Decolorization of organic dyes on Pilkington Activ™ photocatalytic glass

Abstract The air–solid photocatalytic degradation of organic dye films Acid Blue 9 (AB9) and Reactive Black 5 (RBk5) is studied on Pilkington Activ™ glass. The Activ™ glass comprises of a colorless TiO 2 layer deposited on clear glass. The Activ™ glass is characterized using atomic force microscopy (AFM) and X-ray diffraction (XRD). Using AFM, the TiO 2 average agglomerate particle size is 95 nm, with an apparent TiO 2 thickness of 12 nm. The XRD results indicate the anatase phase of TiO 2 , with a calculated crystallite size of 18 nm. Dyes AB9 and RBk5 are deposited in a liquid film and dried on the Activ™ glass to test for photodecolorization in air, using eight UVA blacklight-blue fluorescent lamps with an average UVA irradiance of 1.4 mW/cm 2 . A novel horizontal coat method is used for dye deposition, minimizing the amount of solution used while forming a fairly uniform dye layer. About 35–75 monolayers of dye are placed on the Activ™ glass, with a covered area of 7–10 cm 2 . Dye degradation is observed visually and via UV–vis spectroscopy. The kinetics of photodecolorization satisfactorily fit a two-step series reaction model, indicating that the dye degrades to a single colored intermediate compound before reaching its final colorless product(s). Each reaction step follows a simple irreversible first-order reaction rate form. The average k 1 is 0.017 and 0.021 min −1 for AB9 and RBk5, respectively, and the corresponding average k 2 is 2.0 × 10 −3 and 1.5 × 10 −3  min −1 . Variable light intensity experiments reveal a p  = 0.44 ± 0.02 exponent dependency of initial decolorization rate on the UV irradiance. Solar experiments are conducted outdoors with an average temperature, water vapor density, and UVA irradiance of 30.8 °C, 6.4 g water/m 3 dry air, and 1.5 mW/cm 2 , respectively. For AB9, the average solar k 1 is 0.041 min −1 and k 2 is 5.7 × 10 −3  min −1 .