Photooxidation of an azo dye induced by visible light incident on the surface of TiO2

Oxidation of Acid Orange 7 (AO7) induced by visible light on TiO2 surfaces has been probed by FT-IR spectroscopy for identification and kinetic studies of degradation products. The tautomerism has been considered for this type of azo dye. The hydrazone form of AO7 triggers and undergoes the photooxidation process initiated by an electron injection into the conduction band of TiO2. Identification of degradation products by FT-IR spectroscopy reveals the presence of C-2 carboxylic aliphatic acids, carbonates and oxygenated sulfur compounds on TiO2 surfaces. Kinetics data suggest the existence of several mechanisms and that the photooxidation process is controlled by the supply of molecular oxygen onto the TiO2 surface. (C) 2001 Elsevier Science B.V. All rights reserved.