Electroreduction of molecular oxygen on carbon electrode modified by dispersed silver

Silver particles are formed by electrochemical deposition on the carbon electrode surface. It is found that the deposition process occurs according to the progressive nucleation mechanism, which results in formation of silver particles with the size of 95 to 190 nm as dependent on the electrodeposition time. The values of silver particle size and support surface coverage by metal obtained on the basis of microphotographs indicate that cathodic polarization in the presence of dissolved oxygen results in particle size redistribution due to the reaction of silver particle dissolution with further deposition simultaneously with oxygen electroreduction. The reaction of molecular oxygen electroreduction on a carbon electrode with deposited dispersed silver occurs via a mixed two- and four-electron mechanism. The observed limiting reaction current is of diffusion nature.     

Photochemical formation of silver nanoparticles in elastomer films

Photochemical deposition of silver nanoparticles in poly(butyl acrylate) and poly(butadiene-styrene) under the action of monochromatic UV light (254 nm) was studied. Changes in the polymer structure in the course of photolysis were revealed and analyzed. A mechanism of formation of silver nanoparticles was suggested. Electron microscopic examination showed that the efficiency of the particle formation is determined by the residual moisture content of the polymer films. Physicomechanical properties (tensile strength and relative elongation) of the elastomer films containing silver nanoparticles were studied.     

Preparation, characterization, and surface modification of silver nanoparticles in formamide

The reduction of silver ions in formamide is shown to take place spontaneously at room temperature without addition of any reductant. The growth of Ag particles was found to be dependent on Ag+ ion concentration. In the absence of any stabilizer, deposition of silver film on the glass walls of the container takes place. However, in the presence of poly(N-vinyl-2-pyrrolidone) (PVP) or colloidal silica (SiO2), which are capable of stabilizing silver nanoparticles by complexing and providing support, a clear dispersion was obtained. The formation of the silver nanoparticles under different conditions was investigated through UV-visible absorption spectrophotometry, gas chromatography, and also electron and atomic force microscopic techniques. Atomic force microscopy results for silver films prepared in the absence of any stabilizer showed the formation of polygonal particles with sizes around 100 nm. Transmission electron microscopy results showed that the prepared silver particles in the presence of PVP were around 20 nm. The Ag nanoparticles get oxidized in the presence of chloroform and toluene. Surface modification of silver film was done in the presence of the tetrasodium salt of ethylenediaminetetraaceticacid (Na4EDTA). It was shown that the reactivity of the silver film increased in its presence. The Fermi potential of silver particles in the presence of Na4EDTA seems to lie between -0.33 and -0.446 V vs NHE.     

ATR-SEIRAS study of the adsorption of acetate anions at chemically deposited silver thin film electrodes

The adsorption of acetate anions at silver thin film electrodes has been studied by in-situ infrared spectroscopy experiments with a Kretschmann internal reflection configuration. Stable silver thin films were chemically deposited on germanium substrates. Ex-situ STM images show mean grain sizes ranging from ca. 20 to 90 nm for deposition times between 2 and 20 min, respectively. The thickness of the silver film, measured by AFM, is typically around 10 nm for a deposition time of 10 min and increases up to 50 nm for a deposition time of 20 min. Roughness factors around 2.3 have been obtained for the silver films from the charge involved in lead underpotential deposition (UPD). A noticeable enhancement of the infrared absorption of adsorbed species (SEIRA effect) is observed when the silver films are used as electrodes under internal total reflection conditions. Maximum intensities of the adsorbate bands were observed for a deposition time of 10 min and an angle of incidence around 65 degrees . The potential-dependent infrared spectra of acetate and interfacial water are consistent with previously proposed models involving the existence of weakly hydrogen-bonded water molecules at potentials below the potential of zero charge and the reorientation of water molecules at potentials above the potential of zero charge. Results reported in this work suggest a weak interaction between acetate and water molecules adsorbed at the silver thin film electrodes.     

