Temperature Influence on the Morphology and Roughness of Silver Deposit Formed by Cementation

The morphology and surface roughness of silver deposits formed by cementation in 0.5M H₂SO₄ solution containing 0.5M CuSO₄ was investigated at various temperatures. The influence of O₂ on the morphology of deposited Ag on the Cu surface was studied in solutions containing 20 or 100 mg/dm³ initial Ag⁺. Surface‐height‐distribution diagrams were calculated from scanning‐electron‐microscopic (SEM) images. For the lower Ag⁺ concentration, the formation of granular deposits occurred in the presence of O₂. In contrast, under anaerobic conditions, rather flat deposits with tiny Ag crystals were observed. For the higher Ag⁺ concentration, the presence of O₂ did not significantly affect the morphology of the Ag deposit, but increasing temperature resulted in more‐compact and denser dendrites. Differences in the Ag‐deposit morphology and surface roughness were attributed to a different mechanism in the absence of O₂. Under anaerobic conditions, a competitive reaction between Ag⁺ and Cu⁺ occurs in bulk solution, which consumes additional Ag⁺ ions. The SEM images and, especially, distribution diagrams of the surface height provided useful information on the formation and expansion of anodic sites on the Cu surface at various temperatures.     

Surface‐Roughness Evolution During the Cementation of Silver Ions on Solid Copper in Aqueous Sulfuric Acid Solution

The evolution of the surface roughness during cementation of Ag⁺ conducted either in O₂‐free or O₂‐saturated aqueous H₂SO₄/CuSO₄ was investigated at two different initial concentrations of Ag⁺. The kinetics data of the process determined previously in the rotating cylinder were linked directly with scanning‐electron‐microscope (SEM) images and surface‐height‐distribution diagrams calculated for various cementation times. It was found that, at the beginning of the process, the surface roughness decreases due to formation of a flat Ag layer on the top of the surface, independent of the presence or absence of O₂ in the system. With increasing reaction time, an increase in the surface roughness was observed. The rate enhancement of the process is mainly responsible for the increase of the surface roughness in the O₂‐saturated solutions, especially at the higher initial Ag⁺ concentration (100 mg/dm³). The rate enhancement observed at a latter stage of the process, connected with the increase of the effective surface area of the cathodic sites, was separated from the rate enhancement induced by the competitive chemical process occurring in O₂‐free solution. The difference in the mechanisms of the processes conducted under aerobic and anaerobic conditions was reflected in the surface‐heigth distributions calculated from the SEM images.     

Nature of the silver precipitation obtained by cementation from thiosulphate solutions

The morphology and composition of the deposits formed on the surface of magnesium disk during cementation from thiosulphate solutions (0.0025–0.1M) [Ag(S₂O₃)₂]³⁻ + 0.5M S₂O₃ ²⁻ have been studied. A porous deposit with low adhesion is formed on the surface of the magnesium metal substrate. Within a wide range of [Ag(S₂O₃)₂]³⁻ ion concentrations, sulfur as well as silver are constituents of the deposit at the initial stages of cementation and at the end of the reaction. This is attributed to the electrochemical behaviour of magnesium in thiosulphate solutions resulting in the exceeding of current limit on cathode for pure silver reduction. Hence, parallel electrochemical reactions take place that are very close in their values to the standard redox potentials of reduction of [Ag(S₂O₃)₂]³⁻ ions to Ag⁰ and S₂O₃2− ions to S²⁻. Sulfur content in the cement deposits increases with the decrease in [Ag(S₂O₃)₂]³⁻ ion concentration and increase in cementation time. This tendency is also observed with the decreasing solution temperature.     

