New porous oxides from layered semiconductors
This thesis represents three separate projects. Chapter 2 through Chapter 4 describe the whole process of preparing and characterizing unique, stable, porous transition metal oxides. Chapter 5 and 6 describe the surface derivatization of these new porous metal oxides with phosphonic acids. Chapter 7 describes photocatalysis experiments done using the new porous metal oxides developed in Chapter 2-4. For the first project, titaniumniobate and triniobate porous metal oxides, derived from KTiNbO5 and KNb3O8 were prepared. The preparation involves a series of reactions that starts with solid-state synthesis followed by cation exchange, exfoliation, condensation and super critical drying process of porous metal aggregates. The products were then characterize using XRD, BET, UV-Vis, ESEM, ICP-OES, TGA, AFM and TEM. Various concentrations and temperatures were used to optimize the morphology, thermal properties, and surface parameters such as pore size, pore volume and surface area. Results show that the new materials are crystalline in structure. BET results indicate that these materials have high surface areas with large pores. For all samples, the pore size distribution was random within a range of 1 to 300 nm. TGA and other thermal studies show the materials are thermally stable. For the second project, the new porous metal oxide materials developed in the first project were tested for the possibility of surface derivatization. Surfaces of triniobate and titaniumniobate porous metal oxide material were derivatized with a monolayer of octylphosphonic acid (OPA) and a layer of amino phosphonic acid, allowing for further reactions. Results show that it is possible to add layers of molecules to the surface of the POX material by covalent bond formation. Derivatizing the surface with OPA during the wet stage of the synthesis caused rearrangement of the particle sheets, which in turn may be responsible for the lower pore volume, lower pore size, and increased surface area observed. For the third project, the new porous oxide materials were tested for photocatalytic activity for the photolysis of organic compounds in water. The photodegradation of micromolar solutions of a test compound, bromocresol green dye, was used to evaluate the material's catalytic activity under ultraviolet light irradiation. The photolysis experiments were performed at pH 2.1, 3.6, and 7.0 and the dye concentrations were monitored over time down to 0.15 ppm using the optical absorbance of the dye in its basic form at a wavelength of 616 nm. Results indicate that the new porous material had much better sedimentation characteristics than the commercial TiO2 powder, and this can be exploited to help solve catalyst retrieval and filtration problems after water decontamination of micro pollutants. The reactivity of the porous catalyst was comparable with that of one of the best commercial catalysts, nanopowder Tio2, P25 by Degussa (Germany).
Yesu, Nageswar Rao, "New porous oxides from layered semiconductors" (2006). ETD Collection for University of Texas, El Paso. AAI1439461.