Gold Nanoparticles with Different Capping Systems:  An Electronic and Structural XAS Analysis

• Published in: The journal of physical chemistry. B 2005-05, Vol.109 (18), p.8761-8766
• Main Authors: López-Cartes, C, Rojas, T. C, Litrán, R, Martínez-Martínez, D, de la Fuente, J. M, Penadés, S, Fernández, A
• Format: Article
• Language: English
• ISSN: 1520-6106; 1520-5207
• DOI: 10.1021/jp050184+

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 TiO2 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.