Publications Internationales
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Item Synthesis and characterization of MoO3: application to the photo production of oxygen under visible light(Springer, 2024) Koriche, Nesrine; Abbas, Moussa; Trari, MohamedOne of the most striking features of molybdenum oxide is the versatility of its catalytic properties, which are determined by the valence states of molybdenum and its coordination. It may be anticipated that MoO3 surface must contain catalytic sites which are active in different types of elementary steps. MoO3 was successfully synthesized by hydrothermal route at 400 °C, acquiring n-type conduction, due to oxygen deficiency. The single phase, elucidated by X-ray diffraction, crystallizes in an orthorhombic unit cell (Space Group (SG) Pbnm, N° 62) with a crystallite size of 12 nm. MoO3 is a direct band gap semiconductor with a forbidden band value of 2.93 eV where the electrical conduction occurs by low polaron hopping between mixed valences Mo+6/+5 with an activation energy of 0.14 eV. The thermo-power indicates n-type conduction, and confirmed by the capacitance-potential measurement; the latter gives an electrons density of 1.87 × 1020/cm3and a mobility of 1.77 × 10−6 m2/V.s. The flat band potential Vfb (0.11 VSCE) is determined from the capacitance measurement. The physical and chemical characterizations are correlated for the construction of the potential diagram in order to assess the photo electrochemical properties of MoO3 for the oxygen evolution. The valence band, is located above the O2/H2O potential ( ~ 1.3 VSCE), allowing O2 evolution upon visible light and the oxide is photocathodically protected against corrosion. An evolution rate of 0.13 mL/(mg. h) is obtained within 20 min. at optimal conditions (100 mg of catalyst and 50 °C).Item 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 diffractionItem 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)Item Synthesis, structural, and opto-electrochemical properties of cobalt aluminate type spinel and its use with ZnO for Cr(VI) photoreduction(Springer, 2021) Bouallouche Née Saadi, Rachida; Kebir, Mohammed; Nasrallah, Noureddine; Saib, Faouzi; El Jery, Atef; Khezami, Lotfi; Trari, MohamedThe discovery of the occurrence of inorganic pollutants in surface waters is identified in the system assessment quality. The most harmful elements are pesticides, persistent organic pollutants, pharmaceuticals, personal care products, and heavy metals are still dangerous to the environment due to their general uses. Chromate has the largest concentration compared to the other metals in the wastewater industries. This work evaluates the application of the spinel p-CoAl2O4 as a photocatalyst prepared by the nitrate synthesis process to reduce Cr(VI), a hazardous metal for the environment. The photocatalyst was characterized using thermal analysis (TG), X-ray diffraction, UV-diffuse reflectance spectroscopy, scanning electron microscopy, fluorescent X-ray, Fourier transform infrared spectroscopy, electrical conductivity, and photoelectrochemically. The results showed that the efficiency of optimum reduction of Cr(Vl) to Cr(IIl) photoreduction is more effective (77%) for pH = 3.6 than that at high pH values up to 8 (7%). Moreover, the effect of the hetero-system CoAl2O4/ZnO on photocatalytic efficiency was investigated. The photocatalytic activity increases up to 99% with 1 g L-1, a total catalyst dosage over the hetero-system CoAl2O4/ZnO at a ratio of 75%/25%. This data is better relative to CoAl2O4 or ZnO alone. The Cr(VI) photoreduction activity improvement was caused by the best separation and the photogeneration of electron-hole on the CoAl2O4/ZnO surfaces. Finally, the Lagergren pseudo-first-order and the Langmuir-Hinshelwood models fit well the experimental kineticsItem Preparation and physical properties of the layered niobate Cu0.5Nb3O8 : application to photocatalytic hydrogen evolution(Elsevier, 2015) Belmokhtar, N.; Brahim, R.; Nedjar, R.; Trari, M.