Abstract
Growths of silver nanoparticles are changed abruptly from sigmoid facing up to facing down with ammonia concentrations. For short reaction time, nucleation, absorbance is directly proportional to the ammonia concentrations.
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► Shape of the reaction–time curves changed abruptly with increasing ammonia concentrations. ► Silver nanoparticles with two distributions of size (≤7
nm and 20 nm) are formed. ► Quantum dots are aggregated in an irregular manner, resulting in the formation of branches-like silver. ► Glucose concentrations have no effect on the shape of the reaction–time curves.
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 [NH
3]. 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 [NH
3], 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.