Preparation of Ni nanoparticles by liquid-phase reduction to fabricate metal nanoparticle-polyimide composite films

Nickel-nanoparticle-containing polyimide composite films were prepared by liquid-phase reduction of Ni²⁺ ions with potassium borohydride (KBH₄). The nanoparticles were amorphous with diameters of approximately 10-20 nm, depending on the KBH₄ concentration and reduction temperature. At high KBH₄ concentrations, the nanoparticles appeared to contain various nickel boride species. The number of nanoparticles and Ni content both increased upon repeated adsorption/reduction of Ni²⁺ ions, where the particle growth was inhibited by the rigid polymer chain and the formation of smaller particles was favored.