Design and control of hierarchically structured nanomaterials



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Texas A&M University


Hierarchically ordered porous oxides have garnered much interest because of the numerous applications that can be developed from these materials. The catalytic properties, separation ability, and ion exchangeability of these materials, specifically zeolites, make them great candidates for applications. One area which has not been heavily studied is ways to control the morphology and particle size of these materials through soft chemistry approaches. This dissertation looks at two methodologies which can be used to alter zeolitic particle morphology. The first is a dual templating approach which attempts to incorporate microporous walls within a mesoporous structure. The zeolitic material, silicalite-1, is used as a siliceous precursor for the formation of the mesoporous SBA-15 material. A battery of characterization techniques were used to identify the structural properties of the material, including porosimetry, diffraction, microscopy, and spectroscopy. The overall conclusion was that a material with different properties than the parent SBA-15 were obtained, but that no characterization technique could be used to show the definitive presence of the zeolite in the walls. Another technique studied is the growth of zeolitic materials within the water domains of microemulsions. The concept of a reverse microemulsion, a confined water droplet in a continuous oil phase makes it an interesting system for morphological control. The zeolitic materials should only be able to grow within the water domain, and the reactive materials should be less available as they are trapped in separate micelles. Zeolite A (LTA) and zeolite L (LTL), two technologically important zeolites, were studied. Enhanced growth, larger particles, and unique material aggregates are just a few of the observations made for the two systems. The development of these materials should facilitate the application of zeolite in emerging technologies. In particular, preliminary work has been done on the development of large zeolite crystals with tuned orientations and particle sizes. This research shows multiple ways in which particle size and morphology can be tuned simply by altering the chemistry and reaction conditions of the system. This research has led to unique findings dealing with large zeolite crystals, and should open the door for continued research in this area.