Insights Into Formation and Growth of Colloidal Multielement Alloy Nanoparticles in Solution through In Situ Liquid Cell TEM Study

The nucleation and growth of nanoparticles are critical processes determining the size, shape, and properties of resulting nanoparticles. However, understanding the complex mechanisms guiding the formation and growth of colloidal multielement alloy nanoparticles remains incomplete due to the involvement of multiple elements with different properties. This study investigates in situ colloidal synthesis of multielement alloys using transmission electron microscopy (TEM) in a liquid cell. Two different pathways for nanoparticle formation in a solution containing Au, Pt, Ir, Cu, and Ni elements, resulting in two distinct sets of particles are observed. One set exhibits high Au and Cu content, ranging from 10 to 30 nm, while the other set is multi-elemental, with Pt, Cu, Ir, and Ni, all less than 4 nm. The findings suggest that, besides element miscibility, metal ion characteristics, particularly reduction rates, and valence numbers, significantly impact particle composition during early formation stages. Density functional theory (DFT) simulations confirm differences in nanoparticle composition and surface properties collectively influence the unique growth behaviors in each nanoparticle set. This study illuminates mechanisms underlying the formation and growth of multielement nanoparticles by emphasizing factors responsible for chemical separation and effects of interplay between composition, surface energies, and element miscibility on final nanoparticles size and structure. Real-time observation of colloidal nanoparticles synthesis inside a homogenous equimolar solution of multi-metal ions reveals the formation of two sets of alloy nanoparticles through different nucleation and growth pathways. The first set of particles are 10-30 nm Au-Cu binary alloys, and the second set consists of sub-4 nm Pt-Cu-Ir-Ni multielement alloys. This study highlights the factors responsible for the chemical separation of certain elements in the mixture and explores how the constituent elements of the alloy impact the size and structure of the final nanoparticles.image