Host guest composites based on nanoporous materials.
Item
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Title
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Host guest composites based on nanoporous materials.
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Identifier
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AAI3187806
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identifier
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3187806
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Creator
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Zhang, Xiaoming.
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Contributor
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Adviser: Daniel L. Akins
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Date
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2006
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Language
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English
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Publisher
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City University of New York.
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Subject
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Chemistry, General
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Abstract
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Porous materials are used as adsorbents, catalysts and catalyst supports owing to their high surface areas and large pore volumes. This dissertation describes methods of preparing nanocomposites from mesoporous silicates with uniform channel structures, as well as some of their applications. Functional groups have been placed selectively on the internal or external pore surfaces. Organic functionalization of these solids permits tuning of the surface properties (hydrophilicity, hydrophobicity, binding to guest molecules), alteration of the surface reactivity, protection of the surface from attack, and modification of the bulk properties (e.g., mechanical or optical properties) of the material. Recent applications of modified mesoporous silicates are highlighted, including catalysis, adsorption of metals, anions, and organics, fixation of biologically active species, and optical applications.;For these reasons, three different kinds of molecules were successfully encapsulated within the channels of the mesoporous materials. Novel properties were found to be result from the confinement within the cavity of the matrices.;DCM is a well-known laser dye that has high fluorescence efficiency and is photochemically stable. We have been able to observe the dual emission from the by encapsulation of dye molecules within an alumino-MCM-41. The interaction between DCM and the internal surface of MCM-41 was found to modify the optical properties of the confined DCM molecules. The dynamics of DCM in MCM-41 was found to correspond to a biexponential relaxation with one component of 0.6 ns (57%) and a very long component of 1.9 ns (43%).;Nanostructural ferric oxide was encapsulated within porous silicate matrices, resulting in the formation of nanocomposites. The resulting nanocomposites were characterized by UV-vis, IR, TEM, EPR and X-ray diffraction. EPR measurements indicate that the various nanocomposites (whose dimensions were controllable by the pore sizes of the silicate materials), when sufficiently loaded with small Fe2O3 nanoparticles, possess nonzero absorptions at zero applied magnetic field, as well as significant microwave absorption capacities as a function of applied magnetic field strength.;The novel polyoxometalate (Eu8P4W43) has been immobilized inside the channels of MCM-41 mesoporous molecular sieve material by means of the incipient wetness method. For proper host-guest interaction, amine groups were introduced into the system as a result of an aminosilylation procedure. A stable and integrated Eu8P4W43 polyoxometalate was shown to be formed inside the channels of the modified MCM-41. The products were characterized by XRD, UV-Vis absorption, emission, Raman excitation, Raman and 31P solid-state NMR measurements. A strong photoluminescence suggests the potential utility of the polyoxometalate as a luminescent material.
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Type
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dissertation
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Source
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PQT Legacy CUNY.xlsx
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degree
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Ph.D.
