MOF@MOF Composite Membranes for Carbon Dioxide Capture and Separation

There are already over 60,000 reported MOFs, and many of them are promising adsorbents and membranes for many applications. Therefore, another synthetic route for the development of task-specific materials rather than designing new MOFs is to fabricate composites based on these well-characterized MOFs that combine the advantages of their constituents. Here, we present the first examples of pure inorganic MOF@MOF membranes constructed from different MOFs with lattice mismatch: SIFSIX-3-Ni@SIFSIX-1-Cu and SIFSIX-3-Ni@HKUST-1. The CO₂/N₂ selectivities of the HKUST-1 and SIFSIX-1-Cu membranes were improved from 5.7 to 13.4 and 2.3 to 7.4, respectively, after the growth of a selective layer of SIFSIX-3-Ni onto the surface of those materials. The integration of multiple layers into a single composite membrane allows for improved control over the membrane properties including gas selectivity, permeability, stability and mechanical properties—factors that must be tuned to meet the requirements for practical membrane-based separations.