Preparation and gas separation performance of fluorinated non-coplanar copolyimide/Zr-MOF mixed matrix membranes

Mixed matrix membranes (MMMs) combine the flexibility of polymer membranes and the excellent gas separation performance of porous materials, and have attracted extensive attention in the field of gas separation in recent years. In this work, a novel fluorinated non-coplanar diamine monomer 2,2-bis(4-(4-amino-2-methoxyphenoxy)phenyl)hexafluoropropane (AMPH) was synthesized through molecular design. Fluorinated non-coplanar copolyimide (AFPI) was fabricated by copolymerizing AMPH with 4,4′-(hexafluoroisopropylidene)diphthalic anhydride (6FDA) and 9,9-bis(4-amino-3-fluorophenyl)fluorene (FFDA). Subsequently, Zr-BTB, a zirconium-based metal-organic framework with high CO 2 affinity and structural stability, was incorporated into the AFPI matrix to fabricate AFPI/Zr-BTB MMMs with different mass loadings. Benefiting from the introduced fluorine groups, AFPI possesses enlarged free volume to accelerate gas permeation. Meanwhile, two-dimensional Zr-BTB facilitates selective CO 2 adsorption over N 2 through thermodynamic adsorption affinity for improved separation performance. Compared with the pristine membrane, the CO 2 and O 2 permeabilities of MMMs increase by 277% and 237% at 15 wt% Zr-BTB loading, and the ideal CO 2 /N 2 and O 2 /N 2 selectivities rise by 45% and 33% at 5 wt% loading. This confirms that embedding Zr-BTB into copolyimide to fabricate MMMs is a promising strategy for developing high-performance gas separation membranes.