Solar photocatalytic degradation of Naphthol Blue Black

Abstract

The solar photocatalytic activity of AgBr–ZnO was investigated for the degradation of Naphthol Blue Black (NBB) in aqueous solution. Removal of azo dyes from wastewater is a challenging process, since these dyes are nonbiodegradable. Presence of a visible light absorbing component, AgBr, makes this catalyst solar active. AgBr–ZnO is found to be more efficient than commercial ZnO and prepared ZnO for solar degradation of NBB azo dye. The effects of operational parameters, such as the amount of photocatalyst, dye concentration, and initial pH on photo mineralization have been analyzed. The optimum pH and catalyst amount for the efficient removal of dye are found to be 11 and 3 g L⁻¹, respectively. Increase of initial dye concentration decreased the degradation rate. The mineralization of NBB has also been confirmed by chemical oxygen demand measurements. The higher photocatalytic activity of AgBr–ZnO towards NBB degradation in solar light is explained by a mechanism involving band energy levels of AgBr and ZnO. The catalyst was found to be reusable.

Keywords:

• AgBr loaded ZnO
• Photocatalysis
• Solar light
• Naphthol Blue Black
• Reusability

Acknowledgments

The authors thank the Ministry of Environment and Forests (MOEF), New Delhi, India for the financial support through research grant No. 315-F-36, F. No. 19/9/2007-RE. One of the authors B. Krishnakumar is thankful to CSIR, New Delhi, India for the award of Senior Research Fellowship.