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|Title:||Factors Affecting the Morphology and Composition of MOF Crystals|
|Abstract:||Porous materials have become a subject of great scientific interest in recent decades due to their broad range of applications, and their ability to interact with atoms, ions, and molecules both on the surface and throughout the bulk of a material. Among porous materials, zeolites and activated carbons have been the most intensively researched. However, in last two decades, a new class of porous materials known as metal-organic frameworks (MOFs) has drawn great attention from researchers. Metal-organic frameworks (MOFs), also known as coordination polymers, are porous crystalline materials that were first synthesized in 1999; since that time, these materials have attracted significant interest due to their attractive properties. This class of porous materials generally consists of crystalline compounds that are built from metal ions or metal ion clusters, which act as connectors and organic linkers. The synthesis of an MOF is dependent on the chemical structures and properties of all of its constituent components, with a huge range of network topologies (i.e., one-, two-, and three- dimensional topologies) having been developed since the first MOFs were reported. In addition, the ability to change ligands allows a variety of organic linkers with different functional groups to be introduced to the network. Furthermore, pore size, pore shape, functionality, and network topology can all be tuned, thus allowing the properties of an MOF to be adjusted to suit a particular application. Most reported MOFs were synthesised via solvothermal and hydrothermal methods using organic solvent or water as a medium and high temperatures. To avoid the longer reaction times usually required for these methods, researchers have developed new methods, such as microwave/ultrasound-assisted process, which allow MOFs to be synthesized in only a few minutes. Aside from the above-noted methods, other commonly used methods include electrochemical methods, mechanochemical methods, and synthesis under solvent-free conditions, among others. Although researchers have become interested in MOFs due to the huge number of different MOFs that can be synthesized using relatively simple preparation methods, the root of interest in MOFs is due to their unique properties. Unlike other porous materials such as activated carbons and zeolites, MOFs offer thermal and chemical stability, ordered structure with various reactive sites, tunable pore properties, ultra-low densities, and large internal surface areas of up to 7000 m2g-1. As a result of these properties, MOFs have emerged as an interesting class of materials with various applications. One of the most commonly researched MOF applications is for the storage of gases (methane and hydrogen). In particular, MOFs are well-suited for hydrogen storage due to their high surface areas and low densities. Similarly, MOFs have also been examined as good candidates for hydrogen storage due to their high surface areas and pore volumes. Furthermore, adjustable pore sizes and controllable surface properties, along with high surface areas, make MOFs ideal candidates for gas separation applications. Some of the other most commonly investigated MOF applications include their use as drug delivery systems, as chemical sensors, for catalysis, and for air purification. Even though MOFs possess unique properties, the study of their potential is often limited due to the form in which they are produced, which is most often a powder. To overcome this problem, researchers have attempted to fabricate MOFs as membranes, as well as attempted to deposit them onto cost-effective polymeric substrates or ceramics, to name a few notable formats. One attractive approach that has been garnering more attention is the fabrication of composites using MOFs and cellulose based materials. The manipulation of the size and shape of the crystals is important because it can help determine the physical properties of the final material and enable specific applications. Given the recent surge in interest on attaching MOFs to various surfaces, we examine potential approaches to controlling the morphology of MOF-assemblies. In addition, we grew MOF crystals using natural substrates, and attempted to manipulate their shape by altering some of the initial parameters. Furthermore, since it is always desirable to discover new MOFs, we modified well-known MOFs by introducing another metal into the framework to examine how doing so affects the morphology of the parent MOF.|
|Appears in Collections:||Open Access Dissertations and Theses|
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