Single Gold Atom Research Articles

Surface isolation of single metal complexes or clusters by a coating sieving layer via atomic layer deposition

Surface immobilization of metal complexes or clusters with an exact metal number and coordination structure on solid supports is essential in many industrial applications. However, methods for physically isolating individual homogeneous catalyst molecules on a support surface are rare. By selectively depositing TiO2 sieving layers around supported Co(salen) single molecules or gold clusters with hydrophobic ligands, we realize molecular surface isolation via selective atomic layer deposition. The obtained catalysts are reusable in chiral hydrolytic kinetic resolution and styrene oxidation. Surface isolation also prevents the leaching and aggregation of gold clusters after removing the ligands at high temperature. The activity and selectivity for styrene oxidation to benzaldehyde over isolated single gold atoms are optimized with an enhanced Au-TiO2 interface. This method provides a simple way to immobilize homogeneous catalysts on inexpensive supports and shows excellent potential for industrialization.

Ostwald ripening microkinetic simulation of Au clusters on MgO(0 0 1)

Sintering is one of the most common processes responsible for the loss of supported metal nanoparticle catalysts' activity. We have combined ab-initio calculations with microkinetic simulations to investigate the digestion and growth mechanism on Au clusters supported on MgO(001) following a bottom-up approach. The energy barrier for diffusing a single gold atom on the clean MgO surface was found to be 0.29 eV in full agreement with previous reports. Additionally, and as an extension to the entire energy profile related to Ostwald mechanisms, we found all of the activation energies to be below 1.05 eV in the cases investigated. An odd–even cluster trend was observed during ripening, attributed to the stability of pairing the unpaired electrons associated with the single gold atoms. Microkinetic analyses showed that Au single atoms are present on the surface of magnesia up to a temperature of 160 K. At higher temperatures, the system has enough energy for the single atom to diffuse across the surface and attach to other atoms or clusters. At temperatures akin to room temperature, the cluster undergoes ripening to form larger particles in order to achieve a more stable equilibrium.

The Diffusion and Clustering Formation of Gold Atoms on Alpha-Graphyne

Motivated by the experiment, high mobility of gold atoms on two-dimensional carbon sheets, we examine the ground-state structures, mobility, and clustering formations of small gold clusters (Au_n, n = 1-4) on monolayer alpha-graphyne using first-principles DFT calculations and finite temperature MD simulations. We reveal that Au_n cluster prefers to locate at the center of a hexagon in alpha-graphyne. The binding energy of Au_n on alpha-graphyne increases with increasing the number (n) of gold atoms. Moreover, we predict the step-wise formation of Au_2 out of two pre-adsorbed Au_1 ad-atoms. Likewise, the formation of Au_3 and Au_4 is also considered in the same way. The diffusion energy barrier of Au_1 on alpha-graphyne is found to be only 0.26 eV, indicating the high mobility of gold atoms on alpha-graphyne. Remarkably, the energy required for the cluster formation of gold atoms on alpha-graphyne is about less than 0.2 eV. According to our MD simulations at room temperature (RT), the Au_n cluster is subsequently formed on alpha-graphyne. Considering the high mobility of a single gold atom, the strong binding energy of small gold clusters, and the easy clustering of Au_n at RT on alpha-graphyne, we suggest that alpha-graphyne is a suitable substrate for gold cluster formation.

Interactions of noxious molecules on a single gold atom decorated an ultra-small carbon nanotube: A density functional theory study

We investigated the interaction of five noxious molecules such as CO, CO2, H2S, NO2, and SO2 on a single gold (Au) atom decorated an ultra-small (5, 5) CNT using the density functional theory (DFT) method. We also calculated and observed the changes in geometry as a result of each molecule’s interaction on a single Au atom decorated an ultra-small (5, 5) CNT, as well as the changes in their respective adsorption energy, charge transfer, and even the changes in their electronic structure. The results of this investigation indicated that the five molecules have good and strong interactions on a single Au atom decorated an ultra-small (5, 5) CNT. Thus, we believe that a configuration of a single Au atom decorated an ultra-small (5, 5) CNT is very likely to be developed into a sensor material for detecting molecules of CO, CO2, H2S, NO2 and SO2 in the near future.

Comparative study of single-atom gold and iridium on CeO2{111}.

Oxide-supported single-atom catalysts have shown promise for a variety of heterogeneous processes. In addition to their inherent activity and selectivity, these materials come at much lower financial cost, avoiding the use of full-bodied precious-metal catalysts, but at the conceptual expense that more complex structural and electronic considerations need to be understood if we are to exploit their full potential. Here, we focus on the adsorption of single-atom iridium at both stoichiometric and defective CeO2{111} surfaces, by means of first-principles density functional theory. Reference calculations for the adsorption of single-atom gold, on the same set of substrates, provide a valuable set of benchmarks against which to interpret our iridium results.

