Novel morphologies of nickel sulfides: nanotubes and nanoneedles derived from rolled nanosheets in a w/o microemulsion

Abstract

Nickel sulfide nanocrystals with novel morphologies of two-dimensional nanosheets and one-dimensional (1D) nanoneedles or nanotubes have been successfully achieved in the CTAB/n-pentanol/n-hexane/water microemulsion under hydrothermal condition at 130°C. X-ray powder diffraction, transmission electron microscopy (TEM) and field emission scanning electron microscopy were used to characterize the as-synthesized samples. The result shows that nickel sulfide nanosheets with small thickness (less than 5 nm) and nanoneedles with hollow center (or nanotubes), ca. 50–150 nm in diameters and several microns in lengths, can be obtained by hydrothermally treating for 5 and 15 h, respectively. The sulfuration reaction mechanism and the low-dimensional nanocrystal growth process have been discussed in detail. TEM images reveal that the nanosheets firstly formed under the soft template action of the w/o microemulsion, and then the resulting nanosheets rolled up into 1D nanoneedles or nanotubes. The sulfuration reaction is a sequential process in which a lower sulfide initially forms and then it goes on to react with S 2− to produce more sulfur-rich sulfides.