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Ion-specific Adsorption on Bare Gold (Au) Nanoparticles in aqueous Solution: Double-Layer Structure and Surface Potentials

preprint
revised on 16.09.2020 and posted on 17.09.2020 by Zhujie Li, Victor G. Ruiz, Matej Kanduč, Joachim Dzubiella
We study the solvation and electrostatic properties of bare gold (Au) nanoparticles (NPs) of 1-2 nm in size in aqueous electrolyte solutions of sodium salts of various anions with large physicochemical diversity (Cl-, BF4-, PF6-, Nip-(nitrophenolate), 3- and 4-valent hexacyanoferrate (HCF)) using nonpolarizable, classical molecular dynamics computer simulations. We find a substantial facet selectivity in the adsorption structure and spatial distribution of the ions at the Au-NPs: while sodium and some of the anions (e.g., Cl-, HCF3-) adsorb more at the `edgy' (100) and (110) facets of the NPs, where the water hydration structure is more disordered, other ions (e.g., BF4-, PF6-, Nip-) prefer to adsorb strongly on the extended and rather flat (111) facets. In particular, Nip-, which features an aromatic ring in its chemical structure, adsorbs strongly and perturbs the first water monolayer structure on the NP (111) facets substantially. Moreover, we calculate adsorptions, radially-resolved electrostatic potentials, as well as the far-field effective electrostatic surface charges and potentials by mapping the long-range decay of the calculated electrostatic potential distribution onto the standard Debye-Hückel form. We show how the extrapolation of these values to other ionic strengths can be performed by an analytical Adsorption-Grahame relation between effective surface charge and potential. We find for all salts negative effective surface potentials in the range from -10 mV for NaCl down to about -80 mV for NaNip, consistent with typical experimental ranges for the zeta-potential. We discuss how these values depend on the surface definition and compare them to the explicitly calculated electrostatic potentials near the NP surface, which are highly oscillatory in the ± 0.5 V range.

Funding

ERC 646659

Slovenian Research Agency (Contracts P1-0055 and J1-1701)

DFG INST 39/963-1 FUGG (bwForCluster NEMO)

History

Email Address of Submitting Author

zhujie.li@physik.uni-freiburg.de

Institution

University of Freiburg

Country

Germany

ORCID For Submitting Author

0000-0002-8509-2594

Declaration of Conflict of Interest

No conflict of interest

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