The Chemistry of the Sulfur-Gold Interface: In Search of a Unified Model

Instituto de Investigaciones Fisicoquímicas Teóricas y Aplicadas, Universidad Nacional de La Plata - CONICET, Argentina.
Accounts of Chemical Research (Impact Factor: 22.32). 03/2012; 45(8):1183-92. DOI: 10.1021/ar200260p
Source: PubMed


Over the last three decades, self-assembled molecular films on solid surfaces have attracted widespread interest as an intellectual and technological challenge to chemists, physicists, materials scientists, and biologists. A variety of technological applications of nanotechnology rely on the possibility of controlling topological, chemical, and functional features at the molecular level. Self-assembled monolayers (SAMs) composed of chemisorbed species represent fundamental building blocks for creating complex structures by a bottom-up approach. These materials take advantage of the flexibility of organic and supramolecular chemistry to generate synthetic surfaces with well-defined chemical and physical properties. These films already serve as structural or functional parts of sensors, biosensors, drug-delivery systems, molecular electronic devices, protecting capping for nanostructures, and coatings for corrosion protection and tribological applications.

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    • "The S 2p spectra obviously differ from those reported for gold sulfide materials [23–25,35], which exhibit a major line at about 162.5 eV and two weaker ones at about 163.2 eV and 161.5 eV. The latter spectra suggest substantial S–S bonding, alike to sulfur adsorbed onto metallic gold [26] [27], and it was proposed that the surface layer of gold sulfides decomposed yielding Au "
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    • "However, such agents might become poison for the Stöber silica doped/coated/supported gold nanoparticles especially when they are applied in the catalysis field that is another renowned field of gold. Take the thiol-contained agent for instance, the S component as the impurity of the agents can be strongly adsorbed onto gold nanoparticles [24], thus hinders the adsorption of reactants and even changes the sample structure [25]. Besides, the removal of these agents requires higher temperature [26] that is undesired for the gold nanoparticles in the catalysis field. "
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    ABSTRACT: The homogeneous and tiny colloidal gold nanoparticles (2–4 nm) were utilized as the precursor and coated onto the non-porous Stöber silica by a facile method. For the first time, the coating process is fulfilled without either organosilanes or thiols compounds, which was invariably applied for Stöber silica to fix the gold particles and thus limited the application of the gold material in catalysis field. For better understanding, the mechanism of the synthesis process was further analyzed. During the coating process, the gold nanoparticles protected by polyvinyl alcohol (PVA) surrounded with hydroxyl species were higher dispersed on the surface of Stöber silica. The following calcination facilitated the combining removal of hydroxyl species in both PVA and silica structure, and the gold nanoparticles anchored by residual hydroxyl species on the surface of Stöber silica. Major of the small particles about 3 nm remained their sizes even after calcination, which was just the satisfied size for some reactions such as CO oxidation. This simple and environmental synthesis method provided an available strategy for synthesizing gold catalysts with very small and orderly sizes that can be used for further investigation in the catalysis field.
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    ABSTRACT: A combination of Polarization Modulation Infrared Reflection Absorption Spectroscopy (PMIRRAS) under electrochemical control, Electrochemical Scanning Tunneling Microscopy (ECSTM) and Molecular Dynamics (MD) simulations has been used to shed light on the reductive desorption process of dodecanethiol (C12) and octadecanethiol (C18) SAMs on gold in aqueous electrolytes. Experimental PMIRRAS, ECSTM and MD simulations data for C12 desorption are consistent with formation of randomly distributed micellar aggregates stabilized by Na(+) ions, coexisting with a lying-down phase of molecules. The analysis of pit and Au island coverage before and after desorption is consistent with the thiolate-Au adatoms models. On the other hand, PMIRRAS and MD data for C18 indicate that the desorbed alkanethiolates adopt a Na(+) ion-stabilized bilayer of interdigitated alkanethiolates, with no evidence of lying down molecules. MD simulations also show that both the degree of order and tilt angle of the desorbed alkanethiolates change with the surface charge on the metal, going from bilayers to micelles. These results demonstrate the complexity of the alkanethiol desorption in the presence of water and the fact that chain length and counterions play a key role in a complex structure.
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