Lotus-root-like NiO nanosheets and flower-like NiO microspheres: Synthesis and magnetic properties

The synthesis of lotus-root-like NiO nanosheets and flower-like NiO microspheres was realized through a simple hydrothermal method and subsequent calcination. The diameter of the lotus-root-like NiO nanosheets is about 400 nm and the pore size is about 5∼20 nm. The diameter of the flower-like NiO microspheres is about 2.5 μm, and are composed of staggered lotus-root-like nanosheets. During the synthetic procedure, aqueous ammonia was used as an alkaline complexing reagent, and PVP was used as the template. Interestingly, when the pH value of the precursor solution increased from 8.30 to 10.80, the NiO nanosheets gradually assembled into microspheres, indicating that aqueous ammonia plays a key role in controlling the final morphology. Based on the experimental observation and analysis, a possible mechanism is proposed to understand the formation of the NiO nanostructured materials. In addition, the resultant NiO nanostructures present anomalous magnetic properties and display a spin-glass state at low temperature.