Formation of mixed d- and f-block metal clusters in inert matrices: comparison of the observed and theoretical optical spectra of AgHo

The UV visible spectra obtained after simultaneous cocondensation of silver and holmium atoms with argon matrices at 9 K have been studied in the 200-800 nm region. While no new feature can be observed upon deposition, selective irradiation into both silver or holmium atomic absorptions results in growth of a new band at 430 nm, associated with formation of a mixed silver holmium species, tentatively assigned as AgHo. To support the assignment of the observed bands ab initio quantum chemical calculations were carried out for the dinuclear and trinuclear silver and holmium species, using pseudopotential approaches. Results for the electronic excitation energies and corresponding transition dipole moments for the diatomic molecules Ag2, Ho2, AgHo provide evidence that the 430 nm band should be attributed to the mixed cluster AgHo (theoretical band position at 436 nm), while the doublets at 498/504 and 558/563 nm belong to the homonuclear species Ho2 (theoretical values are at 482 and 562 nm). First conclusions are drawn with respect to the formation of the metal trimers Ho3, Ag2Ho, AgHo2.     

Surface State of a Silver Catalyst for Ethylene Glycol Oxidation

The surface state of electrolytic silver before and after treatment with a reaction mixture in the course of ethylene glycol oxidation to glyoxal was studied using X-ray photoelectron spectroscopy and scanning electron microscopy. It was found that electrophilic forms of adsorbed oxygen, which participate in the selective conversion of ethylene glycol, were formed on the surface of electrolytic silver crystals under exposure to oxygen under conditions similar to catalytic process conditions. The treatment of the catalyst with a reaction mixture resulted in the formation of filamentous carbon deposition products. A mechanism of formation of carbon-containing products was proposed.     

Silver nanocomposite layer-by-layer films based on assembled polyelectrolyte/dendrimer

Silver nanocomposite multilayer films were prepared through the in situ method. Multilayer thin films, prepared through the sequential electrostatic deposition of a positively charged third-generation poly(amidoamine) dendrimer (PAMAM) and negatively charged poly(styrenesulfonate) (PSS) and poly(acrylic acid) (PAA), were utilized as nanoreactors for the formation of silver nanoparticles. The silver ions were preorganized in layer-by-layer (LBL) films composed of PAMAM dendrimers and subsequently reduced with hydrogen to prepare the silver nanoparticles. The UV-vis spectrum and profilometer were used to characterize the regular growth of bilayers. UV-vis absorption from plasmon resonance at 435 nm and TEM images indicated the formation of the silver nanoparticles in the multilayer films. The silver nanocomposite LBL films were also constructed on the indium tin oxide-glass and investigated using cyclic voltammetry. The silver nanoparticles in the multilayer films have a stronger negative redox potential. The silver nanocomposite LBL films may have a potential application in the catalysis of reduction of 4-nitrophenol with sodium borohydride.     

Ag活化的p型硅(111)表面化学镀Ag膜表面形貌研究

A method of electroless silver deposition on silver activated p-type silicon（111） wafer was proposed. The silver seed layer was deposited firstly on the wafer in the solution of 0.005 mol/L AgNO3 ＋0.06 mol/L HE Then the silver film was electrolessly deposited on the seed layer in the electroless bath of AgNO3＋NH3＋acetic acid＋NH2NH2 （pH 10.2）. The morphology of the seed layer and the silver films prepared under the condition of the different bath composition was compared by atomic force microscopy. The reflectance of the silver films with different thickness was characterized by Fourier transform infrared spectrometry. The experimental results indicate that the seed layer possesses excellent catalytic activity toward electroless silver deposition and rotating of the silicon wafer during the electroless silver deposition could lead to formation of the smoother silver film.     

Metal-enhanced fluoroimmunoassay on a silver film by vapor deposition

We studied a fluoroimmunoassay using metal-enhanced fluorescence (MEF) detection on silver film generated by vapor deposition method. The morphology of the silver film was controlled through the thickness of the film. A silica layer was coated on the silver film to protect the film and separate the fluorophore from the metal surface. Rabbit immunoglobulin G (IgG) was adsorbed on the silica by physiosorption and then dye-labeled anti-rabbit IgG was bound to the immobilized rabbit IgG. It was observed that the fluorophore was quenched on a thin silver film (2 nm), enhanced on a thick film (>5 nm), and reached saturation (ca. 10 times enhancement) at 20 nm. The MEF was also dependent on the thickness of the silica with a maximum at 10 nm. The lowest lifetime was observed on the 20 nm silver film, which was consistent with the saturation of MEF. These results showed the properties of a silver film needed for a maximum increase of fluorescence intensity in a fluoroimmunoassay. Dependence of the MEF on the emission wavelength was also studied using different dye-labeled anti-rabbit IgGs.     

