Controlled synthesis of spherical α-NiS and urchin-like β-NiS microstructures

Spheres and self-assembled wires of α-NiS (the hexagonal phase) have been successfully synthesized by a facile mix solvothermal route (glycol and water). Varying the volume ratio between glycol and water, and leaving the other conditions unchanged, the urchin-like β-NiS (the rhombohedral phase) microstructures were also prepared. The as-obtained products were characterized by means of X-ray powder diffraction patterns (XRD), transmission electron microscopy (TEM) and high-resolution transmission electron microscopy (HRTEM). The TEM results show that the wires of α-NiS are constructed by a number of spheres of α-NiS as primary building units. On the basis of the TEM results, a phenomenological elucidation of the growth mechanism of α-NiS architectures has been presented as the directional aggregating and the Ostwald ripening. Moreover, the optical properties of the α-NiS and β-NiS microstructures were investigated by the room-temperature ultraviolet-visible (UV-Vis) absorption spectroscopy and the photoluminescence (PL) spectroscopy.