Search Results (6)

TiO₂ nanotubes (TiO₂NTs) are beneficial for photogenerated electron separation in photocatalysis. In order to improve the utilization rate of TiO₂NTs in the visible light region, an effective method is to use Au_n cluster deposition-modified TiO₂NTs. It is of great significance to investigate the mechanism of Au_n clusters supported on TiO₂NTs to strengthen its visible-light response. In this work, the structures, electronic properties, Mulliken atomic charge, density of states, band structure, and deformation density of Au_n (n = 1, 8, 13) clusters supported on TiO₂NTs were investigated by DMOL3. Based on published research results, the most stable adsorption configurations of Au_n (n = 1, 8, 13) clusters supported with TiO₂NTs were obtained. The adsorption energy increased as the number of Au adatoms increased linearly. The Au_n clusters supported on TiO₂NTs carry a negative charge. The band gaps of the three most stable structures of each adsorption system decreased compared to TiO₂NTs; the valence top and the conduction bottom of the Fermi level come mainly from the contribution of 5d and 6s-Au. The electronic properties of the 5d and 6s impurity orbitals cause valence widening and band gap narrowing. Full article

Using a modulated pulse power magnetron sputtering (MPP-MSP) coupled with a quadrupole mass spectrometer (Q-MS), intensive size-selected gold nanoclusters (Au_n) ranging from n = 5 to 40 in size are synthesized and soft landed onto a strontium titanate (STO) crystal surface as a co-catalyst for photocatalytic water splitting. The photocatalytic reactivity of the Au_n/STO is investigated by measuring the photocurrent density of the sample under visible light radiation. It is found that the Au_n co-catalysts enable the visible light response of the Au_n/STO photocatalyst. The photocurrent density is sensitively dependent on the size of the Au_n on the STO, and Au₁₆ exhibits its maximum photocurrent under visible light. The underlying physics of the size-specific photocurrent are explained in terms of the size-dependent electron affinity of Au_n. Full article

Gold nanoclusters (Au_n NCs) exhibit a size-specific electronic structure unlike bulk gold and can therefore be used as catalysts in various reactions. Ligand-protected Au_n NCs can be synthesized with atomic precision, and the geometric structures of many Au_n NCs have been determined by single-crystal X-ray diffraction analysis. In addition, Au_n NCs can be doped with various types of elements. Clarification of the effects of changes to the chemical composition, geometric structure, and associated electronic state on catalytic activity would enable a deep understanding of the active sites and mechanisms in catalytic reactions as well as key factors for high activation. Furthermore, it may be possible to synthesize Au_n NCs with properties that surpass those of conventional catalysts using the obtained design guidelines. With these expectations, catalyst research using Au_n NCs as a model catalyst has been actively conducted in recent years. This review focuses on the application of Au_n NCs as an electrocatalyst and outlines recent research progress. Full article

Au clusters with the precise numbers of gold atoms, a novel nanogold material, have recently attracted increasing interest in the nanoscience because of very unique and unexpected properties. The unique interaction and electron transfer between gold clusters and reactants make the clusters promising catalysts during organic transformations. The Au_nL_m nanoclusters (where L represents organic ligands and n and m mean the number of gold atoms and ligands, respectively) have been well investigated and developed for selective oxidation, hydrogenation, photo-catalysis, and so on. These gold clusters possess unique frameworks, providing insights into the catalytic processes and an excellent arena to correlate the atomic frameworks with their intrinsic catalytic properties and to further investigate the tentative reaction mechanisms. This review comprehensively summarizes the very latest advances in the catalytic applications of the Au nanoclusters for the C−C cross-coupling reactions, e.g., Ullmann, Sonogashira, Suzuki cross-couplings, and A³−coupling reactions. It is found that the proposed catalytically active sites are associated with the exposure of gold atoms on the surface of the metal core when partial capping organic ligands are selectively detached under the reaction conditions. Finally, the tentative catalytic mechanisms over the ligand-capped Au nanoclusters and the relationship of structure and catalytic performances at the atomic level using computational methods are explored in detail. Full article

The reducing and capping sites along with their local structure impact photo properties of the red bovine serum albumin-capped Au nanocluster (BSA-AuNC), however, they are hard to identify. We developped a workflow and relevant techniques using mass spectrometry (MS) to identify the reducing and capping sites of BSA-AuNCs involved in their formation and fluorescence. Digestion without disulfide cleavages yielded an Au core fraction exhibiting red fluorescence and [Au_nS_m] ion signals and a non-core fraction exhibiting neither of them. The core fraction was identified to mainly be comprised of peptides containing cysteine residues. The fluorescence and [Au_nS_m] signals were quenched by tris(2-carboxyethyl)phosphine, confirming that disulfide groups were required for nanocluster stabilization and fluorescence. By MS sequencing, the disulfide pairs, C75–C91/C90–C101 in domain IA, C315–C360/C359–C368 in domain IIB, and C513–C558/C557–C566 in domain IIIB, were identified to be main capping sites of red AuNCs. Peptides containing oxidized cysteines (sulfinic or cysteic acid) were identified as reducing sites mainly in the non-core fraction, suggesting that disulfide cleavages by oxidization and conformational changes contributed to the subsequent growth of nanoclusters at nearby intact disulfide pairs. This is the first report on precise identification of the reducing and capping sites of BSA-AuNCs. Full article

The emphasis of this review is atomically monodisperse Au_n nanoclusters catalysts (n = number of metal atom in cluster) that are ideally composed of an exact number of metal atoms. Au_n which range in size from a dozen to a few hundred atoms are particularly promising for nanocatalysis due to their unique core-shell structure and non-metallic electronic properties. Au_n nanoclusters catalysts have been demonstrated to exhibit excellent catalytic activity in hydrogenation and oxidation processes. Such unique properties of Au_n significantly promote molecule activation by enhancing adsorption energy of reactant molecules on catalyst surface. The structural determination of Au_n nanoclusters allows for a precise correlation of particle structure with catalytic properties and also permits the identification of catalytically active sites on the gold particle at an atomic level. By learning these fundamental principles, one would ultimately be able to design new types of highly active and highly selective gold nanocluster catalysts for a variety of catalytic processes. Full article