Silver Monomers Research Articles

Vacuum thermal decomposition behavior of Ag2Te

Silver and tellurium are crucial valuable metallic elements in anode slimes. During pyrometallurgical processing, tellurium exists in the alloy as the stable compound Ag2Te. The current process of separating tellurium from silver-tellurium compounds in crude silver by oxidizing tellurium into slag leads to undesirable loss of silver, low recovery rates of tellurium, and considerable slag. An environmentally friendly and efficient vacuum thermal decomposition process of Ag2Te was proposed, and the effects of temperature, pressure, and holding time on the decomposition of Ag2Te were investigated. The Experimental temperature was thermodynamically calculated to be in the range of 1473–1673 K and pressure in the range of 1–100 Pa. As the temperature increases, especially above 1573 K, the silver volatiles increase significantly, and silver and tellurium vapors react strongly to form stable silver-tellurium compounds. Investigating the volatilization and condensation mechanisms of silver and tellurium highlights the importance of inhibiting silver volatilization to achieve efficient separation of silver and tellurium. Volatiles containing 98.85% tellurium mainly as tellurium monomer, and a remained melt consisting of 95.56% silver primarily as silver monomer were produced at 1523 K, 50 Pa, and an 8-h holding time.

Double regulation of conductivity by adhesive hydrogel based on catechol‐modified sodium alginate /acrylamide hydrogel with silver ions

AbstractThe purpose of this study is to explore how to control the conductivity of gel conveniently and effectively through experiments. First, a kind of acrylamide‐based composite with adhesion and conductivity adjustment was prepared by adding silver ions and silver monomers to the gel in one step. The semi interpenetrating network structure formed by the molecular chain of polyacrylamide and catechol modified sodium alginate in the composite is cross‐connected with silver ions to form a double network structure. This change of network structure not only makes the structure of gel more stable, but also brings extraordinary conductivity. Secondly, different types of conductive ions and organic solutions were added to the gel system. Electrochemical impedance spectroscopy showed that the addition of silver enhanced the conductivity of the material; When NaNO3 is used to replace water molecules in PAM, the ionic conductivity can be increased by 75.3% (from 2.44 × 10−5 to 20.8 × 10−5 mscm−1). When PDA/PAM was soaked in AgNO3, the ionic conductivity increased in the range of 10.4% ~ 674%. It provides a novel strategy for controlling the conductivity of composite materials.

Nanosilver-stimulated heterophil extracellular traps promoted liver and kidney injury in chicken

Nanosilver is a metallic silver monomer with a diameter of <100 nm, which has excellent antibacterial activity and is widely used in the fields of medicine and sanitation, disinfection of drinking water in daily life and feed additives in livestock and poultry farming. Heterophil extracellular traps (HETs) are an important part of innate immunity in chickens and have an excellent antimicrobial effect, but their excessive release caused tissue damage. Nanosilver overdose caused toxic effects in chickens, while immunotoxic effects of nanosilver on chickens have not been reported. In this study, we explored the effects of nanosilver-induced HETs on chicken liver and kidney damage and further investigated the molecular mechanism of nanosilver-induced HETs release. The results showed that nanosilver significantly upregulated serum HETs and caused liver and kidney damage. The classical structure of nanosilver-induced HETs was also observed, and nanosilver-induced HETs were dependent on reactive oxygen species (ROS), extracellular regulatory protein kinase (ERK)1/2, p38 and glycolysis pathways. In summary, this research suggests that nanosilver induced HETs release, but excessive HETs release also caused damage to chicken. It also helps to understand the importance of moderate application of nanosilver, which may improve animal immunity but avoid negative effects in safeguarding the economic efficiency of poultry farming.

Multicolorimetric and fluorometric dual-modal immunosensor for histamine via enzyme-enabled metallization of gold nanorods and inner filter effect of carbon dots

Histamine (HA) is one of the key causative agents associated with allergies and food poisoning. The accurate and convenient detection of HA is highly required to avert HA toxicity and ensure food safety. Herein, a multicolorimetric and fluorometric dual-readout immunosensor for HA detection was developed based on an alkaline phosphatase (ALP) enabled multicolor change reaction and fluorescence quenching of carbon dots (CDs) resulting from the metallization of gold nanorods (Au NRs). In this immunosensor, ALP is employed as labeling enzyme which can efficiently catalyze the hydrolysis of ascorbic acid 2-phosphate into ascorbic acid (AA). Then, the resultant AA can reduce Ag+ into silver monomer, and a silver shell is deposited on the surface of Au NRs to form Au/Ag core-shell nanorods (Au NRs@Ag). This leads to the blue-shift of the longitudinal local surface plasmon resonance peak of Au NRs and a vivid multicolor variation. Meanwhile, the fluorescence of CDs can be gradually quenched via inner-filter effect by the resultant Au NRs@Ag. Multicolorimetric assay allows a semiquantitative detection with a visible detection limit of 0.25 mg/L, and fluorometric assay provides a sensitive and accurate quantitative detection with a detection limit of 0.08 mg/L. The immunosensor not only fulfills the reliable and accurate detection requirements but also fits different testing needs for both laboratory and on-site detection.

