Kinetic study of gold nanoparticle growth in solution by Brust-Schiffrin reaction.

Nanoparticle growth in solution is a rather complicated process governed by many thermodynamic and kinetics factors. A better understanding of nanoparticle growth kinetics is of primary importance leading to a better control on the nanoparticle size and size distribution. In this work we conducted both experimental and theoretical study on the kinetics of Brust-Schiffrin reaction for the synthesis of gold nanoparticles. Using an excessive amount of thiol ligands, the nanoparticle growth was stopped at different intermediate stages. Our study revealed and confirmed that the reproducibility of Brust-Schiffrin reaction for the synthesis of gold nanoparticles with diameters around 2 nm is rather poor due to the intrinsic complexity of this two-phase reaction. The analysis results of each intermediate product by TEM showed that nanoparticles grew very rapidly at the early stage of reaction and reached a maximum value of 2.6 nm at reaction time of around 10 minutes. Further increase of reaction time led to a decrease of nanoparticle size. In addition to the experimental study, we proposed a kinetic model for nanoparticle growth in solution by assuming that the nanoparticle core expands through incremental addition of gold atoms to the existing nanoparticle nuclei. This model not only gave a relatively good fitting to the experimental data, but also provided further insight into the nucleation and core expansion stage of the nanoparticle growth, which had not been revealed in previous modeling studies.