A Cryptate Reference Electrode for Ionic Liquids

The cryptate electrode (Ag/Ag⁺222), prepared by immersing silver wire in a solution of silver(I) salt and the cryptand 222 (4,7,13,16,21,24‐hexaoxa‐1,10‐diazabicyclo[8.8.8]hexacosane) in ionic liquids have been studied. The potential of the electrode is stabilized by the equilibrium of the Ag⁺ ion complexation by the cryptand, similarly to the potential stabilization by the ionic product of slightly soluble salts, used in aqueous electrodes of the second kind. The Ag/Ag⁺222 cryptate electrode (concentration of the cryptate was much higher than the silver(I) cation concentration, [222]>[Ag⁺]) may be used as a reference electrode in room temperature ionic liquids. The potential of the Ag/Ag⁺222 electrode is less sensitive to the presence of impurities, such as halides or water, in comparison to the Ag/Ag⁺ electrode. After anodic or cathodic polarization, the potential of the Ag/Ag⁺222 electrode comes back to the initial open circuit potential quickly. Preparation of the Ag/Ag⁺222 reference electrode is very easy: a silver wire is immersed in a solution of Ag⁺ salt and cryptand 222 (both available commercially) in the ionic liquid under study.     

γ-Ray induced catalytic properties of the silica nanoparticles dispersed in the aerated aqueous solution

Silica nanoparticles (NPs) dispersed in an aerated aqueous solution containing Ag⁺ were irradiated to a dose of 10 kGy using ⁶⁰Co γ-rays. The typical surface plasmon band of Ag NPs was observed around 400 nm, indicating that even in the presence of dissolved oxygen the reduction of Ag⁺ occurred by silica NPs. Transmission electron microscopy images indicated that Ag NPs formed on the surface of the silica NPs. The subtraction spectra showed broad absorption around 500 nm with the absorbance depending on the dose. The electrons generated by charge separation from silica NPs with a size of about 12 nm reduce Ag⁺ to Ag⁰ and form (Ag⁰) _n species on the silica NPs, and the type of (Ag⁰) _n species formed depended on the silica NP, and Ag⁺ contents, and the dose. In the co-presence of organic molecules on the silica NP such as rhodamine, the absorbance of the surface plasmon band of both Ag NPs and rhodamine decreased, indicating the electrons to participate in the reductive decomposition of rhodamine molecules adsorbed on the silica NP. Furthermore, in the case when the silica NPs contained fluorescein molecules, the fluorescein molecules were also decomposed, indicating that the fluorescein molecules adsorbed on the inner surface of the silica NPs. The addition of I₂ as an oxidative reagent prevented the decomposition of the fluorescein molecules, indicating that electrons are the main species emitted from irradiated silica NPs.     

The Geometric Structure of Silver‐Doped Silicon Clusters

Cationic silver‐doped silicon clusters, Si_nAg⁺ (n=6–15), are studied using infrared multiple photon dissociation in combination with density functional theory computations. Candidate structures are identified using a basin‐hopping global optimizations method. Based on the comparison of experimental and calculated IR spectra for the identified low‐energy isomers, structures are assigned. It is found that all investigated clusters have exohedral structures, that is, the Ag atom is located at the surface. This is a surprising result because many transition‐metal dopant atoms have been shown to induce the formation of endohedral silicon clusters. The silicon framework of Si_nAg⁺ (n=7–9) has a pentagonal bipyramidal building block, whereas the larger Si_nAg⁺ (n=10–12, 14, 15) clusters have trigonal prism‐based structures. On comparing the structures of Si_nAg⁺ with those of Si_nCu⁺ (for n=6–11) it is found that both Cu and Ag adsorb on a surface site of bare Si_n⁺ clusters. However, the Ag dopant atom takes a lower coordinated site and is more weakly bound to the Si_n⁺ framework than the Cu dopant atom.     

Reactivity Control of C?H Bond Activation over Vanadium–Silver Bimetallic Oxide Cluster Cations

Vanadium–silver bimetallic oxide cluster ions (V_xAg_yO_z⁺; x=1–4, y=1–4, z=3–11) are produced by laser ablation and reacted with ethane in a fast‐flow reactor. A reflectron time of flight (Re‐TOF) mass spectrometer is used to detect the cluster distribution before and after the reactions. Hydrogen atom abstraction (HAA) reactions are identified over VAgO₃⁺, V₂Ag₂O₆⁺, V₂Ag₄O₇⁺, V₃AgO₈⁺, V₃Ag₃O₉⁺, and V₄Ag₂O₁₁⁺ ions, in which the oxygen‐centered radicals terminally bonded on V atoms are active sites for the facile HAA reactions. DFT calculations are performed to study the structures, bonding, and reactivity. The reaction mechanisms of V₂Ag₂O₆⁺+C₂H₆ are also given. The doped Ag atoms with a valence state of +1 are highly dispersed at the periphery of the V_xAg_yO_z⁺ cluster ions. The reactivity can be well‐tuned gradually by controlling the number of Ag atoms. The steric protection due to the peripherally bonded Ag atoms greatly enhances the selectivity of the V–Ag bimetallic oxide clusters with respect to the corresponding pure vanadium oxide systems.     

