Kinetics of the decoloration of reactive dyes over visible light-irradiated TiO2 semiconductor photocatalyst

Photocatalytic decoloration kinetics of triazine (Reactive Red 11, Reactive Red 2, and Reactive Orange 84) and vinylsulfone type (Reactive Orange 16 and Reactive Black 5) of reactive dyes have been studied spectrophotometrically by following the decrease in dye concentration with time. At ambient conditions, over 90-95% decoloration of above dyes have been observed upon prolonged illumination (15 h) of the reacting system with a 150 W xenon lamp. It was found that the decoloration reaction followed first-order kinetics. The values of observed rate constants were found to be dependent of the structure of dyes at low dye concentration, but independent at higher concentration. It also reports for the first time the decoloration of two different dyes together in a binary dye mixture using visible light-irradiated TiO2 photocatalyst. Rate of decoloration of two different dyes together in a binary dye mixture using visible light-irradiated TiO2 photocatalyst is governed by the adsorptivity of the particular dye onto the surface of the TiO2 photocatalyst.