Photodegradation of Reactive Black 5 in a ZnO/UV slurry membrane reactor

This paper describes the photodegradation of commercial azo dye, Reactive Black 5 (RB5) in a slurry membrane reactor operated under batch and continuous modes. Initially, the photocatalytic activity of TiO2 and ZnO for decolorization of RB5 was evaluated and the best results were achieved with ZnO. Based on these results, the effect of operating parameters including catalyst load (0.5-1.5 g/L), initial dye concentration (25-150 mg/L) and pH (3.0-11.0) on color removal was investigated in detail. The results showed that the decolorization of RB5 depended on reaction time and dye concentration. The color removal rate is faster in low initial dye concentration and it increased with increasing ZnO concentration upto 1.25 mg/L. At ZnO concentration beyond this level, reduction of color removal was observed. As a result of combined effects between dye photolysis and photoactivity of ZnO, the highest RB5 removal rate was found at pH 11 with a nearly 100% removal within 60 min. The photocatalytic decolorization of RB5 by ZnO/UV follows the pseudo-first-order kinetics. Reusability study and the continuous experiments indicated that ZnO catalyst has a potential for long-term use without losing its activity and the reactor can be easily extended to pilot scale applications.