Photooxidation of the phenylazonaphthol AO20 on TIO2: kinetic and mechanistic investigations.

The results of the photocatalytic and photosensitized degradations of the monoazo dye AO20 in aqueous solution using suspended titanium dioxide are presented. Kinetic and mechanistic details have been elucidated using UV/Vis, FTIR and TCO techniques. It was proven that adsorption of dye molecules onto the support material is essential for the processes to be effective. Moreover, even if their mechanisms differ during the early stages, photocatalysis and photosensitization lead to very similar ultimate breakdown products. Indeed, the original dye anchored to the oxide surface systematically undergoes fast decomposition until it is transformed into CO2 or aliphatic acids (formic, acetic, oxalic acids), which react rather slowly with hydroxyl radicals or trapped holes.