The Control of Intramolecular Through-Bond and Through-Space Coupling in Single-Molecule Junctions

The Control of Intramolecular Through-Bond and Through-Space Coupling in Single-Molecule Junctions

Water‐Based Synthesis of Gold Single Atoms‐Embedded, Metal–Organic Frameworks‐Derived Nanoporous Carbon Nanoparticles with Enhanced Reduction Ability

AbstractSingle‐atom catalysts (SACs) have emerged to be a new research frontier in catalysis due to their distinctive physical and chemical properties, including better catalytic performance, stability, and recyclability. However, the widely used organic synthesis methods for SACs limit the ability to uniformly distribute single atoms’ water‐soluble precursors on the support of the catalysts. A water‐based synthesis of single gold (Au) atom catalyst is used in this work. Through this method, water‐soluble Au precursors are successfully turned into Au single atoms embedded in metal–organic framework‐derived nitrogen‐containing nanoporous carbon. The resulting catalyst is applied on the reduction of 4‐nitropenol. The catalytic performance of the reaction reaches 100% conversion in 30 min, while utilizing Au nanoparticles as active sites on the same support can only get 70% conversion under the same reaction conditions.

Catalytic CO Oxidation by O2 Mediated with Single Gold Atom Doped Titanium Oxide Cluster Anions AuTi2 O4-6.

Gas-phase studies on catalytic CO oxidation by O2 mediated with gold-containing heteronuclear metal oxide clusters are vital to obtain the structure-reactivity relationship of supported gold catalysts, while it is challenging to trigger the reactivity of clusters with closed-shell electronic structure in O2 activation. Herein, we identified that CO oxidation by O2 can be catalyzed by the AuTi2 O4-6- clusters, among which AuTi2 O4- with closed-shell electronic structure can effectively activate O2 . The reactions were characterized by mass spectrometry and quantum chemical calculations. Theoretical calculations showed that in the initial stage of O2 activation, the Ti2 O4 moiety in AuTi2 O4- contributes dominantly to activate O2 into superoxide (O2- ⋅) without participation of the Au atom. In subsequent steps, the intimate charge transfer interaction between Au and the Ti2 O4 moiety drives the direct dissociation of the O2- ⋅ unit.

Cascaded nanooptics to probe microsecond atomic-scale phenomena

Plasmonic nanostructures can focus light far below the diffraction limit, and the nearly thousandfold field enhancements obtained routinely enable few- and single-molecule detection. However, for processes happening on the molecular scale to be tracked with any relevant time resolution, the emission strengths need to be well beyond what current plasmonic devices provide. Here, we develop hybrid nanostructures incorporating both refractive and plasmonic optics, by creating SiO2 nanospheres fused to plasmonic nanojunctions. Drastic improvements in Raman efficiencies are consistently achieved, with (single-wavelength) emissions reaching 107 counts⋅mW-1⋅s-1 and 5 × 105 counts∙mW-1∙s-1∙molecule-1, for enhancement factors >1011 We demonstrate that such high efficiencies indeed enable tracking of single gold atoms and molecules with 17-µs time resolution, more than a thousandfold improvement over conventional high-performance plasmonic devices. Moreover, the obtained (integrated) megahertz count rates rival (even exceed) those of luminescent sources such as single-dye molecules and quantum dots, without bleaching or blinking.

Single-Site Au/Carbon Catalysts with Single-Atom and Au Nanoparticles for Acetylene Hydrochlorination

Single-site cationic Au supported on carbon (Au SAs/AC) has been identified as the active site for acetylene hydrochlorination, and single-site cationic Au tends to sinter into devitalized particles during a reaction. Many efforts have been devoted to the preparation and stabilization of the Au SAs. Herein, we report an unexpected phenomenon that the Au SAs can be dynamically created from Au nanoparticles during the acetylene hydrochlorination reaction, and the single-site cationic Au sites can be stabilized by the defective carbon support. The dynamic formation and stabilization of single gold atoms under realistic conditions provide a new strategy for the design of stable Au-based acetylene hydrochlorination catalysts.

The spin-dependent transport properties of endohedral transition-metal-fullerene X@C66H4 (X=Fe, Co, Mn, Ni)

Inspired by recent experiments on the successful synthesis of hydrofullerene C66H4 in Tian et al. (2019) [12] with two negatively curved heptagons. Based on the density functional theory and nonequilibrium Green's function method, we report the spin-dependent transport through transition-metal-atom-encapsulated C66H4 hydrofullerene, i.e., X@C66H4(X=Fe, Co, Mn, Ni), contacted by single gold atoms via semi-infinite non-magnetic Au electrodes. It is found that, Mn- and Fe-doped systems show highly spin-polarized transmission as well as considerable magnetic moments whereas Ni-doped systems show completely spin-unpolarized transmission and nonmagnetic. Interestingly, Co-doped systems show two spin states, i.e., spin-polarized and spin-unpolarized ones. Further analysis shows that, for Mn-, Fe- and Ni-doped systems, the spin-polarized/unpolarized state is caused by the finite/(nearly-)zero magnetism of the encapsulated metal atom. While the magnetism in Co-doped systems is quenched for the top hexagonal doping case, but not for the side heptagonal doping one, which induces the spin-unpolarized/spin-polarized state. And the screening effect of electrodes on the magnetism of Co is the underlying physical mechanism. Our findings would be beneficial to the design of spintronics devices.

