Enhanced photoelectrocatalytic performance of Zn-doped WO3 photocatalysts for nitrite ions degradation under visible light

WO3 and Zn-doped WO3 thin films were prepared on indium-tin oxide glass by a dip-coating. The composite films were characterized by UV-Vis absorption spectra, X-ray diffraction and scanning electron microscope. The effect of preparation conditions (concentration of Zn, annealing temperature, number of layers) on the photocurrent was studied. It was found that the photocurrent under visible light displayed the highest value for 2% Zn-WO3 films annealed at 400 degrees C. The photocatalytic activity of the Zn-doped WO3 was evaluated in terms of decay rate of nitrite ions under visible light. The influence of applied potential, initial pH and nitrite concentration on the reaction rate was studied. The experiments demonstrated that NO2 could be efficiently degraded on the doped photoanode that showed a higher activity than the undoped WO3 especially under high anodic potential (>0.7 V). The rate of degradation was enhanced in aqueous NaCl solutions. Furthermore, it was demonstrated that the photodegradation mechanism of NO2- proceeded mainly indirectly via OH radicals. The possible reason of enhancement of reaction rate was also discussed. (C) 2007 Elsevier Ltd. All rights reserved.