Probing Kinetics and Mechanism of Formation of Mixed Metallic Nanoparticles in a Polymer Membrane by Galvanic Replacement between Two Immiscible Metals: Case Study of Nickel/Silver Nanoparticle Synthesis.

Galvanic replacement between metals has received notable research interest for the synthesis of heterometallic nanostructures. The growth pattern of the nanostructures depends on several factors such as extent of lattice mismatch, adhesive interaction between the metals, cohesive forces of the individual metals, etc. Due to the difficulties in probing ultrafast kinetics of the galvanic replacement reaction and particle growth in solution, real-time mechanistic investigations are often limited. As a result, the growth mechanism of one metal on the surface of another metal at the nanoscale is poorly understood so far. In the present work, we could successfully probe the galvanic replacement of silver ions with nickel nanoparticles, stabilized in a polymer membrane, using two complementary methods, namely, small-angle X-ray scattering (SAXS) and radiolabeling, and the results are supported by density functional theory (DFT) computations. The silver-nickel system has been chosen for the present investigation because of the high degree of bulk immiscibility caused by the large lattice mismatch (15.9%) and the weak adhesive interaction, which makes it a perfect model system for immiscible metal pairs. Membrane, as a host medium, plays a crucial role in retarding the kinetics of atomic and particle rearrangements (nucleation and growth) due to slower mobility of the atoms (monomers) and particles within the polymer network. This allowed us to examine the real-time concentration of silver monomers during galvanic replacement of silver ions with nickel nanoparticles and evolution of Ni/Ag nanoparticles. From combined experiment and DFT computations, it has been demonstrated, for the first time to the best of our knowledge, that the majority of silver atoms, which are produced on the nickel nanoparticle surface by galvanic reactions, do not form traditional core-shell nanostructures with nickel and undergo a self-governing sequential nucleation and growth of silver nanoparticles via formation of intermediate prenucleation silver clusters, leading to the formation of mixed metallic nanoparticles in the membrane. The surface of NiNPs has a heterogeneous effect on the silver nucleation pathway, which is evident from the reduced critical free energy barrier of nucleation (ΔGcrit). The present work establishes an original mechanistic pathway based on a sequential nucleation model for formation of mixed metallic nanoparticles by the galvanic replacement route, which opens up future possibilities for size-controlled synthesis in mixed systems.

Factors affecting the solubility of ionic compounds

In order to provide a more robust understanding for the general solubility rules provided in most chemistry introductions, the charge densities for common ionic cations and anions are computed via quantum chemical methods. It is shown that low charge densities on either the cation or, especially, the anion promote solubility. The lowest anion charge densities produced correspond to chlorate, perchlorate, and acetate which are known always to be soluble for the analyzed cations. Silver has the lowest charge density of the cations examined, but is rarely soluble, only with these three singly-charged polyatomic anions and the related nitrate anion. The silver chloride bond is 8kcal/mol stronger than silver chlorate and 12kcal/mol stronger than silver nitrate. Sodium chloride is 6kcal/mol weaker than silver chlorate with potassium chlorate 8kcal/mol weaker. Hence, silver monomer salts are shown here to produce high bond energies to atomic anions showcasing why charge density alone cannot explain aqueous solubility, even though it is a good marker in a general sense.

Partial Ionic Character beyond the Pauling Paradigm: Metal Nanoparticles

A canonical perspective on the chemical bond is the Pauling paradigm: a bond in a molecule containing only identical atoms has no ionic character. However, we show that homonuclear silver clusters have very uneven charge distributions (for example, the C2v structure of Ag4 has a larger dipole moment than formaldehyde or acetone), and we show how to predict the charge distribution from coordination numbers and Hirshfeld charges. The new charge model is validated against Kohn–Sham calculations of dipole moments with four approximations for the exchange–correlation functional. We report Kohn–Sham studies of the binding energies of CO on silver monomer and silver clusters containing 2–18 atoms. We also find that an accurate charge model is essential for understanding the site dependence of binding. In particular we find that atoms with more positive charges tend to have higher binding energies, which can be used for guidance in catalyst modeling and design. Thus, the nonuniform charge distribution of silver clusters predisposes the site preference of binding of carbon monoxide, and we conclude that nonuniform charge distributions are an important property for understanding binding of metal nanoparticles in general.

