Au Clusters Research Articles

Functional structures assembled based on Au clusters with practical applications.

The advancement of gold nanoclusters (Au NCs) has given rise to a new era in fabricating functional materials due to their controllable morphology, stable optical properties, and excellent biocompatibility. Assemblies based on Au NCs demonstrate significant potentiality in constructing multiple structures as acceptable agents in applications such as sensing, imaging technology, and drug delivery systems. In addition, the assembled strategies illustrate the integration mechanism between each component while facing material requirement. It is necessary to provide supplementary and comprehensive reviews on the assembled functional structures (based Au NCs), which hold promise for applications and could expand their functional range and potential applications. This review focuses on the assembled structures of Au NCs in combination with metals, metal oxides, and non-metal materials, which are intricately arranged through various interaction forces including covalent bonds and metal coordination, resulting in a diverse array of multifunctional Au NC assemblies. These assemblies have widespread applications in fields such as biological imaging, drug delivery, and optical devices. The review concludes by highlighting the challenges and future prospects of Au NC assemblies, emphasizing the importance of continued research to advance nanomaterial assembly innovation.

High-throughput screening of bifunctional catalysts for oxygen evolution/reduction reaction at the subnanometer regime.

The development of low-cost, stable, and highly efficient electrocatalysts for the bifunctional oxygen evolution reaction (OER) and oxygen reduction reaction (ORR) is crucial for advancing future renewable technologies. In this study, we systematically investigated the OER and ORR performance of subnano clusters across the 3d, 4d, and 5d transition metal (TM) series of varying sizes using first-principles calculations. The fluxional identity of these clusters in the subnanometer regime is reflected in their non-monotonic catalytic activity. We established a size-dependent scaling relationship between OER/ORR intermediates, leading to a reshaping of the activity volcano plot at the subnanometer scale. Our detailed mechanistic investigation revealed a shift in the apex of the activity volcano from the Pt(111) and IrO2 surfaces to the Au11 clusters for both OER and ORR. Late transition metal subnano clusters, specifically Au11, emerged as the best bifunctional electrocatalyst, demonstrating significantly lower overpotential values. Furthermore, we categorized our catalysts into three clusters and employed the Random Forest Regression method to evaluate the impact of non-ab initio electronic features on OER and ORR activities. Interestingly, d-band filling emerged as the primary contributor to the bifunctional activity of the subnano clusters. This work not only provides a comprehensive view of OER and ORR activities but also presents a new pathway for designing and discovering highly efficient bifunctional catalysts.

Computational insights into the zeolite-supported gold nanocluster-catalyzed ethanol dehydrogenation to acetaldehyde.

Zeolite-supported gold nanoclusters play increasingly important roles in heterogeneous catalysis and exhibit unique catalytic properties for ethanol dehydrogenation to acetaldehyde. Nevertheless, the reaction mechanism and potential roles of the zeolite-encapsulated gold nanoclusters during the catalytic process remain unclear. Herein, computational studies were carried out to gain mechanistic insights into ethanol dehydrogenation to acetaldehyde under both aerobic and anaerobic conditions catalyzed by a silicalite-1 zeolite-encapsulated Au3 cluster cation (Au3+-S1). The presence of O2 can significantly promote the ethanol dehydrogenation catalyzed by Au3+-S1. A feasible mechanistic pathway could be initiated via the O2 induced H-atom transfer (HAT) step from the hydrogen of the hydroxyl group to afford ethoxy and OOH radical species. Subsequently, the OOH induced second HAT from α-C-H of the ethoxy intermediate could follow to afford the acetaldehyde product. Moreover, the possible confinement and stabilization effect of the zeolite channels on the ethanol dehydrogenation reaction was discussed.

Na+ detection via brightening of synergistically originated noble metal nanoclusters.

Weakly fluorescent AuAg nanoclusters were obtained from glutathione, chloroauric acid, and silver nitrate aqueous solution under a modified hydrothermal method. Such glutathione-capped synergistically evolved clusters were obtained for the first time by employing our experimental conditions. Such weak fluorescence was made significantly brighter by employing Na+ and a Na+ sensor was obtained with a linear detection range of 10-5-5 × 10-9 M, while the limit of detection was 1.02 × 10-6 M. Na+ made the GSH matrix positively charged to stabilize AuAg clusters resulting in strong emissive properties. Furthermore, the effect of solvents, sunlight exposure, and temperature was gauged. Estimation of Na+ concentration was undertaken for natural water samples to demonstrate the practical utility of the designed nanosensor.

