Browsing by Author "Brahimi, R."

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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 delafossite CuCoO2 synthesized by co-precipitation /hydrothermal route
    (Elsevier, 2021) Bouakaz, H.; Abbas, Moussa; Brahimi, R.; Trari, M.
    CuCoO2 crystallizing in the delafossite structure was prepared by co-precipitation/hydrothermal method at low temperature (~ 150 °C). It is stable in air up to ~400 °C beyond which it turns into the spinel. The oxide has a direct optical transition attributed to the crystal field splitting of Cu+, linearly coordinated. It exhibits p-type behavior due to O2− insertion in the layered lattice. Such property is corroborated by a cathodic photocurrent in the intensity-potential (J – E) plot and a negative slope of the capacitance potential (C−2– E) plot. The latter traced in NaOH (0.01 M) electrolyte, exhibits a straight line from which a flat band potential of +0.411 V and a hole density of 6.9 × 1023 m−3 were extracted. An exchange current density of 7.36 μA cm−2and a polarizarion resistance (6.69 kΩ cm2), derived from the semi-logarithmic curve (log(J) – E), indicate a good electrochemical stability with a medium hysteresis loop and a low H2-over potential. The anisotropy of the 2 D dimensional crystal structure allows reversible oxygen insertion in the (0 0 n) planes evidenced from the (J – E) profiles. The Electrochemical Impedance Spectroscopy (EIS) measurements give two well-distinguished depressive semicircles in the dark. The diameter of the semicircle at high frequencies (1.49 kΩ cm2) decreases down to (1.28 kΩ cm2) under irradiation, a behavior typical of a non-degenerate semi conductivity of CuCoO2
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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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    Semiconducting and electrochemical properties of the spinel FeCo2O4 synthetized by co-precipitation. Application to H2 production under visible light
    (Elsevier, 2023) Bouakaz, H.; Abbas, Moussa; Benallal, S.; Brahimi, R.; Trari, M.
    FeCo2O4 elaborated by co-precipitation was characterized photo-electrochemically for the first time in order to assess its performance for the hydrogen production. The X-ray diffraction revealed a single phase crystallizing in the spinel structure with a lattice constant of 8.1075 Å and a crystallite size of 35 nm. The UV–Visible diffuse reflectance of the black product exhibits an absorption above 650 nm and a direct optical transition at 1.53 eV was determined, assigned to the crystal field splitting of Co3+: 3d orbital hexa-coordinated. The transport properties indicated semi-conducting properties of FeCo2O4, the positive thermo-power (S300k = 666 μV K−1) demonstrated that holes are majority charge carriers. The Electrochemical Impedance Spectroscopy (EIS) realized in Na2SO4 (0.1 M) electrolyte showed two semicircles at high and intermediate frequencies, characteristic of the charge transfer and grain boundaries respectively. The first diameter (1249 Ω cm2) decreases under visible light down to 742 Ω cm2, thus supporting the semiconducting behavior and no inhibiting effect is observed due to the appearance of the photo-effect. The inverse of the square of the capacitance as a function of the potential (C−2 – E) exhibits a line, negatively slopped, characteristic of p-type behavior with a hole concentration of 21.9 × 1020 cm−3. The conduction band (−0.76 VSCE), made up of Co3+: 3d orbital is more cathodic than the H2-level leading to a spontaneous H2 evolution under visible irradiation (29 mW cm−2) with a liberation rate of 0.58 μmol H2/h−1/g. FeCo2O4 an showed excellent chemical stability after its reuse for the H2 production, as evidenced by X-ray diffraction
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    Study of Congo Red removal from aqueous solution by using the deficient perovskite SrTiO3-δ under solar light
    (Elsevier, 2022) Merrad, S.; Abbas, Moussa; Brahimi, R.; Trari, M.
    The deficient perovskite SrTiO3-δ (STO) synthesized by nitrate route was identified by X-ray diffraction (XRD) and characterised by BET analysis, Attenuated Total Reflectance (ATR) and X-ray photoelectron spectroscopy (XPS). The latter enables us to determine the valence states of Sr2+, Ti4+ and O2−. A band gap of 3.32 eV was determined from the diffuse reflectance, assigned to the charge transfer O2−: 2p → Ti4+: 4s and white coloration of STO. The conduction band (−0.60 VSCE) and the valence band (2.72 VSCE) derived respectively from O2−: 2p and Ti4+: 4s orbitals are within the gap region of STO, thus generating O2·− and ·OH radicals responsible for the photo oxidation of Congo Red (CR), a hazardous dye. The photo-catalytic efficiency of STO was confirmed by the CR adsorption and degradation under solar light. Various physical parameters like the catalyst dose, dye concentration, initial pH, irradiation source and inhibitory effect of anions were studied. The synergetic effect of the electron injection from Congo Red into the STO-conduction band was confirmed by the electrochemical measurements through the photocurrent-potential plots and contribute to the photoactivity. An abatement of 62% and 97% are obtained under UV light and solar irradiation respectively
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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