Gold nanoparticles with different capping systems: an electronic and structural XAS analysis.
Gold nanoparticles (NPs) have been prepared with three different capping systems: a tetralkylammonium salt, an alkanethiol, and a thiol-derivatized neoglycoconjugate. Also gold NPs supported on a porous TiO(2) substrate have been investigated. X-ray absorption spectroscopy (XAS) has been used to determine the electronic behavior of the different capped/supported systems regarding the electron/hole density of d states. Surface and size effects, as well as the role of the microstructure, have been also studied through an exhaustive analysis of the EXAFS (extended X-ray absorption fine structure) data. Very small gold NPs functionalized with thiol-derivatized molecules show an increase in d-hole density at the gold site due to Au-S charge transfer. This effect is overcoming size effects (which lead to a slightly increase of the d-electron density) for high S:Au atomic ratios and core-shell microstructures where an atomically abrupt Au-S interface likely does not exist. It has been also shown that thiol functionalization of very small gold NPs is introducing a strong distortion as compared to fcc order. To the contrary, electron transfer from reduced support oxides to gold NPs can produce a higher increase in d-electron density at the gold site, as compared to naked gold clusters.
López-Cartes
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Instituto de Ciencia de Materiales de Sevilla, and Grupo Carbohidratos, Laboratory of Glyconanotechnology IIQ, CSIC-Universidad Sevilla, Américo Vespucio nr. 49, 41092-Sevilla, Spain.
Rojas
T C
TC
Litrán
R
R
Martínez-Martínez
D
D
de la Fuente
J M
JM
Penadés
S
S
Fernández
A
A