A rapid, straight-forward method for controlling the morphology of stable silver nanoparticles

A rapid, straight-forward method for the preparation of silver colloidal solutions of various colours has been developed. This is based on the reduction of silver ions by ascorbic acid in the presence of citrate-stabilized silver seeds, additional trisodium citrate and a polymer such as polyvinylpyrrolidone. The colour of the sol is controlled by varying the concentration of only one reagent, namely the trisodium citrate. TEM studies show that this effect is due to changes in morphology of the particles. Working at temperatures above 50 degrees C yields well-defined triangular plates, which are stable in the reaction medium. Samples prepared at lower temperatures and left in the reaction medium experience etching and a consequent change in particle shape. The mechanisms of the initial particle growth and the etching process are discussed.