Agn Nanoclusters Research Articles

An Ultrastable, Small {Ag7}5+ Nanocluster within a Triangular Hollow Polyoxometalate Framework

AbstractSmall Agn nanoclusters (n<10) have been emerging as promising materials as sensing, biolabeling, and catalysis because of their unique electronic states and optical properties. However, studying synthesis, structure determination, and exploration of their properties remain major challenges as a result of the low stability of small Ag nanoclusters. Herein, we synthesized an atomically precise face‐centered‐cubic‐type small {Ag7}5+ nanocluster supported by a novel triangular hollow polyoxometalate (POM) framework [Si3W27O96]18−. The cluster showed unique {Ag7}5+‐to‐POM charge transfer bands in both visible and UV light regions. Furthermore, this small {Ag7}5+ nanocluster exhibited an unprecedented ultrastability in solution, despite having exposed Ag sites that can be accessed by small molecules, such as O2, water, and solvents.

An Ultrastable, Small {Ag7 }5+ Nanocluster within a Triangular Hollow Polyoxometalate Framework.

Small Agn nanoclusters (n<10) have been emerging as promising materials as sensing, biolabeling, and catalysis because of their unique electronic states and optical properties. However, studying synthesis, structure determination, and exploration of their properties remain major challenges as a result of the low stability of small Ag nanoclusters. Herein, we synthesized an atomically precise face-centered-cubic-type small {Ag7 }5+ nanocluster supported by a novel triangular hollow polyoxometalate (POM) framework [Si3 W27 O96 ]18- . The cluster showed unique {Ag7 }5+ -to-POM charge transfer bands in both visible and UV light regions. Furthermore, this small {Ag7 }5+ nanocluster exhibited an unprecedented ultrastability in solution, despite having exposed Ag sites that can be accessed by small molecules, such as O2 , water, and solvents.

Influence of the surface decoration of phosphorene with Ag nanoclusters on gas sensing properties

Easy aggregation of metal nanoclusters and less selectivity and sensitivity of 2D materials always limit their further applications in the design of commercial gas-sensors. To overcome these deficiencies, we propose a combined system of Ag nanoclusters and 2D phosphorene for the design of new gas nanosensors based on the first-principles calculation. The AgN nanoclusters (1 ≤ N ≤ 13) can reduce the degradation of phosphorene and present a variety of structures with different active adsorption sties exposed, which can greatly increase the selectivity and sensitivity of the system to the adsorbed molecules. The sensitivity of phosphorene can be improved by the decoration of Ag atom due to the participation of valence electrons of Ag atom coming from the s and d electronic orbitals, which can modulate the charge distribution between the adsorbed molecules and the phosphorene. Moreover, the work function changes significantly when gas molecules adsorbed on Ag1-phosphorene, especially it increases by 30.5% for NO2 molecule. The I-V curves show that NO2 adsorption requires the higher bias voltage than Ag1-phosphorene. Our theoretic results serve to deepen our insights into surface modification of phosphorene via the decoration of noble metal Ag and to provide a novel pathway to design high performance phosphorene-based gas sensors.

Density functional theory study of small Ag cluster adsorbed on graphyne

Based on the density functional theory study, we investigated the adsorption behavior of small Agn nanoclusters (n = 1 to 4) on γ-graphyne including the adsorption configurations with the minimum total energy, the charge transfer and charge density. The electronic properties including the band structure and density of states (DOS) were also discussed. The results indicated that Ag2 cluster had the minimum adsorption energy and charge transfer which might result in difficult adsorption process. Except for Ag2, all the introduction of Ag cluster exhibited n-type doping. For different Ag cluster, the interactions of atomic orbitals between Ag and C atom also varied. Our results can have certain guidance meaning for future study of the physical and chemical properties of modified graphyne or other monolayer materials.

First principles study of the Ag nanoclusters adsorption effect on the photocatalytic properties of AgBr(1 1 0) surface

The electronic structures and photocatalytic performance of Agn/AgBr(110)(n = 7–13) are studied using density functional theory (DFT). The adsorption of Agn (n = 7–13) nanoclusters on AgBr(110) surface induces a new metal-induced gap band (MIGB) located between the valence band (VB) and the conduction band (CB), the variety of the electronic characters of AgBr(110) favor the visible and infrared light absorption, which improves the sunlight utilization. The dominant localization of the photo-excited electrons on the Agn clusters of Agn/AgBr(110)(n = 7–13) facilitates the oxidation-reduction reactions occurring on the surface and also effectively reduces the photolysis of AgBr under the sunlight irradiation. The overpotentials of the CB and VB edges indicate that photocatalytic conversion of CO2 with H2O to methanol is possible on AgBr(110) deposited with the Agn nanoclusters, which has been realized experimentally (An et al., 2012). The substantial strengthening of visible and infrared light absorption and the free energy profiles for the conversion of CO2 with H2O to methanol indicate that Ag13/AgBr(110) surface can be expected to be the excellent photocatalysts.

