Abstract
In this study, silver nanoparticles were synthesized by seed-mediated growth method, following the procedures described by Jana et al. In seed-mediated growth method, it starts with the synthesis of silver nano-seeds using chemical reduction of a silver salt with a strong reducing agent such as sodium borohydride in the presence of AOT as a capping agent to prevent particle growth. The synthesized silver nano-seeds are 3~5 nm in diameter and served as the seeds to grow more anisotropic nanostructures. These silver nano-seeds were added in the growth solution containing more silver salt, ascorbic acid (weak reducing agent) and cetyltrimethylammonium bromide (CTAB). The effects of various processing parameters on the morphology and uniformity of silver nanoparticles were investigated by UV-Vis spectroscopy and scanning electron microscopy. Preparation of silver nanoparticles by seed-mediated methods generally yielded a wide range of sizes and morphologies. At lower nano-seed concentration, longer silver nanorods can be produced. Increase the reaction temperature led to a decrease of aspect ratio of nanorods. When the pH of solution was increased by adding NaOH, the reducing power of ascorbic acid was increased. The high pH of the reaction solution caused short nanorods to form and the low pH might induce the formation of longer nanowires. But if the pH is too low, silver ions will not be reduced. The concentration of CTAB also has significant effect for low seed concentration cases. When the concentration of CTAB was vary law (a few mM), small irregular silver nanoparticles would be synthesized. Few cubic particles of micron size were synthesized at CTAB concentrations around 20 mM. On the other hand, nano-seeds annealed at higher temperature were also used and quite large silver nanoplates were synthesized.