Photocatalytic degradation of gaseous toluene by using immobilized titania/silica on aluminum sheets

The aim of this study was to prepare a highly active immobilized titania/silica photocatalyst and to test its performance in situ toward degradation of toluene as one of the major toxic indoor contaminants. In this work, two different titania layers immobilized on Al sheets were synthesized via low temperature sol-gel method employing presynthesized highly active titania powders (Degussa P25 and Millennium PC500, mass ratio 1:1): (a) with a silica/titania binder and a protective layer and (b) without the binder. The photocatalysts were characterized by X-ray diffraction, nitrogen sorption measurements, scanning electron microscopy (SEM), infrared spectroscopy, and UV-vis diffuse reflectance spectroscopy (DRS). The in situ photocatalytic degradation of gaseous toluene was selected as a probe reaction to test photocatalytic activity and to verify the potential application of these materials for air remediation. Results show that nontransparent highly photocatalytically active coatings based on the silica/titania binder and homogeneously dispersed TiO2 powders were obtained on the Al sheets. The crystalline structure of titania was not altered upon addition of the binder, which also prevented inhomogeneous agglomeration of particles on the photocatalyst surface. The photoactivity results indicate that the adsorption properties and photocatalytic activity of immobilized photocatalysts with the silica/titania binder and an underlying protective layer were very effective and additionally, they exhibited considerably improved adhesion and uniformity. We present a new highly photocatalytically active immobilized catalyst on a convenient metallic support, which has a potential application in an air cleaning device.

Titania-based organic-inorganic hybrid planar waveguides

Eu3+ -doped titania-silica planar waveguides were prepared from tetraethylorthotitanate (TEOT) and modified silane 3-amino-propyltriethoxysilane (APTS). Films were deposited on borosilicate glass substrates by a dip-coating technique. The refractive index, the thickness and the total attenuation coefficient of the waveguides were measured at 632.8 and 1550 nm by prism coupling technique. Starting from pure titania films, the addition of modified silane leads to a decrease in the refractive index and an increase in thickness. Squared electric field simulation has shown that the light confinement in the waveguide increases with the silane content of the so]. Emission spectra present a broad emission band due to the modified silane and EU emission transitions arising mainly from the D-5(0) level to the F-7(J) (J = 0-4) manifolds. The dependence of transition intensities and excited state lifetimes on the initial composition and also on the heat treatment performed was interpreted in terms of structural changes occurring during the preparation process. (C) 2002 Elsevier B.V. B.V. All rights reserved.

Epoxidation of styrene on Si/Ti/SiO2 catalysts prepared by chemical grafting

Titania-silica (Ti/SiO2) and silica-titania-silica (Si/Ti/SiO2) catalysts were:prepared by chemical grafting using TiCl4 and tetraethyl orthosilicate (TEOS) as precursors and SiO2 as support. The prepared catalysts were characterized by UV Raman and visible Raman spectroscopies, XRD and the epoxidation of styrene; Ti/SiO2: catalyst grafted with only titanium species is not very active for epoxidation using H2O2 (30%), but is active and-selective when one uses tert-butyl hydroperoxide (TBHP). The catalyst grafted at high temperatures shows better epoxide selectivity. Si/Ti/SiO2 catalyst, the titanium-silica grafted further with TEOS, is active and selective for the epoxidation of styrene using either dilute H2O2 or TBHP, possibly due to the fact that the grafting of Ti/SiO2 with TEOS modifies the coordination structure of titanium and makes the titanium sites of Si-O-Ti-O-Si species less hydrophilic. A characteristic band at 1085cm(-1) due to Ti-O-Si species is detected for the grafted catalysts by UV resonance Raman spectroscopy. Reaction between TiCl4 and SiO2 at high temperatures favors the formation of Ti-O-Si species. Better activity and selectivity to epoxide,is found for the catalysts with more Ti-O-Si species. It is assumed that the active sites are the highly isolated Ti-O-Si species. For Si/Ti/SiO2 catalyst, the gas phase O-2 can participate in the catalytic oxidation of styrene when H2O2 is present ana:ii causes the formation of benzaldehyde. (C) 2000 Elsevier Science B.V. All rights reserved.

