Preparation of silver nanorods through the control of temperature and pH of reaction medium

Silver nanorods were prepared by seed-mediated growth method, following the procedures recently described by Jana et al. In seed-mediated growth method, small metal particles are prepared first and later used as seeds for the preparation of nanorods. The silver seeds were prepared by reduction of silver ions with sodium borohydride in the presence of sodium citrate dihydrate as stabilizer. These silver seeds were added into the solution containing more silver salt, an ascorbic acid (weak reducing agent) and a cetyltrimethylammonium bromide (CTAB). The effects of temperature and pH of solution on the morphology and uniformity of silver nanorods were investigated by UV-Vis spectroscopy, transmission electron microscopy (TEM). Increase of reaction temperature and pH led to a decrease of aspect ratio of silver nanorods and an increase of monodispersity. Also gold nanoshells have been synthesized by reacting aqueous HAuCl4 solutions with silver nanorods as solid templates.