Number Of Metal Atoms Research Articles

Bridging the gas and condensed phases for metal-atom encapsulating silicon- and germanium-cage superatoms: electrical properties of assembled superatoms.

With the development of nanocluster (NC) synthesis methods in the gas phase, atomically precise NCs composed of a finite number of metal and semiconductor atoms have emerged. NCs are expected to be the smallest units for nanomaterials with various functions, such as catalysts, optoelectronic materials, and electromagnetic devices. The exploration of a stable NC called a magic number NC has revealed a couple of important factors, such as a highly symmetric geometric structure and an electronic shell closure, and a magic number behavior is often enhanced by mixing additional elements. A synergetic effect between geometric and electronic structures leads to the formation of chemically robust NC units called superatoms (SAs), which act as individual units assembled as thin films. The agglomeration of non-ligated bare SAs is desirable in fabricating the assembled SAs associated with intrinsic SA nature. The recent development of an intensive pulsed magnetron sputtering method opens up the scalable synthesis of SAs in the gas phase, enabling the fabrication of SA assembly coupled with the non-destructive deposition of a soft-landing technique. This perspective describes our recent progress in the investigation of the formation of binary cage SA (BCSA) assembled thin films composed of metal-atom encapsulating silicon-cage SAs (M@Si16) and germanium-cage SAs (M@Ge16), with a focus on their electrical properties associated with a conduction mechanism toward the development of new functional nanoscale materials.

Micelle Formation of Dodecanoic Acid with Alkali Metal Counterions.

Alkali series with different atomic numbers affect the physicochemical properties of aqueous solutions. The micellar properties of aqueous solutions of dodecanoate as surfactants were measured by changing the counterions (C12-Na, C12-K, C12-Rb, and C12-Cs). A plot of Krafft temperature vs. alkali metal atomic number showed a downward convex curve, with its minimum temperature (20°C) in the C12-K system. By contrast, a plot of the critical micelle concentration (CMC) vs. alkali metal atomic number exhibited an upward convex curve with the maximum CMC (25.6 mmol L-1) at C12-K. Furthermore, the minimum surface tension (γ min ) of the solution at the CMC increased with increasing atomic number (C12-Na ≈ C12-K < C12-Rb < C12-Cs). The size of the dodecanoate micelles decreased with increasing atomic number. The ionization degree of the micelles also increased with increasing atomic number of the alkali metal. Small-angle X-ray scattering (SAXS) measurements revealed that alkali dodecanoate micelles formed spherical to ellipsoidal structures. In addition, micelles from the shell region showed large electrostatic repulsion, judging from the shape of the spectrum in the higher Q -1 region. From the measurement results of the solubilization of naphthalene into the micelles, the size of the micelles corresponded to the maximum solubilization quantity of naphthalene.

Polyacrylamide gel electrophoresis: a versatile tool for the separation of nanoclusters.

Atomically precise nanoclusters comprising 1-100 atoms have emerged as a new class of nanomaterials with intriguing size-dependent physicochemical properties. The significant changes in the properties of nanoclusters were observed in tailoring the number of metal atoms and ligands that determines their functions and applicability. Since 1990, thiolated gold nanoclusters have been studied. The separation of monodispersed clusters was crucial and time-consuming. To address these shortcomings, several separation techniques have made it possibleto separate the series of metalnanoclusters with a precise composition of metals and ligands. Among these techniques, polyacrylamide gel electrophoresiswas utilized for hydrophilic cluster separation. This review shall focus on the principle, operation and application of thepolyacrylamide gel electrophoresistechnique to encourage a greater understanding of the characteristics and usefulness of this method.

Structural Quasi-Isomerism in Au/Ag Nanoclusters

Atomically precise metal nanoclusters are a new kind of nanomaterials that appeared in recent years; a pair of isomer nanoclusters have the same metal types, numbers of metal atoms, and surface-protected organic ligands but different metal atom arrangements. This article summarizes the structure features of isomer nanoclusters and concentrates on synthesis methods that could lead to isomer structure. The pairs of isomer inorganic nanoclusters’ conversion to each other and their applications in catalyst and photoluminescence are also discussed. We found that the structure conversions are relevant to their stability. However, with the same molecule formulas, different atom arrangements significantly influence their performance in applications. Finally, the existing challenges and some personal perspectives for this novel field in the nano-science investigation are proposed. We hope this minireview can offer a reference for researchers interested in inorganic isomer nanoclusters.

