Comparative photocatalytic studies of degradation of a cationic and an anionic dye

Photocatalytic degradation of Methylene Blue, a cationic dye and Procion Red, an anionic dye, has been examined in TiO2 dispersions under visible light (λ 400-580 nm). Adsorption is a prerequisite for the TiO2 assisted photodegradation and the extent of degradation has been discussed in terms of the Langmuir-Hinshelwood model. Like most semiconductors the photocatalytic nature of TiO2 is pH dependent because of its amphoteric nature. It has been found that pH ∼ 9.5 and pH ∼ 3.22 were suitable for Methylene Blue and Procion Red, respectively. The degradation pathway of Procion Red was found to be somewhat different from Methylene Blue.