Formation Mechanism of Silver Nanoparticles Stabilized in Glassy Matrices

In any given matrix control over the final particle size distribution requires a constitutive understanding of the mechanisms and kinetics of the particle evolution. In this contribution we report on the formation mechanism of silver nanoparticles embedded in a soda-lime silicate glass matrix. For the silver ion-exchanged glass it is shown that at temperatures below 410 °C only molecular clusters (diameter <1 nm) are forming which are most likely silver dimers. These clusters grow to nanoparticles (diameter >1 nm) by annealing above this threshold temperature of 410 °C. It is evidenced that the growth and thus the final silver nanoparticle size are determined by matrix-assisted reduction mechanisms. As a consequence, particle growth proceeds after the initial formation of stable clusters by addition of silver monomers which diffuse from the glass matrix. This is in contrast to the widely accepted concept of particle growth in metal-glass systems, in which it is assumed that the nanoparticle formation is predominantly governed by Ostwald ripening processes.

Argon Solvent Effects on Optical Properties of Silver Metal Clusters

Argon gas at a high pressure (∼80 bar) has been expanded using a miniaturized pulsed valve at room temperature, producing a supersonic beam of cold, large argon droplets. Atoms of silver are subsequently embedded into the droplet using the pick-up technique. The resulting Ag(n)Ar(droplet) distribution was analyzed using multiphoton laser ionization time-of-flight mass spectrometry. Besides bare metal clusters, snowballs of silver monomers and dimers encapsulated in up to 50 argon atoms have been observed. The influence of the solvent on the optical absorption of the solute was studied for embedded Ag(8) using resonant two-photon ionization in the ultraviolet. A redshift and broadening of the Ag(8)Ar(droplet) optical spectrum compared to that measured in pure [Federmann et al., Eur. Phys. J. D 1999, 9, 11] and Ar-doped helium droplets [Diederich et al., J. Chem. Phys.2002, 116, 3263] was observed, which is attributed to the interaction with the larger Ar matrix environment.

Enhanced Bonding of Silver Nanoparticles on Oxidized TiO2(110)

The nucleation and growth of silver nanoclusters on TiO2(110) surfaces with on-top O adatoms (oxidized TiO2), surface O vacancies and H adatoms (reduced TiO2) have been studied. From the interplay of scanning tunneling microscopy/photoelectron spectroscopy experiments and density functional theory calculations, it is found that silver clusters are much more strongly bonded to oxidized TiO2(110) surfaces than to reduced TiO2(110) model supports. It is shown that electronic charge can be transferred from silver clusters to the oxidized TiO2(110) surface, as evidenced by the reappearance of the Ti3d defect state upon silver exposure. Furthermore, from both scanning tunneling microscopy data and density functional theory calculations the most favorable adsorption site of silver monomers on oxidized TiO2(110) is one that bridges between on-top O adatoms and regular surface O atoms nearby.

Self-Assembly of Silver(I) Coordination Polymers Formed through Hydrogen Bonding with Ditopic Heteroscorpionate Ligands

Eight coordination polymers of silver Ag(I) derived from bidentate coordinating heteroscorpionate ligands, (4-carboxyphenyl)bis(3,5-dimethylpyrazolyl)methane (L4c) and (3-carboxyphenyl)bis(3,5-dimethylpyrazolyl)methane (L3c), have been synthesized and characterized by X-ray diffraction, ESI-MS, IR spectroscopy, and elemental analysis. By varying the solvent polarity, the protonation state of the uncoordinated carboxylate groups and hence their solid-state interactions can be controlled. While the silver monomers (tectons) possess chirality due to the asymmetric coordination of the achiral ligands to the silver ion, all of the solid-state materials were isolated as racemic mixtures.

Theoretical study of the interaction of nitric oxide with small neutral and charged silver clusters

The adsorption of NO molecule on small neutral, anionic, and cationic silver clusters Ag n ( n = 1–7) has been studied using density functional theory method with the generalized gradient approximation (PW91PW91). The adsorption energies of NO molecule on the silver clusters have an odd–even alternation pattern except for the cationic silver monomer and dimer, on which the adsorption energies are almost the same. Natural bond orbital analysis shows that NO molecule often attracts electrons from the silver clusters except for some silver cluster cations ( n = 1 and 4).

Energy-controlled depositions of size-selected silver nanoparticles on HOPG substrates

Abstract Silver monomer (Ag+1) or heptamer (Ag+7) ions were deposited on highly oriented pyrolytic graphite (HOPG) substrates at various, well-controlled collision energies. The total amount of silver (Ag) atoms remaining on the substrates after the collision was examined by measuring the Ag 3d5/2 photoelectron intensities. The collision energy dependence of the number of deposited Ag atoms revealed that there exist, for both species, three well-defined energy regions, for which soft landing, rebounding, or implantation is a dominant process. It was found that the collision energy dependence for Ag7 is well scaled to that for Ag1 by the factor 1/72/3 rather than 1/7, reflecting the compactness of Ag7.

