Time dependence of nucleation and growth of silver nanoparticles

This paper describes a simple procedure based on the modified silver-mirror process for the preparation of colloidal silver quantum dots (diameter ≤7 nm). All reactions were monitored with respect to reaction time by using UV–visible studies to understand the growth kinetics and the influence of different [ammonia], [glucose] and temperature on the formation of silver nanoparticles. Shape of the reaction–time curves (sigmoid facing up and sigmoid facing down) strongly depend on the [NH3]. Glucose concentrations have no significant effect on the progress of the reaction. For the nucleation and growth processes, surface plasmon absorbance is directly proportional and increase–decrease with increasing [NH3], respectively. Transmission electron microscopy (TEM) results show that the quantum dots are aggregated in an irregular manner, resulting in the formation of branches-like structures of silver. The activation energy, enthalpy and entropy of activation have been evaluated. Mechanism consistent with the observed kinetics results has been suggested.