Photoelectrochemical properties of CaWO^sub 4^ synthetized by chemical route. Application to the phenobarbital electro-photocatalysis

The semiconducting properties of the Scheelite CaWO4, synthesized by nitrate route, were investigated by the photocurrent technique and capacitance measurements in acidic solution (pH ~ 5). CaWO4 crystallizes in the tetragonal symmetry with a large optical gap (4.88 eV) and a low electrical conductivity (σ300K = 2.63 x 10-5 Ω-1 cm-1). The photo-electrochemical characterization shows n type semi conductivity with a wide depletion length (~110 nm). The Nyquist representation, measured in the range (10-3-105 Hz), indicates a predominant bulk contribution with a constant phase element which takes its origin from the electrode roughness. The results of CaWO4 are relevant for its applications to electro-photocatalysis. The conversion percentages of Phenobarbital reached respectively 54% and 66% with electro-catalysis and electro-photocatalysis under UV/C irradiation. The oxidation obeys to a first order kinetic with a rate constant of 1.98 x 10-3 min-1 and 2.7 x 10-3 min-1, respectively.