Tuning photoluminescence properties of Au clusters by surface modification and doping: lessons from case studies of icosahedral Au13

This review article focuses on the ubiquitous icosahedral Au13 core protected by organic ligands as a benchmark and derives empirical rules for tuning and enhancing photoluminescence properties through surface modification and heterometal doping.

Frame-by-frame observations of structure fluctuations in single mass-selected Au clusters using aberration-corrected electron microscopy.

The multi-dimensional potential energy surface (PES) of a nanoparticle, such as a bare cluster of metal atoms, controls both the structure and dynamic behaviour of the particle. These properties are the subject of numerous theoretical simulations. However, quantitative experimental measurements of critical PES parameters are needed to regulate the models employed in the theoretical work. Experimental measurements of parameters are currently few in number, while model parameters taken from bulk systems may not be suitable for nanosystems. Here we describe a new measurement methodology, in which the isomer structures of a single deposited nanocluster are obtained frame-by-frame in an aberration-corrected scanning transmission electron microscope (ac-STEM) in high angle annular dark field (HAADF) mode. Several gold clusters containing 309 ± 15 atoms were analysed individually after deposition from a mass-selected cluster source onto an amorphous carbon film. The main isomers identified are icosahedral (Ih), decahedral (Dh) and face-centred-cubic (fcc) (the bulk structure), alongside many amorphous (glassy) structures. The results, which are broadly consistent with static ac-STEM measurements of an ensemble of such clusters, open the way to dynamic measurements of many different nanoparticles of diverse sizes, shapes and compositions.

Characterisation of the morphology of surface-assembled Au nanoclusters on amorphous carbon.

In this study, aberration-corrected scanning transmission electron microscopy is employed to investigate the morphology of Au clusters formed from the aggregation of single atoms sputtered onto an amorphous carbon surface. The morphologies of surface-assembled clusters of N > 100 atoms are referenced against the morphologies of size-selected clusters determined from previously published results. We observe that surface-assembled clusters (at the conditions employed here) are approximately spherical in shape. The structural isomers of the imaged clusters have also been identified, and the distribution of structural types is broadly in agreement with those from size-selected cluster deposition sources. For clusters of approximately 147 atoms, we find a preference for icosahedra over decahedra and truncated octahedra, but at this size there is a high proportion of unidentified/amorphous structures. At around 309 atoms, we find a preference for decahedra over icosahedra and truncated octahedra, but over half the structures remain unidentifiable/amorphous. For sizes above approximately 561 atoms we are able to identify most of the structures, and find decahedra are still the most favoured, although in competition with single-crystal fcc morphologies. The similarity in structure between surface-assembled and size-selected clusters from a cluster source provides evidence of the relevance of size-selected cluster studies to clusters synthesised by other, industrially relevant, methodologies.

Ultra small gold nanoclusters supported on two-dimensional bismuth selenium nanosheets for synergistic photothermal and photodynamic tumor therapy.

Two-dimensional (2D) bismuth selenium (Bi2Se3) nanosheets have exceptional surface area and superior surface modification capabilities, facilitating the effective loading of nanoprobes, metal particles, and other substances. Additionally, thiolated ultrasmall gold nanoclusters (Au NCs), distinguished by their high photoluminescent activity and modulatable surface charges, enable efficient loading onto the 2D Bi2Se3 surfaces. In this study, we successfully prepared Bi2Se3 nanosheets by sonication-assisted liquid phase exfoliation and loaded Au clusters on their surface through an amide bond reaction. The loading of Au NCs significantly augments the photothermal and photocatalytic capabilities of Bi2Se3 nanosheets and exhibits obvious anti-cancer therapeutic effects through in vitro and in vivo experiments. In summary, the as-prepared AuNC@Bi2Se3 nanocomposites showed combined near-infrared light-initiated photothermal/photodynamic therapy (PTT/PDT) against tumors, demonstrating their potential as novel theranostic agents for biomedical applications.

Size-dependent catalytic activity for CO oxidation over sub-nano-Au clusters.

