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The location of dopant ions and the effect of doping level on the photocatalytic activity have been investigated on Co-doped ZnO nanopowders. A co-precipitation method was used to prepare ZnO nanoparticles of <50 nm in diameter doped with up to 5 at% of Co. The crystal structure of nanoparticles and local atomic arrangements around dopant ions were analysed by X-ray diffraction and extended X-ray absorption fine structure spectroscopy using synchrotron radiation. The results showed the Co ions substituted the Zn ions in ZnO crystal lattice and induced lattice shrinkage. The photocatalytic activity under simulated sunlight irradiation was characterised by the decomposition of Rhodamine B dye molecules, which revealed the successful reduction of photocatalytic activity by Co-doping.

The detrimental effects of UV radiation are having a significant impact on our life and environment. The development of effective UV shielding agents is therefore of great importance to our society. ZnO nanoparticles are considered to be one of the most effective UV blocking agents. However, the development of ZnO-based UV shielding products is currently hindered due to the adverse effects of the inherent photocatalytic activity exhibited by ZnO. This paper reports our recent study on the possibility of reducing the photoactivity of ZnO nanoparticles via surface modification and impurity doping. It was found that the photoactivity was drastically reduced by SiO 2-coatings that were applied to ZnO quantum dots using the Stöber method and a microemulsion technique. The effect of transition metal doping on the photoactivity was also studied using mechanochemical processing and a co-precipitation method. Cobalt doping reduced the photoactivity, while manganese doping led to mixed results, possibly due to the difference in the location of dopant ions derived from the difference in the synthesis methods.

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