Boosting hydrogenation properties of Pt single-atom catalysts via tailoring the electronic structures by coordination number regulation

Clarifying the relationship of single metal atom coordination structures and catalytic properties is crucial for the fine-design of highly-efficient catalysts, but systematically manipulating the coordination structure (e.g., coordination numbers (CN) of metal atoms) without changing atomic dispersion is challenging. Herein, we develop a precursor-atomization strategy for the synthesis of single-atom catalysts (SACs) and further precisely tailor Pt-N CN by changing the pyrolysis sequence and atmosphere. It is found that as Pt-N CN decreases (from Pt-N5 to Pt-N3), the electron density of Pt atoms increases and the energy barrier for H2 dissociation decreases, thus achieving a ∼550-fold increase in activity of selective hydrogenation of 3-nitrophenylacetylene (reduction of nitro group while maintaining the highly sensitive alkyne group), successfully breaking the selectivity-activity seesaw. Additionally, Pt-N3 SACs also show remarkably broad applicability for the hydrogenation of nitroarenes (even for iodo-nitrobenzene) due to its unique heterolytic cleavage path of H2 and preferential adsorption of nitro group.

Unraveling the Key Atomic Interactions in Determining the Varying Li/Na/K Storage Mechanism of Hard Carbon Anodes

AbstractHard carbons have been identified as competitive anodes for Li/Na/K‐ion batteries but their Li/Na/K‐ion storage mechanisms significantly vary in different batteries. It is fundamental to understand the basic science behind the difference. Herein, it is theoretically revealed that defects on the carbon layers generally have an influential impact on the atomic interactions including the metal–metal (M–M) and metal–carbon (M–C) interactions, thereby determining whether the stored alkali‐metal atoms are in ionic or quasi‐metallic states. Upon increasing the number of metal atoms on a carbon layer composed of only hexatomic rings, K tends to be stored in an ionic state similar to Li due to the dominant M–C interaction, while on a carbon layer with defects, K tends to be stored in a quasi‐metallic state similar to Na due to the dominant M–M interaction. For experimental verification, a glassy carbon, the extreme form of hard carbon with dominant sp2 hybridization and only Stone–Wales defects, is selected as a model anode, and its Li/Na/K‐ion storage mechanisms are exactly consistent with the theoretical prediction. More profoundly, for the first time, the quasi‐metallic K cluster information is captured by ex situ electron paramagnetic resonance.

Homogeneity of Supported Single-Atom Active Sites Boosting the Selective Catalytic Transformations.

Selective conversion of specific functional groups to desired products is highly important but still challenging in industrial catalytic processes. The adsorption state of surface species is the key factor in modulating the conversion of functional groups, which is correspondingly determined by the uniformity of active sites. However, the non‐identical number of metal atoms, geometric shape, and morphology of conventional nanometer‐sized metal particles/clusters normally lead to the non‐uniform active sites with diverse geometric configurations and local coordination environments, which causes the distinct adsorption states of surface species. Hence, it is highly desired to modulate the homogeneity of the active sites so that the catalytic transformations can be better confined to the desired direction. In this review, the construction strategies and characterization techniques of the uniform active sites that are atomically dispersed on various supports are examined. In particular, their unique behavior in boosting the catalytic performance in various chemical transformations is discussed, including selective hydrogenation, selective oxidation, Suzuki coupling, and other catalytic reactions. In addition, the dynamic evolution of the active sites under reaction conditions and the industrial utilization of the single‐atom catalysts are highlighted. Finally, the current challenges and frontiers are identified, and the perspectives on this flourishing field is provided.

Structural Control and Chiroptical Response in Intrinsically Tetra- and Pentanuclear Chiral Gold Clusters.

