| CO2capture is of great significance to our sustainable civilization. Membrane separation is considered as an alternative technology to CO2capture due to the low energy requirements and friendly to the environment. Most recently, metal-organic frameworks (MOFs) are considered as promising candidates for molecular separation especially for CO2capture due to their large adsorption capacity and their structural and chemical tunability. However, most MOF membranes have difficulties to separate CO2over N2efficiently. The CO2/N2separation selectivity mainly influenced by the pores sizes, adsorption capacity and the flexiblility of the framework, strong interaction affinity of CO2with the MOFs. These factors make MOFs always show reversible diffusivity selectivity of CO2over N2compared to zeolite based membranes. In order to further understand the pore structures in relation to CO2selectivity and provide new strategy for developing MOF membranes for CO2capture. This thesis mainly focused on preparing microporous MOF membranes from ZIF-8, ZIF-7and CAU-1, investigating CO2/N2separation selectivity for the obtained MOF membranes.(1) ZIF-8nano particles (NPs) were prepared in inverse microemulsion through the droplets confinement combining with CTAB capping effect that reduced the2-Hmim/Zn2+mole ratio greatly from57:1to4:1. The crystal growth mechanism was studied and the seeds for growth of ZIF-8membrane were obtained. ZIF-8NPs of50-700nm with good crystallinity were obtained under the conditions of Zn2+/2-Hmim/H2O (mole ratio) of1:3.5:1400-1:8:1400,25℃,1-24h and the H2O/CTAB mass ration of1.5-1.2. ZIF-8showed high CO2adsorption capacity over N2. Continuous ZIF-8membrane exhibiting CO2permeance of7.79x10-8mol·m-2·s-1·Pa-1, ideal selectivity for CO2/N2of3.25was achieved by secondary growth method using an optimized ZIF-8seeds.(2) A "two-in-one" approach was used to reduce the pore size and promote high heterogeneous nucleation sites. ZIF-7membranes were prepared with such approach by deposition of APTES-functionalized Al2O3particles onto a coarse macroporous support. The effect of molar ratio of APTES and Al2O3particles on the formation of ZIF-7membranes were investigated in detail. When nAPTEs:nAl2O3=1:3. a continuous ZIF-7membrane exhibiting H2permeance of4.70×10-7mol·m-2·s-1·Pa-1with the ideal selectivity for H2/CO2, H2/N2of5.87,4.59,0.84was achieved.(3) CAU-1membranes were prepared on the asymmetric porous a-Al2O3tubes with α-Al2O3buffer layers of a nominal pore size of200nm by simple in-situ growth method. Continuous and dense CAU-1membrane of1-2μm was obtained under optimized conditions. The CAU-1membrane was tested by single and binary gas permeation of CO2/N2or CO2/CH4, exhibiting single CO2permeance of1.36x10-6mol·m·s-1·Pa-1with ideal selectivity for CO2/N2and CO2/CH4of15.89and14.79, for1:1CO2/N2, CO2permeance and CO2/N2separation factor of8.00×10-7mol·m-2·s-1·Pa-1and14.39respectively,which is better than that of MOFs membranes reported in literature under the similar experimental conditions. The-OH and Al of α-Al2O3tubes play the key roles in the formation of CAU-1membranes, which may provide a new solution to solve the problem of weak binding forces between the MOFs and the inorganic support.(4) Base on the induced effect of-OH and Al of α-Al2O3tubes combining with CAU-1seeds. A thin tubular CAU-1membrane of2-3μm was obtained by secondary growth method using an optimized CAU-1seeds. The membrane exhibited single CO2permeance of1.32x10-6mol·m-2·s-1·Pa-1with ideal selectivity for CO2/H2, CO2/N2, CO2/CH4and CO2/SF6of2.6,26.2,14.8and79.3. At a CO2molar fraction of0.5, a CO2permeance of7.27×10-7mol·m-2·s-1·Pa-1and a CO2/N2separation factor of20.3were obtained. At a CO2molar fraction of0.1-0.2, which is similar to flue gas composition, the CO2permeance was5.0-5.70×10-7mol·m-2·s-1·Pa-1with CO2/N2separation factor of about17.4. Such result was better than other MOFs membranes under the same experimental conditions, the reproducibility of our CAU-1membrane was higher than90%, demonstrating the potential applications of MOF membranes for CO2capture from flue gas. |
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