Ion-molecule reactions catalyzed by a single gold atom.

We report that Au atoms within van der Waals complexes serve as catalysts for the first time. This was observed in ionization-induced chemistry of 1,6-hexanediol–Au and 1,8-octanediol–Au complexes formed in superfluid helium nanodroplets, where the addition of Au atom(s) made C2H4+ the sole prominent product in dissociative reactions. Density functional theory (DFT) calculations showed that the Au atom significantly strengthens all of the C–C bonds and weakens the C–O bonds in the meantime, making the C–C bonds stronger than the two C–O bonds in the ionized complexes. This leads to a preferential cleavage of the C–O bonds and thus a strong catalytic effect of the Au atoms in the reactions.

Molecular junction stretching and interface recognition: Decode the mystery of high/low conductance switching in stretching process of 4, 4′-bipyridine molecular junction

The high/low conductance switching in stretching process of 4,4′-bipyridine molecular junction is a distinctive phenomenon in molecular electronics, which is still a mystery and has been unsolved for more than one decade. Based on the techniques and processes of experimental measurement, the <i>ab initio</i>-based adiabatic molecule-junction-stretch simulation (AMJSS) method is developed, by which the stretching processes of 4,4′-bipyridine molecular junctions are calculated. The conductance traces of the molecular systems in the stretching processes are studied and the mystery of high/low conductance switching in the stretching processes of 4,4′-bipyridine molecular junction is decoded by using the one-dimensional transmission combined with the three-dimensional correction approximation (OTCTCA) method. The numerical results show that, in the stretching process of 4,4′-bipyridine molecular junction, the upper terminal nitrogen atom in the pyridine ring is easy to vertically adsorb on the second gold layer of the probe electrode. At the same time, the molecule produces unique lateral-pushing force to push the tip atoms of the probe electrode aside. Thus, the high conductance plateau arises. With the molecular junction further stretched, the upper terminal nitrogen atom of the molecule shifts from the second gold layer to the tip gold atom of the probe electrode with the tip gold atom moving back to the original lattice position. Consequently, the conductance value decreases by about 5–8 times, and the low conductance plateau is presented. According to our calculations, the phenomenon of high/low conductance switching in the stretching process of 4,4′-bipyridine molecular junction also indicates that, single surface gold atom often lies on the surface of substrate electrode. Moreover, the phenomenon of high/low conductance switching can only be found when the molecule is adsorbed on the surface gold atom of the substrate electrode. Thus, using conductance traces measured in the stretching processes of molecular junction and with the help of theoretical calculations, the interface structures of molecular junctions can be recognized efficiently. Our study not only decodes the physical process and intrinsic mechanism of the high/low conductance switching phenomenon of 4,4′-bipyridine molecular junction, but also provides significant technique information for using pyridine-based molecule to construct functional molecular devices, such as molecular switch, molecule memory, molecular sensor, etc.

Single-atom gold oxo-clusters prepared in alkaline solutions catalyse the heterogeneous methanol self-coupling reactions.

In an effort to obtain the maximum atom efficiency, research on heterogeneous single-atom catalysts has intensified recently. Anchoring organometallic homogeneous catalysts to surfaces creates issues with retaining mononuclearity and activity, while the several techniques developed to prepare atomically dispersed precious metals on oxide supports are usually complex. Here we report a facile one-pot synthesis of inorganometallic mononuclear gold complexes formed in alkaline solutions as robust and versatile single-atom gold catalysts. The complexes remain intact on impregnation onto supports or after drying in air to give a crystalline powder. They can be used to interrogate the nuclearity of the catalytically active gold site for reactions known to be catalysed by oxidized gold species. We show that the [Au1-Ox]- cluster directs the heterogeneous coupling of two methanol molecules to methyl formate and hydrogen with a 100% selectivity below 180 °C. The reaction is industrially important as well as the key step in methanol steam reforming on gold catalysts.

Real Time Monitoring of the Dynamic Intracluster Diffusion of Single Gold Atoms into Silver Nanoclusters.

