TiO2-catalyzed photo-decolorization of some dyes

UV-irradiated TiO 2 -catalyzed photodegradation of the dyes, reactofix yellow ME7GL, reactofix red 3BFN 150% and reactofix supra red HBSL, has been studied. The kinetics has been followed spectrophotometrically at the wavelength of the maximum absorption, λ max , of the dyes in the visible region. The rate of the reaction depends on [dye] and [O 2 ], and on [TiO 2 ] when its concentration is below 0.2 g L -1 . On increasing [TiO 2 ] beyond 0.2 g L -1 , the rate attains a limiting value. On increasing pH, the rate decreases only slightly. At 7.0 pH and 0.2 g L -1 TiO 2 , the photodegradation kinetics is in conformity with the following experimental rate law. R obs = k 0 [dye] + k 2 [dye][O 2 ] + k 3 K 1 K 2 [dye][O 2 ]/(1 + K 1 [O 2 ])(1 + K 2 [dye]) where the rate constants k 0 and k 2 are related to uncatalysed and k 3 to TiO 2 -catalyzed pathways. The complete decolorization of the dye is achieved in about 20 min.