Decolorization and degradation of reactive azo dyes via heterogeneous photocatalytic processes

Abstract

Reactive dyes are extensively used in textile industry in the last years due to their superior performance, but they are environmentally hazardous and difficult to treat effectively by classical methods. In the present work. the decolorization and degradation of four commercial reactive azo dyes, namely Remazol Red RR, Remazol Yellow RR, Procion Crimson H-exl and Procion Yellow H-exl. were studied using photocatalytic processes (TiO(2)/UV and TiO(2)/UV/H(2)O(2)). Decolorization and degradation were found to strongly depend on the system parameters (TiO(2) loading, dye and H(2)O(2) initial concentrations, and pH). Decolorization efficiency (%) sharply increases with increasing the TiO(2) loading. especially up to 1 g/L, as well as with decreasing the initial dye concentration from 250 down to 50 mg/L At pH = 3, a > 90% decolorization of all dyes can be achieved in only 15 min. Addition of H(2)O(2) increases the decolorization rates up to an optimum value (97.9% Remazol Red RR decolorization at 12 min irradiation, with a 0.5%w/w initial H(2)O(2) concentration and pH = 3). Among the four dyes examined, significant differences in decolorization and degradation rates were revealed, but decolorization and degradation efficiencies up to 100% (in 25 min and 4 h respectively) are possible with proper combinations of the system parameters. (C) 2009 Elsevier B.V. All rights reserved.