Oriented Zeolitic Imidazolate Framework-8 Membrane with Sharp H2/C3H8 Molecular Sieve Separation

A highly oriented zeolitic imidazolate framework 8 (ZIF-8) composite membrane was prepared by seeding and secondary growth. By dip-coating, preformed ZIF-8 nanocrystals were attached to the surface of a porous a-alumina support using polyethyleneimine is the coupling agent. After solvothermal treatment, a continuous and well-intergrown ZIF-8 layer was obtained. X-ray diffraction analysis of the membrane showed preferred orientation of the {100} plane parallel to the support. Further time-dependent investigations by scanning and transmission electron microscopy as well as X-ray diffraction indicated that the preferred orientation develops during an evolutionary growth process. In gas mixture permeation experiments, the membrane showed good performance in H-2/hydrocarbon separation. A sharp molecular sieve separation is observed for an equimolar H-2/C3H8 mixture with a separation factor above 300.