Formation mechanism of nanostructured Ag films from Ag2O particles using a sonoprocess

Nanostructured Ag films composed of nanoparticles and nanorods can be formed by the ultrasonication of ethanol solutions containing Ag₂O particles. The present work examined the formation process of these films from ethanol solutions by two different agitation methods, including ultrasonication and mechanical stirring. The mass-transfer process from Ag₂O particles to ethanol solvent is accelerated by the mechanical effects of ultrasound. Ag⁺ ions and intermediately reduced Ag clusters were released into the ethanol. These Ag⁺ ions and Ag clusters provide absorption bands at 210, 275 and 300 nm in UV-vis spectra. These bands were assigned to the absorption of Ag⁺, Ag ₄ ²⁺ and Ag_n (n?≈?3). The Ag_n clusters that readily grow to become Ag nanoparticles were formed due to the surface reaction of Ag₂O particles with ethanol under ultrasonication. The reactions of Ag⁺ ions in ethanol to form Ag nanomaterials (through the formation of Ag ₄ ²⁺ clusters) were also accelerated by ultrasonication.     

Mass spectrometric study of the dissociation of Group XI metal complexes with fatty acids and glycerolipids: Ag2H+ and Cu2H+ ion formation in the presence of a double bond

Results of mass spectrometric studies are reported for the collisional dissociation of Group XI (Cu, Ag, Au) metal ion complexes with fatty acids (palmitic, oleic, linoleic and α-linolenic) and glycerolipids. Remarkably, the formation of M₂H⁺ ions (M = Cu, Ag) is observed as a dissociation product of the ion complexes containing more than one metal cation and only if the lipid in the complex contains a double bond. Ag₂H⁺ is formed as the main dissociation channel for all three of the fatty acids containing double bonds that were investigated while Cu₂H⁺ is formed with one of the fatty acids and, although abundant, is not the dominant dissociation channel. Also, Cu(I) and Ag(I) ion complexes were observed with glycerolipids (including triacylglycerols and glycerophospholipids) containing either saturated or unsaturated fatty acid substituents. Interestingly, Ag₂H⁺ ion is formed in a major fragmentation channel with the lipids that are able to form the complex with two metal cations (triacylglycerols and glycerophosphoglycerols), while lipids containing a fixed positive charge (glycerophospocholines) complex only with a single metal cation. The formation of Ag₂H⁺ ion is a significant dissociation channel from the complex ion [Ag₂(L–H)]⁺ where L = Glycerophospholipid (GP) (18:1/18:1). Cu(I) also forms complexes of two metal cations with glycerophospholipids but these do not produce Cu₂H⁺ upon dissociation. Rather organic fragments, not containing Cu(I), are formed, perhaps due to different interactions of these metal cations with lipids resulting from the much smaller ionic radius of Cu(I) compared to Ag(I).     

Synthesis, Structure and Growth Mechanism of Size and Shape Tunable Au/Ag Bimetallic Nanoparticles

By simply adding ascorbic acid in advance of AgNO₃, the size and shape controllable Au/Ag bimetallic nanoparticles (NP) were prepared in the traditional Au growth solution free of seed at room temperature. The size distribution of NP is well uniform with ca. 10%–15% standard deviation in diameter. By changing CTAB concentration, the size and shape of NPs are tunable. After researching the surface‐enhanced Raman spectroscopy (SERS) behavior of the prepared NPs, an enhancement factor varied from 4.3×10⁴ to 1.1×10⁵ was obtained for the NP centered at ca. (64±8) nm. Electrochemical cyclic voltammetric results revealed that the so formed nanoparticles were Au riched Au/Ag bimetallic NP, and this formation might be due to the disproportionation reaction of Au⁺ prompted by Ag⁺ and the under potential deposition process of Ag⁺ on Au.     