Controlling the synthesis of chiral metal clusters in the aspects of nuclearity number, metal-metal interaction, and spatial arrangement of metal atoms is crucial for establishing the correlation of detailed structural factors with chiroptical activity. Herein, a series of enantiopure gold complexes with nuclearity numbers ranging from 2 to 5 were constructed and structurally characterized. On the basis of the annulation reaction between two aurated μ2-imido nucleophilic units with various aldehydes, we finely adjusted the metal-metal interaction and torsion angles of a characteristic tetranuclear metal cluster by introducing different substituents into the resulting imidazolidine dianionic chiral skeleton. Further structural investigations, contrast experiments, and time-dependent density functional theory calculations confirmed that the chiroptical response of the acquired asymmetric metal clusters was mainly affected by the geometrically twisted arrangement of metal atoms. Finally, the tetranuclear gold cluster compound with the shortest intermetallic interaction and the largest torsion angle of a Au4 core showed the highest absorption anisotropy factor up to 2.2 × 10-3. In addition, the correlation of structural factors with the stability of chiral gold clusters was thoroughly evaluated by monitoring the CD, UV-vis, and NMR spectra at elevated temperatures. Insight into the relationship between the structural factors with the chiroptical property and stability of chiral gold clusters in this work will help us to design and achieve more stable chiral metal clusters and stimulate their practical applications in chiroptical functional materials.

Ligand Induced Double-Chair Conformation Ln12 Nanoclusters Showing Multifunctional Magnetic and Proton Conductive Properties.

Many methods have been utilized to adjust the size of superatomic metal nanoclusters, while tuning the geometric conformations of specific nanoclusters is rare. Here, we demonstrate that conformation variation can be realized by slightly modifying the ligand under maintaining the nuclei number of metal atoms. A series of novel "double-chair" conformation Ln12 (Ln = Sm (1), Eu (2), Gd (3), Tb (4), and Dy (5)) clusters were generated by replacing 3-formylsalicylic acid with 2,3-dihydroxybenzoic acid in the Ln12 nanocluster. Intriguingly, Dy12 displays slow magnetic relaxation at low temperatures, while Gd12 shows a large magnetocaloric effect (MCE) of 35.63 J kg-1 K-1 at 2 K for ΔH = 7 T. Additionally, the introduction of numerous coordination water molecules in these clusters enables Dy12 and Gd12 with high proton conductivity, namely, 2.13 × 10-4 and 3.62 × 10-4 S cm-1 under 358 K and 95% RH humidity conditions.

Development of functionalized carbon nanofibers with integrated palladium nanoparticles for catalytic hydrogen generation

The noble metals have the intrinsic ability to catalyze variety of useful reactions, however, their applications are hindered due to their high cost. One of the potential solutions is to reduce size of metal particles to enhance the number of surface metal atoms and thereby the catalytic activity. Herein, we synthesize palladium based heterogeneous catalysts using carbon nanofibers (CNFs) as support for the dehydrogenation of formic acid to hydrogen gas. The nitrogen species have been widely reported to enhance the metal-support interaction, therefore, CNFs were further functionalized with amine groups. We utilized strong electrostatic adsorption (SEA) method where charged metal precursors were strongly adsorbed onto oppositely charged carbon surface by controlling the pH relative to the point of zero charge (PZC). The effect of palladium loading on amine-functionalized carbon nanofibers (NH2-CNFs) over the range of pH from 2 to 12 as well as the effect of ionic strength of the solution on metal loading were thoroughly studied. These optimizations resulted in the best activity for dehydrogenation of formic acid using 4 nm Pd nanoparticles integrated over functionalized CNFs. Overall, the results indicate that Pd@NH2-CNFs were reusable, recyclable and active for the dehydrogenation of formic acid at ambient conditions.

Х-ray Study and Computer Simulation of the Structure of Amorphous-Crystalline Titanite

The structure of amorphous-crystalline titanite obtained by mechanical activation was studied by X-ray diffraction and simulation methods. The short-range order characteristics were calculated using Finbak-Warren's method. It was found that the coordination numbers of metal atoms decreased as the result of titanite grinding. The atomic configurations of short-range order of ground titanite were constructed by translation of titanite unit cell. The theoretical X-ray patterns were calculated using Debye's method and were compared with the experimental curves. The structure of ground titanite in the mill with centrifugal factor 40 g was described satisfactorily by the model of mechanical mixture of clusters containing 2016 atoms, disordered during the molecular dynamics with clusters containing 12096 atoms. The increase of grinding intensity led to the sharp decrease of sizes of small cluster.

