Role of the environment in the stability of anisotropic gold particles

Abstract

Despite the long-lasting interest in the synthesis control of nanoparticles (NPs) in both fundamental and applied nanosciences, the driving mechanisms responsible for their size and shape selectivity in an environment (solution) are not completely understood, and a clear assessment of the respective roles of equilibrium thermodynamics and growth kinetics is still missing. In this study, relying on an efficient atomistic computational approach, we decipher the dependence of energetics, shapes and morphologies of gold NPs on the strength and nature of the metal-environment interaction. We highlight the conditions under which the energy difference between isotropic and elongated gold NPs is reduced, thus prompting their thermodynamic coexistence. The study encompasses both monocrystalline and multi-twinned particles and extends over size ranges particularly representative of the nucleation and early growth stages. Computational results are further rationalized with arguments involving the dependence of facet and edge energies on the metal-environment interactions. We argue that by determining the abundance and diversity of particles nucleated in solution, thermodynamics may constitute an important bias influencing their final shape. The present results provide firm grounds for kinetic simulations of particle growth.

Twinned Gold Nanoparticles under Growth: Bipyramids Shape Controlled by Environment

“…For each initial configuration, quenched molecular dynamics runs were performed under conditions that preserve their shape and symmetry. In line with the conclusions of our recent study, we have found two sets of parameters (ϵ, p ) for which the reduction of NP surface and edge energies due to the interaction with the environment diminishes drastically the stability gap between elongated particles and the isotropic decahedral seeds (i-Dh).…”

“…The difference Z B – Z i between the coordination number Z B in the bulk ( Z B = 12 for gold fcc) and the Z i of an atom i is equal to the number of free bonds available to bind to species in the environment. The pair of positive parameters (ϵ, p ) defines the strength and the nature of the gold–environment interaction. , …”

“…The pair of positive parameters (ϵ, p) defines the strength and the nature of the gold−environment interaction. 47,49 In order to focus on gold pentatwinned nanostructures, a motif optimization technique 50,51 was used to generate families of closed-shell NPs in the size range 2500 < N < 3500 atoms, terminated by different proportions of {111}, {100}, {110}, {311}, and {210} facets. For each initial configuration, quenched molecular dynamics runs were performed under conditions that preserve their shape and symmetry.…”

Competitive Seeded Growth: An Original Tool to Investigate Anisotropic Gold Nanoparticle Growth Mechanism

“…For type I seeds, HRTEM images and fast Fourier transform (FFT) analysis reveal that a typical 2.1 nm particle adopt the SC structure with well-defined facets (Figure a). For highly symmetrical crystalline material like gold, thermodynamic equilibrium shape of the small-sized SC seed in vacuum is generally predicted as truncated octahedron by using the Wulff condition. , However, it has been recently demonstrated that Wulff conditions are insufficient to describe the structure when the surface and edge are strongly interacting with the environment, which is the case here in the presence of CTAB. This interaction could explain the stabilization of such small-sized SC seeds.…”

DFT-Assisted Spectroscopic Studies on the Coordination of Small Ligands to Palladium: From Isolated Ions to Nanoparticles

“…The metal reduction potential, the nature and concentration of precursors, the reducing agent, the solvent, the temperature, and the mass transfer phenomena have a considerable impact on the mechanisms of nucleation and growth. − In addition, capping agents are commonly used in solution-phase synthesis to stabilize MNPs and to prevent their aggregation. The capping agents are often selected from various types of molecules, such as thiols, amines, halides, carboxylic acids, phosphines, polymers, and surfactants. − Capping agents can play multiple roles including providing colloidal stabilization and acting as structure-directing agents. ,,− Furthermore, as with conventional ligands, the capping agents can coordinate metal centers during different stages from metal precursors to MNPs. During the synthesis process, the metal precursor is decomposed and reduced into metal atoms, which then aggregate and evolve toward the formation of clusters and then nanoparticles (NPs).…”