Large-scale synthesis of Ni-Ag core-shell nanoparticles with magnetic, optical and anti-oxidation properties

The large-scale synthesis and characterization of Ni-core/Ag-shell (Ni@Ag) nanoparticles by the successive hydrazine reduction of nickel chloride and silver nitrate in ethylene glycol using polyethyleneimine (PEI) as a protective agent are described. The resultant Ni@Ag nanoparticles had a mean core diameter of 6.2 nm and a shell thickness of 0.85 nm, without significant change in the nickel concentration of 0.25 - 25 mM for the Ag coating. Also, both Ni cores and Ag nanoshells had an fcc structure and PEI was capped on the particle surface. X-ray photoelectron spectroscopy analysis confirmed that the Ni cores were fully covered by Ag nanoshells. In addition, the Ni@Ag nanoparticles exhibited a characteristic absorption band at 430 nm and were nearly superparamagnetic. Based on the weight of Ni cores, the saturation magnetization (M-s), remanent magnetization (M-r) and coercivity (H-c) were obtained as 17.2 emu g(-1), 4.0 emu g(-1) and 81 Oe, respectively. Furthermore, the resultant Ni@Ag nanoparticles exhibited better anti-oxidation properties than Ni nanoparticles did due to the protection of the Ag nanoshells.