(315b) Hierarchical Metal-Organic Frameworks Networks for Enhanced Gas Separation Performance and Plasticization Resistance for Mixed-Matrix Membrane Approach

Metal–organic frameworks (MOFs) have drawn great interest in molecular separations for a wide range of structures due to their permanent nanopores, which endow them with fast and selective molecular transport. For gas separation membranes, the approach of using mixed-matrix membranes (MMMs) has been extensively studied to access high separation performance, enhance plasticization resistance, and enable scalability and processability of MOF-based materials. To maximize high separation performance, uniform distributions of high MOF content are necessary, yet achieving such materials requirements is challenging due to aggregation of the filler materials and poor polymer–MOF interactions. Here, we report the use of multi-dimensional MOFs (MDMs) that form a hierarchical MOF structure, which can be incorporated into a polyimide matrix to form MMMs. The MDM structure has a characteristic morphology of 1D nanorods that are interconnected at random branch points into 3D hierarchical structures. The uniform distribution of MDM particles in the polymer matrix was confirmed by cross-section scanning electron microscopy (SEM). The MDM MMMs exhibited enhanced gas transport properties with molecular sieving separation at relatively low MOF loadings when compared to the control MMMs formed with MOFs of traditional shape. Interestingly, the MDM MMMs showed a molecular sieving window at smaller length scales compared to traditional MOF MMMs, suggesting a restriction of framework flexibility. Additionally, the MDM MMMs showed significantly enhanced plasticization resistance due to the hierarchical MOF network confining polymer chains, and thus, hindering polymer chain mobility.