The photo-electrochemical properties of the layered perovskite Ba 2 SnO 4 , 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 O 2-: 2p ? Sn 4? : 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 E fb of -0.84 V SCE and an electron density N D of 1.14 9 10 17 cm -3 . The electrochemical impedance spectroscopy reveals the bulk and grain boundaries contributions. Ba 2 SnO 4 is of interest for the environmental protection. At pH 2.5, its conduction band (CB, -0.86 V SCE ) is below the HCrO 4 -level, yielding a spontaneous reduction to Cr 3? 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.
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