Surface Plasmon Resonance-Laser Desorption/Ionization-Time-of-Flight Mass Spectrometry

The laser desorption/ionization (LDI) process is investigated under surface plasmon resonance (SPR) conditions using time-of-flight mass spectrometry (TOFMS). We demonstrate that LDI-TOFMS at the SPR angle requires a lower minimum laser fluence for the production of silver monomer and cluster cations from ablation of a thin silver film substrate. In the LDI of gramicidin S deposited on a thin silver film substrate, the largest intensity for the molecular cation peak occurs when the laser light is incident on the substrate at a specific SPR angle. These results fully confirm SPR enhancement of the LDI process. The capability to perform SPR-LDI on a larger molecular weight analyte (1141 amu for gramicidin S) represents a new milestone beyond the previous achievement with rhodamine B (479 amu). A better understanding of the SPR mechanism is gained with respect to the substrate metals (silver vs aluminum), desorption (microscopic vs mesoscopic), and ionization (chemical vs multiphoton). These findings may be useful in the future design of SPR-LDI techniques for better TOFMS analysis of higher mass biomolecules.

Reduction of AgI1(NH3)2+to Ag01(NH3)2in Solution. Redox Potential and Spectral Study

Pulse radiolysis is used to determine the absorption spectra of the transient species formed during the decay of the hydrated electron in an aqueous solution of AgI1(NH3)2+. The absorption spectrum attributed to Ag01(NH3)2 presents three peaks at 345, 385, and 435 nm. A theoretical estimation of the redox potential of the couple AgI1(NH3)2+/Ag01(NH3)2 yields the value −2.4 VNHE. This value is consistent with the fact that AgI1(NH3)2+ is not directly reduced by (CH3)2ĊO- and shows that the redox potential of the silver monomer couple is lowered by ammonia ligands.

Enhancement of Metallic Silver Monomer Evaporation by the Adhesion of Polar Molecules to Silver Nanocluster Ions

Abstract : We have compared the metallic evaporation channels from metastable Ag(X=5,7,11)(AgI)(Y=1-4)(+) clusters in the 1st FFR of a double focussing mass spectrometer with that of the corresponding pure metallic clusters, Ag(X=5,7,11) (+). It is found that the presence of the polar AgI molecules increases the rate of silver monomer evaporation relative to that of silver dimer evaporation. Using thermodynamic expressions for the heat of evaporation of the different evaporation processes and assuming the absence of reverse activation energies, an expression for the difference between the activation energy of silver monomer and dimer evaporation is derived. It is shown that dipole/induced-dipole forces resulting from the presence of AgI polar molecules lead to an enhancement of silver monomer evaporation if the polarizability of the pure metallic cluster ions increases with the number of Jellium electrons. Our theoretical calculations of the static polarizabilities of (Ag(x))(+) using time dependent density functional theory within the local density approximation, shows a smooth increase in the polarizabilities with the number of the Jellium electrons in these clusters. Finally, we observe that the enhancement of Ag monomer evaporation per AgI added is smaller for clusters with even number of AgI molecules than with odd numbers. This was proposed to result from the contribution of configurations with dipole 'pairing' of the AgI molecules in clusters with even number of AgI molecules. Dipole pairing would decrease the average dipole/induced-dipole interaction between the AgI molecules and the metallic part of these 'mixed' clusters.

Diffusion properties and collisional dynamics of Ag adatoms and dimers on Pt(111)

We studied diffusion properties of silver monomers and dimers on the (111) surface of platinum by molecular dynamics simulations. Activation energies calculated from Arrhenius plots of diffusion coefficients up to T = 300 K turn out to be equal to E d,1 = 0.058 eV for the monomer and E d,2 = 0.090 eV for the dimer. Simulations of the impact of Ag 2 on the surface reveal that the dimer has the largest probability of being found stable on the surface when the temperature is in the range 150 < T < 300 K.

Diffusion properties and collisional dynamics of Ag adatoms and dimers on Pt(111)

Abstract We studied diffusion properties of silver monomers and dimers on the (111) surface of platinum by molecular dynamics simulations. Activation energies calculated from Arrhenius plots of diffusion coefficients up to T = 300 K turn out to be equal to Ed,1 = 0.058 eV for the monomer and Ed,2 = 0.090 eV for the dimer. Simulations of the impact of Ag2 on the surface reveal that the dimer has the largest probability of being found stable on the surface when the temperature is in the range 150