Preparation of highly positively charged silver nanoballs and their stability

Reduction of AgNO3 by sodium borohydride in the presence of quaternary ammn oium disulfide gave a stable aqueous dispersion of silver nanoballs. The ob tained Ag nanoballs showed a strong plasmon absorption peak, indicating tha t they consisted of metal Ag, although the counteranion of the stabilizer w as Br-. They are obtainable in a powder form by reprecipitation and can be kept without any change under air. Redispersibility of the obtained powder into water was high, and even in slightly acidic condition, they can be kep t stably for more than a week. The stabilization mechanism is also discusse d.