Stabilized Silver Nanoparticles and Nanoclusters Agn in Humic-Based Bioactive Nanocomposites

Silver-containing nanocomposites synthesized from the compounds of a humic series have been studied using modern physical–chemical methods (EPR, TEM, IR and XRD, etc.). It is shown that the humic substances with different functional groups and isolated from different sources have also different ability of stabilizing the silver nanoparticles. Long-term stable nanoparticles and silver clusters have been found. A multiplet, observed in the EPR spectra of silver-containing nanocomposites, which are obtained from humic substances isolated from therapeutic muds and shales, is assigned to the formed Agn nanoclusters. Formation of the silver molecular clusters depends on the kind of humic substances and depth of their decomposition.

Adsorption of He–Ar binary mixture on the silver nanoclusters: A molecular dynamics investigation on the effects mole fraction of mixture, shape and size of the nanocluster

Adsorption of supercritical He–Ar binary mixture with different mole fractions on the AgN nanoclusters with different shapes and sizes was studied by molecular dynamics simulation at various temperatures. Adsorption energy per Ag atom, diffusion coefficients of Ar and He, and their activation energy of diffusion were calculated for the mentioned nanocluster/(gas mixture) systems. Results for adsorption energy propose (icosahedron>octahedron>truncated-octahedron>spherical>cubic) trend for the cluster-gas interaction strength which is decreased by cluster size and increased by mole fraction of Ar. The obtained data for diffusion coefficient proposes the (icosahedron<octahedron<truncated-octahedron<spherical<cubic) trend for both of He and Ar adsorbates in which diffusion ability is decreased by size of the cluster. The effect of mole fraction of Ar for diffusion coefficients of He and Ar is in reverse direction in such a way that diffusion coefficient of Ar is increased by its mole fraction. For activation energy of diffusion, the trend of shape effect is similar to that of the diffusion coefficient with a little difference in truncated-octahedron and spherical geometries. Also, the effect of size of the cluster and mole fraction of Ar for activation energy of diffusion is the same as diffusion coefficient. Finally, effect of temperature on the mentioned properties is straightforward in such a way that as temperature increases, the absolute value of adsorption energy decreases, but diffusion coefficient and its activation energy increases.

Adsorption of He gas on the Agn nanoclusters: A molecular dynamic study

Using molecular dynamics simulations, the adsorption of He gas on the Ag nanoclusters were investigated as a function of pressure, temperature and diameter of nanoclusters. We have calculated the average interaction energy between the gas atoms and the Ag nanoclusters, adsorption constant and enthalpy of adsorption for all of the Ag nanoclusters. Results show that the adsorption constant, the value of average interaction energy and the enthalpy of adsorption decrease when cluster size increases.

Formation and Control of Ultrasharp Metal/Molecule Interfaces by Controlled Immobilization of Size‐Selected Metal Nanoclusters onto Organic Molecular Films

The formation of metallic layers on ultrathin molecular films via a well‐controlled interface is essential for constructing organic nanodevices composed of metal/molecule/metal sandwich junctions. The scanning tunneling microscopy and spectroscopy studies demonstrate that an ultrasharp metal/molecule interface is realizable by depositing size‐selected Ag nanoclusters (Agn) from the gas phase on few‐layer films of C60 molecules. It is also demonstrated that Agn nanoclusters can be immobilized on monolayer films of oligothiophene molecules via C60 molecules, although they three‐dimensionally aggregate on bare oligothiophene films. It is also shown that electrons and holes are injected into the topmost layer of C60 films via the Agn/C60 interface. Moreover, the barrier height for carrier injection at the Agn/C60 interface can be modified depending on the size of Agn nanoclusters and the kinetic energy during the deposition. The present results demonstrate that the controlled immobilization of metallic nanoclusters on molecular films can be used as a fabrication technology for metal/molecule/metal junctions.

Ag2SO4 decorated with fluorescent Agn nanoclusters

Here we report on the production of an Ag2SO4/Ag2O mixed-grain powder during the anodization of Ag foil in a HF-H2SO4 electrolyte. We propose that there are three competing reactions during the anodization process: (i) the production of Ag2O at the Ag foil anode surface from the presence of water in the electrolyte, (ii) the dissolution of the Ag2O in the presence of HF releasing Ag+ ions, (iii) the precipitation of Ag+ and SO42− ions, as Ag2SO4 on the Ag foil anode surface. This co-precipitation/dissolution process ultimately results in a mixed-grain powder. We then show that the Ag2O embedded within the mixed-grain is photo-decomposed to produce highly fluorescent silver nanoclusters (Agn) which decorate the Ag2SO4 crystals. The Ag2SO4 salt offers a stable matrix for the photo-decomposed Agn nanoclusters to emit their strong fluorescence.

Mechanism of Agn Nanocluster Photoproduction from Silver Oxide Films

Thin AgO films are readily photoactivated at room temperature to produce dynamic, multicolored fluorescent Agn nanoclusters. Writing efficiencies were separately examined as functions of excitation wavelength, intensity, and environmental interactions. The effects of external conditions on written nanocluster fluorescence are interpreted in terms of a mechanistic understanding of fluorescent Agn nanocluster creation and subsequent spectral dynamics, illustrating the equilibrium between nanocluster creation and destruction.