Synthesis and Morphology of AgReO4 Plates,Rods, and Stars

AgReO₄ nanoplates and micron‐sized AgReO₄ rods and stars are obtained for the first time from controlled particle growth in THF. [NBu₄][ReO₄] or [NMe₄][ReO₄] and Ag(OTf) (OTf: triflate) are used as the starting materials. The crystal growth is directed by the presence (i.e., plates) or absence (i.e., rods, stars) of trioctylphosphine (TOP) as a coordinating agent as well as by the temperature of the reaction (i.e., plates, rods in refluxing THF; stars at room temperature). Altogether, the growth of the respective morphology can be attributed to the availability and diffusion rate of dissolved Ag⁺ that is influenced by the reaction temperature and the presence of TOP. The differently shaped AgReO₄ particles are characterized by scanning electron microscopy (SEM), X‐ray diffraction analysis (XRD), and Fourier‐transform infrared (FT‐IR) spectroscopy.     

Molten Ag2SO4‐based Ion‐Exchange Preparation of Ag0.5La0.5TiO3 for Photocatalytic O2 Evolution

Ag_0.5La_0.5TiO₃ with an ABO₃ perovskite structure was synthesized by a newly developed ion‐exchange method. Molten Ag₂SO₄ instead of traditional molten AgNO₃ was used as Ag⁺ source in view of its high decomposition temperature (1052 °C), thereby guaranteeing the complete substitution of Ag⁺ for Na⁺ in Na_0.5La_0.5TiO₃ with a stable ABO₃ perovskite structure at a high ion‐exchange temperature (700 °C). Under full‐arc irradiation, the O₂‐evolution activity of Ag_0.5La_0.5TiO₃ was about 1.6 times that of Na_0.5La_0.5TiO₃ due to the optimized electronic band structures and local lattice structures. On the one hand, the substitution of Ag⁺ for Na⁺ elevated the VBM and thus narrowed the band gap from 3.19 to 2.83 eV, thereby extending the light‐response range and, accordingly, enhancing the photoexcitation to generate more charge carriers. On the other hand, the substitution of Ag⁺ for Na⁺ induced a lattice distortion of the ABO₃ perovskite structure, thereby promoting the separation and migration of charge carriers. Moreover, under visible‐light irradiation, Ag_0.5La_0.5TiO₃ displayed notable O₂ evolution whereas Na_0.5La_0.5TiO₃ showed little O₂ evolution, thus demonstrating that the substitution of Ag⁺ for Na⁺ enabled the use of visible light to evolve O₂ photocatalytically. This work presents an effective route to explore novel Ag‐based photocatalysts.     

反应性模板法合成硫化银中空球-银纳米粒子异质结构

以Cu₂S中空球为反应性模板, 通过在水溶液中与银离子的阳离子交换和氧化还原反应制备了大小均匀的Ag₂S中空球-Ag纳米粒子异质结构, 即Ag₂S-Ag异质中空球. 该异质结构中每个Ag₂S中空球的直径约为600 nm, 壁厚约20–30 nm, 其表面均附着一个Ag纳米粒子. 采用扫描电子显微镜(SEM)、透射电子显微镜(TEM)、X射线衍射(XRD)和能量色散X射线谱(EDS)对所得Ag₂S-Ag异质中空球的结构和组成进行了表征. 若以CuS中空球为反应性模板, 在相似转化条件下则主要得到不含Ag粒子的Ag₂S中空球. 该结果表明, Cu₂S中的Cu(I)的还原性在Ag₂S-Ag异质中空球的形成中发挥了重要作用. 通过对所制备的Ag₂S-Ag异质中空球进行二次生长, 还可以得到Ag₂S中空球的半球表面均被Ag膜所包覆的Ag₂S-Ag异质中空球.     

