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promotes their catalytic performance [ 13 ]. Serna et al. [ 14 ] indicated that the presence of Pt on gold catalysts increases the rate of H 2 dissociation resulting in a solid having almost one order of magnitude more active than the monometallic Au/TiO 2

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Summary  

The sorption of Th(IV) onto TiO2 was studied by the batch technique as a function of pH and ionic strength at moderate concentration (10-4-10-5 mol/l) and in the presence and absence of phosphate. It was found that the sorption rate of Th(IV) was relatively slow, the sorption percent was abruptly increased from pH 2 to 4, and the sorption was decreased with increasing ionic strength as a whole. In the concentration range of Th(IV) from trace concentration to 1.4 . 10-4 mol/l and in the absence of phosphate, the sorption isotherms were roughly fitted the Freundlich equation at different ionic strengths and approximately constant pH. These sorption characteristics of Th(IV) onto TiO2 were compared with those of uranyl on the same sorbent. In addition, the positive effect of phosphate on the sorption of Th(IV) onto TiO2 was demonstrated obviously and can be attributed to strong surface binding of phosphate, and the subsequent formation of ternary surface complexes of Th(IV). The difference between the sorption characteristics of Th(IV) ions and uranyl ions onto TiO2 is discussed.

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Abstract  

Temperature-programmed reductions (TPR) with H2 of both pure V2O5 and coprecipitated V2O5−TiO2 systems with different titanium concentrations was performed. The original and the reduced samples following each TPR step were characterized by X-ray diffraction, Fourier transform infrared analysis and scanning electron microscopy. Within the temperature range in which TPR analysis was carried out (100–600°C) the V2O5 phase was reduced in two or three steps, while no variation in the TiO2 phase (anatase or rutile) was observed. In the first reduction step only superficial reduction of the oxides was detected. In the following steps, the H2 reacted with oxygen atoms of the V=O and V−O−V bonds. This led to important changes in the structure and morphology of the system. The experimental evidence allowed the conclusion that titanium stabilizes certain phases of vanadium oxides in which vanadium appears as V(+4) or as a mixture of V(+4) and V(+5). Moreover, when moderate and high titanium concentrations were used, the reduction temperature of the bulk V2O5 decreased markedly.

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Abstract  

The carrier technique has been used to concentrate Cr(VI) radiometrically by studying the carrying efficiency as a function of pH of aqueous medium, added ions, carrying capacity, amount of carrier and subsequent desorption of the activity adsorbed under optimum experimental conditions. The study shows that under optimum experimental conditions, 0.15 g of ZrO2 and 0.25 g of TiO2 carry 0.01 mg and 0.001 mg of chromium respectively. Further, the activity carried under the specified conditions can be recovered more or less quantitatively by leaching the carrier.

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Abstract  

To evaluate the thermal stability of materials, various criteria have been used. Not only the simple parameters, as characteristic temperatures, but also the combined criteria E/RT p , k f (T) and criterion based on the length of induction period of crystallization have been taken into account. Four gels with the composition Li2O–2SiO2nTiO2 (n = 0.00, 0.03, 0.062, and 0.1) were prepared and the validity of the criteria was tested by applying them to these gels. The results indicate that thermal stability of the studied gels decrease with amount of TiO2.

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development of a method for simulating metabolism with the use of photocatalysis. Irradiation of a drug substance solution in the presence of photocatalyst molecules (TiO 2 ) with a specific wavelength causes the oxidation in a manner similar to the processes

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Summary  

Organic substances present in radioactive waste lower the sorption of metal ions at the high pH in cement matrices and, hence, enhance their possible migration. The aim of this study was to develop a method to compare organic substances or their degradation products with respect to what extent they affect metal sorption. Batch sorption studies were performed with cement or TiO2 as solid phase and Eu(III) as a model element for trivalent lanthanides and actinides at pH 12.5 (representative of a cement waste matrix during the first approximately 100,000 years). Different kinds of ligands were studied in a broad concentration range, e.g., organic acids, cement additives, cleaning agents and degradation products from ion-exchange resin.

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Abstract  

The sorption of UO2 2+ on TiO2 was studied as a function of pH and ionic strength at moderate concentration (10-4-10-5mol/l) in the presence and absence of fulvic acid (FA, 20 mg/l). It was found that the sorption rates in the presence and absence of FA are fast and similar, slowly and similarly increased with increasing pH from 2 to 10. The sorption in the absence of FA increased with increasing ionic strength while, in the presence of FA it decreased. FA caused a relative enhancement in the sorption at pH<6. The sorptions in the presence and absence of FA at constant pH followed the linear sorption isotherm, and the distribution coefficients found are of the order of 10 to 103 ml/g.

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Journal of Thermal Analysis and Calorimetry
Authors:
János Madarász
,
Ana Brăileanu
,
Maria Crişan
,
Malina Răileanu
, and
György Pokol

Abstract  

Thermal decomposition of an amorphous precursor for S-doped titania (TiO2) nanopowders, prepared by controlled sol–gel hydrolysis–condensation of titanium(IV) tetraethoxide and thiourea in aqueous ethanol, has been studied up to 800 °C in flowing air. Simultaneous thermogravimetric and differential thermal analysis coupled online with quadrupole mass spectrometer (TG/DTA-MS) and FTIR spectrometric gas cell (TG-FTIR) have been applied for analysis of released gases (EGA) and their evolution dynamics in order to explore and simulate thermal annealing processes of fabrication techniques of the aimed S:TiO2 photocatalysts with photocatalytic activities under visible light. The precursor sample prepared with thiourea, released first water endothermically from room temperature to 190 °C, carbonyl sulfide (COS) from 120 to 240 °C in two stages, ammonia (NH3) from 170 to 350 °C in three steps, and organic mater (probably ether and ethylene) between 140 and 230 °C. The evolution of CO2, H2O and SO2, as oxidation products, occurs between 180 and 240 °C, accompanied by exothermic DTA peaks at 190 and 235 °C. Some small mass gain occurs before the following exothermic heat effect at 500 °C, which is probably due to the simultaneous burning out of residual carbonaceous and sulphureous species, and transformation of amorphous titania into anatase. The oxidative process is accompanied by evolution of CO2 and SO2. Anatase, which formed also in the exothermic peak at 500 °C, mainly keeps its structure, since only 10% of rutile formation is detected below or at 800 °C by XRD. Meanwhile, from 500 °C, a final burning off organics is also indicated by continuous CO2 evolution and small exothermic effects.

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The thermal decompositions of NH4VO3 and NH4VO3-TiO2 mixtures were investigated by mass-spectrometry and DTA. Three stages of decomposition were distinguished, in which the contribution of redox-type reactions increased successively. The bulk of the decomposition was independent of the nature of the atmosphere; only the third stage displayed a variation. In vacuo and in argon there was continuous reduction of the vanadium oxide system, but in air its reoxidation took place.

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