Phototoelectrochemical characterization of Ag/ CuCo2O4 prepared at low temperature: application to solar light oxidation of methyl orange
2022
Bagtache, R. | Boudjedien, K. | Djaballah, A. M. | Trari, M.
The Schottky junction Ag/ CuCo₂O₄ (5/95% wt.) was elaborated by co-precipitation to evaluate its performance for the oxidation of methyl orange (MO) upon solar light. The X-ray diffraction exhibited narrow peaks assigned to the spinel CuCo₂O₄ and Ag. The SEM analysis showed grains with regular shapes and sizes in the range (0.3–0.5 µm). The direct forbidden band of CuCo₂O₄ (1.38 eV), extracted from the diffuse reflectance, was well adapted to the solar spectrum. This value decreased down to 1.15 eV due to the synergy effect. The thermal variation of the electrical conductivity obeyed an exponential law: σ = 0.67 exp{− 0.38/kT (eV)}. The current–potential (J-E) profile plotted in Na₂SO₄ electrolyte displayed a medium hysteresis, characteristic of a good chemical stability. The capacitance⁻²–potential (Cdₗ⁻²–E) graph showed that the spinel works as p-type semiconductor, a property supported by chrono-amperometry. The electrochemical impedance spectroscopy (EIS) confirmed the semiconductor comportment under visible light illumination. The conduction band, located at 4.05 eV (− 0.94 VNHE), was formed mainly from Co³⁺: 3d orbital where the excited electrons were focalized to Ag clusters, to reduce oxygen into O₂•⁻ radicals, responsible for the MO oxidation. Such electrons transfer was facilitated in the bi-functional Schottky junction because of the small over-voltage on Ag clusters. Batch experiments of the MO degradation showed a total abatement after 2 h of illumination under solar light and the kinetic obeyed a first-order model with a photocatalytic half-life of 40 min at pH ~ 7.
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