X-ray Study and Computer Simulation of the Structure of Amorphous-Crystalline Titanite

The structure of amorphous-crystalline titanite obtained by mechanical activation was studied by X-ray diffraction and simulation methods. The short-range order characteristics were calculated using Finbak-Warren's method. It was found that the coordination numbers of metal atoms decreased as the result of titanite grinding. The atomic configurations of short-range order of ground titanite were constructed by translation of titanite unit cell. The theoretical X-ray patterns were calculated using Debye's method and were compared with the experimental curves. The structure of ground titanite in the mill with centrifugal factor 40 g was described satisfactorily by the model of mechanical mixture of clusters containing 2016 atoms, disordered during the molecular dynamics with clusters containing 12096 atoms. The increase of grinding intensity led to the sharp decrease of sizes of small cluster. Keywords: amorphous-crystalline titanite, X-ray diffraction, computer simulation, mechanical activation, Debye's method.

Additive-mediated intercalation and surface modification of MXenes.

2D carbides and nitrides of transition metals, also known as MXenes, are an emerging class of 2D nanomaterials that have shown excellent performances and broad application prospects in the fields of energy storage, catalysis, sensing, electromagnetic shielding, electronics and photonics, and life sciences. This unusual diversity of applications is due to their superior hydrophilicity and conductivity, high carrier concentration, ultra-high volumetric capacitance, rich surface chemistry, and large specific surface area. However, it is difficult to make MXenes with the desired surface functional groups that deliver high reactivity and high stability, because most MXenes are extracted from ceramics (MAX phase) by an etching process, where a large number of metal atoms are inevitably exposed on the surface, with other anions and cations embedded uncontrollably. The exposed metal atoms and implanted ions are thermodynamically unstable and readily react with trace oxygen or oxygen-containing groups to form the corresponding metal oxides or degrade chemically, resulting in a sharp decline in activity and loss of excellent physicochemical properties. The addition of certain synergistic additives during the intercalation and chemical modification of surface functional groups under non-hazardous conditions can result in stable and efficient MXene-based materials with exceptional optical, electrical, and magnetic properties. This review discusses several such methods, mainly additive-mediated intercalation and chemical modification of the surface functional groups of MXene-based materials, followed by their potential applications. Finally, perspectives are given to discuss the future challenges and promising opportunities of this exciting field.

Superalkali-alkalide ion pairs δ+(M-HMHC)-M’ δ - (M, M’ = Li, Na and K) serving as high-performance NLO molecular materials

For the stable superalkali-alkalide ion pairs in alkalide solutions, a DFT study was performed to investigate the nonlinear optics (NLO) responses of δ +(M−HMHC)-M’ δ - (M, M’ = Li, Na and K). The NLO responses display obvious alkali metal atomic number dependence (M’). From δ +(M−HMHC)-Li δ - to δ +(M−HMHC)-K δ -, the increases of the static and dynamic first hyperpolarizabilities constitute a 1 ∼ 3 orders of magnitude improvement.

Cluster Materials as Traceable Antibacterial Agents

ConspectusThe precise design of nanomaterials is essential for both basic and applied materials research. However, it is difficult to precisely synthesize and manipulate nanomaterials with adjustable physicochemical properties and functions at the molecular and atomic levels. For example, the emerging precision nanomedicine requires not only the precise design of nanomaterials (or atomically precise nanochemistry) but also real-time observations of the theranostic process. Metal nanoclusters (NCs) are molecule-like metal nanomaterials with well-defined molecular formulas, structures, and properties, which can meet the above requirements. Metal NCs can be easily synthesized and manipulated, and they have strong luminescence properties, which can be used to monitor biomedical processes under working conditions and environments. Moreover, unlike metal nanoparticles and other molecules, the core (i.e., size (number of metal atoms in each NC) and composition) and surface of metal NCs can be individually adjusted at the atomic level. The atomic-level tailoring of metal NCs has a significant impact on their physicochemical properties and further applications. In addition, the atomic-level control of metal NCs can also help us to understand the respective functions of metal NCs in biomedical applications at the molecular and atomic levels. This knowledge will facilitate the accurate screening and design of metal NCs, with the desired functions and required efficacy to realize precision nanomedicine.In this Account, we focus on the design of antibacterial agents based on atomically precise metal NCs. We first discuss the antibacterial mechanisms of gold (Au) and silver (Ag) NCs, which can induce the production of reactive oxygen species (ROS) inside the bacteria to achieve the killing effect. Au nanomaterials are generally regarded as noble and nonantibacterial, but ultrasmall Au NCs can show good (and unexpected) antibacterial ability. In addition, the luminescent Au NCs can be used as traceable antibacterial agents to monitor real-time interactions with bacteria. Moreover, we can individually engineer the core (i.e., size and composition) and surface of metal NCs at the atomic level. We have constructed three libraries of metal NCs with different physicochemical properties: Au NCs with the same surface but different sizes, (AuAg)25 alloy NCs with the same surface but different compositions, and Au25 NCs with different surfaces. Through these libraries, we conclude that the core size of metal NCs would not affect the antibacterial ability, but the composition of the metal core and the surface ligands of metal NCs would greatly influence their antibacterial efficacy. In turn, this allows us to understand the killing mechanism of antibacterial materials at the molecular level, which is conducive to the design of antibacterial agents with controllable effects. In addition, the surface of metal NCs can be combined with a second antibacterial agent with a different working mechanism to achieve an enhanced synergistic antibacterial effect. Successful examples include Ag NCs with commercial antibiotics and Au NCs with two-dimensional (2D) nanomaterials (e.g., graphene oxide (GO) and MXene nanosheets). This Account is concluded with our perspectives on the future development of atomically precise nanochemistry in the design of antibacterial agents and other theranostic agents. The systematic study of antibacterial metal NCs can also serve as a good paradigm for understanding precision nanomedicine at the molecular level from the aspects of both materials and biomedicine.

