Abstract
We report a comprehensive study of aqueous halide adsorption on nanoparticles of gold and palladium that addresses several limitations hampering the use of atomistic modeling as a tool for understanding and improving wet-chemical synthesis and related applications. A combination of thermodynamic modeling with density functional theory (DFT) calculations and experimental data is used to predict equilibrium shapes of halide-covered nanoparticles as a function of the chemical environment. To ensure realistic and experimentally relevant results, we account for solvent effects and include a large set of vicinal surfaces, several adsorbate coverages as well as decahedral particles. While the observed stabilization is not significant enough to result in thermodynamic stability of anisotropic shapes such as nanocubes, non-uniformity in the halide coverage indicates the possibility of obtaining such shapes as kinetic products. With regard to technical challenges, we show that inclusion of surface-solvent interactions lead to qualitative changes in the predicted shape. Furthermore, accounting for non-local interactions on the functional level yields a more accurate description of surface systems.
Highlights
Wet-chemical synthesis has emerged as one of the primary routes for obtaining metal nanoparticles (NPs) with tailored properties
The set of XC functionals includes local density approximation (LDA), PBE, and Perdew-Burke-Ernzerhof for solids (PBEsol), all of which are commonly used in surface calculations
Before presenting any results related to halide adsorption, we note that typical wet-chemical synthesis concentrations are on the order of 0.01–1 M
Summary
Wet-chemical synthesis has emerged as one of the primary routes for obtaining metal nanoparticles (NPs) with tailored properties. The propensity of halides to adsorb is highly sensitive to the atomic structure of the surface, resulting in facet-dependent adlayer structures Since this can in turn stabilize different NP morphologies [5,6,7] and guide NP growth, halides are commonly considered as “shape-directing agents.”. Experiments take place in a complex chemical environment where the metal precursor commingles with other reactants such as surfactants and reducing agents, which is often neglected completely in modeling work This holds true in particular for density functional theory (DFT) calculations, which despite being the main workhorse of computational surface science face technical challenges, e.g, with respect to obtaining accurate surface energies [17,18] and accounting for solvation effects [19,20,21]. Additional material, including a detailed description of the modeling approach as well as complementary results, is presented in the Supplemental Material (SM) [34]
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