Browsing by Author "Sizgek, GD"
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- ItemDelineating the first few seconds of supramolecular self-assembly of mesostructured titanium oxide thin films through time-resolved small angle x-ray scattering(American Chemical Society, 2008-10-07) Luca, V; Bertram, WK; Sizgek, GD; Yang, B; Cookson, DJThe early stages of evaporation induced self-assembly of titanium oxide mesophases from a precursor solution containing TiCl4 and the Pluronic triblock copolymer F-127 in HCl-water-ethanol solution have been studied using time-resolved SAXS techniques. Two experimental protocols were used to conduct these experiments. In one of these, the precursor solution was pumped around a closed loop as solvent was allowed to evaporate at a constant humidity-controlled rate. In the second protocol, a film of precursor solution was measured periodically as it dried completely to a residue under a stream of dry air. This permitted the detailed monitoring of changes in solution chemistry as a function of the elimination of volatile components followed by the actual drying process itself. The SAXS data were modeled in terms of two Guinier radii for soft nanoparticles while a broad Gaussian feature in the scatter profiles was accounted for by particle-article scattering interference due to close packing. For the initial precursor solution, one Guinier radius was found to be about 17 (A) over circle while the other ranged from 4 to 11 (A) over circle. Changing the rate of evaporation affected the two radii differently with a more pronounced effect on the smaller particle size range. Analysis gave an interparticle distance in the range 55-80 (A) over circle for the initial precursor solution which decreased steadily at both of the humidities investigated as evaporation proceeded and the particle packing increased. These results represent the first attempts to monitor in a precise fashion the growth of nano building blocks during the initial stages of the self-assembly process of a titanium oxide mesophase. © 2008, American Chemical Society
- ItemMesoporous zirconium titanium oxides. Part 3. Synthesis and adsorption properties of unfunctionalized and phosphonate-functionalized hierarchical polyacrylonitrile-f-127-templated beads(American Chemical Society, 2009-10-06) Sizgek, GD; Griffith, CS; Sizgek, E; Luca, VA method is presented for the preparation of zirconium titanate mixed oxides in bead form having hierarchical pore structure. This method entailed the use of both preformed polyacrylonitrile (PAN) polymer beads and surfactants as templates. The templates were removed by calcination at temperatures below about 500°C, resulting in mixed oxide beads with trimodal pore size distributions and interconnected pores. The pore size distributions as determined using nitrogen adsorption−desorption showed clear maxima at 4.5 and 45 nm length scales and also clear evidence of microporosity. The macroporous framework morphology was a replica of the PAN beads with radial structure. The mesoporous framework possessed wormhole-like pores with pore size of about 6 nm that was consistent with the F-127 triblock copolymer template used. The mixed oxide beads exhibited surface areas of 215 and 185 m2/g after calcination at 500 and 600°C. Thermal stability up to 650°C is unprecedented for bulk systems. The adsorption properties were characterized using uranyl as the target cation and the mass transport in the beads with the present hierarchical architectures has been shown to be exceptional. The beads were functionalized with 4-amino,1-hydroxy,1,1-bis-phosphonic acid (HABDP) and amino-tris-methylene phosphonic acid (ATMP) and the adsorption properties for the extraction of uranyl sulfate complexes from acidic solution examined. Of the two molecules investigated, ATMP functionalization resulted in the best extraction efficiency with equilibrium uptake of about 90% of uranium available in solution between pH 1 and 2. The beads could potentially be utilized as catalysts, catalyst supports, adsorbents, and separation materials. © 2009, American Chemical Society