Annealing of silver nanolayers sputtered on polytetrafluoroethylene

Silver nanolayers sputtered on polytetrafluoroethylene and their changes induced by post‐deposition annealing at 100–300 °C are studied. Changes in surface morphology and roughness are examined by atomic force microscopy and by measurement of electrical sheet resistance by two‐point technique. Chemical composition was determined by X‐ray photoelectron spectroscopy (XPS) and electrokinetic analysis in dependence on the gold layer thickness. The annealing at 300 °C leads to significant rearrangement of the silver layer, and the transition threshold increases to 35 nm. The presence of oxidized structures on silver‐coated samples is observed in XPS spectra and by electrokinetic analysis, too. Annealing of pristine and silver‐coated poly(tetrafluoroethylene) at 300 °C results in significant change of the sample surface morphology and chemistry. There is observed formation of isolated silver islands on the surface, which could be connected with silver melting. Later, the silver agglomeration takes place. Copyright © 2013 John Wiley & Sons, Ltd.     

Electrochemical behavior of silver thin films interfaced with yttria-stabilized zirconia

Thin silver films (100–800 nm) were deposited by physical vapor deposition (PVD) on yttria-stabilized zirconia solid electrolyte. The electric percolation as a function of the film thickness was studied during deposition and annealing using a two-electrode in-situ resistance measurement technique. Electrical percolation was achieved in as-deposited films greater than 5.4?±?0.4 nm; however, thermal treatment (550 °C in air) resulted in film dewetting for Ag films as thick as 500 nm and formation of electronically isolated Ag nanoparticles, as was confirmed by SEM and XPS. In thermally treated samples, stable electronic conductivity associated with a continuous percolated network was only observed in samples greater than 600 nm in thickness. The effect of polarization on the electrochemical reactions at the three-phase (electrode-gas-electrolyte) and two-phase (electrode-electrolyte) boundaries of the electrode was investigated by solid electrolyte cyclic voltammetry (SECV) at 350 °C and P _O2?=?6 kPa. With the application of positive potential, silver oxide (Ag₂O) was found to form along the three-phase boundary and then extends within the bulk of the electrode with increasing anodic potentials. By changing the hold time at positive potential, passivating oxide layers are formed which results in a shift in favor of the oxygen evolution reaction at the working electrode. This oxide forms according to a logarithmic rate expression with thick oxides being associated with decrease in current efficiency for subsequent oxide formation.     

Photochemical formation of silver-gold (Ag?Au) composite colloids in solutions containing sodium alginate

Photochemical formation of colloidal silver, colloidal gold and silver-gold (Ag-Au) composite colloids under mild conditions has been studied. Irradiation of either aqueous AgCIO₄ or HAuCI₄ solution in the presence of sodium alginate (SA) with 253.7 nm light yielded colloidal silver or gold, whose particle diamter was 10-30 nm or 40-60 nm, respectively. The Ag-Au composite colloids consisting of mixtures of silver and gold domains (particle diameter 30-150 nm) have been prepared and their extinction spectra have been examined on the basis of a conventional Mie theory in combination with an effective medium theory to estimate the optical constants of these colloids. It has been shown that the extinction spectra of the Ag-Au composite colloids are completely different from those of Ag-Au alloy colloids, in that the former have two extinction maxima close to the colloidal extinction bands of pure silver and gold, in contrast to a single extinction maximum of the latter. The importance of natural, high-molecular carboxylic acids such as alginic acid in the photochemical formation of metal colloids and thin films has been stressed.     

