| Metal-Organic Frameworks (MOFs), readily self-assembled from their corresponding metal ions and/or metal-containing clusters with suitable organic linkers, is one of the most rapidly developed porous materials over the past two decades. Due to its richness and diversification in organic ligands and fuctional groups, a large number of porous MOFs with diverse structures and/or topologies can be synthesized. Besides, the huge specific surface areas and pore volume have led MOFs to be extensively assessed for a number of applications including gas storage and separation, catalysis, and sensing.In this dissertation, we aimed at fabricating MOFs with active metal sites or functional groups through rational design of experiment scheme based on MOFs with special pore structures. During the synthesis process, the loading condition and optimum loading amounts were investigated and optimized. We clarified and further investigated the interactive relationship between the active metal sites/functional group immobilized on structure of MOFs and the property of materials in the field of gas storage and separation. Meanwhile, by the rational design of organic ligands and optimization of the solvethermal condition, we realized the control synthesis of the framework interpenetration, through which, the porosity and pore size can be judiciously mediated. Overall, the above strategy realized the increasement of the separation selectivity of light hydrocarbons, and high storage and working capacity of methane. Our work will largely enrich the design and loading method of MOFs with active sites and provide aboundant ideas for synthesis MOFs as excellent sorbent for gas storage and separation.To take advantage of the selective interaction of Cu(Ⅰ) with ethylene, various amounts of cuprous chloride nano-particles were succesfully immobilized into the meso-pore cage of hydrothermally stable metal-organic framework MIL-101-(Cr) with a double-solvents impregnation method, of which the cuprous chloride is an active site for ethylene selective adsorption. Due to the selective interaction of Cu(Ⅰ) with the carbon-carbon double bond in ethylene through π-complexation and the decrease of porosity, the uptake of ethylene increased first with the doping amount of CuCl and then decreased, while, the uptake of ethane decreased with the doping amount of CuCL An optimized, cuprous-loaded MIL-101 was shown to have an enhanced ethylene adsorption capacity and higher ethylene-ethane selectivity (14.0) compared to pure MIL-101 (1.6). The high performance of ethylene-ethane (equimolar) separation is also confirmed by simulated breakthrough results.Considering the instability of Cu(I) exposed to air, a silver ion functionlized MIL-101-SO3H, of which silver also shows selective interaction with ethylene moleculer, whereas much stable than Cu(I), was successfully prepared through ion exchange. The introduce of Ag(I) in MIL-101-SO3H led to the lower pore volume of 1.00 cm3g-1 compared with the original one of 1.35 cm3 g’in (Cr)-MIL-101-SO3H, however, the adsorption amount of ethylene and propene were remarkably increased, especially in low pressure. Thus, extremely high separation selectivity of olefin/ paraffin was obtained. Particularly, its adsorption selectivity for ethylene/ethane at 1 kPa of 238 is even two times that recently reported for PAF-1-SO3Ag (Sads=125 at 296 K), highest ever reported for the adsorptive separation of ethylene-ethane mixtures. Besides, its high stability in moisture and good recyclability show its potential in industrial application.The strategy of synthesizing polymorphous MOFs which constructed from the same organic ligand and secondary building units (SBUs) provides another approach for investigating the interaction between the framework and gas molecules. Here, a novel non-interpenetrated three-dimensional porous metal-organic framework UTSA-68 and a doubly interpetrated metal-organic framework ZJU-30 have been controllably synthesized by altering the reaction conditions based on the same organic ligand. The non-interpenetrated UTSA-68 shows larger channels than the doubly interpenetrated ZJU-30. More importantly, UTSA-68 takes up a moderately high amount of C2H2 of 70.1 cm3 g-1 at 1 atm and 296 K, which is much higher than 51.8 cm3 g-1 in ZJU-30, while its CO2 uptake of 39.6 cm3 g-1 is slightly lower than 42 cm3 g-1 in ZJU-30a. At 296K, the selectivity of UTSA-68a lies in the range of 5-3.4 during the entire pressure range, which is two times higher than that of ZJU-30a (2.4-1.7) and also comparable to those of the most promising MOFs HKUST-1 (5.8) and UTSA-50a (5.0), highlighting its promise for C2H2/CO2 separation. This work demonstrated that the gas adsorption and separation properties can be judiciously tuned through suitable control of interpenetration in the frameworks, which provides another approach for designing new MOFs with good gas separation performance.To investigate the effect of secondary interactive sites on high pressure methane storage, two functional groups -CF3 and -F with strong electronegativity were grafted separately onto the framework of a NbO-type metal-organic framework NOTT-101 to form two isoreticular MOF UTSA-88a and NOTT-108a, respectively. Compared to NOTT-101, although the specific surface area and pore volume are decreased, especially for UTSA-88a, they exhibit a notably high methane storage capacity (at room temperature and 65 bar) and working capacity. Specifically, the total volumetric storage capacity for UTSA-88a and NOTT-108a approaches 250 cm3 (STP) cm-3 at room temperature and 65 bar, which is very close to the DOE new target for methane storage. Meanwhile, the working capacity for UTSA-88a and NOTT-108a is 184 cm3 (STP) cm-3 and 186 cm3 (STP) c-"3, respectively, which is among the top five highest reported for all MOFmaterials. The interaction energy between the functionalized ligand and methane calculated by DFT method indicates that the higher polarity/dipole moment of C-F bonds compared to that of C-H bonds provides enhanced electrostatic interaction with the methane molecules. This work might motivate more extensive research to develop new MOFs with enhanced methane storage capacities through the introduction of some specific adsorption sites on the pore surfaces for their stronger interactions with methane molecules. |
PDF Full Text Request