In situ formation of zeolitic-imidazolate framework thin films and composites using modified polymer substrates

It is of great interest to form polycrystalline metal-organic framework (MOF) thin films on polymer substrates or MOF/polymer composites for their practical applications in sensing and separation. It is, however, quite challenging to fabricate high-quality MOF thin films on polymer substrates or MOF/polymer composites in a facile manner. Herein, we report a simple in situ method to fabricate high-quality zeolitic-imidazolate framework ZIF-8 thin films supported on polymers as well as ZIF-8/polymer composites by doping polymers with zinc ions followed by solvothermal treatment in a linker solution. The effects of key synthesis parameters on the microstructures of ZIF-8 thin films and composites were systematically studied. Formation of ZIF-8 crystals was confirmed using ATR-FTIR, EDX, XRD, SEM, and TEM. While continuous ZIF-8 films were observed on the substrate surfaces, it was revealed that ZIF-8 particles formed inside the substrates as well (i.e., ZIF-8/polymer mixed-matrix layers). The thicknesses of the mixed-matrix layers were demonstrated to be controllable by varying the kinetics of alkali hydrolysis. The method was applied to a family of ZIFs (i.e., ZIF-8 and ZIF-67) and mixed-metal ZIF-8 analogues, proving its versatility. Finally ultra-thin well-intergrown ZIF-8 membranes were prepared by secondarily growing ZIF-8 films on Matrimid® hollow fibers, showing promising propylene/propane separation performances.