Studies On Synthesis And Adsorption Separation Property Of Metal-Organic Frameworks

Metal-organic frameworks (MOFs), emerging as a new class of crystalline nanoporous solid multi-purpose materials, have a broad potential application in many fields such as energy gases storage, adsorption/membrane separation, heterogeneous catalysis, drug delivery and optical devices due to their high surface area and large free pore volume, and fine adjustable pore surface and size on molecular level. In particular, some MOFs have shown excellent performance on adsorption and separation and many stable MOFs were reported in past few years, which make it more and more possible to apply MOFs in industry. As a new tool, calculational chemistry is widely used in design, microscopic mechanism, structure-activity relationship of MOF, and shows unique advantages in exploitation and application of MOFs.In this work, computational chemistry and experimental methods are adopted to study the design and synthesis of MOFs and their adsorption separation performance.The main works are as follows: 1. Molecular simulations were performed to investigate the effect of trace amount of water on CO2capture in natural gas upgrading process in a diverse collection of25metal-organic frameworks (MOFs). The effect of trace amount of water on the adsorption selectivity of CO2in the CO2/CH4mixture is MOF dependent, and the effect becomes significant only when the interactions between water molecules and MOFs are large enough, in which the electrostatic interactions between the framework and fluids play a crucial role. It is clear that when the interactions between water molecules and MOFs are weak enough to allow the adsorbed water molecules in the channel of MOFs move freely, the effect on selectivity is negligible. However, at moderate interaction strength, the effect can be either negligible or significant, depending on the competition of the two opposite contributions of water molecules to the adsorption of CO2. The knowledge obtained may provide useful information to guide the application of MOFs in industrial separations.2. In view of the effect of some critical operating parameters on gases adsorption and separation performance in MOFs, we systematically studied the effect of temperature on gases adsorption and separation in ZIF-8using multi-scale method, including experimental measurements and molecular simulations. From the interaction perspective, we explained how temperature affects the adsorption and separation in ZIF-8. For gases with large isosteric heat of adsorption, such as CO2, the effect of temperature becomes more evident, which is mainly due to the sensibility of the interaction between adsorbate fluid molecules with temperature; for gas mixtures, mixture gases with high selectivity are more sensitive to temperature. In addition, concept of temperature swing adsorption (TSA) was introduced into separation field of MOF for the first time and we studied the effect of temperature on working capacity of ZIF-8in temperature swing adsorption process.3. A new functional MOF UiO-67-SO2was designed on molecule-level, and its CO2adsorption and separation perfprmace were predicted by molecular simulaton. The simulated results showed that the new-SO2functional group in UiO-67can substantially enhance CO2adsorption and separation, and the microscopic mechanism revealed that-SO2group has a strong interaction with CO2molecule. Furthermore, the designed MOF was experimentally synthesized and its properties were tested to verify the result of moleculer simulation.The experiment results agree well with our predictions.4. Considerating that typical microporous MOFs cannot efficiently storage CH4or CO2at relative high pressure, we synthesized a non-interpenetrated high porosity Zr-MOF with long carboxylate ligand, which was prepared by condensation anhydride and amidogen. On this basis of the material, several other Zr-MOFs with similar structures were further computationally designed and their CH4storage capacities and CO2/H2separation capabilities were predicted using molecular simulations. The results show that these new hypothetical Zr-MOFs exhibit much higher CH4storage capacities and CO2working capacities compared to the existing typical MOFs.5. Considerating that Zr and Hf are in the same group in periodic table of elements and have similar atomic radii, we successfully synthesized a novel material UiO-66(Hf), which has the same structure as that of the Zr-version of this material. Our experimental characterizations show that UiO-66(Hf) has excellent chemical and thermal stabilities. Starting from this material, we further synthesized several other Hf-MOFs by using some ligands with different functional groups and lengths. Gas adsorption measurements show that introducing polar groups into Hf-MOFs or narrowing their pore sizes can be effectively used to enhance performance of the materials for CO2stoarge and gas separation.