Studies on the synergistically improved reactivity of spinel NiFe2O4 oxygen carrier for chemical-looping combustion

The investigation of the synergistically improved reactivity of spinel NiFe2O4 oxygen carrier during chemical-looping combustion was conducted by the thermogravimetric analysis (TGA) experiments and implemented within the density functional theory (DFT) calculations. TGA results demonstrated that spinel NiFe2O4 could be directly reduced into Ni–Fe alloy in the CO atmosphere. The reaction rate of NiFe2O4 showed two times faster as compared with Fe2O3. The increase of reaction temperature, CO concentration and heating rate can boost the reaction rate of NiFe2O4. The oxygen vacancy formation energy is a good indicator for the reactivity of lattice oxygen in NiFe2O4. DFT calculations indicate that the lattice oxygen coordinated with Ni atom shows higher reactivity than that with Fe atom. The reactivity of lattice oxygen in NiFe2O4 is primarily owing to the coordination environment of oxygen formed by different Ni/Fe atoms, which is not only related to the type and number of coordination metal atoms, but also correlated with the surface structure. It can be found that the calculated results are in good agreement with the improved reactivity of NiFe2O4 oxygen carrier that has been observed in the TGA experiments. These results are of importance to generally understand the synergistically improved reactivity in the spinel NiFe2O4 oxygen carrier.

Engineering reversible isomerization at the nanoscale via intermolecular interactions

Engineering reversible isomerization at the nanoscale via intermolecular interactions

Reversible isomerization of metal nanoclusters induced by intermolecular interaction

Reversible isomerization of metal nanoclusters induced by intermolecular interaction

Numerical investigation on the influence of metal particles on the characteristics of a high-current vacuum arc

In the arc-burning process of a high-current vacuum arc (HCVA), the metal particles (MPs) splashed from the active anode will have a significant influence on the plasma characteristics of the arc column. In this paper, the influence of varying MPs on the characteristics of HCVA are studied by establishing a HCVA model containing single or multiple MPs. The simulation results show that when the MPs vaporized metal vapor (MV) enters the interelectrode region and once the arc column plasma cannot ionize all atoms immediately, the ionization layer and the neutral atom vapor area (NAVA) will be formed in the adjacent region of the MPs. When the MP diameter and temperature increase, the number of vaporized metal atoms increases, so that the influence range of MV increases, and the area of ionization layer and the NAVA increases. In addition, when the arc current increases or the MPs are closer to the cathode surface, the greater the ion number density and ion pressure around the MPs are, the stronger the compression on the MV will be, resulting in the decrease of the area of ionization layer and the neutral atom vapor, and the increase of the net ionization rate of the ion number density. When multiple MPs exist in the interelectrode region at the same time, the MV from the MPs will affect each other. In the central region of multiple MPs, the density of MV becomes the largest, while the net ionization rate of ion number density is distributed in the periphery region of the MP group.

Conflicting Roles of Coordination Number on Catalytic Performance of Single-Atom Pt Catalysts

Tailoring the coordination number (CN) of metal atoms has been increasingly recognized as one of the strategies to enhance the catalytic performance of single-atom catalysts (SACs). We here present...