Bi2O3, BiVO4, and Bi2WO6: Impact of Surface Properties on Photocatalytic Activity under Visible Light
Résumé
Bismuth-based oxides have attractive photocatalytic properties under visible light. A better understanding of the origin of that good photocatalytic activity should allow its control and its optimization. In this Article, we have studied the impact of surface properties on photocatalytic activity for three bismuth-based oxides Bi2O3, BiVO4, and Bi2WO6. The surface acidity of particles was investigated by pyridine adsorption using infrared spectroscopy and the photocatalytic activity was investigated by the degradation of an aqueous solution of rhodamine B (Rho) and of stearic acid deposited on films under visible light. From the results obtained for the three bismuth-based oxides, we established a relation between surface acidity and photocatalytic mechanism of Rho degradation. The best photocatalytic efficiency for RhB and stearic acid degradation has been obtained with Bi2WO6 that also exhibits the highest surface acidity. The most acid sites promote a strong interaction with the pollutant, implying a short distance between the pollutant and the photocatalyst. Consequently, the photogenerated electrons, holes, and radicals can reach more easily the pollutant, leading to an efficient degradation under visible light. The development of strong acid solids such as Bi2WO6 emerged as promising materials for the degradation of pollutants. Because the good photocatalytic properties are related to the high acidity of Bi2WO6, we are interested in its origin using the multi site complexation model (MUSIC model). We found high acidity sites that are located on the lateral faces of the Bi2WO6 platelets (crystallographic planes (101), (10 (1) over bar), (100), and (001)).