Synthesis of Size-Tunable Monodispersed Metallic Nickel Nanocrystals without Hot Injection

Size-tunable monodispersed hierarchical metallic Ni nanocrystals (58-190 nm in diameter) have been prepared by the reduction of Ni2+ with hexadecylamine under atmospheric pressure. The diameter of the particles could be tuned by simply changing the reaction time. The products were characterized with X-ray powder diffraction (XRD), field emission scanning electron microscopy (FESEM), transmission electron microscope (TEM), energy-dispersive X-ray (EDX), and selected area electron diffraction (SAED) techniques. The reaction mechanism was proposed, and the relationships between the size, hierarchical surfaces and the magnetic properties have been investigated. The as-synthesized Ni crystals exhibit higher coercivities than the bulk metallic material owing to the reduced size and the hierarchical surface structure. The saturation magnetization (Ms) and the ratio of remanence to saturation (Mr/Ms) increased with increasing particle size.