Photo electrochemical properties of LaCoO3 synthetized by chemical route. Application to orang II photo-oxidation

Abstract

The perovskite LaCoO3 prepared from nitrates was successfully applied in the oxidation Orange II (OII) under sunlight. The X-ray diffraction (XRD), Scanning Electron Microscopy and electrical conductivity were used for its characterization. The XRD pattern showed that the single phase is completed at 850 °C and the oxide crystallizes in a distorted structure. The optical gap (1.35 eV), determined from the diffuse reflectance, is due to the crystal field splitting of Co3+ octahedrally bonded with a low spin configuration (3d6). A hole mobility of 10−2 cm2 V−1 s−1 and an activation energy of 0.11 eV were deduced from the conductivity measurement. LaCoO3 attractive with regard to toxicity concern exhibits a chemical inertness at neutral pH (Na2SO4, 0.1 M) with an exchange current density of 40 μA cm−2. The variation of the capacitance (C−2) with the potential (E) is characteristic of p type comportment with a flat band potential of 0.30 VSCE. The EIS date showed an arc due to the resistance of the bulk material (1153 kΩ cm2) whose center center is below the real axis (-16°) assigneed to a constant phase element (CPE). The conduction band (-0.94 VSCE), deriving from Co3+: 3d wave function, allows the generation of O2•− species and as application, the oxide was positively tested for the mineralization of OII upon sunlight. The hetero-system p-LaCoO3/n-ZnO improves significantly the photo catalytic performance -activity, due to the facile electronic transfer with an oxidation of 86%. The oxidation kinetic obeys a first order model with a half life of 23 min.