Influence of operational parameters and kinetics analysis on the photocatalytic reduction of Cr(VI) by immobilized ZnO

Abstract

In the present work the performance of immobilized ZnO on a glass plate with the heat attachment method has been described for photoreduction of Cr(VI) to the less harmful Cr(III) at different operational parameters. The photoreduction of Cr(VI) on the surface of the immobilized ZnO catalyst was studied as a function of the pH of solution, initial Cr(VI) concentration and ultraviolet (UV) light intensity. Results indicated that the reduction rate decreases with increasing initial concentration of Cr(VI) and initial pH of solution, whereas it increases with increasing UV light intensity. The photoreduction rate of Cr(VI) on the surface of the immobilized ZnO in the presence of O₂ as mobile gas is more than Ar and N₂. The reduction process of Cr(VI) by immobilized ZnO also could be done under visible light irradiation. Pseudo first-order kinetics were observed for the photoreduction of Cr(VI) at different operational conditions. With non-linear regression analysis a mathematical kinetics model was developed for the pseudo first-order constant (k _ap) as a function of operational parameters.

Keywords:

• photoreduction
• heterogeneous photocatalysis
• immobilized ZnO
• Cr(VI)
• kinetics model

Acknowledgement

The authors thank the Islamic Azad University, Tabriz Branch, for financial and other supports.