B. Bakiz

Structural, vibrational study and UV photoluminescence properties of the system Bi(2−x)Lu(x)WO6 (0.1 ≤ x ≤ 1)

The bismuth lutetium tungstate series Bi(2−x)Lu(x)WO6 with 0.1 ≤ x ≤ 1 were synthesized by solid state reaction of oxide precursors at 1000 °C for 3 h. The as-prepared polycrystalline compounds were characterized by X-ray diffraction (XRD), scanning electron microscopy (SEM), Raman spectroscopy and photoluminescence (PL) analyses. Biphasic samples were obtained in the composition range of 0.1 ≤ x ≤ 0.3. Solid solutions were obtained in the composition range of 0.4 ≤ x ≤ 1, and their monoclinic crystal structure was refined using the Rietveld method. SEM micrographs showed that solid solutions presented homogeneous morphologies. Attributions of Raman vibrational modes were proposed. A shift in the vibrational wavenumber depending on the lutetium composition was observed. The specific broadening of the spectral bands was interpreted in terms of long range Bi/Lu disorder and local WO6 octahedron distortions in the structure. The PL experiments were performed under UV-laser light irradiation. Each PL band was decomposed into three Gaussian components with energies close to 1.25, 1.80 and 2.1 eV. Their integrated intensities increased with the value of x. The presence of the near infrared band at 1.25 eV is discussed.

Electronic band structure and visible-light photocatalytic activity of Bi2WO6: elucidating the effect of lutetium doping

Bismuth tungstate and 5% Lu-doped bismuth tungstate photocatalysts were synthesized by coprecipitation method and characterized by X-ray diffraction (XRD), scanning electron microscopy (SEM), transmission electron microscopy (TEM), UV-Vis diffuse reflectance spectra (DRS), and Brunauer–Emmett–Teller (BET) surface area. The effect of lutetium doping on electronic structure was investigated using density functional theory calculations (DFT). The change of morphological and optical band gap was conditioned by lutetium doping. Under visible light irradiation, the as-prepared sheet-like Lu-Bi2WO6 sample exhibits the highest visible-light-responsive photocatalytic performance than pure Bi2WO6 for the degradation of Methylene Blue (MB). The photocatalytic mechanism was explained on the basis of electrochemical impedance spectroscopy (EIS), photoluminescence (PL) spectra, active trapping measurements and optoelectronic properties.

Electrical Properties of a CeO2-Mix System Elaborated at 600∘C

The electrical conduction of a series of polycristalline [(1−x)CeO2·x/2Bi2O3] samples has been analyzed using electrical impedance spectroscopy, in the temperature range 25 to C. Samples have been prepared via a coprecipitation route followed by a pyrolysis process at C. For compositions , Ce1−xBixO2−x/2 solid solutions, with fluorite cubic structure, are obtained. In the composition range , the system is biphasic with coexistence of cubic and tetragonal structures. To interpret the Nyquist representations of electrical analyses, various impedance models including constant phase elements and Warburg impedances have been used. In the biphasic range (), the conductivity variation might be related to the increasing fraction of two tetragonal β′ and β-Bi2O3 phases. The stabilization of the tetragonal phase coexisting with substituted ceria close to composition is associated with a high conduction of the mix system CeO2-Bi2O3.

Synthesis and characterization of nanosized Ce1−xbixo2−δ solid solutions for catalytic applications

Abstract This study consists of elaborating and characterizing some nanometric materials in basic of rare-earth oxides by the soft chemistry technique. the first step of this work consists of synthesizing nanometric pure ceria by sol-gel process. In the second one, the Bismuth doped ceria by co-precipitation method was realized in order to obtain ceria-based solid solution, to improve its catalytic property by creation of oxygen vacancies. The solubility limit of Bi2O3 in CeO2 was determined to be around 20 atom %. The effect of thermal treatment temperatures on the average crystallite sizes and lattice parameters was done for pure ceria and Ce1-xBixO2-x/2 (x = 0.15 and 0.2). The different elaborated samples are subject of structural characterization (XRD). Catalytic reactivity of these materials in presence of “air- toxic gas” mixtures is studied by Fourier Transform Infra-Red Spectroscopy (FTIR).

Infrared spectroscopy analyses of air-CH4 or air-CO gas flows interacting with polycrystalline CeO2, La2O3 and Lu2O3 oxides

Abstract A comparative study of reactivity between air-CH4 or air-CO gas flows and CeO2, La2O3 and Lu2O3 rare earth oxides was performed using Fourier transform infrared spectroscopy analyses of CO2 gas resulted from the conversion of CH4 or CO gases. Polycrystalline samples of CeO2, La2O3 and Lu2O3 were first prepared by specific precipitation methods followed by low temperature calcination process. In the case of Lu2O3 oxide, a new specific route was proposed. Crystallite dimensions were determined by X-ray diffraction and transmission electron microscopy analyses. Morphologies were characterized using scanning electron microscopy. Specific surface areas were determined from Brunauer-Emmett-Teller (BET) technique. Using infrared spectroscopy analyses, the conversion rates of CH4 or CO into CO2 were determined from the evolutions of CO2 vibrational band intensities, as a function of time and temperature. It was clearly established that, despite its low specific surface, the Lu2O3 oxide presented the highest capacity of conversion of CH4 or CO into CO2.

Electrical impedance spectroscopy analyses and optical properties of the bismuth lutetium tungstate BiLuWO6

ABSTRACT BiLuWO6 was synthesized by a solid state reaction at 1000°C. The sample was initially compacted under ambient conditions to form a cylindrical pellet and then characterized by scanning electron microscopy, the electrical properties were determined from Electrical Impedance Spectrometry, under air, in the temperature range of 400 to 700°C. Nyquist representations were interpreted in terms of equivalent circuits, involving intrinsic and extrinsic conduction mechanisms. UV-Vis diffuse reflectance spectra infers the presence of an indirect bandgap, both direct and indirect assumption were carried out to calculate the band gap. The CIE chromaticity diagram were presented on the basis of the photoluminescence under UV, BiLuWO6 exhibits an orange emission and a warm color temperature.

Time-Dependent Oxidative Capacities of La2O3 , Lu2O3 , CeO2 , and Bi2O3 Materials Interacting with Air-CO or Air- CH4 Flows

Using Fourier transform infrared (FTIR) spectroscopy analyses, we have studied the oxidation processes of methane or carbon monoxide in air-CH4 or air-CO flows interacting with polycrystalline catalytic oxides, as a function of temperature (T) and time (t). The gas flows crossed through La2O3, Lu2O3, CeO2, or Bi2O3 porous walls with constant composition and rate. The oxidation capacities of materials were determined from the intensities of CO2 vibrational bands resulting from the total oxidation of CH4 or CO into CO2. To interpret the time-dependent variations of these intensities, we have applied a model derived from Johnson-Mehl-Avrami approaches. This simple approach delivers pertinent parameters describing time-dependent oxidation rates.