Alloying metal materials with heterometal atoms is an efficient way to diversify the function of materials, but in-depth understanding of the dynamic heterometallic diffusion inside the alloying materials is rather limited, especially at the atomic level. Here, we report the real-time monitoring of the dynamic diffusion process of a single gold (Au) atom into an atomically precise silver nanocluster (Ag NC), Ag25(MHA)18 (MHA = 6-mercaptohexanoic acid), by using in situ UV-vis absorption spectroscopy in combination with mass and tandem mass spectrometry. We found that the Au heteroatom first replaces the Ag atom at the surface Ag2(MHA)3 motifs of Ag25(MHA)18. After that, the Au atom diffuses into the surface layer of the icosahedral Ag13 kernel and finally occupies the center of the alloy NCs to form the thermodynamically stable Au@Ag24(MHA)18 product. Density functional theory (DFT) calculations reveal that the key thermodynamic driving force is the preference of the Au heteroatom for the central site of alloy NCs. The real-time monitoring approach developed in this study could also be extended to other metal alloy systems to reveal the reaction dynamics of intracluster diffusion of heteroatoms, as well as the formation mechanisms of metal alloy nanomaterials.

A new trick for an old support: Stabilizing gold single atoms on LaFeO3 perovskite

Single-atom catalysts (SACs) have shown great potential for achieving superior catalytic activity due to maximizing metal efficiency. The key obstacle in developing SACs lies in the availability of supports that can stabilize SACs. Here we report the first successful development of single gold (Au) atom catalysts supported on high-surface-area hierarchical perovskite oxides. The resulting Au single-atoms are extremely stable at calcination temperatures up to 700 °C in air and under reaction conditions. A high catalytic activity for CO oxidation and distinct self-activating property were also achieved. Furthermore, evidenced by theoretical calculations and experimental studies including X-ray absorption fine structures and in situ Fourier-transform infrared spectra, the surface Au active sites are confirmed to be predominately positively charged. This work provides a generalizable approach to fabricating highly stable Au single-atom catalysts with tunable catalytic performance, and we anticipate that this discovery will facilitate new possibilities for the development of single atom catalysts.

Green gold nanoparticles from plant-derived materials: an overview of the reaction synthesis types, conditions, and applications

Abstract Many studies have examined metallic nanoparticles (NPs) produced according to the principles of green chemistry. Gold NPs have drawn much more attention than other metallic NPs in recent years. Moreover, among all gold NP synthesis studies, using plant-derived molecules is one of the commonly used reductants in studies on NP synthesis because of its convenience in terms of shape, size control advantage, and nontoxic specifications. The present review focused on studies of the synthesis of gold NP types, including single gold atom NPs, alloyed AU NPs, and core-shell Au NPs as well as their conditions and applications. The effect of those structures on application fields such as catalysis, antifungal action, antibacterial activities, sensors and so on are also summarized. Furthermore, the morphology and synthesis conditions of the primer and secondary NP were discussed. In addition to synthesis methods, characterization methods were analyzed in the context of the considerable diversity of the reducing agents used. As the reducing agents used in most studies, polyphenols and proteins usually play an active role. Finally, the challenges and drawbacks in plant-derived agent usage for the preparation of Au NPs at various industries were also discussed.

Stable Adsorption of Single Gold Atoms on the SrTiO3(111)-(9 × 9) Reconstructed Surface

Scanning tunneling microscopy is used to study the SrTiO3(111)-(9 × 9) reconstructed surface and its single gold atom adsorption behavior. Each unit cell of the (9 × 9) reconstruction is composed o...

Cover Picture: Design of Single Gold Atoms on Nitrogen‐Doped Carbon for Molecular Recognition in Alkyne Semi‐Hydrogenation (Angew. Chem. Int. Ed. 2/2019)

Cover Picture: Design of Single Gold Atoms on Nitrogen‐Doped Carbon for Molecular Recognition in Alkyne Semi‐Hydrogenation (Angew. Chem. Int. Ed. 2/2019)

Design of Single Gold Atoms on Nitrogen-Doped Carbon for Molecular Recognition in Alkyne Semi-Hydrogenation.

Single-atom heterogeneous catalysts with well-defined architectures are promising for deriving structure-performance relationships, but the challenge lies in finely tuning the structural and electronic properties of the metal. To tackle this point, a new approach based on the surface diffusion of gold atoms on different cavities of N-doped carbon is presented. By controlling the activation temperature, the coordination neighbors (Cl, O, N) and the oxidation state of the metal can be tailored. Semi-hydrogenation of various alkynes on the single-atom gold catalysts displays substrate-dependent catalytic responses; structure insensitive for alkynols with γ-OH and unfunctionalized alkynes, and sensitive for alkynols with α-OH. Density functional theory links the sensitivity for alkynols to the strong interaction between the substrate and specific gold-cavity ensembles, mimicking a molecular recognition pattern that allows to identify the cavity site and to enhance the catalytic activity.