Gold (Au) nanocatalysts present outstanding activity for many reactions and have long attracted much attention, but the size effect of sub-nano-clusters on catalytic activity lacks systematic research. Using CO oxidation as a probe reaction, the size-dependent catalytic capability of sub-nano-Au clusters was explored. The global-minimum (GM) structures of AuN (N = 2-300, <2.5 nm) were obtained utilizing revised particle swarm optimization (RPSO) combined with density functional theory (DFT) calculations and the Gupta empirical potential. Geometric structural descriptors built a bridge among geometric features, adsorption energy, and the CO oxidation rate of each site of any given sub-nano-Au clusters, making it possible for high-throughput evaluation of the adsorption energy and catalytic activity of the whole sub-nano-Au cluster. The activity per unit mass of sub-nano-Au clusters shows a volcano-shaped relationship with the cluster size, where the sub-nano-Au clusters with a 0.75 nm diameter possess the highest CO2 formation rate per unit mass. The Edge and Kink sites have a higher turnover frequency (approximately 106) than the Face sites (approximately 102), which contribute the most to CO2 formation. The weak adsorption of CO and O2 was found to be a crucial factor determining the inferior activity of the Face site to the Kink and Edge sites. The adsorption process rather than the surface reaction step becomes the rate-determining step on the Face site, attributed to the decreased activity per unit mass of sub-nano-Au clusters. This work provides an in-depth mechanistic understanding of size-dependent catalytic activity for Au clusters at the sub-nano level.

New insights on the role of perimeter sites in oxygen and methanol activation during furfural oxidative esterification over gold supported catalysts

Au/ZrO2 catalysts (1.5 wt% Au loading) undergone to a final calcination at different temperature (423, 573, 773 and 923 K) to opportunely modulate the Au size were proven to be highly active and selective in furfural oxidative esterification to methyl-2-furoate. The catalysts were tested according to previously optimized reaction conditions, employing O2 as benign oxidant and without any base co-catalyst. The strong dependence of the catalytic activity on the Au size was previously ascribed to the presence of Au clusters able to dissociate O2 and producing atomic O that can activate methanol. However, despite the absence of clusters, also the catalysts containing larger Au nanoparticles were active, even if conversion and selectivity were remarkably lower if compared to the other samples. The nature and the role of Au active sites exposed at the surface of clusters and nanoparticles were then investigated by HR-TEM, CO chemisorption and FTIR spectroscopy of adsorbed CO, molecular oxygen, methanol and furfural to establish structure-activity relationships. Metal nanoparticles can activate oxygen and form superoxo species and atomic O, whereas experiments performed on the pre-hydrated samples revealed that Au perimeter sites at the metal-support interface play a key role in methanol activation during furfural oxidative esterification.

Photocatalytic degradation of benzotriazole through synergy of electron donor–acceptor units and Au clusters in covalent organic frameworks

Covalent organic frameworks (COFs) have attracted great attention in photocatalysis, but the high recombination rate of photo-induced electron − hole pairs limits their photocatalytic performance. We report a synergy strategy based on the donor − acceptor (D-A) effect and Au clusters to enable the effective transfer and separation of photogenerated electrons to rationally fabricate visible light driven photocatalyst (MT-COF-Au) for the degradation of benzotriazole (BTA). MT-COF-Au displayed superior photocatalytic activity. The degradation efficiency of BTA was 93 % within 110 min, which was significantly improved 6.7 times than COF. For BTA degradation, O2− played a prominent role based on reactive species trapping experiments. The products of the last stage of the reaction were ketone, imidazole, acetamide, and nitrogen, which were formed via ring opening and isomerization reactions. MT-COF-Au could be reused for at least 5 cycles without significantly deteriorating its catalytic activity. Experiments and theory calculations confirmed the electron transfer mode and photocatalytic mechanism. This work provides new prospects for the design and synthesis of high-efficiency photocatalyst photocatalysts.

Effect of Specific Heavy Doping of Silver Atoms into the Icosahedral Au13 on Electronic Structure and Catalytic Performance.

The exploration of specific heavy doping of silver atoms into icosahedral Au13 clusters and their electronic structures and properties has been somewhat limited. Herein, we report two heavily Ag doped nanoclusters, [Au7Ag6(C7H4NOS)4(Dppf)3Cl]0 and [Au7Ag6(C7H4NOS)3(Dppf)3Cl](SbF6) (Au7Ag6-0 and Au7Ag6-1, respectively) [C7H4NOSH = 2-mercaptobenzoxazole, and Dppf = 1,1'-bis(diphenylphosphino)ferrocene]. The electronic structures and superatomic orbitals of nanoclusters were determined by density functional theory (DFT) calculations, and the energy degeneracy of the superatomic orbitals of Au7Ag6-1 is higher than that of Au7Ag6-0. Transient absorption spectroscopy was performed, revealing that Au7Ag6-0 significantly extends the excited-state lifetime. Both nanoclusters were supported on activated carbon for the oxygen reduction reaction. DFT calculations confirm that the catalytic activities mainly stem from the carbon atom of ferrocene rather than the iron atom. This study not only sheds light on the preparation of icosahedral alloy clusters but also provides insights into the regulation of icosahedral superatomic structure and electrocatalytic properties.

