Preparation and characterization of nano structured Ba2SnO4 as a novel photocatalyst material for the chromate reduction

The photo-electrochemical properties of the layered perovskite Ba2SnO4, prepared by nitrate route are reported for the first time. The oxide exhibits a direct optical transition at 2.98 eV, attributed to the charge transfer O2−: 2p → Sn4+: 5s and possesses a chemical stability over the whole pH range. The Mott Schottky plot in acidic medium is characteristic of n type conductivity with a flat band potential Efb of −0.84 VSCE and an electron density ND of 1.14 × 1017 cm−3. The electrochemical impedance spectroscopy reveals the bulk and grain boundaries contributions. Ba2SnO4 is of interest for the environmental protection. At pH 2.5, its conduction band (CB, −0.86 VSCE) is below the HCrO4− level, yielding a spontaneous reduction to Cr3+ under UV light. The reduction is optimized with respect to the Cr(VI) concentration. The photo reduction follows a pseudo-first-order kinetic and the data fit well the Langmuir–Hinshelwood (L–H) model with an apparent rate constant of 0.18 h−1 for an initial concentration of 50 ppm. The chromate reduction under solar light is studied under optimized conditions. In presence of oxalic acid, 73 % of initial concentration disappears after ~2 h of irradiation.