Nickel nanoparticles including an aqueous solution including a nickel precursor, a surfactant, a hydrophobic solvent, and distilled water, the hydrophobic solvent being one or more compounds selected from the group consisting of hexane, cyclohexane, heptane, octane, isooctane, decane, tetradecane, hexadecane, toluene, xylene, 1-octadecene, and 1-hexadecene; a compound including hydrazine which is added to the aqueous solution to form a nickel-hydrazine complex; and a reducing agent added to the compound including the nickel-hydrazine complex.