On the agent role of Mn2+ in redirecting the synthesis of Zn(OH)2 towards nano-ZnO with variable morphology

Abstract

One of the simplest routes to prepare polycrystalline Zn(OH)₂ is by coprecipitation, with zinc nitrate as a cation source. However, the addition of even minute amounts of manganese nitrate to the precursors used to prepare pure Zn(OH)₂ results in Mn²⁺ doped nanostructured ZnO. The comparison with other Mn²⁺ doped metal hydroxides prepared by the same coprecipitation method, involving metal nitrates precursors, shows that this behavior is unique, pertaining only to Zn(OH)₂. A systematic study of the samples prepared without and with variable amounts of Mn²⁺ ions, in the 1 to 5000 ppm nominal concentrations range showed that the re-routing of the reaction takes place even for the lowest nominal dopant concentration of 1 ppm. According to X-ray diffraction, transmission electron microscopy and Fourier transform infrared spectroscopy investigations, both crystallite size and morphology of the resulting nanostructured ZnO samples varied with the Mn²⁺ nominal concentration. Moreover, quantitative electron paramagnetic resonance investigations showed that the incorporation rate of the Mn²⁺ ions at different sites in the nanostructured ZnO depended on the nominal Mn²⁺ concentration. The results are discussed in terms of the coordination properties of the Mn²⁺ and Zn²⁺ ions and the nature of the reaction precursors.