Freezing Contra-diffusion: A New Protocol for Synthesizing Co-Gallate MOF Membranes toward Superior Ethylene/Ethane Separation Performance

Gallate MOF membranes show great promise for efficient C2H4/C2H6 separation due to the ability to precisely discriminate the subtle difference in molecular cross-section size of C2H4 and C2H6. Nevertheless, it remains a huge challenge to prepare high-performance gallate MOF membranes with optimized structure due to uncontrollable gallate MOF nucleation and growth in the bulk solution, which leads to poor nucleation on the substrate surface. In this study, we facilely prepared Co-gallate membranes showing unprecedented C2H4/C2H6 separation through the development of a freezing contra-diffusion protocol. Maintaining the frozen state of the metal precursor inside substrate pores enabled precisely tuned nucleation and growth kinetics, resulting in the formation of the preferred c-oriented Co-gallate membranes with abundant open metal sites in the framework. The multiscaled structural advantage endowed the Co-gallate membranes with C2H4/C2H6 separation performance superior to that of state-of-the-art polycrystalline MOF membranes, thus highlighting the promising application of the freezing contra-diffusion protocol in structure optimization and performance enhancement of versatile MOF membranes.