Carbon nanotubes/ceria composite layers deposited on surface acoustic wave devices for gas detection at room temperature

International audienceSurface acoustic wave (SAW) sensor on ATquartz piezoelectric substrate has been designed and fabricated. Test devices were based on asynchronous single-port resonators operating near the 434-MHz-centered industrial, scientific, and medical band. Multi-Walled Carbon Nanotubes/Ceria (MWNTs/CeO 2 ) nanocomposites were used as sensitive layers. The MWNTs were synthesized by catalytic chemical vapor deposition method and coated with nanosized ceria oxide. The composites were deposited on SAW quartz resonator using air-brush technique. MWNTs/CeO 2 nanocomposites were characterized using X-ray diffraction, transmission electron and atomic force microscopy. The sensor responses were tested under acetone (C 3 H 5 OH) and ethanol (C 2 H 5 OH) gases. The output signal was done by S 11 parameter of the SAW device and was monitored using a network analyzer. Frequency changes were observed under acetone and ethanol vapors. These changes depended on the surface conductivity of the nanocomposites deposited on the sensor. The single-port SAW gas sensor coated with the MWNTs/CeO 2 presented the highest sensitivity in the case of acetone vapor interacting with these layers, with a frequency shift of 200 kHz at room temperature

X-ray diffraction and microscopy investigations of structural inhomogeneities in NiMnSb crystallised from the melt

Our present work investigates the structural properties of bulk NiMnSb prepared by growth from the melt, using various thermal regimes. We studied the compositional behaviour of the polycrystalline material obtained from stoichiometric 1:1:1 and respectively off-stoichiometric melts. The latter samples were grown with Mn excess up to 10% and respectively Ni deficiency between 2 and 10%. The X-ray diffraction and the Scanning electron microscopy complement each other in the characterisation of the phases occurring in the samples. The synthesis of NiMnSb starting from an initially stoichiometric mixture associated with a thermal treatment presenting plateaus gives the best results. Also, it seems that the presence of an excess of Mn is not sufficient to prevent the occurrence of the NiSb stray phase

Novel Lu-doped Bi2WO6 nanosheets: Synthesis, growth mechanisms and enhanced photocatalytic activity under UV-light irradiation

International audiencePolycrystalline systems of lutetium doped bismuth tungstates Bi2WO6: Lu (Lu at% 0, 2, 5 and 8) were synthesized using the coprecipitation method, followed by thermal treatment at 500 degrees C. The Bi2WO6:Lu samples were characterized by X-Ray diffraction (XRD), scanning electron microscopy (SEM), energy dispersive X-Ray analysis (EDS) and UV-vis diffuse reflectance spectra (DRS). The XRD and SEM analyses showed that the as-prepared samples crystallized in the same orthorhombic structure and consist of agglomerated nanosheets. To characterize the photocatalytic activities, UV-visible spectrometry was used to analyze the evolution of Rhodamine B photodegradation in presence of the Bi2WO6: Lu photo catalysts. The characteristic absorption band of Rhodamine B at 554 nm shifted to lower wavelengths under UV irradiation. The pure Bi2WO6 and the 5% Lu doped Bi2WO6 photocatalysts presented the lowest and highest efficiencies, respectively. An interpretation of improved photocatalytic efficiencies was proposed. (C) 2016 Elsevier Ltd and Techna Group S.r.l. All rights reserved

Multifunctional rare earth or bismuth oxide materials for catalytic or electrical applications

We present a review on catalytic or electrical properties of materials based on rare earth (RE) oxides (CeO2, La2O3, Lu2O3) or bismuth based composite systems CeO2-Bi2O3, susceptible to be integrated into catalytic microsystems or gas sensors. The polycrystalline solids can be used as catalysts allowing conversion of CO or CH4 traces in air-gas flows. Fourier Transform infrared spectroscopy is used to determine the conversion rate of CO or CH4 into CO2 through the variations versus time and temperature of vibrational band intensities. The time dependent reactivities are interpreted in terms of an adapted Avrami model. In these catalytic analyses the nature of surfaces of polycrystalline solids seems to play a prominent role in catalytic efficiency. Electrical impedance spectroscopy allows analyzing the variation of conductivity of the system CeO2-Bi2O3. In this system, the specific high ionic conduction of a Bi2O3 tetragonal phase might be linked to the high catalytic activity

Novel Lu-doped Bi2WO6 nanosheets: Synthesis, growth mechanisms and enhanced photocatalytic activity under UV-light irradiation (vol 42, pg 8552, 2016)

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Effects of lutetium doping on the X-ray-excited luminescence properties of the tungstate Zn1-xLuxWO4

International audiencePolycrystalline samples in the lutetium-doped zinc tungstate system Zn1-xLuxWO4 with 0 <= x <= 0.08 were synthesized using the coprecipitation method followed by thermal treatment at 1000 degrees C during 4 h. The polycrystalline samples were characterized by X-ray diffraction analysis, scanning electron microscopy (SEM), infrared spectroscopy, and luminescence analysis under X-ray excitation. Rietveld analyses were performed. The variation of the wolframite structure cell parameters in the range 0 <= x <= 0.05 were congruent with substitution of Zn2+ by Lu3+. SEM micrographs of the obtained samples presented improved crystallization with morphology depending on the lutetium fraction. The luminescence spectra obtained under X-ray excitation (E < 40 keV) were in the blue-green region, and their intensity increased with x up to x = 0.05. The differences in the intensities of the X-ray luminescence spectra could be related to additional cation vacancies resulting from substitution of Zn2+ by Lu3+

Role of chemical substitution in the photoluminescence properties of cerium samarium tungstates Ce(2-x)Smx (WO4)3 (0≤x≤0.3)

In the general framework of the development of materials with tunable photoluminescence, a series of cerium samarium tungstates Ce(2-x)Smx(WO4)3 with x≤0.3 was synthesized by a coprecipitation method followed by thermal treatment at 1000 °C. The polycrystalline compounds were characterized by X-ray diffraction, scanning electron microscopy and photoluminescence experiments. In the present work, the objective would be to determine the role of PL emitting centers in the variations of PL intensities. Firstly, Rietveld analysis showed a decrease of cell parameters and confirmed that a solid solution was obtained. Diffraction profile analyses showed that structural distortions increasing with composition x were observed: they were ascribed to difference in cation sizes of Ce3+ and Sm3+, and to defects generated during crystal growth. The photoluminescence (PL) spectra were obtained under X-Ray (45 kV-35 mA) and UV (364.5 nm) excitations. Two PL emissions of Ce3+ were observed only under UV excitation. Four PL emissions of Sm3+ were observed under UV and X-ray excitations, and their intensities decreased with increasing composition x. Two additional transitions were observed under UV and X-ray excitations: they were attributed to oxygen vacancy defects. In the range 800 to 1000 nm, an increasing IR emission is observed: it was ascribed to emissions due to other oxygen vacancies. The main results are reported in Table 1. The chromaticity diagram (see Figure 1) showed that the colors associated with PL responses vary with Sm composition and excitation energies. This offers the opportunity to develop materials with tunable PL. To better understand this complex behavior, now, we plan to study the solid solution in the composition range x>0.3

Photocatalytic and photoluminescent properties of a system based on SmPO4 nanostructure phase

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

International audienceBismuth 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