Photocatalytic decolourization of reactive azo dye: A comparison between TiO2 and CdS photocatalysis

This study examined the photocatalytic degradation of reactive black 5 (RB5), a reactive azo dye, by TiO2 and CdS. An aerated semiconductor suspension was illuminated in a batch-lab-scale reactor. Both reactions followed first order kinetics. The effects of initial pH, semiconductor dosage, light intensity, initial dye concentration and temperature were investigated. CdS photocatalysis of RB5 followed the Langmuir-Hinshelwood equation while TiO2 photocatalysis did not. The RB5 wastewater was decolourized and detoxified by TiO2 photocatalysis. By contrast, CdS photocatalysis increased the toxicity due to CdS photocorrosion. The efficiencies of photocatalytic decolourization using new and recycled TiO2 were not significantly different. However, the efficiency of the reaction using recycled CdS was lower than for new CdS. (C) 1997 Elsevier Science Ltd.