C-axis oriented ZIF-95 sheets intermixed with polyimide matrix with enhanced gas separation performance

Abstract

The fabrication of mixed matrix membranes (MMMs) by intermixing suitable fillers with organic polymers is an effective strategy to surmount the well-known trade-off effect between gas permeability and selectivity, which can promote separation performance of membranes to a great extent. Two-dimensional (2D) metal-organic frameworks (MOFs) are considered as potential fillers for strengthening the separation performance of MMMs as they possess high aspect ratio and distinctive chemical characteristics. However, it remains challenging in engineering the morphology of the MOFs with desired pore structure and high aspect ratio. In this study, we firstly prepare c-axis oriented ZIF-95 sheets with lateral dimension exceeding 22 μm and thickness of around 3 μm by the solvothermal method. And then the ZIF-95 sheets are incorporated into the polyimide (PI) matrix to fabricate highly c-axis oriented ZIF-95@PI MMMs (denoted as COZIF-95@PI MMMs thereafter). Attributing to the straight permeation channel of ZIF-95 (3.6 Å) for gas permeation as well as its high compatibility with polyimide substrates, the COZIF-95@PI MMMs show a high gas separation capability. At 373 K and 100 kPa for the COZIF-95@PI MMM with 40 wt% loading, the mixture separation factors of H2/CH4 and H2/CO2 are 134 and 58, respectively, and the H2 permeability exceeds 967 barrer, which is hopeful for the separation and purification of hydrogen.