The gas-surface interactions of zirconium based metal-organic frameworks

Lawrence, Mason Chester (2023) The gas-surface interactions of zirconium based metal-organic frameworks. Doctoral (PhD) thesis, Memorial University of Newfoundland.

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Abstract

Metal-organic frameworks (MOFs) are a class of porous materials that are formed when inorganic metal cations or clusters (nodes) are combined with organic anions (ligands). With careful choice of both node and ligand a porous material that contains a large internal surface area can be formed. With a large internal surface area, the study of many real-world applications of MOFs have been investigated such as catalysis, gas separations, gas storage and drug delivery. This thesis explores how the modification of structural features (e.g., pore sizes, functional groups, defect concentration) in zirconium-based MOFs impacts the gas/vapour adsorption of two atmospherically abundant compounds. Chapter 2 explores how water adsorption capabilities changes as the previously mention structural features are changed. The obtained results suggest that the water adsorbs by a water cluster growth mechanism that starts around the node. Estimation of the contact angle of water in the pore suggests that as the size of the ligand (i.e., pore size) is increased, the material becomes more hydrophobic. With the addition of pendant amine groups, the MOFs become more hydrophilic but the impact of the addition of the amine group decreases as the length of the ligand increases. Chapter 3 focuses on how structural features impacts the carbon dioxide gas adsorption properties. Pore size, number of defects, cluster dehydration, and cluster functionalization were examined to determine which features had the biggest enhancements on the carbon dioxide gas adsorption. The experiments found that pore size had the largest impact on the enthalpy of adsorption of carbon dioxide gas. MOFs that naturally had small pores, or were functionalized to reduce the pore size, had more confinement effects that lead to an increased enthalpy of adsorption. Furthermore, the experiments showed how important the cluster-containing μ3-OH units were on carbon dioxide gas adsorption. Finally, Chapter 4 outlines some projects that have been started, but due to the COVID-19 pandemic were unable to be completed. Some of these are direct extensions to the work in Chapter 2 and Chapter 3, while others are new projects that were thought of during my graduate program.

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