Dynamic behaviour of platinum and copper dopants in gold nanoclusters supported on ceria catalysts

Understanding the behaviour of active catalyst sites at the atomic level is crucial for optimizing catalytic performance. Here, the evolution of Pt and Cu dopants in Au25 clusters on CeO2 supports is investigated in the water-gas shift (WGS) reaction, using operando XAFS and DRIFTS. Different behaviour is observed for the Cu and Pt dopants during the pretreatment and reaction. The Cu migrates and builds clusters on the support, whereas the Pt creates single-atom active sites on the surface of the cluster, leading to better performance. Doping with both metals induces strong interactions and pretreatment and reaction conditions lead to the growth of the Au clusters, thereby affecting their catalytic behaviour. This highlights importance of understanding the behaviour of atoms at different stages of catalyst evolution. These insights into the atomic dynamics at the different stages are crucial for the precise optimisation of catalysts, which ultimately enables improved catalytic performance.

Assembly of Luminescent Chiral Gold(I)-Sulfido Clusters via Chiral Self-Sorting.

Due to the ubiquity of chirality in nature, chiral self-assembly involving self-sorting behaviors has remained as one of the most important research topics of interests. Herein, starting from a racemic mixture of SEG-based (SEG=SEGPHOS) chlorogold(I) precursors, a unique chiral butterfly-shape hexadecanuclear gold(I) cluster (Au16 ) with different ratios of RSEG and SSEG ligands is obtained via homoleptic and heterochiral self-sorting. More interestingly, by employing different chlorogold(I) precursors of opposite chirality (such as RSEG -Au2 and SBIN -Au2 (BIN=BINAP)), an unprecedented heteroleptic and heterochiral self-sorting strategy has been developed to give a series of heteroleptic chiral decanuclear gold(I) clusters (Au10 ) with propellor-shape structures. Heterochiral and heteroleptic self-sorting have also been observed between enantiomers of homoleptic chiral Au10 clusters to result in the heteroleptic chiral Au10 clusters via cluster-to-cluster transformation. Incorporation of heteroleptic ligands is found to decrease the symmetry from S4 of homoleptic meso Au10 to C2 of heteroleptic chiral Au10 clusters. The chirality has been transferred from the axial chiral ligands and stored in the heteroleptic gold(I) clusters.

Assembly of Luminescent Chiral Gold(I)‐Sulfido Clusters via Chiral Self‐Sorting

AbstractDue to the ubiquity of chirality in nature, chiral self‐assembly involving self‐sorting behaviors has remained as one of the most important research topics of interests. Herein, starting from a racemic mixture of SEG‐based (SEG=SEGPHOS) chlorogold(I) precursors, a unique chiral butterfly‐shape hexadecanuclear gold(I) cluster (Au16) with different ratios of RSEG and SSEG ligands is obtained via homoleptic and heterochiral self‐sorting. More interestingly, by employing different chlorogold(I) precursors of opposite chirality (such as RSEG‐Au2 and SBIN‐Au2 (BIN=BINAP)), an unprecedented heteroleptic and heterochiral self‐sorting strategy has been developed to give a series of heteroleptic chiral decanuclear gold(I) clusters (Au10) with propellor‐shape structures. Heterochiral and heteroleptic self‐sorting have also been observed between enantiomers of homoleptic chiral Au10 clusters to result in the heteroleptic chiral Au10 clusters via cluster‐to‐cluster transformation. Incorporation of heteroleptic ligands is found to decrease the symmetry from S4 of homoleptic meso Au10 to C2 of heteroleptic chiral Au10 clusters. The chirality has been transferred from the axial chiral ligands and stored in the heteroleptic gold(I) clusters.

Very Low Temperature CO Oxidation over Atomically Precise Au25 Nanoclusters on MnO2.

