Browsing by Author "Bellal, B."

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    Photoelectrochemical characterization of nano-crednerite AgMnO2 synthesized by Auto-Ignition : a novel Pphotocatalyst for H2 evolution
    (Springer, 2022) Koriche, N.; Brahimi, R.; Bellal, B.; Trari, M.
    AgMnO2 nanocrystallites (31 nm) were prepared by sol-gel auto-ignition at 400°C in air. The crednerite characterized by X-ray diffraction (XRD) showed a single phase, crystallizing in a monoclinic unit cell (SG: C2/m). The refinement was made by isotypy with CuMnO2. The oxide is a narrow band-gap semiconductor with an indirect transition at 1.43 eV. The electrical conduction occurs predominantly by small polaron hopping between mixed valences Ag2+/+ in the (a, b) planes with an activation energy of 0.35 eV. The density of holes (NA = 2 × 1015 cm–3) and their mobility (μh = 0.8 × 10–4 m–2 V–1 s–1) indicate a conduction being thermally activated. The oxygen insertion in the layered crystal lattice induces p-type conductivity, a fact confirmed by the electrochemical measurements. The flat band potential (Efb = –0.04 V) indicates a cationic character of both valence and conduction bands deriving mostly from Ag+ 4d-orbital. The electrochemical impedance spectroscopy shows the predominance of the bulk contribution followed by diffusion of O2– species. The energetic band diagram of AgMnO2 established from the photoelectrochemical study, predicts a spontaneous hydrogen formation; a rate evolution of 39 µmol g–1 min–1 and a power conversion of 0.37% were obtained under visible light irradiation (27 mW cm–2)
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    Physical properties of the perovskite SrTiO3−δ synthetized by chemical route
    (Springer, 2023) Merrad, S.; Abbas, M.; Brahimi, R.; Bellal, B.; Trari, M.
    The perovskite SrTiO3−δ elaborated by chemical route was characterised by physical and electrochemical methods. The oxide crystallizes in a cubic structure with a lattice parameter of 3.907(5) Å and a crystallite dimension of 71 nm. The morphology visualized by the SEM-EDX analysis shows spherical grains with a mean size of 0.2 μm, formed by agglomeration of crystallites. The diffuse reflectance gave a gap (Eg) of 3.21 eV, ascribed to the charge transfer O2−: 2p → Ti4+: 3d. The thermal variation of the conductivity (σ) obeys an exponential law {σ = σoexp-0.27 eV/T} assigned to low hopping polarons. The electrochemical characterization was undertaken in Na2SO4 solution (10− 1 M) and the n-type character demonstrated from the capacitance measurement and cyclic voltammetry under UV-irradiation, is due to oxygen deficiency. A flat band potential (Efb) of − 0.31 VSCE was determined with a depletion width extended up to ~ 4 μm, advantageous for the formation of electron / hole (e− / h+) pairs. The electrochemical stability against photocorrosion was also shown from the semi-logarithmic plot (log J–E). As application, the Congo Red a diazo dye (CR) is successfully oxidized under UV light on SrTiO3−δ; an abatement of 63% was reached. According to the scavengers mechanism, hydroxyl •OH is the main specie responsible for the CR oxidation. The discoloration follows a pseudo-first-order kinetic with a half-life of 189 min
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    Synthesis, characterization and application of tetragonal BaTiO3-δ in adsorption and photocatalysis of congo red
    (Elsevier, 2023) Merrad, S.; Abbas, Moussa; Brahimi, R.; Bellal, B.; Trari, M.
    The synthesis by a simple approach of the deficient Barium Titanate BaTiO3-δ (BTO) crystallizing in a perovskite structure is reported along with the physicochemical properties. Thermal analysis (TG/DSC) was performed to elucidate the synthesis process. The X-ray diffraction (XRD), BET analysis, scanning electron microscopy (SEM-EDS) and electrochemistry were investigated. The catalyst revealed a single phase with a tetragonal symmetry obtained by treatment at 650 °C. The direct band gap (3.34 eV), obtained from diffuse reflectance spectroscopy (DRS), is assigned to the charge transfer O2-: 2p-Ti4+: 3d. The electrical characterization indicated a non-degenerate conductivity due to oxygen vacancies with an activation energy of 0.33 eV. The capacitance measurements indicated n-type behavior with a flat band potential (Efb) of − 0.43 V and a carrier concentration (ND) of 3.90 1018 cm−3. The photocatalytic process was elucidated by the electrical impedance spectroscopy (EIS). The performance of BTO was assessed by a combination of the adsorption of Congo Red (CR) followed by its degradation under UV light. The photodegradation kinetic was well fitted by a pseudo-first-order model with an abatement of 50% and 91% under UV and solar lights respectively. Different scavengers were used to evaluate the reaction mechanism and the radicals O2•- are the main reactive species of the CR oxidation. Four regeneration cycles demonstrated the catalyst stability. A degradation mechanism was established based on the scavengers effect