Browsing by Author "Merrad, S."

Now showing 1 - 3 of 3

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
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
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