Defect engineering and conversion of metal-organic frameworks for adsorption and electrical energy storage applications
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Metal-organic frameworks (MOFs) are hybrid porous materials, constructed by the assembly of inorganic metal ions or clusters and organic ligands. MOFs have attracted considerable research interest in the fields of gas adsorption and separations, owing to their high surface areas, permanent porosity, tailorable pore sizes, and remarkable tunability. Numerous modification strategies have been developed for engineering MOF crystals based on their desired characteristics. MOFs can have intentionally generated crystal imperfections by using defect engineering strategies during their synthesis. Defect engineering is an effective strategy that can be used to tune the physical and chemical features of MOFs such as their chemical stability, textural and adsorption properties. Understanding the impact of defects on the changes in these properties of MOFs is imperative to the development of next-generation defective MOFs. Chapters 3 and 4 provide detailed studies on two typical defect types (e.g. mixed-metal and missing cluster defects) that are commonly found in defective MOFs. In chapter 3, experimental investigations revealing trends related to the effect of mixed-metal centers on CO2 adsorption and water stability properties are addressed. Chapter 4 provides insight into the impact of missing cluster defects on chemical stability and adsorption properties through experimental and computational methods. Beyond being used as adsorbents, these hybrid crystals can also be converted to metal oxides, metal hydroxides and carbons via facile chemical treatments. These MOF-derived materials usually possess high surface areas, large pore volumes, diverse functional groups, controllable morphology, and hierarchical-pore architectures. These features make MOFs-as-templates strategies promising choices for electrical energy storage applications such as supercapacitors. Chapter 5 investigates the relationship between MOF stability and the cycling stability of MOF-derived electrode materials via complimentary experimental techniques. Chapter 6 evaluates the electrochemical performance of both positive and negative electrode materials that are synthesized from a single MOFs-reduced graphene oxide (rGO) precursor. In general, this dissertation explores the possibilities of defect engineering and MOFs-as-templates (MOF conversion) strategies that could be used to design and engineer MOFs or MOF-derived materials for adsorption and electrical energy storage applications.