Desenvolvimento de biocidas inorgânicos a base de óxidos de titânio e silício com prata para desinfecção de águas contaminadas com microrganismo

Pós-graduação em Ciência e Tecnologia de Materiais - FC

Titania–Silica Materials for Enhanced Photocatalysis

Mesoporous titania–organosilica nanoparticles comprised of anatase nanocrystals crosslinked with organosilica moieties have been prepared by direct co-condensation of a titania precursor, tetrabuthylortotitanate (TBOT), with two organosilica precursors, 1,4-bis(triethoxysilyl) benzene (BTEB) and 1,2-bis(triethoxysilyl) ethane (BTEE), in mild conditions and in the absence of surfactant. These hybrid materials show both high surface areas (200–360 m2 g−1) and pore volumes (0.3 cm3 g−1) even after calcination, and excellent photoactivity in the degradation of rhodamine 6G and in the partial oxidation of propene under UV irradiation, especially after the calcination of the samples. During calcination, there is a change in the TiIV coordination and an increase in the content of Si[BOND]O[BOND]Ti moieties in comparison with the uncalcined materials, which seems to be responsible for the enhanced photocatalytic activity of hybrid titania–silica materials as compared to both uncalcined samples and the control TiO2.

Nucleation and crystallization of titania nanoparticles in silica titania planar waveguides: A study by low frequency Raman scattering

SiO2 (1-x) - TiO2 (x) waveguides, with the mole fraction x in the range 0.07 - 0.20 and thickness of about 0.4 μm, were deposited on silica substrates by a dip-coating technique. The thermal treatments at 700-900°C, used to fully densify the xerogels, produce nucleation of TiO2 nanocrystals even for the lowest TiO2 content. The nucleation of TiO2 nanocrystals and their growth by thermal annealing up to 1300°C were studied by waveguide Raman spectroscopy, for the SiO2 (0.8) - TiO2 (0.2) composition. By increasing the annealing temperature, the Raman spectrum evolves from that typical of the silica-titania glass to that of anatase, but brookite phase is dominant at intermediate temperatures. In the low. frequency region (5-50 cm-1) of the Raman spectra, acoustic vibrations of the nanocrystals are observed. From the measured line shapes, we can deduce the size distribution of the particles. The results are compared with those obtained from the line widths in the X-ray diffraction patterns. Nanocrystals with a mean size in the range 4-20 nm are obtained, by thermal annealing in a corresponding range of 800-1300°C.

Investigation of the Young's modulus and thermal expansion of amorphous titania-doped tantala films

The current generation of advanced gravitational wave detectors utilize titania-doped tantala/silica multilayer stacks for their mirror coatings. The properties of the low-refractive-index silica are well known; however, in the absence of detailed direct measurements, the material parameters of Young's modulus and coefficient of thermal expansion (CTE) of the high refractive index material, titania-doped tantala, have been assumed to be equal to values measured for pure tantala coatings. In order to ascertain the true values necessary for thermal noise calculations, we have undertaken measurements of Young's modulus and CTE through the use of nanoindentation and thermal-bending measurements. The measurements were designed to assess the effects of titania doping concentration and post-deposition heat-treatment on the measured values in order to evaluate the possibility of optimizing material parameters to further improve thermal noise in the detector. Young's modulus measurements on pure tantala and 25% and 55% titania-doped tantala show a wide range of values, from 132 to 177 GPa, dependent on both titania concentration and heat-treatment. Measurements of CTE give values of (3.9 +/- 0.1) x 10^-6 K^-1 and (4.9 +/- 0.3) x 10^-6 K^-1 for 25% and 55% titania-doped tantala, respectively, without dependence on post-deposition heat-treatment.

Europium complexes immobilization on titania via chemical modification of titanium alkoxide

We report a facile strategy to tether lanthanide complexes to organic-inorganic hybrid titania materials via sol-gel processing by employing chemically modified titanium alkoxide as the precursor where the organic ligand sensitizing the luminescence of lanthanide ions is bonded to titanium.

