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Abstract
The hydroxide, oxalate and citrate precursors of the metal oxides such as γ-Fe2O3, (MnZn)Fe2O4, Cu(K)Fe2O4, BaTiO3, La(Sr)MnO3, La(Sr)AlO3, La/Gd(Ca/Ba/Sr)CoO3, and anatase TiO2 on modifications with the hydrazine decompose at low temperatures give single phase oxides of superior properties, while the complexes without such modification require higher temperatures for achieving the phases. The hydrazine released at lower temperatures reacts with the oxygen in the atmosphere, N2H4+O2→N2+2H2O; ΔH=−625 kJ mol−1, and liberates enormous energy that is sufficient for the oxidative decomposition of the complexes now devoid of hydrazine. Such extra energy is not available in the case of the precursors without such modifications. The reaction products of hydrazine oxidation provide desired partial pressure of moisture needed for the stabilization of γ-Fe2O3. Also, the nitrogen that is formed in the reaction of hydrazine with oxygen gets trapped in the lattice of TiO2 giving yellow color nitrogen doped TiO2−xNx photocatalyst. Thus, hydrazine method of preparation has many advantages in the preparation of metal oxides of superior properties.
Kinetic studies on the effect of metal oxide catalysts, (25% w/w) such as Cr2O3, CuO, MnO2, Al2O3 and TiO2, on the thermal decomposition of KBrO3 have been carried out. The kinetic parameters of the catalysed and uncatalysed decompositions were calculated by the Freeman-Carroll, Coats-Redfern and Horowitz-Metzger methods. It has been found that Al2O3 is almost as good a catalyst as any other oxide used unlike in the thermal decomposition of KClO3. In the case of TiO2 there was an increase in the activation energy of decomposition. Of the other oxides Cr2O3 underwent reaction and was converted to dichromate and so the parameters of the reaction were not calculated. The effect of varying amounts of Al2O3 on the thermal decomposition was also studied.
-cleaning applications using semiconducting powders or thin films have become a subject of increasing interest especially in the last 20 years. Among semiconductor oxides, TiO 2 is one of the most widely used materials for self-cleaning application [ 4 – 9
Abstract
A multistage process combining photocatalytic degradation of organic complexes and complexants followed by separation of the radionuclides by ion exchange was developed and tested for the treatment of aqueous waste from chemical or electrochemical decontamination of NPP primary circuit internals. In these solutions, both the oxalic and citric acids could be quantitatively degraded within 10-12 hours of irradiation by 254 nm UV radiation in the presence of TiO2 photocatalyst. For the group radionuclides separation, a standard cation exchanger was found to be preferable to any of the set of the tested inorganic-organic composite absorbers.
Abstract
The effect of additives (CuO, MnO2 and TiO2) on the thermal decomposition kinetics of potassium metaperiodate (KIO4) to potassium iodate (KIO3) has been studied in air by thermogravimetry under isothermal conditions. Irrespective of whether p- or n-type, the metal oxides show only a little or no influence on the rate of the decomposition except for the small decrease when the oxide concentration is as high as 10 wt%. The rate law for the decomposition of KIO4 (Prout–Tompkins model) remained unaffected by the additives.
Abstract
Two samples of the microporous titanosilicate ETS-10 synthesised by different preparation procedures were compared for their ability to take up uranium from aqueous solutions using a batch-type technique. The ETS-10 samples were synthesised using either TiO2 or TiCl3 as a titanium source. The uptake of uranium on the materials was compared by determining the distribution coefficient and percentage sorption as a function of contact time, uranium concentration, and sorbent concentration. It was found that the difference in the synthesis procedures of the materials had a significant influence on the uptake of uranium.
Abstract
The synthesis of cyanoferrates of quadrivalent metals and the sorption of caesium ions by these materials have been studied. It has been found that the compositions of the compounds and their properties are strongly influenced by the degree of hydrolysis of the metal. These is no sorption of caesium by Zr4+ and Th4+ cyanoferrates, while the compounds of oxygencontaining bivalent complex cations exhibit behaviour similar to that of the other bivalent metals. The sorption of caesium by (TiO)2R is govermed by an ion-exchange mechanism; with (ZrO)2R changes occur in the crystal lattice, and (ThO)2R exhibits a low affinity towards caesium.
Abstract
Neutron capture γ-ray spectrometry has been applied for the simultaneous determination of Co, Mo, Ni, W and moisture in hydrodesulfurization catalysts. The Co, Mo and water content are determined in a 10 min irradiation using a 500–2500 keV calibration. Ni and W, if present, require, and additional 30 min irradiation, using a 5000–9000 keV calibration. In both cases TiO2 is used as internal standard. Results are in good agreement with those obtained by NAA for metals and by TGA for moisture.
Abstract
Alumina, zirconia and titania pillared montmorillonites additionally modified with silver were tested as catalysts of NO reduction with NH3 or C2H4. Ammonia was much more effective reducer of NO than ethylene. The silver containing TiO2-pillared clay has been found to be the most active catalyst for NO reduction both with NH3 or C2H4. Oxidation of the reducing agents by oxygen limited the NO conversion in the high temperature region. The ammonia and nitric oxide adsorption sites were studied by the temperature programmed desorption methods (TPD).
Abstract
The potential uses of hydrous oxides in the treatment of radioactive wastes may be affected by the physical-chemical properties of these materials. The sorption behavior of trace level (less than 10-14 g/ml) 235U fission products in aqueous solutions was studied under static conditions on TiO2, MnO2 and SnO sorbents. A variety of anions, cations and neutral species of 132Te,95Zr, 99Mo and 103Ru in aqueous solutions at 1, 3, 5, 7 and 10 pH values were identified and their retention values were calculated. High voltage electrophoresis was used to establish the chemical species of these radioisotopes formed in the solution.
