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Abstract  

Electrical conductivity and Seebeck voltage developed in -irradiated TiO2 was studied as a function of temperature. The conversion of n-type TiO2 into p-type observed after irradiation was explained on the basis of formation of inversion layer of p-type TiO2 due to the chemisorption of oxygen on the oxide surface during irradiation. Sign of the EMF of the electrochemical concentration cell of Ag/Ag+ with the addition of irradiated TiO2 was found to be exactly opposite to that due to the addition of nonirradiated oxide.

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Abstract  

A TiO2/monazite photocatalyst was prepared by embedding TiO2 nanoparticles into a monazite substrate surface. TiCl4 hydrolysis/citric acid chelating procedure under acidic conditions were used to synthesize the nanophase TiO2 particles. The anatase TiO2/monazite photocatalyst surface area, morphology, crystalline and elemental concentrations were characterized using Brunauer-Emmett-Teller (BET) method, scanning electron microscopy (SEM), X-ray diffraction (XRD), and inductively coupled plasma-atomic emission spectrometry (ICP-AES). Monazite contains a large amount of Ce-, La-, Nd- and Th-PO4 compounds; it has been known as a natural mineral material with minor radioactivity. TiO2-CeO2 composite is a kind of radiation sensitive photocatalyst in which the radiations of thorium nuclides give energy to trigger TiO2 and cerium ions which play an energy absorber with charge separator. The result showed that methylene blue and phenol were spontaneously photocatalytic decomposed by TiO2/monazite composite even in a dark environment. A synergistic effect was also examined with applied exterior UV or 60Co irradiation. A hybrid mechanism is proposed; according by the radioluminescence (RL) from excited Ce ion by γ-radiation soliciting CeO2/TiO2 heterojunction (HJ). This seems to be a possible mechanism to explain this self-activated photo-catalytic behavior.

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Preparations were characterized by specific surface area, thermogravimetry, and X-ray diffractometry. Thermal effects observed were (a) sulfur loss, (b) sintering, (c) crystallization and transformation of the crystalline phase(s). Thermoanalytical curves indicate that decomposition of the sulfate occurs in two distinct steps. Decrease of surface area due to (b) and (c) is concomitant to decomposition of sulfate. Sulfate was found to hinder sintering, crystallization and phase transformations of ZrO2 and TiO2. In low-titania and -zirconia sulfated TiO2-ZrO2 the minor component enhances the effect of sulfate. In equimolar TiO2-ZrO2 sulfate decomposition is accompanied by rapid formation of crystalline TiZrO4.

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Journal of Thermal Analysis and Calorimetry
Authors:
M. Crişan
,
Ana Brăileanu
,
M. Răileanu
,
D. Crişan
,
V. Teodorescu
,
R. Bîrjega
,
V. Marinescu
,
J. Madarász
, and
G. Pokol

Abstract  

Pure TiO2 and S-doped TiO2 sol–gel nanopowders were prepared by controlled hydrolysis-condensation of titanium alkoxides. The influence of different Ti-alkoxides (tetraethyl-, tetraisopropyl- and tetrabutyl-orthotitanate) used in obtaining TiO2 porous materials in similar conditions (water/alkoxide ratio, solvent/alkoxide ratio, pH and temperature of reaction) has been investigated. The relationship between the synthesis conditions and the properties of titania nanosized powders, such as thermal stability, phase composition, crystallinity, morphology and size of particles, BET surface area and the influence of dopant was investigated. The nature of the alkyl group strongly influences the main characteristics of the obtained oxide powders, fact which is pointed out by thermal analysis, X-ray diffraction, TEM and BET surface area measurements.

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Abstract  

The physicochemical properties (crystal structure, surface acidity, surface area, catalytic activity and electrical conductivity) of TiO2-silica gel mixed oxides have been investigated. A series of mixed oxides of various compositions in the range of 0–100% for each component were prepared by calcining the mixed oxides in air at temperatures of 115, 300, 600 and 1000°C. The results obtained have been discussed and correlated.

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Abstract  

Amorphous SiO2, TiO2 and xSiO2–(1–x)TiO2 ceramic materials with selected values of x 0.5, 0.7 and 0.9, have been prepared via sol-gel process using silicon tetraethoxysilane (TEOS) and titanium tetraisopropoxide Ti(OPri)4. By means of the combined use of differential thermal analysis (DTA),thermogravimetry (TG), X-ray diffraction (XRD), scanning electron microscopy (SEM),X-ray photoelectron spectroscopy (XPS) and X-ray induced Auger electron spectroscopy(XAES), the surface microchemical structure and morphology of the sol-gel materials have been studied as a function of thermal treatments carried out in air up to 1200C. In the range of temperature from 50 to 450C, DTA-TG results evidence a remarkable mass loss due to the evaporation of organic solvents entrapped in the sol-gel materials and of the remnant organic components of the precursor metal alkoxides. In the range of temperature from 400 to about 1000C, by means of the combined use of DTA, XRD, XPS and XAES techniques as a function of temperature and of chemical composition, it is possible to evidence the formation of crystalline phases such as quartz, anatase and rutile. Furthermore, line shape analysis of O1s XPS peak allows to distinguish between single O–Ti and O–Si bonds and also to disclose the presence of cross linking Si–O–Ti bonds, that act as bridges between SiO2and TiO2 moieties. As a function of temperature, Si–O–Ti bonds are broken and the formation of new Ti–O and Si–O bonds as in TiO2 and SiO2takes place as well as a silica segregation phenomenon.

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Abstract  

Iron (Fe3+) loaded TiO2 nanocatalysts were prepared by the photochemical reduction process. These supported nanocatalysts were characterized by X-ray diffraction (XRD), surface area (BET) measurements, scanning electron microscopy SEM with energy dispersive X-ray (EDX-elemental mapping) analysis and atomic force microscopy (AFM) with adhesion force measurements. XRD and BET results showed adsorption of iron species on the surface of the TiO2 support. AFM and SEM images revealed obvious variations in the surface morphology of the support after loaded with Fe3+ ions. Photocatalytic activities of the supported nanocatalysts were examined for decolorization and degradation processes of Congo red (CR) under UV irradiation. Fe3+ ions improved the performances of the supported nanocatalysts by suppressing the electron–hole recombination reactions. Effects of Fe3+ ion content and initial CR concentration were investigated. A tentative model was proposed for the photocatalytic degradation of CR.

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Thermal analysis (TG and DTA) was employed for the characterization of V2O5/TiO2 catalysts supported on high surface area TiO2. The results obtained are consistent with a uniform spreading of vanadium oxide on TiO2 surface for V2O5 content less than 15% by weight.

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have a tendency to surface crystallize if there is no site for heterogeneous nucleation. Therefore, depending upon the composition chosen, LAS glasses have been nucleated by addition of TiO 2 , Ta 2 O 5 , Y 2 O 3 , CeO 2 , F − , etc. [ 8 – 12 ] and

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Abstract  

A homogeneous TiO2 gel was obtained by hydrolysing titanium(IV) isopropoxide that was previously modified by reaction with acetic acid. The so stabilized precursor was hydrolysed under strong acidic medium (pH=0 by HCl). Dried TiO2 powders were characterized by FT-IR, XRD, N2 adsorption analyses, coupled thermogravimetric (TG) gas chromatographic (GC) and `mass spectrometric (MS) analyses. A semiquantitative analysis of the main evolved chemical species allowed to depict both the chemical rearrangements occurring in the TiO2 matrix during pyrolysis and the chemical composition of the initial gel.

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