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Kerfah A.,University of Science and Technology Houari Boumediene | Taibi K.,University of Science and Technology Houari Boumediene | Trari M.,Laboratory of Storage and Valorization of Renewable Energies
Solar Energy | Year: 2011

The composition of Ba0.785Bi0.127Y0.017TiO3 (BaBiYTiO) belongs to the BaTiO3-Bi2O3-Y2O3 system. A dielectric study on ceramics performed at temperatures in the range (77K-500K) and frequency (102-2×105Hz) revealed ferroelectric relaxor behaviour with a phase transition close to room temperature. The conductivity of BaBiYTiO obeys to an Arrhenius-type law with activation energy equals to 0.21eV, in conformity with a small polaron hopping where most electrons are localized. The oxide is lightly doped leading to a wide space charge region (480nm) in which photoeffect occurs. The presence of domains promotes the separation of the charge carriers through conversion of light into chemical energy. The electrode acquired n-type behaviour, evidenced from the negative thermopower and anodic photocurrent. The flat band potential Vfb (-0.46VSCE) and the electron density ND (2.82×1015cm-3) were determined in KOH solutions (0.5M). The Nyquist plot exhibits two well defined time constants characteristic of bulk and grains boundaries contributions and an equivalent electrical circuit has been proposed according to the Randles model. The energy band diagram shows the potentiality of the oxide for the solar-energy conversion. BaBiYTiO has been tested successfully for H2 production upon visible light when combined to the delafossite CuFeO2 as sensitizer. An evolution rate of 24μmolmn-1 and a quantum yield of 0.4% under polychromatic light were obtained. © 2010 Elsevier Ltd. Source


Belmokhtar N.,Laboratory of Materials science | Belmokhtar N.,University of Boumerdes | Brahimi R.,Laboratory of Storage and Valorization of Renewable Energies | Nedjar R.,Laboratory of Materials science | Trari M.,Laboratory of Storage and Valorization of Renewable Energies
Materials Science in Semiconductor Processing | Year: 2015

The new layered niobate Cu0.5Nb3O8 is synthesized by soft chemistry in aqueous electrolyte via Cu2+→H+ exchange between copper nitrate and HNb3O8·H2O. The characterization of the exchanged product is made by means of thermal gravimetry, chemical analysis, X-ray diffraction and IR spectroscopy. Thermal analysis shows a conversion to anhydrous compound above 500°C. The oxide displays a semiconductor like behavior; the thermal variation of the conductivity shows that d electrons are strongly localized and the conduction is thermally activated with activation energy of 0.13 eV. The temperature dependence of the thermopower is indicative of an extrinsic conductivity; the electrons are dominant carriers in conformity with an anodic photocurrent. Indeed, the Mott-Schottky plot confirms n-type conduction from which a flat band potential of -0.82 VSCE, an electronic density of 8.72×1019 m-3 and a depletion width of 4.4 nm are determined. The upper valence band, located at ~5.8 eV below vacuum is made up predominantly of Cu2+: 3d with a small admixture of O2-: 2p orbitals whereas the conduction band consists of empty Nb5+: 5s level. The energy band diagram shows the feasibility of the oxide for the photocatalytic hydrogen production upon visible light (29 mW cm-2) with a rate evolution of 0.31 mL g-1 min-1. © 2015 Elsevier Ltd.All rights reserved. Source


Chergui A.,Laboratory of Electrochemistry Corrosion | Madjene F.,Laboratory of Storage and Valorization of Renewable Energies | Trari M.,Laboratory of Storage and Valorization of Renewable Energies | Khouider A.,Laboratory of Electrochemistry Corrosion
Journal of Environmental Health Science and Engineering | Year: 2014