Atomically precise Au25 nanoclusters have garnered significant interest in the field of heterogeneous catalysis due to their remarkable activity and selectivity. However, for the extensively studied reaction of low-temperature CO oxidation, their performance has not been competitive compared to other known gold nanocatalysts. To address this, we deposited Au25(SR)18 (R = CH2CH2Ph) nanoclusters onto a manganese oxide support (Au25/MnO2), resulting in a very stable and highly active catalyst. By optimizing the pretreatment temperature, we were able to significantly enhance the performance of the Au25/MnO2 catalyst, which outperformed most other gold catalysts. Impressively, 100% conversion of CO was achieved at temperatures as low as -50 °C, with 50% conversion being reached below -70 °C. Furthermore, the existence of ligands could also influence the negative apparent activation energy observed at intermediate temperatures. Analysis using X-ray photoelectron spectroscopy (XPS), scanning transmission electron microscopy (STEM), and X-ray diffraction (XRD) techniques indicated that the Au25 nanoclusters remained stable on the catalyst surface even after pretreatment at high temperatures. In-situ modulation excitation spectroscopy (MES) spectra also confirmed that the Au cluster was the active site for CO oxidation, highlighting the potential of atomically precise Au25 nanoclusters as primary active sites at very low temperatures.

Precious metal clusters as fundamental agents in bioimaging usability.

Fluorescent nanomaterials (NMs) are widely used in imaging techniques in biomedical research. Especially in bioimaging systems, with the rapid development of imaging nanotechnology, precious metal clusters such as Au, Ag, and Cu NMs have emerged with different functional agents for biomedical applications. Compared with traditional fluorescent molecules, precious metal clusters have the advantages of high optical stability, easy regulation of shape and size, and multifunctionalization. In addition, NMs possess strong photoluminescent properties with good photostability, high release rate, and sub-nanometer size. They could be treated as fundamental agents in bioimaging usability. This review summarizes the recent advances in bioimaging utilization, it conveys that metal clusters refer to Au, Ag, and Cu fluorescent clusters and could provide a generalized overview of their full applications. It includes optical property measurement, precious metal clusters in bioimaging systems, and a rare earth element-doped heterogeneous structure illustrated in biomedical imaging with specific examples, that provide new and innovative ideas for fluorescent NMs in the field of bioimaging usability.

Binding Mechanism and Surface-Enhanced Raman Scattering of the Antimicrobial Sulfathiazole on Gold Nanoparticles.

A combined study using the surface-enhanced Raman scattering (SERS) technique and quantum chemical calculations was carried out to elucidate the adsorption behavior of sulfathiazole, an antibiotic drug, on gold nanoparticles. The tetrahedral Au20 cluster was used as a simple model to mimic a nanostructured gold surface. Computations using density functional theory with the PBE functional were performed in both the gas phase and aqueous medium using a continuum model. The drug is found to bind to the Au metals via the nitrogen of the thiazole ring. The interaction is also partially stabilized by the ring-surface π coupling rather than a sideway adsorption as previously proposed. In an aqueous solution, the drug molecule mainly exists as a deprotonated form, which gives rise to a much greater affinity toward Au nanoparticles as compared to the neutral forms. The drug adsorption further induces a significant alteration on the energy gap of the gold cluster Aun, which could result in an electrical noise. Notable SERS signals below 1600 cm-1, which result from a coupling of several vibrations including the ring breathing, C-C stretching, and N-H bending, could be employed for both qualitative and quantitative detection and assessment of sulfathiazole at trace concentrations.

Mechanism and dynamics of Baeyer–Villiger oxidation of furfural to maleic anhydride in presence of H2O2 and Au clusters

Mechanism and dynamics of Baeyer–Villiger oxidation of furfural to maleic anhydride in presence of H2O2 and Au clusters

Study on the structure, electronics, and optics of gold cluster functionalized Mo2C based on strong metal support interaction: A comprehensive DFT study

The electronic and optical properties of Mo2C are commonly regulated by loaded metal with strong metal-support interactions. Therefore, this study comprehensively studied the electronic and optical properties of Mo2C loaded Au clusters (Aun @Mo2C) using the density functional theory (DFT) method. The structural optimizations demonstrate that the Au clusters on the surface of Mo2C undergo a transition from a two-dimensional (2D) to three-dimensional (3D) configuration once the number of gold atoms within the cluster reaches 14. The projected state density (PDOS) exhibits the interaction between the loaded Au clusters and Mo2C, and a weakening of the interaction promotes the transition of the Au clusters from 2D to 3D configuration. Furthermore, the findings from the analysis of work function and charge density difference (CDD) indicate that an electric field guides electrons and holes separation by directing towards to Au clusters from Mo2C(001). This results in enhanced surface light absorption capabilities under visible light. This study provides theoretical guidance for the design of metal-Mo2C materials by revealing the inherent relationship between the geometric, electronic and optical properties of Aun @Mo2C.