Controlled growth of silver nanoparticles in a hydrothermal process

A two-step synthesis was used to control the shape of silver nanoparticles. First, a few spherical silver nanoparticles, ∼10 nm in size, were prepared via reduction of Ag⁺ ions in aqueous Ag(NH₃)₂NO₃ by poly(N-vinyl-2-pyrrolidone) (PVP). Then, in a subsequent hydrothermal treatment, the remaining Ag⁺ ions were reduced by PVP into polyhedral nanoparticles, or larger spherical nanoparticles formed from the small spherical seed silver nanoparticles in the first step. The morphology and size of the resultant particles depend on the hydrothermal temperature, PVP/Ag molar ratio and concentration of Ag⁺ ions. By using UV–visible spectroscopy (UV–vis), transmission electron microscopy (TEM) and powder X-ray diffraction (XRD), the possible growth mechanism of the silver nanoparticles was discussed.