Negative‐Imaging of Citrate Layers on Gold Nanoparticles by Ligand‐Templated Metal Deposition: Revealing Surface Heterogeneity

Surface heterogeneity of a metal nanoparticle is typically regarded as boundary defects and various crystalline facets. While organic capping ligands of a single type are assumed to be homogeneously distributed on the nanoparticle surface, heterogeneous surface coverage of citrate molecules on indiv...

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Bibliographic Details
Published in:Particle & particle systems characterization 2019-01, Vol.36 (1), p.n/a
Main Author: Park, Jong‐Won
Format: Article
Language:English
Subjects:
Adatoms
alcoholic hydroxyl groups
Anions
Chemical reactions
Citrates
Citric acid
Crystal defects
Deposition
Epitaxial growth
Gold
gold adatoms
Heterogeneity
Hydroxyl groups
Infrared spectroscopy
IR spectroscopy
Ligands
molecule–nanoparticle interactions
nanoparticle surfaces
Nanoparticles
Organic chemistry
Platinum
Transmission electron microscopy
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Summary:Surface heterogeneity of a metal nanoparticle is typically regarded as boundary defects and various crystalline facets. While organic capping ligands of a single type are assumed to be homogeneously distributed on the nanoparticle surface, heterogeneous surface coverage of citrate molecules on individual facets of gold nanoparticles (AuNPs) is revealed. Pt metallic clusters with 2 nm in diameter, epitaxially grown on the surface of AuNPs by chemical reaction and imaged by high‐resolution transmission electron microscopy, are utilized as negative‐imaging probes for densely packed adlayers where the underneath gold surface may not be accessible for Pt deposition. At pH > 5.0, citrate anions form only a loosely packed layer. At pH 4.5, citrates and citric acids form both loosely packed and densely packed layers that appear phase separated, and the densely packed domain as small as 5 nm × 5 nm is likely composed of fully protonated citric acids. IR spectra indicate that citric acid binds to a surface Au adatom through the oxygen atom of the central hydroxyl group, and similarly, citrate anions bind to Au adatoms through the carboxylate oxygen atom. This study also reveals the role of Au adatom in the adsorption of citrate species on the metallic surface of AuNPs. Gold adatoms present on the surface of gold nanoparticles interact with citrate anions and citric acids.
ISSN:0934-0866
1521-4117
DOI:10.1002/ppsc.201800329