Solar/UV-induced photocatalytic degradation of three commercial textile dyes

The photocatalytic degradation of three commercial textile dyes with different structure has been investigated using TiO2 (Degussa P25) photocatalyst in aqueous solution under solar irradiation. Experiments were conducted to optimise various parameters viz. amount of catalyst, concentration of dye, pH and solar light intensity. Degradation of all the dyes were examined by using chemical oxygen demand (COD) method. The degradation efficiency of the three dyes is as follows: Reactive Yellow 17 (RY17) > Reactive Red,2 (RR2) > Reactive Blue 4 (RB4), respectively. The experimental results indicate that TiO2 (Degussa P25) is the best catalyst in comparison with other commercial photocatalysts such as, TiO2 (Merck), ZnO, ZrO2, WO3 and CdS. Though the UV irradiation can efficiently degrade the dyes, naturally abundant solar irradiation is also very effective in the mineralisation of dyes. The comparison between thin-film coating and aqueous slurry method reveals that slurry method is more efficient than coating but the problems of leaching and the requirement of separation can be avoided by using coating technique. These observations indicate that all the three dyes could be degraded completely at different time intervals. Hence, it may be a viable technique for the safe disposal of textile wastewater into the water streams. (C) 2002 Elsevier Science B.V. All rights reserved.