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Ion-Specific Adsorption on Bare Gold (Au) Nanoparticles in Aqueous Solutions: Double-Layer Structure and Surface
Zhujie Li1, Victor G Ruiz2, Matej Kanduč3
1Applied Theoretical Physics-Computational Physics, Physikalisches Institut, Albert-Ludwigs-Universität Freiburg, Freiburg D-79104, Germany.
Langmuir : the ACS Journal of Surfaces and Colloids
|November 3, 2020
Summary
Molecular dynamics simulations reveal facet-selective ion adsorption on gold nanoparticles (NPs). Different anions show preferences for specific NP facets, influencing solvation and electrostatic properties, with implications for nanoparticle behavior in solutions.
Area of Science:
- Computational Chemistry
- Materials Science
- Physical Chemistry
Background:
- Understanding the behavior of bare gold nanoparticles (Au NPs) in aqueous solutions is crucial for their applications.
- Ion adsorption at the nanoparticle-electrolyte interface significantly influences NP stability and reactivity.
- The interplay between NP facet structure, ion chemistry, and solvation effects is complex and requires detailed investigation.
Purpose of the Study:
- To investigate the solvation and electrostatic properties of bare gold nanoparticles (1-2 nm) in various aqueous electrolyte solutions.
- To determine the facet selectivity of ion adsorption on different gold nanoparticle surfaces.
- To calculate effective surface charges and potentials and their dependence on ionic strength.
Main Methods:
- Classical molecular dynamics (MD) simulations using nonpolarizable models.
- Simulation of gold nanoparticles in contact with aqueous solutions of sodium salts with diverse anions (Cl-, BF4-, PF6-, Nip-, HCF).
- Analysis of ion adsorption, water structure, electrostatic potentials, and effective surface charges.
Main Results:
- Significant facet selectivity observed: anions like Cl- and HCF3- favor 'edgy' (100) and (110) facets, while BF4-, PF6-, and Nip- prefer flat (111) facets.
- Nitrophenolate (Nip-) strongly adsorbs on (111) facets, significantly perturbing the water monolayer.
- Calculated effective surface potentials are negative, ranging from -10 mV (NaCl) to -80 mV (NaNip), consistent with experimental zeta potentials.
Conclusions:
- The facet structure of gold nanoparticles dictates ion adsorption behavior and influences interfacial electrostatics.
- Anion chemistry plays a key role in determining adsorption strength and location on Au NP facets.
- The study provides a framework for predicting and understanding nanoparticle-electrolyte interactions using molecular dynamics and electrostatic modeling.
