The synthesis of metal nanoparticles with good control over size, size distribution, and shape has attracted much attention due to their wide applications in the fields of catalysis, photonics, electronics, and medicine. Tailoring the nanoparticle size requires a thorough understanding of the mechanism and kinetics of nucleation and growth. However, due to the complex interactions of capping ligands with the metal precursor and nanoparticles, developing a robust kinetic model that can explain the chemistry of nucleation and growth has been a challenging task. In this work, we developed a novel kinetic model that captures the in-situ nucleation and growth kinetics of colloidal palladium (Pd) nanoparticles in the presence of trioctylphosphine (TOP) capping ligand. In-situ small angle X-ray scattering (SAXS), was used to measure the diameter and number of particles during the synthesis. Our kinetic model for the first time accounts separately for both the nucleation and growth events obtained from in-situ SAXS. This is achieved by fitting the time evolution of number of nanoparticles (nucleation event) and number of atoms in nanoparticles (both nucleation and growth events) simultaneously as opposed to fitting only the number of atoms in nanoparticles or the nanoparticles size as in previous models. Based on the results we show that nucleation is slow, while growth is fast. Our modeling results show that the capping ligands interaction with both the precursor and nanoparticle's surface are responsible for controlling the rates of nucleation (binding to precursor) and growth (binding to the nanoparticle surface). The modeling and experimental results demonstrate that the final size of the nanoparticles is governed by the growth/nucleation rate which can be tuned by the ligand type, concentration and/or type of solvent. Finally, our kinetic model was used to predict the final particle size under different ligands and precursor concentrations and we show excellent quantitative agreement between the predicted and experimentally measured nanoparticle sizes. Our new kinetic model takes into account the interactions of capping ligands with both precursor and particle's surface, which can be applied to other synthesis systems (i.e. different metals) and therefore can provide a powerful tool for predictive synthesis of colloidal nanoparticles.

Modeling the nucleation and growth of palladium nanoparticles in the presence of capping ligands

253rd National Meeting (2017)

The official archive and repository for all ACS Meetings & Expositions abstracts and select posters or presentations.