Photocatalytic degradation of azo-dyes reactive black 5 and reactive yellow 145 in water over a newly deposited titanium dioxide

Reactive black 5 (RB5) and reactive yellow (RY145), two azo-dyes, were degraded by using UV-irradiated TiO2 coated on non-woven paper. The adsorption capacity of the photocatalyst was studied at natural pH and at various pHs of the aqueous solutions of azo-dyes. It can be stated that pH is a very important parameter in dye adsorption. The silica binder played an important role in decreasing the pzc of the coated TiO2. The effect of initial dye concentration and pH on photocatalyst degradation was studied. The rate of degradation was modeled by the Langmuir Hinselwood equation only in acid pH zone. A direct correlation between pH, adsorption and rate of degradation was found. The discoloration and complete mineralization of the two dyes could be achieved. The by-products of the photocatalytic degradation were biodegradable and non-toxic for bacteria from activated sludge. These results suggest that UV-irradiated TiO2 coated on non-woven paper may be considered as an adequate process for the discoloration and detoxification of the treatment of diluted colored textile wastewater. (c) 2004 Elsevier B.V. All rights reserved.