Browsing by Author "Mirad, S."

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    Characterization and application of the hetero-system LaCoO3/ZnO for degradation of Orange II under solar light
    (Springer, 2023) Ouatizerga, A.; Rekhila, G.; Mirad, S.; Trari, M.
    LaCoO3 elaborated by nitrate route was characterized physically and electrochemically to be applied in the Orange II (OII) oxidation upon solar light. The X-ray difraction (XRD), SEM analysis and electrical conductivity were undertaken. The difractogram showed that the single phase is completed at 850 °C and the oxide crystallizes in a distorted perovskite structure. The peak at 643 cm−1 in the attenuated total refection (ATR) spectrum confrmed the purity of the phase. The forbidden band (1.35 eV), determined from the difuse refectance, is assigned to Co3+: d-d transition in a low spin confguration (3d6 , E5/2) in conformity with the black color of the oxide. The feld-dependent magnetization was measured at 300 K in the range±25 kOe, and the perovskite exhibits a low magnetism with a saturation magnetization (0.28 emu/g) confrming the low spin state Co3+. The thermal variation of the conductivity is characteristic of non-degenerate behavior and a hole mobility of 10−2 cm2 V−1 s −1 and an activation energy of 0.11 eV. The latter is diferent from that obtained from the thermo-power, a signature of a conduction mechanism by small polaron hopping. LaCoO3 is chemically stable above pH 5; an exchange current density of 40 μA cm−2, a polarization resistance of 1.92 kΩ cm2 and a corrosion potential of 0.99 VSCE were obtained at pH~ 7 (Na2SO4, 0.1 M). Curiously and unlike the perovskites, the variation of the inverse of the square of the capacitance as a function of potential (C−2−E) indicates p type behavior with a fat band potential of 0.30 VSCE and holes density of 1.97× 1017 cm−3. The conduction band (−0.94 VSCE), made up of Co3+: 3d orbital, enables the formation of the radical O2 •−, and as application, the oxide was successfully experimented for the oxidation of OII upon solar irradiation. The hetero-junction p-LaCoO3/n-ZnO enhances considerably the photo-activity, due to the facile transfer of electrons with an abatement of 86% at neutral pH. The oxidation follows a frst-order kinetic with a half photocatalytic life of 23 min