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Molecular Simulation Study of Gases Adsorption and Separation in Metal-Organic Frameworks and Design of New MOFs

Author: XuQing
Tutor: ZhongChongLi
School: Beijing University of Chemical Technology
Course: Chemical Engineering and Technology
Keywords: Metal - organic framework materials Adsorption Separate Modified design Molecular modeling Quantum mechanical calculations .
CLC: TB383.1
Type: PhD thesis
Year: 2010
Downloads: 920
Quote: 4
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Metal - organic framework materials (metal-organic frameworks, MOFs) is a new nano-porous material similar to zeolite species diversity, the structure can be designed with adjustable resistance, a high specific surface area and good thermal stability, etc., materials in the field has become a front and hot, and access to a wide range of applications expected in gas storage, separation, catalysis, biochemistry and pharmaceutical fields. However, due to the wide variety of MOF materials, complex structure, purely experimental method is difficult to its system, greatly hindered the practical application of such materials. Calculate the chemical has been increasingly used to explore the relationship between the structure and performance of the MOF material law in recent years, as the chemical theory and efficient computation method has matured, and the rapid development of computer technology, to provide scientific and technical support for the synthesis of the material . At the same time, the use of computational chemistry pre-screening materials, saving a lot of resources to promote the practical application of the MOF materials. Therefore, for gas adsorption, separation and other properties in the MOF material, and the material of the modified design, the use of two methods of quantum mechanics and molecular simulation system, the main content and innovations are as follows: 1, by molecular simulation method, the quantum effects of adsorption of hydrogen in the MOF materials, investigated the effects of pore size and temperature, and provides a theoretical basis for hydrogen storage applications and the design of new materials for MOF materials. The results showed that, under a lower pressure (adsorbed amount), the smaller the aperture of the material, hydrogen in which the quantum effect is more obvious when the adsorption; the contrary, in the higher pressure (adsorbed amount), the opposite trend appears . The study also found that, as the pressure changes, the quantum effect depends on the contribution to the force between the fluid molecules and materials, and the contribution of the fluid intermolecular forces. In addition, the simulation results also illustrate how the quantum effect is the temperature change. 2, using the grand canonical ensemble Monte Carlo (GCMC) simulation method to study under CO2/H2 gas mixture at room temperature in three pairs, no cross-wearing structure of MOF materials separation. The results show that the CO: separation selectivity coefficient, in interpenetrating structure of MOF material than in its corresponding no interpenetrating structure of MOF material to be much higher. The simulation results also indicate that electrostatic interaction plays a crucial role in the separation and the size of its contribution, which depends primarily on the proportion of pore size, pressure and composition of the mixture. At low pressure, the electrostatic interaction between the fluid molecules and materials play a leading role on the separation, such a role in the mutual structure of MOF materials wear more obvious, as the pressure increased, the electrostatic interaction between the fluid molecules gradually play a leading role. 3, has developed a quick method to estimate the MOF material backbone atoms charge - based on the contribution of atom connectivity (connectivity-based atom contribution method, CBAC). In this method, it is assumed that, as long as it has the same atomic connectivity, have the same value of the charge in different MOF. Skeleton results given 43 MOF materials (containing 30 kinds of building a database material, and 13 kinds of test materials) the estimated value of the atomic charges, C02 and N2 CO adsorption results in 43 kinds of MOF material proved this method reliability. This method is easy to add new atoms, therefore, very easy to be applied to the the MOF structure known material. This method can also be applied to other porous materials, to facilitate the practical application of the material is suitable for large-scale screening, and also to better understand the relationship between the structure and nature of the MOF materials laid the foundation, which is conducive to guiding MOF development and application of the material. 4, the MOF-5 as the parent material, by using the O-Li group substituted on its organic ligands, H, the design of three lithium-modified metal - organic framework materials. Then, using a combination of molecular modeling and density functional theory calculations, CO2/CH4 gas mixture separation material, including three new design materials, a successful lithium used in hydrogen storage research modified materials and MOF-5. The results show that the adding of the metal can improve the MOF material the electrostatic potential gradient, thereby greatly improving the separation selectivity of CO2/CH4 mixture of CO2. The work in the design of a new material - chem-4Li, the CO2/CH4 mixture has a good separation performance reported MOF materials separation selectivity values ??are higher than the current. Accordingly, the present work for the dipole moment or four quadrupole differences larger separation of the mixed gas of a strategy for improving the separation selectivity. Furthermore, from the molecular level to clarify the mechanism of improving the separation selectivity of lithium-modified materials, found the location of the different metal is added may be changed CO2 adsorption position, which can be inferred, when such MOF materials used as the catalyst may also be Changing the active site. 5, the promotion of the new design of lithium-modified materials, used in the capture of CO2 in order to suppress the \The Molecular Simulation results show that the separation of materials for a variety of mixture CO: have a good effect. Also, the separation mechanism of the various systems, and get more useful information to guide the more practical applications.

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