Morphology control and fabrication of multi-shelled NiO spheres by tuning the pH value via a hydrothermal process

Abstract

Controlling the morphology of nickel oxide (NiO) nanostructures is crucial to obtain excellent physical and chemical performance. Hence, the morphology of NiO was tuned by adjusting the pH value of the precursor solutions with NH₃·H₂O via a hydrothermal process and subsequent calcination. Different morphologies, including nanoparticles, porous structures and multi-shelled microspheres, were obtained with pH values varying from 8.30 to 10.90. The morphology evolution of as-synthesized NiO with the pH value indicates the important role of OH⁻ in controlling the product morphology. Moreover, the formation mechanism of different NiO nanostructures at different pH values was discussed. Furthermore, the surface area and magnetic properties of NiO with different morphologies were also investigated, and indeed, these properties are very sensitive to the morphology. This work provides a facile way to control the morphology of NiO nanostructures, which also implies the potential application in modern science and technology with the modified magnetic properties.