MOF Channels within Porous Polymer Film: Flexible, Self-Supporting ZIF-8 Poly(ether sulfone) Composite Membrane

Polymer - metal organic framework (MOP) composite membranes are promising materials for gas separation and could be potentially applied within many industrial applications. However, key limitations of currently reported layered MOF-polymer composites are their lack of scalability and mechanical stability. A big challenge for synthesis of such composites is directing the growth of homogeneous, defect-free MOF crystal layers. Here, a membrane synthesis method allowing the formation of flexible, noncontinuous zeolitic imidazolate framework 8 (ZIF-8) - poly(ether sulfone) (PES) composite membranes is presented. The ZIF-8 growth is restricted to the PES pores by exploiting directed ZnO seed-nanoparticles. The seeding process is part of the membrane formation process itself and allows for specifically integrating ZnO within polymeric membranes enabling easy and scalable control of the MOF-crystal formation. During solvent casting and membrane formation, a phase separation process allows trapping ZnO seed-nanoparticles within bicontinuous PES pores. Because of ZnO serving in parallel as seed and zinc source, ZIF formation can be induced and controlled by adding only one solution containing the organic linker. This ZnO nanoparticle seeding technique enables a pore-specific in situ growth of small (<5 mu m in diameter) ZIF-8 islands via solvothermal synthesis. This leads to mechanically flexible self-supporting ZIF-8 membranes exhibiting gas selectivities of 9.3 +/- 3.1 (H-2/CO2) and 11.5 +/- 2.1 (H-2/N-2).