Constructing mixed‐metal coordination polymers from copper(II)–pyridinedicarboxylate metalloligands

In the mixed‐metal complex catena‐poly[bis[diaquasilver(I)] [bis[aquacopper(II)]‐μ₃‐pyridine‐2,5‐dicarboxylato‐2′:1:1′κ⁵N,O²:O⁵:O⁵,O^5′‐μ‐pyridine‐2,5‐dicarboxylato‐2:1κ⁴N,O²:O⁵,O^5′‐disilver(I)‐μ₃‐pyridine‐2,5‐dicarboxylato‐1:1′:2′′κ⁵O⁵,O^5′:O⁵:N,O²‐μ‐pyridine‐2,5‐dicarboxylato‐1′:2′′′κ⁴O⁵,O^5′:N,O²] hexahydrate], {[Ag(H₂O)₂][AgCu(C₇H₃NO₄)₂(H₂O)]·3H₂O}_n, a square‐pyramidal Cu^II center is coordinated by two N atoms and two O atoms from two pyridine‐2,5‐dicarboxylate (2,5‐pydc) ligands and a water molecule, forming a [Cu(2,5‐pydc)₂(H₂O)]²⁻ metalloligand. One Ag^I center is coordinated by five O atoms from three 2,5‐pydc ligands and, as a result, the [Cu(2,5‐pydc)₂(H₂O)]²⁻ metalloligands act as linkers in a unique μ₃‐mode connecting Ag^I centers into a one‐dimensional anionic double chain along the [101] direction. The other Ag^I center is coordinated by two water molecules, forming an [Ag(H₂O)₂]⁺ cation. Four adjacent Ag^I centers are associated by Ag...Ag interactions [3.126 (1) and 3.118 (1) Å], producing a Z‐shaped Ag₄ unit along the [010] direction and connecting the anionic chains into a two‐dimensional layer structure. This study offers information for engineering mixed‐metal complexes based on copper(II)–pyridinedicarboxylate metalloligands.     

Dependence of the catalytic activity of Ag/Al2O3 on the silver concentration in the selective reduction of NOx with n-hexane in the presence of H2

The activity of 0.25–5% Ag/Al₂O₃ catalysts in the selective catalytic reduction of nitrogen oxides with n-hexane under the conditions of promotion with a small amount of H₂ was studied. It was found that, upon the introduction of ∼1000 ppm of H₂ into the reaction mixture, the Ag/Al₂O₃ samples containing 1–2% Ag exhibited optimum activity and selectivity. It was established that, in the presence of 1000 ppm of H₂, the rate of the selective catalytic reduction of NO _x was higher by a factor of 10–13, and the onset temperature of the reaction was lower by approximately 100°C. It was found by X-ray photoelectron spectroscopy, temperature-programmed reduction, and UV spectroscopy that the high activity of 1–2% Ag/Al₂O₃ catalysts was due to the presence of small Ag _n ^δ+ and Ag _m ⁰ clusters on their surface. A decrease in the concentration of Ag below the optimum value resulted in the predominance of an inactive ionic form on the catalyst surfaces. As the concentration of Ag was increased (>2%), large particles of Ag₂O and Ag⁰, which facilitate the oxidation of n-C₆H₁₄, were formed to lead to a decrease in selectivity and in the degree of reduction of nitrogen oxides.     

Characterization of [peptide+(Ag)n]+ complexes using matrix-assisted laser desorption/ionization time-of-flight mass spectrometry

Silver ion complexes of peptides [M + (Ag)_n]⁺, M = angiotensin I or substance P where n = 1–8 and 17–23 for angiotensin I and n = 1–5 for substance P, are identified and characterized using matrix‐assisted laser desorption/ionization time‐of‐flight mass spectrometry (MALDI‐TOFMS). The Ag⁺ coordination number exceeds the number of available amino acid residues in angiotensin I whereas the number of observed complexes in substance P is less than the number of amino acid residues in it. The larger coordination number of angiotensin I with Ag⁺ indicates the simultaneous binding of several Ag⁺ ions to the amino acid residue present in it. The lower number of observed complexes in substance P suggests the binding of two or more residues to one Ag⁺ ion. The presence of trifluoroacetic acid in the peptide samples reduces the Ag⁺ coordination ability in both the peptides which indicates that the basic residues in it are already protonated and do not participate in the Ag⁺‐binding process. The Ag⁺ ion also forms a complex with the α‐cyano‐4‐hydroxycinnamic acid (CHCA) matrix and is observed in the MALDI mass spectra and the formation of [CHCA + Ag]⁺, [CHCA + AgNO₃]⁺ and [(CHCA)₂ + Ag]⁺ ions is due to the high binding affinity of Ag⁺ to the CN group of CHCA. Copyright © 2010 John Wiley & Sons, Ltd.     

