| Due to its high surface area, large pore volume, high porosity, and fine tuned pore surface properties, the nanoporous materials metal organic frameworks (MOFs) has been widely studied for its potential applications in many fields such as gas storage and separation, catalysis and etc. However, many MOFs materials lack strong binding sites, leading to small CO? loading at low partial pressure, and therefore limit their application in industry. Post-synthesis of the MOFs by creating strong binding sites and thus improving CO2 adsorption capacity at low partial pressure should have significant meaning on this field. In the past decades, ten thousands of new MOFs have been synthesized. Theoretically, the combination of quantum chemistry and molecular simulation based method has been used to design thousands of MOFs, which were then used to study the structure-property relationship. Theoretical predictions allow us to gain atomic level understanding on the adsorption mechanism for the nanoporous materials and may shed light on the design of MOFs for particular applications. In this thesis, the following two projects are mainly studied:1. The two MOFs, UiO-66 and UiO-66-SO3H, have been synthesized and studied for their adsorption properties. More importantly, UiO-66-SO3H was further treated with ammonia hydroxide, forming a new nanoporous material NH3@UiO-66-SO3H. The three different gases, CO2, CH4, and N2 were studied for their single phase adsorption isotherms at three different temperatures,298,310 and 323 K, respectively. Furthermore, the experimental data were fitted using Langmuir or dual-site Langmuir models, based on which the isosteric heat of adsorption were calculated. The obtained results show that all of the three MOFs particularly for NH3@UiO-66-SO3H, have much more larger CO2 adsorption capacity than CH4 and N2, IAST predicted adsorption selectivity show that the NH3@UiO-66-SO3H material have a very high selectivity for both CO2/N2 and CO2/CH4 at the pressure range we studied. To mimic the practical application of the MOFs, breakthrough experiments were conducted to understand the adsorption selectivity for both CO2/N2 and CO2/CH4 gas mixtures using the three different MOFs, and the the results show that the ammonia hydroxide treated NH3@UiO-66-SO3H material have a much better selectivity over the other two MOFs. Breakthrough curves show that, in almost whole range of time interval, the gas mixture were completed separated with only N2 or CH4 flows out of the column while the CO2 gas was not detected at the end of the column for CO2/N2 and CO2/CH4 feed gases, respectively. The experimental breakthrough results agree well with the IAST predicted high adsorption selectivity.2. With the combination of quantum chemical and molecular simulations, we have studied the effect of flexible alkyl groups in the four Bio-MOFs, Bio-MOF-11, Bio-MOF-12, Bio-MOF-13, and Bio-MOF-14 on the adsorption of gases including CO2 and N2. Ab initio molecular dynamics show that there are many different configurational structures available for the Bio-MOFs, especially for the Bio-MOF-13 and Bio-MOF-14, which have long alkyl groups. Our calculations show that the different configurations of Bio-MOF-13 and Bio-MOF-14 greatly affect their pore size, and finally leading to greatly different gas adsorption capacity. Our theoretical calculations suggest that the the high adsorption selectivity of Bio-MOF-13 and Bio-MOF-14 are due to their flexible long alkyl groups, of which the effect could only be directly studied by performing MC/MD molecular simulation, where the flexibility of alkyl group are considered rather than using fixed models. |
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