrane-based separation technology helps to reduce the energy consumption dramatically. Supported metal–organic framework (MOF) layers hold great promise as a molecular sieve membrane, yet only a few MOF membranes showed the expected separation performance. The main reasons include e.g. nonselective grain boundary transport or the flexible MOF framework, especially the inevitable linker rotation. Here, we propose a crystal engineering strategy that balances the grain boundary structure and framework flexibility in Co–Zn bimetallic zeolitic imidazolate framework (ZIF) membranes and exploit their contributions to the improvement of membrane quality and separation performance. It reveals that a good balance between the two trade-off factors enabled a “sweet spot” that offers the best C3H6/C3H8 separation factor up to 200.