Semiconducting and photo-electrochemical properties of the perovskite BaSn 0.95 Co 0.05 O 3 . application to the photo-oxidation of erichrome black

The substituted perovskite BaSn 0.95 Co 0.05 O 3 (BSCO) was synthetized by nitrate route. The X-ray diffraction pattern is characteristic of a single phase with a cubic symmetry (SG: Pm-3 m, N o 221) and a refined lattice constant of 0.41160 nm. The scanning electron microscopy (SEM) shows agglomerate particles with an average grain size of ~ 400 nm. The XPS data confirmed Ba, Sn and Co to be in 2 + , 4 + and 3 + oxidation states, respectively. The direct optical gap E g (= 1.73 eV), obtained from the diffuse reflectance, is ascribed to crystal field splitting of Co 3+ hexa-coordinated to six oxygen ions in conformity with the black colour and low spin configuration. The thermal dependence of the electrical conductivity shows a semiconducting-like behaviour with an activation energy (E a ) of 0.23 eV where the electron hopping occurs between mixed valence Co 3+/2+ . As expected, the negative slope of the (capacitance −2 —potential) curve, plotted in Na 2 SO 4 solution, revealed p type conduction due to the hetero-valent substitution (Co 3+ /Sn 4+ ). A flat band potential (E fb = − 0.086 V) and a hole density N A (= 0.036 × 10 20 m −3 ) were determined, in agreement with the nominal composition. The Electrochemical Impedance Spectroscopy (EIS) shows the predominance of the bulk and grain boundaries, the data were fitted to an equivalent electrical circuit. As application, the photo-degradation of Eriochrome black (ECB, 10 mg/L), a recalcitrant dye, was successfully realized under solar light and the discoloration follows a first order kinetic with a rate constant of 7 × 10 –3 min −1 (t 1/2 = 99 min) and an abatement of 97% under sunlight (920 ± 90 mW/cm 2 ), such fluctuation is due to the solar inclination.