Computational study of understanding porous materials stability upon acid gas treatment
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The stability of porous materials in acid gases and water environments is a critical property as well as an issue that must be addressed when applying porous materials in adsorptions, separations and catalytic processes, where acid gases and water always coexist with the adsorbates, influencing the performance of porous materials. Since this is vital but not widely explored, my research proposed computational modeling to understand the chemical stability and degradation mechanism of porous materials upon humid acid gas treatment, and then developed chemical stable porous materials that are suitable for use with the existence of aggressive contaminants such as H2S, SOX, and NOX. The porous materials studied in this work range from Metal Organic Frameworks (MOFs) to Porous Organic Cages (POCs) with different types of covalent bonds, i.e. MOF-2 with metal to charged ligand bond, UiO-66 with metal oxide cluster to charged ligand bond, and Cage crystal 3 (CC3), one of the imine-based POCs with non-metal to non-metal bond. Since POCs are relatively new emerging porous materials, apart from studying their chemical stability, its formation pathway was thoroughly explored and understood. With a detailed understanding of POCs formation mechanism, two strategies have been applied to adjust the crystal structure of POCs to improve crystal properties. Firstly, “missing-linker” type of point defects were introduced into the CC3-R crystal, and defective CC3-R crystal was found to have enhanced CO2 interaction and improved CO2 uptake capacity due to the additional functional groups present within the defective CC3-R crystals. In addition to defect engineering, a modification to the chirality of CC3 crystals was intentionally designed, forming mixed-chirality CC3-racemic crystals. The improved sorption properties and stability of CC3-racemic crystals relative to homochiral CC3 crystals led us to fully resolve the structure of this racemic crystal. Finally, an in silico prediction methodology was introduced that combines electronic structure calculations and atomistic calculations to predict the structure of CC3-racmeic crystal, which were not currently available from experiments alone.