Oxidation‐induced nanostructures on Cu{100}, Cu(Ag) and Ag/Cu{100} studied by photoelectron spectroscopy

Initial surface oxidation and nanoscale morphology on Cu{100}, Cu(Ag) and Ag/Cu{100} have been investigated in situ by X‐ray photoelectron spectroscopy (XPS), X‐ray induced Auger electron spectroscopy (XAES) and the inelastic electron background analysis as a function of oxygen exposure at 3.7 × 10^?2 and 213 mbar pressures at a surface temperature of 373 K. Relative Cu₂O concentrations have been quantified by analysis of the peak shape of the XAES Cu LMM transition. The surface morphology of Cu₂O islands and the Ag layer has been characterized by inelastic electron background analysis of XAES O KLL and Ag 3d transitions. Oxygen‐induced segregation of Cu, as well as the subsequent Cu₂O island formation on Cu(Ag) and Ag/Cu{100} surfaces, has been investigated quantitatively. Our results indicate that Ag has a clear inhibitive effect on the initial oxidation and Cu₂O island formation on Cu(Ag) and Ag/Cu{100} surfaces. The Cu₂O islands are also observed to remain highly strained on Ag/Cu{100} even at higher O₂ exposures. The results suggest that strained Cu₂O islands eventually penetrate through the buried Ag layer, and in conjunction with segregating Cu atoms enable the oxidation to proceed at a similar rate to or even faster than on the unalloyed Cu surface. Copyright © 2007 John Wiley & Sons, Ltd.     

Monolayer deposition of silver and copper onto platinum electrodes at non-equilibrium conditions

Ag and Cu were deposited in submonolayer amounts onto Pt electrodes at constant cathodic potentials within the hydrogen adsorption region. Rectangular pulses of Cu²⁺ or Ag⁺ fluxes to the Pt surface were generated by a Cu or Ag generator electrode using the twin electrode thin-layer technique. The analysis of the response currents of the Pt electrode yields in formation about the metal deposition process at non-equilibrium conditions. Cu and Ag were found to deposit directly as monolayers and not at random. The displacement of adsorbed hydrogen was measured as a function of the quantity of metal deposited.     

Novel metal cluster complexes synthesized by matrix deposition of mass-selected clusters

Metal complexes produced by depositing size selected Fe and Ag cluster cations in N₂ and O₂ matrices respectively are studied by infrared spectroscopy. Unknown species such as Fe(N₂)x, Fe₃ (N₂)x and Ag₃(O₂)x are observed. The IR spectra of Ag⁺, Ag ₂ ⁺ and Ag ₉ ⁺ in excess O₂ indicate that no complexes involving molecular oxygen are formed. However, the strong silver cluster UV-visible absorptions detected in Ar matrices disappear in the oxygen matrices, suggesting that silver-oxygen complexes are formed with dissociated oxygen.     

Substitution mechanism and structural study of Ag-doped LiCu2O2

Plate-like stoichiometric crystals of Ag-doped LiCu₂O₂ have been grown by slowly cooling Li₂CO₃·4(1 – x)CuO·4xAgNO₃ (0 ≤ x ≤ 0.5) melts. X-ray single crystal diffraction has shown that the crystals are isostructural with LiCu₂O₂ and contain around 5 at % Ag (relative to the Cu atoms). The addition of silver to lithium cuprate crystals significantly increases their electrical conductivity but has little effect on the temperature behavior of their magnetic moment. The possible substitution mechanism is determined which supports Ag⁺ ↔ Cu⁺, rather than Ag⁺ ↔ Li⁺ in the Ag-doped LiCu₂O₂ crystals.