Gold Nanoparticles Stabilized with Aromatic Thiols: Interaction at the Molecule–Metal Interface and Ligand Arrangement in the Molecular Shell Investigated by SR-XPS and NEXAFS

Abstract

Small gold nanoparticles capped with 4trimethylsilylethynyl-1-acetylthiobenzene (SEB) were prepared with spherical shape and different mean sizes (5−8 nm). The functionalized gold nanoparticles (AuNPs-SEB) were deposited onto TiO 2 substrates, and the interaction at the molecule−gold interface, the molecular layer thickness, and the ligand organization on the surface of Au nanospheres were investigated by means of synchrotron radiation induced X-ray photoelectron spectroscopy (SR-XPS) and angular dependent near edge X-ray absorption spectroscopy (NEXAFS) at the C K-edge. In order to obtain better insight into the molecular shell features, the same measurements were also carried out on a self-assembling monolayer (SAM) of SEB anchored on a "flat" gold surface (Au/Si(111) wafer). The comparison between angular dependent NEXAFS spectra collected on the self-assembling monolayer and AuNPs-SEB allowed for successfully probing the molecular arrangement of SEB molecules on the gold nanospheres surface. Furthermore, DFT calculations on the free SEB molecule as well as bonded to a small cluster of gold atoms were developed. The comparison with experimental results allowed better understanding of the spectroscopic signatures in the experimental absorption spectra and rationalization of the molecular organization in the SAM, NPs having a thin molecular shell, and NPs covered by a thick layer of ligands.

Production of monolayer-rich gold-decorated 2H–WS2 nanosheets by defect engineering

“…2i, bottom), an additional doublet can be discerned at a 1 eV lower binding energy and is attributed to S-Au bonds. 40,41 In contrast to the WS 2 reference sample (Fig. 2j, top), a clear signature of Au 0 (at a binding energy of 84 eV) is detected in the Au4f core level spectra of the l-WS 2 -Au4.5 stock (Fig.…”

Untangling the Role of the Capping Agent in Nanocatalysis: Recent Advances and Perspectives

“…It has been observed that the revealed trend in spectral shifts followed the order Au-S (soft-soft) > Au-N (soft-borderline) > Au-O (soft-hard) interaction, in accordance with HSAB theory. The strong interaction between Au and thiols has also been confirmed by X-ray photoelectron spectroscopy with synchrotron radiation (SR-XPS) [47]. The relative amounts of Au and S atoms with different coordinations (i.e., bulk Au atoms, surface Au atoms binding thiol, S atoms chemisorbed on Au, S atoms physisorbed and free thiolate groups) can be quantified by discriminating the corresponding contributions to S 2p and Au 4f signals.…”

“…The relative amounts of Au and S atoms with different coordinations (i.e., bulk Au atoms, surface Au atoms binding thiol, S atoms chemisorbed on Au, S atoms physisorbed and free thiolate groups) can be quantified by discriminating the corresponding contributions to S 2p and Au 4f signals. By evaluating the signal intensity ratios, Polzonetti et al [47] concluded that about 10% of total gold atoms (bulk and surface) are covalently bonded to thiols. In addition, the presence of physisorbed thiols, probably constituting a second layer, has been observed, demonstrating that different interactions are possible at the metal-ligand interphase.…”

“…NEXAFS exploits the interaction between the polarized synchrotron radiation and the molecular antibonding orbitals with strong directional character, in order to determine the orientation of the molecular orbitals of an adsorbed molecule in respect to the surface [75] (for a more complete treatment of NEXAFS the reader could refer to [76]). As an example, by using angular dependent NEXAFS at the C K-edge, Polzonetti et al demonstrated that 4-trimethylsilylethynyl-1-acetylthiobenzene (SEB) arrange according to a flat-lying orientation on the Au NP surface in systems with a thin molecular shell [47].…”

DNA-stabilized bimetallic nanozyme and its application on colorimetric assay of biothiols

“…4d), which is attributable to thiophilic interactions of Cys with Au 0 /Pt 0 . The formation of Au-S/Pt-S bond is susceptible to reduce the electron density of Au 0 /Pt 0 accompanied by the observed shift of binding energy (Battocchio et al 2014;Bourg et al 2000). Therefore, it is obvious that both peroxidase-like activities and thiophilicities are intrinsic properties for Au 2 Pt 1 , Au 1 Pt 1 and Pt, respectively.…”