Mixed matrix membranes containing oriented two-dimensional ZIF-L nanosheets for efficient H2/CO2 separation

Mixed matrix membranes (MMMs) formed by combining two-dimensional (2D) nanostructured metal organic framework (MOF) materials in polymer matrices have attracted much attention due to their potential as an important functional component material for gas separation applications. Here, we report the incorporation of ZIF-L material into polyimide (PI) matrix to prepare MMMs for H2/CO2 gas separation. The loading capacity of the filler varies between 15 wt% and 45 wt%, and MMMs are prepared using three different coating methods: casting, flat scraping, and spin coating. When the filler content is 45 wt%, MMMs prepared by the spin coating method exhibit the best performance, with a gas permeability of 368.9 Barrer and an H2/CO2 separation factor of 19.1. The excellent separation performance is owing to the oriented membrane formed by the ordered arrangement of ZIF-L in the matrix, which provides a fast transport channel for H2 molecules, as evidenced by XRD and SEM results. Meanwhile, the 2D structure of MOF fillers increases the contact area between the fillers and the polymer, promoting the formation of defect-free MMMs. In addition, thermal analysis and tensile testing also indicate that MMMs possess thermal and mechanical stability. This is an important step forward in achieving the excellent performance of MMMs containing two-dimensional porous fillers for gas separation processes.