Doping effects of Co(2+) ions on ZnO nanorods and their photocatalytic properties.

A series of Zn(1-x)Co(x)O nanorods with dopant content ranging from x = 0.00 to 0.10 was prepared by a wet chemical method. All Zn(1-x)Co(x)O samples were investigated by x-ray diffraction, transmission electron microscopy, energy-dispersion x-ray line mapping analysis, and UV-visible absorption spectroscopy. It was found that Co(2+) ions were homogeneously substituted for Zn(2+) ions in ZnO nanorods. Rhodamine B degradation was used as a probe reaction to evaluate the effect of Co(2+) doping on ZnO nanorods and photocatalytic performance under UV light and visible light irradiation. Co(2+) ions acted as the trapping or recombination centers for electrons and holes, leading to a reduction in photodegradation efficiency under UV light illumination. Alternatively, Co(2+) ions enhanced the optical absorption and produced the photoinduced carriers under visible illumination in terms of two charge transfer transitions involving Co(2+) ions. Consequently, Co(2+) ions substituted in the lattice of ZnO nanorods significantly improved the visible light photocatalytic activity.