Electrochemiluminescence detection based on Ruthenium(II) tris(bipyridine) immobilised in sulfonic-functionalised titania nanoparticles by ion exchange strategy

A novel Ruthenium(II) tris(bipyridine)-based solid-state electrochemiluminescence (ECL) sensor was developed in this paper. The sensor was fabricated by immobilising tris(2,2'-bipyridyl) ruthenium(II) (Ru(bpy)(3)(2+)) in sulfonic-functionalised porous titania (TiO2-SO3H) nanoparticles via an ion exchange strategy, followed by employing environment friendly and stable biopolymer chitosan (CHIT) to entrap Ru(bpy)(3)(2+)/TiO2-SO3H onto the ITO electrode.

Preparation of titania-based catalysts for formaldehyde photocatalytic oxidation from TiCl4 by the sol-gel method

Titania sols were prepared by acid hydrolysis of a TiCl4 precursor instead of titanium alkoxides. The effect of acid concentration on the particle size and stability of sol was investigated. Stable titania sols with mean particle size of 14 nm could be obtained when the H+/Ti molar ratio was 0.5. The titania sols were modified with Pt, SiO2, ZrO2, WO3 and MoO3 to prepare a series of modified catalysts, which were used for the photocatalytic oxidation of formaldehyde at 37 degreesC. They showed different photocatalytic activities due to the influence of the additives. Comparing with pure TiO2, the addition of silica or zirconia increased the photocatalytic activity, while the addition of Pt and MoO3 decreased the activity, and the addition Of WO3 had little effect on the activity. It is of great significance that the conversion of formaldehyde was increased up to 94% over the SiO2-TiO2 catalyst. The increased activity was partly due to higher surface area and porosity or smaller crystallite size. A comparison of our catalyst compositions with the literature in this field suggested that the difference in activity due to the addition of a second metal oxide maybe caused by the surface chemistry of the catalysts, particularly the acidity. (C) 2001 Elsevier Science B.V. All rights reserved.

Investigations on Some Titania Supported Catalysts

Titania is a versatile metal oxide with multiple applications. Titania supported catalysts are reported to be much more active compared to conventional silica or alumina supported ones in some reactions. TiO2 (anatase) having high surface area, with better crystallinity and high onset temperature of rutilation can be prepared by thermal hydrolysis of titanyl sulfate solution under controlled conditions. Calcinations at 350oC for 6 hrs were necessary to crystallize anatase. Method of preparation and percentage of the loaded metal oxides have greater influence on surface area. Drastic decrease in surface area was observed upon rutilation. Rutilation started at different temperatures depending on the metal oxide and the method of preparation. TiO2 should be characterized with high surface area, phase purity and high onset temperature of rutilation.Which should be well above the optimum temperature of a designated reaction in which it is employed as a catalyst. Variation in physical properties, depending upon the method of preparation is greater in TiO2 supported catalysts. Methanation activity was found to be highly dependent on nickel concentration present on the surface of the pellets. The methanation activity is strongly influenced by support material. The rate and turn over frequency of methanation and toluene oxidation activity of these catalysts are also equally important from an industrial point of view.

Morphology and topography analysis of mesoporous titania templated by micrometric latex sphere arrays

In this work, mesoporous titania is prepared by templating latex sphere arrays with four different sphere diameters at the micrometric scale (phi > 1 mu m). The mesoporous titania homogeneously covers the latex spheres and substrate, forming a thin coating characterized by N-2 adsorption isotherm, small angle X-rays scattering, atomic force, field emission and transmission electronic microscopies. Mesoporous titania has been templated into different shapes such as hollow particles and monoliths according to the amount of sol used to fill the voids of the close packed latex spheres. Titania topography strongly depends on the adsorption of polymeric segments over latex spheres surface, which could be decreased by changing the dimensions of latex spheres (phi = 9.5 mu m) generating a lamellar architecture. Thus, micrometric latex sphere arrays can be used to achieve new surface patterns for mesoporous materials via a fast and inexpensive chemical route for construction of functional devices in different technological fields such as energy conversion, inclusion chemistry and biomaterials. (C) 2011 Elsevier Inc. All rights reserved.