Papers by Keyword: Vanadate

Abstract: The GdVO₃ and GdVO₄ catalyst has been prepared via solid-phase synthesis. It has been shown by a complex of physical and chemical methods that or GdVO₃, the main one is the phase with the structure of the first homologue of the Roldlesden-Popper series of a rhombical distorted perovskite. Orthovanadate of GdVO₄ crystallize in the structural type of zircon. The catalytic properties of GdVO₃ and GdVO₄ are studied in the propane cracking process to form propylene and ethylene. It was found that GdVO₃ and GdVO₄ has a high selectivity and catalytic properties. It was shown that propane conversion started at 773 K, was only 2% at 873 K, and raising the temperature to 923 K increased propane conversion to 21%. In the presence of GdVO₄ and GdVO₃, a considerable increase in propane conversion was observed that reached 60% at 923 K. The structure of the catalyst is stable under the conditions of preferential C₃H₈ reduction. Deactivation was much faster with GdVO₃, and it was observed after 20 h of operation at a rate that was slightly slower than the one for GdVO₄.

Abstract: To further study the formation and corrosion mechanisms of AM60B vanadate films, a vanadate coating was synthesized on AM60B substrate via a chemical conversion at 50°C. The morphologies of the films and the corrosion samples were observed by using scanning electron microscopy(SEM), energy dispersive X-ray analysis(EDAX) was used to analyze the elemental distribution of the film surface and the Electrochemical Impedance Spectroscopy(EIS) and the polarization curves of the films were tested by an electrochemical workstation. The morphology of conversion film is layered structure with white balls. V element preferentially deposits near the base end and the V-rich phase is easily generated on the β-phase(Mg₁₇Al₁₂). In the course of corrosion, corrosion begins near the α-phase(Mg). During the processes of observation and analysis, the concept of micro-zone pH gradients was discovered and applied, and attempts were made to explain some observed phenomena by using this concept. The results show that the concept of pH gradients in micro zones can be used to explain the film formation and corrosion mechanisms well.

Abstract: Solid solution BiP_0.9V_0.1O₄ from BiP_XV_1-XO₄ system has been synthesized by solid state synthesis at 973 K. It has been shown that the phosphate-vanadate can be prepared as a single phase for x =0.9, while higher degree of (P/V)O₄ substitution in BiVO₄ has not been detected for the range studied. The substitution peculiarities have been investigated by X-Ray powder diffraction, infrared and photoluminescence spectroscopy. The luminescence spectrum of BiP_XV_1-XO₄:Eu³⁺ solid solution reveal intensive photoluminescence lines related to f-f electronic transitions in Eu³⁺ ions.

Abstract: GdVO₄ was synthesized by solid state reaction at high temperature and characterized by XRD, UVvisible DRS, BET and SEM. XRD analysis of GdVO₄ showed its structure was of tetragonal type. When GdVO4 was loaded with 0.3 wt% Pt, it showed the better photocatalytic activity for water splitting under simulated solar irradiation, and the amounts of the produced hydrogen in pure water were about 9.33 μmol under the irradiation of simulated solar for 6 h. Furthermore, photodegradation of Rhodamine B (Rh B ) on the samples were investigated under simulated solar irradiation.

Abstract: Luminescence properties of the two series of the La_1-xEu_xVO₄ (x ranges from to 0.3) solid solutions synthesized by the solid state and co-precipitation methods were investigated.. Luminescence spectra of the investigated samples consist of narrow spectral lines caused by inner f - f electron transitions in the impurity Eu³⁺ ions. Excitation spectra consist of three main bands those correspond to different types of transitions in the investigated matrices. There are O - Eu³⁺ charge transfer transitions, band-to-band transitions in the matrix of the vanadate compounds and electron transitions in the VO₄^3- vanadate anion. Dependences of the structure and luminescence properties on rate compositions and method of synthesis were studied. Origins of the observed differences between luminescence characteristics of the samples obtained by two different methods are discussed.

Abstract: This paper reports the photoluminescence properties of Ca9Eu1-xSmx(VO4)7 (x=0.2-0.4) synthesized at 1250 oC in air for 12 h using traditional solid-state reaction method. With the increase of Sm3+ substitution amount, purity Ca9Eu1-xSmx(VO4)7 phase was obtained even when the Eu3+ ions were totally substituted by Sm3+. The experimental results showed that when Sm3+ was codoped with Eu3+ into Ca9Eu1-xSmx(VO4)7 crystal structure, Sm3+ would act as a sensitizer and transfer the excitation energy to Eu3+ ions and finally enhance the emission intensity of Ca9Eu1-xSmx(VO4)7 under 405 nm excitation, which leads to more favorite of this kind of phosphor used in UV LED based white LEDs.

Abstract: Eu3+ doped and undoped Y(P,V)O4 phosphors were prepared using multi-mode and single-mode microwave oven operated at 2.45 GHz. In the case of the microwave heating method, the phosphor particles were non-aggregated. A homogeneous distribution of Eu ion was observed in the microwave synthesis. No sintering behavior found in the microwave heating may be attributed to a quite shorter heating time. The Eu3+ doped sample synthesized by microwave heating showed intense red emission under UV excitation.

Abstract: We present resonant x-ray scattering experimental data from YVO3. By scattering at the vanadium K edge we are able to observe diffraction from the anisotropic tensor of susceptibility at the Bragg forbidden (010). The resonant energy spectra from these reflections are unusually complex, giving an indication of the crystal field distortions around the vanadium site.