All-Nanoporous Hybrid Membranes: Incorporating Zeolite Nanoparticles and Nanosheets with Zeolitic Imidazolate Framework Matrices

Metal-organic framework (MOF) membranes have attractive molecular separation properties but require challenging thin-film deposition techniques on expensive/specialty supports to obtain high performance relative to conventional polymer membranes. We demonstrate and analyze in detail the new concept of all-nanoporous hybrid membranes (ANHMs), which combines two or more nanoporous materials of different morphologies into a single membrane without the use of any polymeric materials. This allows access to a previously inaccessible region of very high permeability and selectivity properties, a feature that enables ANHMs to show high performance even when fabricated with simple coating and solvent evaporation methods on lowcost supports. We synthesize several types of ANHMs that combine the MOF material ZIF-8 with the high-silica zeolite MFI (the latter being employed in both nanoparticle and nanosheet forms). We show that continuous ANHMs can be obtained with high (similar to 50%) volume fractions of both MOF and zeolite components. Analysis of the multilayer microstructures of these ANHMs by multiple techniques allows estimation of the propylene/propane separation properties of individual ANHM layers, providing initial insight into the dramatically increased permeability and selectivity observed in ANHMs in relation to single-phase nanoporous membranes.