Precipitation of Silver Particles with Controlled Morphologies from Aqueous Solutions

Synthesis of silver particles with controlled morphologies enables their use in a variety of applications. Although several synthetic approaches have been developed to successfully modify the final particle shape, the underlying mechanism controlling the shape development is yet under extensive debate including the so-called classical and nonclassical theories of crystal growth. Here we explore the variation of silver morphologies as a function of reactant concentrations and pH, during reduction of silver nitrate with ascorbic acid in aqueous solutions. It was shown that enhancing the redox potential in solution via increasing the reductant concentration resulted in a stepwise change in morphology from polyhedral to hopper and dendritic particles, whereas the reverse order was observed when the redox reaction was repressed by decreasing the solution pH. Spherulites were obtained under very high driving force that was satisfied via either high precursor concentrations or high pH. Our results demonstrate the strong correlation of particle morphology with solution supersaturation, which was elucidated within the framework of crystallographic and non-crystallographic branching mechanisms for the formation of dendrites and polycrystalline spherulites, respectively.