Preparation And Gas Permeation Of Zeolitic Imidazolate Framework-67 Membrane

Metal-organic frameworks (MOFs) materials can be widely used in gas adsorption and separation, catalysis, sensing, electronics and medicine due to their unique pore strutures, tailorability and functionalities of pore size. Zeolitic imidazolate framework-67(ZIF-67), one branch of MOFs materials, is usually formed by 2-methylimidazole and cobalt cation and has the SOD topological structure. Owing to its thermal and chemical stability, ZIF-67 is very suitable for gas separation, but the preparation of well-intergrowth ZIF-67 membrane for gas separation remains a challenge to researchers because of their poor heterogeneous nucleation, and weak adhesion with support. In this paper, to solve the problem of low heterogeneous nucleation, different strategies, including in situ fluid synthesis, direct transformation by cobalt carbonate hydroxide nanowires(CoNWs) layer and inducing by ZnO layer were adopted to successfully synthesized continuous ZIF-67 membrane and the separation test showed excellent performance in molecular gas separation. The main contents are as follows:(1) ZIF-67 membrane was synthesized on the inner side of ceramic hollow fiber in a simple flow system via in situ direct growth method. Synthesis temperature and flow rate were studied and the optimum condition of forming continuous membrane is at 40 ? and with a flowing speed of 6ml/h. The membrane synthesized in this method had a H2 permeance of 6.19×10-6 mol·m-2·s-1·Pa-1 under ambient temperature and a pressure of 0.1MPa, and its ideal separation factors of H2/CO2, H2/N2, H2/CH4 were 4.81,5.15,3.80, respectively.(2) A green route was used to prepare ZIF-67 membrane on the ?-Al2O3 tube by transformation of cobalt carbonate hydroxide nanowires in the presence of 2-methylimidazole aqueous solution. Continuous ZIF-67 membrane was successfully prepared by carefully controlling experimental conditions (solvent, concentration of solution, temperature and reaction time). Through slow dissolution in the 2-methylimidazole aqueous solution, CoNWs could provide Co2+for the formation of ZIF-67 membrane on the surface of support and avoid homogeneous nucleation in the reaction system. The obtained ZIF-67 membrane showed H2 permeance of 5.22 × 10-7 mol·m-2·s-1·Pa-1 and its ideal separation factors of H2/CO2, H2/N2, H2/CH4 were 4.25,6.60,6.44.(3) Well-intergrown ZIF-67 membrane was prepared under the induction of a nonhomologous ZnO layer for the first time. Firstly, ZnO layer, including ZnO nanorods and nanonets were deposited on ?-Al2O3 support using the hydrothermal synthesis method. Then the highly active ZnO reacted with 2-methylimidazole ligand in the presence of Co2+in the methanol-water solution, which lead to the formation of a 2-methylimidazole-rich region on the surface of ZnO layer. As a result, the Co2+ions also concentrated on the surface of ZnO layer due to its interaction with 2-methylimidazole and finally grown into continuous ZIF-67 membrane. ZIF-67 membrane induced by ZnO nanonets exhibited H2 permeance of 1.55× 10-7mol·m-2·s-1·Pa-1 and the ideal separation factors of H2/CO2, H2/N2, H2/CH4 were 5.50, 7.98,8.32, respectively. ZIF-67 membrane induced by ZnO nanorods exhibited H2 permeance of 2.61×10-7mol·m-2·s-1·Pa-1, the ideal separation factors of H2/CO2, H2/N2, H2/CH4 were 3.83,9.14,9.73, respectively. Both membranes showed excellent molecular sieving performance.