Synthesis of nickel nanoparticles in aqueous cationic surfactant solutions

The synthesis of nickel nanoparticles by the reduction of nickel chloride with hydrazine in an aqueous solution of cationic surfactants CTAB/TC₁₂AB was studied. It was found that an appropriate amount of NaOH, trace acetone, and an elevated temperature were necessary for the formation of pure nickel nanoparticles. Also, it was not necessary to perform the reaction under a nitrogen atmosphere. X-ray diffraction revealed the resultant particles were pure nickel crystalline with a face-centered cubic (fcc) structure. Their mean diameter was 10-36 nm, increasing with increasing nickel chloride concentration or decreasing hydrazine concentration. When the concentration ratio of hydrazine to nickel chloride was above 40, the mean diameter approached a constant value. The magnetic measurement on a typical sample with a mean diameter of 12 nm showed that the resultant nickel nanoparticles were superparamagnetic due to their extremely small size. The saturation magnetization, remanent magnetization, and coercivity were 32 emu g^-1, 5.0 emu g^-1, and 40 Oe, respectively. Also, the magnetization was observed to increase with decreasing temperature. All the observed magnetic properties essentially reflected the nanoparticle's nature.