Crosslinked MOF polymer to enhance gas separation of mixed matrix membranes
Abstract Preparation of mixed matrix membranes (MMMs) from rigid polymers like PIM 1 remains challenging because the contorted and rigid polymer chains of PIM 1 severely inhibit self rearrangement leading to low quality of polymer filler interaction. MMMs prepared by conventional methods, therefore, often suffer from defects at the polymer filler interface. In this work, a novel filler having hydroxyl functional groups on the surface (Mg MOF 74) was used as a filler and mixed with PIM 1 in solution (chloroform) Under optimized solution conditions (65 degC and 24 h) chemical crosslinking between the hydroxyl groups and the fluoride chain ends of PIM 1 was facilitated, to completely remove these interfacial defects. The crosslinked MMMs were then characterized by XRD, FTIR, SEM and mechanical tests, while their separation properties were studied for five gases including H 2 CO 2 CH 4 N 2 and O 2 upon increasing Mg MOF 74 loading (0 20% wt. The two main features of MOF 74 (also known as CPO 27) especially Mg MOF 74, greatly contributing to the membrane gas separation were 1 D hexagonal channels (1.1 nm diameter) and an exceptionally high CO 2 adsorption capacity under reduced pressures. As the ends of PIM 1 are directly linked with the MOF surface, the intrinsic micropores of PIM 1 are connected to the inner pores of MOF 74 forming an inter connected micropore network throughout the MMM. Both selectivities and permeabilities of MMM were improved for all the gases, particularly CO 2 permeability which increased by 3.2 times from 6500 Barrer for the neat polymer (PIM 1) to 21,000 Barrer for PIM 1 with 20% wt. of MOF 74, meanwhile CO 2 /CH 4 selectivity was improved from 12.3 to 19.1, respectively.