Controlled synthesis of spherical α-Ni(OH)2 hierarchical nanostructures via a simple hydrothermal process and their conversion to NiO

Abstract

Hierarchical pure α-nickel hydroxide (α-Ni(OH)2) nanostructures have been successfully synthesized through a one-step hydrothermal synthesis with nickel nitrate hexahydrate, ethylene-1,2-diamine (en) and hydrazine (N2H4) as morphology-directing agents. Optimum conditions to obtain high yield and phase pure α-Ni(OH)2 were identified by varying experimental parameters, such as the en and N2H4 concentration, and the reaction temperature. The products were characterized by X-ray diffraction (XRD), scanning electron microscopy (SEM), transmission electron microscopy (TEM), and photoluminescence (PL) spectroscopy. For determination of the structural formula of such α-nickel hydroxides, Fourier transform infrared (FT-IR) spectra and thermogravimetric analysis (TGA) were carried out on the as-prepared products. These results indicated that the α-nickel hydroxide contains water molecules and anions. The hierarchical NiO nanostructures are obtained on annealing the α-Ni(OH)2 nanostructures at 300°C for 4h. The magnetic properties of the as-prepared NiO nanostructures show a superparamagnetic behavior for the as-synthesized NiO nanostructures.