Nucleation in microemulsions: a case study of Ir-Pd nanoparticles

Area of Science:

• Materials Science
• Nanotechnology
• Computational Chemistry

Background:

• Surface segregation in bimetallic nanoparticles critically impacts their properties and catalytic activity.
• Iridium-Palladium (Ir-Pd) nanoparticles are synthesized, with expectations of a Palladium (Pd) shell due to reduction potential differences.
• Experimental data shows higher Iridium (Ir) fraction at the surface, contradicting theoretical predictions.

Purpose of the Study:

• To investigate the influence of nucleation rates on the surface composition of Ir-Pd nanoparticles.
• To determine the conditions under which Ir can achieve surface enrichment.
• To reconcile simulation predictions with experimental observations of Ir-Pd nanostructures.

Main Methods:

• Utilizing computer simulations to model metal distribution in Ir-Pd nanoparticles.
• Systematically studying the effect of critical nucleus size on nanostructure formation.
• Analyzing the impact of varying reduction rates and reactant concentrations on nucleation and segregation.

Main Results:

• The significant difference in reduction rates primarily drives core-shell formation, favoring Pd shells.
• Near critical nucleus concentrations, slower nucleation rates lead to increased Ir surface enrichment.
• This enrichment is linked to slow homoatomic and heteroatomic nucleation rates of Ir and Pd.
• At higher concentrations, nucleation is facilitated, diminishing the effect of critical nucleus size on segregation.

Conclusions:

• Nucleation kinetics play a crucial role in determining the surface composition of bimetallic nanoparticles, especially when reduction potentials differ significantly.
• The study successfully explains the observed Ir surface enrichment in Ir-Pd nanoparticles by considering nucleation rate variations.
• Simulation results align well with experimental findings, validating the model's predictive capability for nanoparticle synthesis.