Effect of Yttrium Substitution on Microstructural, Optical, and Photocatalytic Properties of ZnO Nanostructures

Zinc oxide (ZnO) nano-powder has been successfully doped, via a solid-state reaction, with different concentrations of yttrium (Y) rare-earth element. The thermal stability of the prepared nanostructures has been studied by thermogravimetric and differential thermal analysis. The results show that Y-doped ZnO nanostructures are thermally stable for temperatures higher than 444°C. Structural, microstructural, optical, and photocatalytic characterizations have been performed. The micro-strain properties were analyzed through the Williamson–Hall analysis. We have identified a pure phase wurtzite material, without any impurities. XRD peaks exhibited a shift toward the lower angles after doping, confirming the Y3+ substitution in the ZnO crystal structure. In accordance with the XRD analysis, morphological surface analysis done by scanning and transmission electron microscope indicates that, with increasing the concentration of the Y3+ ions inside the ZnO matrix, the grain size also increases. Fourier-transform infrared spectra showed that the various bonds were created without any contamination after substitution. Ultraviolet–visible–near-infrared spectroscopic measurements revealed a red-shift of the bandgap energy of 0.1 eV, confirming the success of the substitution process. To assess the photocatalytic activity, the photodegradation of methylene blue was studied. It was observed that the Y-dopant significantly improves the photocatalytic activity of the ZnO nanostructures. Bandgap narrowing by Y doping could be responsible for the improvement of the observed photocatalytic efficiency.