| Metal organic frameworks（MOFs）are novel organic-inorganic hybrid porous materials developed in recent years.As a branch of MOFs,zeolite imidazoles metal organic frameworks（ZIFs）has attracted extensive attention in the preparation of advanced molecular sieve films due to its similar properties with molecular sieves,that is,uniform pore size and excellent hydrothermal stability.Among them,ZIF-7,and ZIF-95 have potential application in the purification and separation of hydrogen due to the pore size between H2 and other gases as well as the adsorption of CO2.ZIF-95 with POZ topology has high thermal stability ZIF-95 shows highly thermally stable,and can keep its structure stable over 500℃.In addition,ZIF-95 has a narrow pore size（0.37 nm）and huge cavities（2.4 nm）.Especially,ZIF-95 shows a preferentially affinity and high capacity to CO2.Therefore,ZIF-95 membrane has wide application value in H2/CO2 separation.In the process of membrane preparation,the growth direction of the crystal as well as the orientation of the membrane,has a crucial effect on its separation performance.Compared with the random oriented membrane,the oriented MOF membrane shows better separation performance,because the perfect orientation can reduce the inter-crystal defects of the membrane and provide a single direction channel for the gas permeability,which helps to improve the selectivity and permeability of the membrane and enhance the separation performance of the membrane.Mixed matrix membrane is a kind of flexible self-supporting membrane prepared by scraping the membrane of inorganic porous material mixed with organic polymer.Mixed matrix membrane has the advantages of both inorganic membrane and organic membrane:the preparation method is simpler than that of inorganic membrane,and the separation performance is much higher than that of organic membrane.So far,MOFs materials,molecular sieves and carbon nanotubes can be used as the filler of mixed matrix membrane.Among them,ZIF-7@PI mixed matrix membrane prepared by doping ZIF-7 into polyimide（PI）can be used for the separation of small molecular gases.In this thesis,the following three aspects of research work are carried out on the zeolite imidazole frameworks of ZIF-7 and ZIF-95In the first part,by optimizing the molar ratio of DMF and water in the synthesis solution,slice-shaped and high crystalline ZIF-95 nano-sheets with a thickness of about 200300 nm are successfully prepared,which are used as seeds for secondary growth of ZIF-95 membranes.First,a thin and continuous ZIF-95 seeding layer was coated on a porous?-Al2O3 support through a simple vacuum filtration of the suspensions of ZIF-95 nano-sheets.And then solvothermal synthesis was done for secondary growth of a dense ZIF-95 membrane.At 200℃and 1 bar,mixture separation factors of H2/CO2,H2/N2,and H2/CH4 are found to be 41.7,36.8,and 40.3,and a relatively high H2 permeances of higher than 1.7 x 10-77 mol·m-2·s-1·Pa-11 can be obtained.In addition,the ZIF-95 also has high thermal stability through a stability test.In the second part,highly oriented and well-intergrown ZIF-95 membranes were successfully prepared through vapor-assisted in-plane epitaxial growth of the oriented and continuous ZIF-95 seeding layer.The developed oriented ZIF-95 membrane with a thickness of only 600 nm displays higher separation performances than a random one.At 100℃and 1 bar,the mixture separation factors of H2/CO2 of 32.2 and H2/CH4 of 53.7 can be obtained for the separation of equal binary mixture,and the H2permeance(7.9 x 10-77 mol·m-2·s-1·Pa-1)is 4.6 times higher than the that of the randomly oriented ZIF-95 membrane.Further,the steam-assisted in-plane epitaxial growth also works well to prepare other MOF membrane,which may provide a new road to form high oriented and well-intergrown MOF membranes/films.In the third part,inspired by the concept of“bi-continuity”,we have developed a novel oriented and penetrating ZIF-7@PI mixed matrix membrane（MMM）with 50wt.%ZIF-7 loading through a simple flat-scraping of polyimide（PI）solution containing highly dispersed ZIF-7 sheets in CHCl3.Because the height of the ZIF-7sheets（5μm）is higher than the polymer film thickness after drying,every ZIF-7sheet penetrates both surfaces of the polyimide film.Since the ZIF-7 channels are the dominant pathways for gas permeation,the ZIF-7@PI MMM displays a high molecular sieve performance for the separation of H2（0.29 nm）from larger gas molecules.At 100℃and 2 Bar,the mixture separation factors of H2/CO2 and H2/CH4are 91.5 and 128.4,with a high H2 permeance of about 3.0 x 10-77 mol·m-2·s-1·Pa-1.Further,the ZIF-7@PI MMM displays a high mechanical and thermal stability. |
