| Metal organic frameworks?MOFs?are a class of organic-inorganic hybrid material formed by transition metal ions and organic ligands.MOFs have many advantages such as adjustable pore channel,large specific surface area and abundant pore channel.Thus,they have a wide application prospect in catalysis,gas separation,adsorption,water treatment,and so on.In particular,Zeolitic Imidazolate Frameworks?ZIFs?,as a member of MOFs,have similar structural with zeolite molecular sieve and have good thermal and chemical stability compared with other MOFs.As a representative of ZIFs,ZIF-8 is a promising membrane candidate in gas separation due to its adjustable channel structure.While the hollow fibers are excellent support for the membrane due to their unique advantages including large specific surface area,simple process,low cost and high flux.This paper investigated the preparation of ZIF-8 membrane on different hollows fibers by secondary seeding growth method,ZnO induction method and embedded seeding method.The effects of synthsis condition on membrane preparation and permeability were investigated in detail.The main contents and results are as follows:1.The?-Al2O3 hollow fiber was first prepared by phase inversion sintering method and then ZIF-8 membranes were prepared on the ceramic hollow fiber by secondary seeding growth method.The effect of the concentration of seeding solution,dipping time and times on the preparation and permeability for the membranes were investigated.The results showed that different seeding solution concentration and dipping time had a great influence on the morphology and permeability of the membrane.The membrane thickness could reach up to 11.6?m when the concentration of seed solution was 2wt.%and the dipping time was 20s with the once crystallization at 100?.The H2 permeation was 8.55×10-7mol·m-2·s-1·Pa-11 and the ideal separation facor of H2/N2 and H2/CH4 were respectively 6.52 and 5.12,indicating that the ZIF-8membranes has certain gas separation performance.2.The?-Al2O3 hollow fiber containing ZnO particles has been developed in one step phase inversion sintering method for preparing ZIF-8 membrane.The effects of activation temperature,activation concentration and ZnO content were investigated.The results showed that the thickness of the prepared ZIF-8 membrane increased with increasing the ZnO content.Higher activation temperature would lead to faster growth of ZIF-8 membrane.The membrane thickness could reach up to 10.1?m when the ZnO content was 25wt.%after activated in 1mol/L Hmim solution at 100?.The H2permeace was 7.99×10-7 mol·m-2·s-1·Pa-1,and the separation factor of H2/N2 and H2/CH4 were 7.51 and 7.27.The reproducibility test revealed that the prepared ZIF-8membrane has good repeatability.3.The PESf hollow fiber incorporated ZIF-8 crystals was first preparaed by phase inversion method and then the well inter-growth ZIF-8 membrane was prepared by in-situ growth method.The effects of seed content and synthesis temperature on the membrane formation were investigated.The results showed that the membrane thickness increased with the increase of the seed crystal content and crystallization temperature.ZIF-8 membrane with 4-5?m thickness can be successfully prepared on PESf hollow fiber containing 1wt.%seed crystals.H2 permeace was 1.3×10-6mol·m-2·s-1·Pa-1,and the separation factor of H2/N2,H2/CH4 and H2/CO2 were 5.48,3.38 and 7.78,indicating that the ZIF-8 membrane has good gas separation performance. |
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