Preparation And Properties Of Metal Organic Framework Membranes

Metal-Organic frameworks (MOFs), as a new category of inorganic-organic hybird materials, have good porosity and highly designable channel, easily functionalized frameworks, unsaturated coordination center and so on. This unique structural feature makes MOFs have promise in a wide range of applications, e.g., catalysis, gas storage and separation, drug delivery and sensor technology. Thus, MOFs have a great potential as new generation of excellent membrane materials. At present, the research on the preparation of MOFs membrane has just started. Moreover, most MOFs membranes are currently grown on small sliced inorganic substrates or dispersing MOFs particles within a macromolecule polymer to make mixed matrix membrane (MMM). Compared to the small sliced substrate, the study on fabricating MOFs membranes on tubular supports or organic hollow fiber substrates is of great challenge.In this paper, a seeded growth procedure was used to successfully prepare continuous and well inter-grown zeolitic imidazolate framework-8(ZIF-8) membranes on porous a-alumina tubes. The effects of some parameters including the content of seeds and PEI in seeding solution, dip-coating time, the concentration of sodium formate in synthesis solution and synthesis temperature on the formation of ZIF-8membranes were discussed in detail. The as-synthesized ZIF-8membranes were characterized with SEM, XRD and gas permeation. The results showed that the best ZIF-8membrane, which was well inter-grown and continuous with a thickness of18m, was achieved under the recipe of seeding solution of ZIF-8:2wt%, PEI:2wt%, the dip-coating time of5s, synthesis recipes of Zn2+:2-mIM:HCOONa=1:1.5:1and crystallization temperature of120℃. Single gas permeation displayed that the permeance for H2was2.47×10-6mol/(m2·s·Pa) and the separation factors of H2/CO2and H2/CH4were5.4and2.56, respectively, indicating that Knudsen diffusion played a controlling role in the gas permeation through the ZIF-8membrane.High quality ZIF-8membranes were for the first time prepared on the surfuce-modified PPBES hollow fibers. The as-synthesized ZIF-8membranes were characterized with SEM, XRD and single-gas permeation tests. The SEM images indicated that the support surface was completely covered by well inter-grown uniform ZIF-8crystals, and no cracks, pinholes, or other defects could be observed. The ZIF-8membrane displayed the permeance of H2was1.029×10-6mol/(m2·s·Pa) and the separation factors of H2/N2, H2/CH4and H2/SF6were7.09,6.05and37.9, respectively, which were higher than the corresponding Knudsen coefficients of3.74,2.83and8.54.