Highly Heterogeneous Polarization and Solvation of Gold Nanoparticles in Aqueous Electrolytes

Abstract

The performance of gold nanoparticles (NPs) in applications depends critically on the structure of the NP−solvent interface, at which the electrostatic surface polarization is one of the key characteristics that affects hydration, ionic adsorption, and electrochemical reactions. Here, we demonstrate significant effects of explicit metal polarizability on the solvation and electrostatic properties of bare gold NPs in aqueous electrolyte solutions of sodium salts of various anions (Cl − , BF 4 − , PF 6 − , nitrophenolate, and 3-and 4-valent hexacyanoferrate), using classical molecular dynamics simulations with a polarizable core−shell model for the gold atoms. We find considerable spatial heterogeneity of the polarization and electrostatic potentials on the NP surface, mediated by a highly facet-dependent structuring of the interfacial water molecules. Moreover, ion-specific, facet-dependent ion adsorption leads to considerable alterations of the interfacial polarization. Compared to nonpolarizable NPs, surface polarization modifies water local dipole densities only slightly but has substantial effects on the electrostatic surface potentials and leads to significant lateral redistributions of ions on the NP surface. Besides, interfacial polarization effects cancel out in the far field for monovalent ions but not for polyvalent ions, as anticipated from continuum "image-charge" concepts. Far-field effective Debye−Huckel surface potentials change accordingly in a valence-specific fashion. Hence, the explicit charge response of metal NPs is crucial for the accurate description and interpretation of interfacial electrostatics (e.g., for charge transfer and interfacial polarization in catalysis and electrochemistry).

Effects of surface rigidity and metallicity on dielectric properties and ion interactions at aqueous hydrophobic interfaces

“…In particular, we observe only marginal differences in the profiles between metallic and nonmetallic graphite, in agreement with previous reports: [51][52][53][54] A slightly stronger orientation of the first water layer on metallic graphite can be deduced from the larger hydrogen number density for z < 0.05 nm in Fig. 5(d) and from the more negative average cos(θ) close to the GDS for z < 0.15 nm in Fig.…”

Unexpectedly High Capacitance of the Metal Nanoparticle/Water Interface: Molecular‐Level Insights into the Electrical Double Layer

“… [29] The high capacitance is attributed to the specific adsorption/solvation that the ions adopt at the interface with a strongly metallic Au electrode. In agreement, another recent theoretical study on Au nanoparticles has found that specific ion adsorption provides significant effects on the induced polarization of the polarizable nanoparticle surface, [30] which has substantial effects on the electrostatic surface potentials and work function [31] and, thus, on the EDL capacitance.…”

“…[5] However,avery recent study on gold-aqueous sodium chloride interfaces demonstrates the influence of the parameterization of the electrostatic parameters on the electrode/ electrolyte properties and shows that larger differential capacitances up to about 125 mFcm À2 can be obtained for strongly metallic electrodes by changing the width of the Gaussian charge distribution used to represent the atomic charges of the gold surface. [29] Theh igh capacitance is attributed to the specific adsorption/solvation that the ions adopt at the interface with astrongly metallic Au electrode.In agreement, another recent theoretical study on Au nanoparticles has found that specific ion adsorption provides significant effects on the induced polarization of the polarizable nanoparticle surface, [30] which has substantial effects on the electrostatic surface potentials and work function [31] and, thus,ont he EDL capacitance.…”

Multiscale Modeling of Bio-Nano Interactions of Zero-Valent Silver Nanoparticles

“…The existence of charged ionic adlayers next to the NP surface suggests that adsorption patterns for biomolecules can be significantly impacted, especially when higher ion concentrations and polyvalent ions are present in the media as a result of interfacial polarization alterations predicted for polarizable NPs (e.g., noble metals). 73 …”

“…The existence of charged ionic adlayers next to the NP surface suggests that adsorption patterns for biomolecules can be significantly impacted, especially when higher ion concentrations and polyvalent ions are present in the media as a result of interfacial polarization alterations predicted for polarizable NPs (e.g., noble metals). 73 Computed PMF profiles (shown in Figures 4 and S1 in the Supporting Information) had no adsorption minima next to the NP surface (SSD < 0.15 nm), suggesting that adsorbates were not able to expel water molecules from the first hydration shell around the AgNP. However, they were able to penetrate through the second interfacial water layer.…”