The role of cobalt doping on the photocatalytic activity enhancement of ZnO nanorods under UV light irradiation

Recently, many efforts have been made to apply the ZnO photocatalyst under visible radiation, which requires narrowing the band gap. However, various modifications by doping with transition metal ions do not change the band gap because of the basic nature of ZnO as a wide band gap semiconductor. Therefore, the effect of Co dopant on the photocatalytic activity under UV light irradiation should be examined to understand it. In this work, ZnO nanorods with 0, 3, 5, and 7 mol% Co concentrations were grown directly on a glass substrate through a simple spray pyrolysis followed by the hydrothermal technique. This study showed that the degradation rate of methyl blue in the presence of ZnO nanorods photocatalysts with 0, 3, 5, and 7 mol% Co are 67, 72, 78, and 80%, respectively. The addition of the Co dopant increased the diameter and crystallite size of the ZnO nanorods, decreased the band gap and increased the number of surface active sites for adsorption of O-2 molecules and hydroxyl ions, which could break the chemical bonds of methyl blue and produce colorless dye molecules.