Modified Finke-Watzky mechanisms for the two-step nucleation and growth of silver nanoparticles

In this work, a new modification was made on the Finke-Watzky mechanism for investigating the nucleation and growth steps in the synthesis of silver nanoparticles (AgNPs). UV-vis spectrophotometry and transmission electron microscopy evaluations proved that the former linear form of Finke-Watzky mechanism is not efficient for describing the nucleation and growth steps of AgNPs synthesis. In this manner, the Finke-Watzky mechanism was modified by considering a reversible pseudo first-order reaction for nucleation step. In addition, no assumptions were made in mathematical calculations related to the rate law which were previously adapted by the researchers in this field; i.e. [A](0) > [A] and k(2) [A] >> k(1). These considerations led to the development of a kinetic model that is more closely related to what really occurs within the synthesis system. Kinetics data were obtained in a well-known synthesis process of AgNPs namely as sodium borohydride reduction. Furthermore, it was elucidated that polyvinylpyrrolidone (PVP) retards both the nucleation and growth steps resulting in the isotropic growth of seeds; this effect subtly provides a tunable synthesis process for achieving desired size of AgNPs. Moreover, Fourier-transform infrared spectroscopy revealed that the nitrogen atoms present in the PVP molecules are responsible for the interaction of PVP with AgNPs.