Photocatalytic decolorization of remazol red RR in aqueous ZnO suspensions

The photocatalytic decolorization of aqueous solutions of Remazol Red RR, a commercial azo-reactive textile dye, in the presence of various semiconductor powder suspensions has been investigated in a quartz batch reactor with the use of artificial light sources (UV-C). ZnO and TiO2 have been found the most active photocatalysts; however ZnO indicated slightly higher efficiency. The effects of various process variables on decolorization performance of the process have been investigated. The results showed that the decolorization efficiency increases with increase in pH, attaining maximum value at pH 10 for ZnO. The zero-point charge for ZnO is 9.0 above which ZnO surface is negatively charged by adsorbed OH- ions, favoring the formation of strong oxidant OH* radicals. The efficiency is inversely related to the dye concentration; increasing dye concentration enhances dye adsorption on the active sites of the catalyst surface, and consequently hinders OH- adsorption on the same sites, this results with a decreasing OH* formation rate. (C) 2004 Elsevier B.V. All rights reserved.