Synthesis and characterization of a nickel selenide series via a hydrothermal process

Abstract

A series of nickel selenides (NiSe and NiSe2) has been successfully synthesized from the reaction of SeCl4 with NiCl2⋅6H2O in the presence of cetyltrimethyl ammonium bromide (CTAB) as surfactant and hydrazine hydrate (N2H4⋅H2O) as reductant at 180°C for 12h through a simple hydrothermal method. The morphology, phase structure and composition of NixSey can be controlled by adjusting the Ni/Se ratio of the raw materials, the quantity of reductant, the reaction temperature and so forth. The products were characterized by X-ray diffraction (XRD), scanning electron microscopy (SEM), transmission electron microscopy (TEM) and energy-dispersive X-ray spectroscopy (EDS) analysis. It was found that when the ratio of Ni/Se is 1:1 or 3:2, flower-like assemblies of NiSe nanosheets are formed, at 180°C for 12h. When the ratio of Ni/Se is 1:2 at 180°C, the products are found to be the mixture of hexagonal NiSe and cubic NiSe2. With decrease of nickel content in molar ratio of 1:2 (Ni:Se), nanospheres are agglomerated and microstructures are formed. With the reaction temperature decreasing from 180°C to 120°C, we reach pure NiSe2 nanoparticles. The formation mechanism of the nickel selenides has been investigated in detail by means of XRD and SEM analyses.