Heterogeneous photocatalytic degradation of reactive dyes in aqueous TiO2 suspensions: Decolorization kinetics

This work assesses the photocatalytic (TiO2/UV) degradation of a simulated reactive dye bath (Black 5, Red 239, Yellow 17, and auxiliary chemicals). Color removal was monitored by spectrophotometry. Mineralization was determined by DOC analyses. Photocatalytic, photolytic, and adsorption experiments were performed, showing that adsorption was negligible. After 30 min of irradiation, it was achieved 97% and 40% of color removal with photocatalysis and photolysis, respectively. No mineralization occurred within 30 min. A kinetic model composed of two first-order in-series reactions was used. The first photocatalytic decolorization rate constant was k1 = 2.6 min−1 and the second k2 = 0.011 min−1. The fast decolorization of Reactive Black 5 dye is an indication that the number of azo and vinylsulfone groups in the dye molecule may be a determining factor for the increased photolytic and photocatalytic color removal and degradation rates.