Ni2+ is a highly toxic above 0.07 mg/L and its removal is of high significance. The biosorption of Ni2+ onto medlar male flowers (MMF) was studied in relation with the physical parameters like pH, contact time, biosorbent dosage, Ni2+ concentration and temperature. The interaction biosorbent-Ni2+ was examined by the FTIR technique. The equilibrium was achieved within 40 min and the data were well fitted by the Langmuir and Redlich-Peterson (R-P) models. The maximum Ni2+ uptake capacity was 17.073 mg/g at 25°C and the Ni2+ removal follows a pseudo-second order kinetic with activation energy of 13.3 kJ/mol. The thermodynamic parameters: ΔS°, ΔH° and ΔG° showed that the biosorption was spontaneous and endothermic. MMF was used as a post treatment technique and the biosorption was coupled with the visible light driven Ni2+ reduction over the spinel ZnMn2O4. The effect of the pH, ZnMn2O4 loading and light intensity on the photoactivity was investigated. 77.5% of Ni2+ was reduced after ∼140 min under optimal conditions. The Ni2+ removal reached a rate conversion of 96% of with the coupled system biosorption/photocatalysis is very promising for the water treatment. © 2014 Chergui et al.; licensee BioMed Central Ltd. Source


Boutal N.,University of Science and Technology Houari Boumediene | Rekhila G.,Laboratory of Storage and Valorization of Renewable Energies | Taibi K.,University of Science and Technology Houari Boumediene | Trari M.,Laboratory of Storage and Valorization of Renewable Energies
Solar Energy | Year: 2014

The perovskite Ba1-xEu2x/3Ti0.75Zr0.25O3 (x=0.025, 0.05) have been prepared by solid state reaction. A dielectric study on ceramics performed in the ranges of temperature (77-500K) and frequency (102-2×105Hz) reveal typical relaxor behavior and diffuse phase transition. The relaxor parameters (Tm, δTm, δεr'/εr') decrease slightly with the increase of Eu-dopant concentration. The dielectric relaxation rate follows the Vogel-Fulcher relation with activation energy of 21meV, an attempt frequency fo=1.1×108Hz and a static freezing temperature Tf=95K for x=0.025. An optical gap of 2.25eV is obtained from the diffuse reflectance spectrum. The photo-electrochemistry throws light on the nature of the electronic bands. The Mott-Schottky plot is characteristic of n-type conduction from which a flat band potential of -0.60 VSCE and an electrons density of 1.2×1018cm-3 are determined for the composition x=0.025. The upper valence band located at 6.4eV below vacuum is made up of O2-: 2p orbital whereas the conduction band consists of empty 3d levels (4.13eV) with a high reducing ability. The energetic diagram clearly assesses the photoactivity of the perovskite. The performance is improved when the crystallite size becomes comparable with the length of the nanodomains. As application, 95% of chromate (10-4M) is reduced after 6h of exposition to sunlight (AM1). © 2013 Elsevier Ltd. Source


Bensemma N.,Crystallography Thermodynamics Laboratory | Rekhila G.,Laboratory of Storage and Valorization of Renewable Energies | Boutal N.,Crystallography Thermodynamics Laboratory | Taibi K.,Crystallography Thermodynamics Laboratory | Trari M.,Laboratory of Storage and Valorization of Renewable Energies
Journal of Materials Science: Materials in Electronics | Year: 2016

The lead-free Ba(Ti0.96Mg0.013Nb0.026)O3 composition has been prepared by solid state reaction. The room temperature X-ray diffraction revealed a perovskite phase with a tetragonal symmetry. The complex dielectric permittivity measured on cooling from 470 to 150 K in the frequency range (102–106 Hz) indicated a ferroelectric behavior and exhibited a large electromechanical response. This ferroelectric perovskite showed photoelectrochemical properties with an optical gap of 2.90 eV, n-type conduction and a flat band potential of −0.57 VSCE. As application, the oxide is successfully tested for the eosin oxidation under solar light. At pH ~ 6.3, 90 % of eosin (15 mg L−1) disappeared after 6 h of illumination for a catalyst dose of 2.5 g L−1. © 2016 Springer Science+Business Media New York Source

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