Computational Study On Separation And Catalytic Properties Of New Framework Materials

Metal-Organic Frameworks and Covalent Organic Frameworks are newfamilies of nanoporous frameworks materials. Due to their extremely highaccessible areas, porosities, chemical diversities and tailored and designedstructures, they have been recongised as the frontier area and hotspot in thefield of materials. They have show potential applications in many fields, suchas in gas storage, separation, catalyst and sensors. However, their structure iscomplex and thus it is difficult to study the materials just by experiments. Withthe development of computer, computational chemical has been wildly used tostudy the structure and properties of materials..This work mainly studies the CO₂storage, CO₂related industry gasseparation in Metal-Organic Frameworks and Covalent Organic Frameworksusing computational tool. The main findings and contents are followed.1. We have studied two typical Zeolitic Imidazolate Frameworks (ZIFs),ZIF-68and ZIF-69. Using a combined molecular dynamic and Monto Carlomethod, we studied the adsorption and diffusion of CO₂in ZIF-68and ZIF-69. The results show that the small pores formed by he nIM linkers in ZIF-68andZIF-69are the preferential adsorption sites. The corners formed by phenylrings in the large pores are the second preferential aadsorption sites. We alsofound that the chlorine atoms in cbIM linkers in ZIF-69lead to enhancedbinding energy but reduced diffusivity for CO₂.2. We report a molecular simulation study for the separation of industrialgas mixtures in different ion-exchanged (Li⁺, Na⁺, K⁺, Rb⁺, Cs⁺, Mg²⁺, Ca²⁺,Sr²⁺, Al³⁺) usf zeolite-like metal-organic framework (usf-ZMOF). Theselectivity of the three systems (CO₂/CH4, CO₂/N2, CO₂/H2) is higher thanaverage. For the different ion-exchanged usf-ZMOF, the selectivity enhanceswhen the ion valences go up from positive one to three. In the same maingroup, the selectivity decreased with the increasing of the atom number.3. This work takes a computational study to investigate the influences offramewok charges on CO₂uptake in metal-organic frameworks. The resultsshow that the contribution of framework charges to CO₂uptake dependslargely on pressure. For applications operated at moderate or high pressures,such as in the natural gas purification process, the framework contributionbecomes less important ansd is usually less than10%. In this case, it isreasonable to neglect the framework contribution in the initial materialscreening, which makes it possible to pursue a large-scale computationalscreening of MOF materials for applications operated at moderate or highpressure. 4. An approach named connectivity-based atom contribution method(CBAC) was developed for estimationg framework charges in metal-organicframeworks in our group. This work extends the approach to covalent Organicframeworks. The results show that those framework atoms with the samebonding connectivity in covalent organic frameworks have identical chargesas that in metal-organic frameworks, this further validates the suitability of theCBAC method and makes it possible to apply to other nanoporous materials.We also extend the CBAC charge databank.5. We explored whether there are catalysis sites in Covalent OrganicFrameworks by Quantum Mechanics. We optimized the structures of bothCOF-1and CO-COF-1,and CO is adopted as probe molecule. We find thatthere is no catalysis activity in COF-1, by comparing frequencies, charges andthe length of bonds.