Hydrothermal growth and morphology modification of β-NiS three-dimensional flowerlike architectures

A series of ss-NiS three-dimensional (3D) flowerlike architectures with an average diameter of 2-4 mu m have been hydrothermally synthesized in the presence of ammonia and trisodium citrate. Morphology modification can be conveniently realized by varying the reaction temperature. At 120 degrees C the flowerlike architectures were composed of naoneedles. At 180 degrees C the flowerlike architectures were composed of nanorods, while mixtures of nanoneedle-based and nanorod-based flowerlike architectures were obtained in the temperature range of 140-160 degrees C. Citrate anion was introduced as both a coordinating reagent and a shape modifier to control the anisotropic growth of ss-NiS. Besides a probable growth mechanism, the citrate-assisted Ostwald ripening process was proposed to explain the formation of flowerlike architectures on the basis of transmission electron microscopy observations. Such a simple and mild synthetic route may be extended to fabricate complex 3D architectures of other materials.