A PHOTOCATALYTIC APPROACH FOR THE REDUCTIVE DECOLORIZATION OF TEXTILE AZO DYES IN COLLOIDAL SEMICONDUCTOR SUSPENSIONS

Two representative commercially used textile azo dyes, Acid Orange 7 and Direct Blue 1, have been decolorized using colloidal TiO2 and WO3 photocatalytic systems. Under UV irradiation, these dyes undergo rapid decolorization as they are reduced at the semiconductor surface by the trapped electrons. The trapping of electrons in irradiated semiconductor colloids and their participation in the dye reduction process have been probed by steady-state and laser flash photolysis techniques. The quantum efficiency for such a reductive process has been determined to be 4.7 %. The rate constant for the electron transfer between the excited semiconductor colloid and the dye is of the order of 10(8) M-1 s-1. This photocatalytic decolorization approach has potential applications in the treatment of textile dye wastes.