Controlled synthesis of double- and multiwall silver nanotubes with template organogel from a bolaamphiphile

Double- and multiwall silver nanotubes were synthesized by using the uniform low-molecular-mass organogel nanotubes self-assembled from an L-glutamic-acid-based bolaamphiphile, N,N-eicosanedioyl-di-L-glutamic acid (EDGA). The EDGA could gel a mixed water/ethanol solvent and form helical nanotubes. When the gel thus formed was mixed with AgNO3 in water/ethanol, the silver(I) cations could be coordinated with both the inner and outer surfaces of the EDGA nanotubes. The reduction of the silver cation under the photoirradiation yielded double-wall silver nanotubes, where two silver layers were separated by one EDGA layer. Elongations of the reduction time of the mixed gels and AgNO3 in the solution lead to the formation of three-, four-, and five-wall silver nanotubes. In these multiwall silver nanotubes, each wall was separated at a distance of about 2.7 nm, which was just the molecular length of the bolaamphiphile. It was suggested that the dissolved EDGA molecules and excess Ag(I) cations were further assembled onto the surface of the formed double-wall silver nanotubes and, as a consequence, the photoreduction caused the formation of the third-wall silver nanotubes. The multiwall silver nanotubes were further formed in a similar way. The factors affecting the formation of the silver wall nanotubes such as the relative amount of AgNO3 to EDGA and the synthetic conditions were discussed.     

Biosynthesis of iron and silver nanoparticles at room temperature using aqueous sorghum bran extracts

Iron and silver nanoparticles were synthesized using a rapid, single step, and completely green biosynthetic method employing aqueous sorghum extracts as both the reducing and capping agent. Silver ions were rapidly reduced by the aqueous sorghum bran extracts, leading to the formation of highly crystalline silver nanoparticles with an average diameter of 10 nm. The diffraction peaks were indexed to the face-centered cubic (fcc) phase of silver. The absorption spectra of colloidal silver nanoparticles showed a surface plasmon resonance (SPR) peak centered at a wavelength of 390 nm. Amorphous iron nanoparticles with an average diameter of 50 nm were formed instantaneously under ambient conditions. The reactivity of iron nanoparticles was tested by the H(2)O(2)-catalyzed degradation of bromothymol blue as a model organic contaminant.     

Controlling the Formation of Silver Nanoparticles on Silica by Photochemical Deposition and Other Means†

Silver nanoparticles (Ag-NP) on silica were produced in aqueous solution by deposition of silver on colloidal silica in a small cuvette using radiation from a xenon-mercury lamp. Ag-NP were also synthesized on a much larger scale with low-level, long-term visible light irradiation for several months. In both cases, the nanoparticle production was monitored by the appearance of the surface plasmon resonance (SPR) band at around 410 nm. The growth of the nanoparticles was directly related to the time exposed to radiation, which could be tracked spectrophotometrically over time. We also investigated the possibilities of rapid nanoparticle production without the assistance of radiation though silver oxide by adding alkali hydroxide, which is a relatively unexplored approach for syntheses of Ag-NP on silica. The SPR absorption of Ag-NP was used as a tool in evaluating the size and shape of the resulting nanoparticles along with dynamic light scattering and transmission electron microscopy data. In order to better utilize and understand Ag-NP, we present various ways to control their production through initial concentration adjustments, irradiation effects, gravitational fractionation, sonication and silver oxide formation.     

Synthesis and characterisation of silver nanoparticles in viscous solvents and its transfer into non-polar solvents

Room temperature synthesis of silver nanoparticles has been successfully achieved by adding NaOH acting as an accelerator for the reduction of silver ions in ethylene glycol and glycerol without adding any external reducing agent. Highly monodisperse silver particles are obtained in the presence of various stabilisers such as PVP, SiO₂ and SDS. Nanoparticles with a mean diameter of 25 nm and a mean deviation of 2 nm could be obtained under experimental conditions. The silver nanoparticles so obtained could be easily transferred to chloroform containing CTAB, giving rise to CTAB stabilised silver nanoparticles having sizes of around 25 nm. The newly found role of OH⁻ stabilisation was used to formulate a mechanism for the formation of silver nanoparticles in ethylene glycol and glycerol. In this mechanism, silver nanoparticles are stabilised in ethylene glycol by the adsorbed OH⁻ ions.     

Preparation of silver nanoparticles with controlled particle size

Silver colloids show different colors due to light absorption and scattering in the visible region based on plasmon resonance. The resonance wavelength depends on particle size and shape. Here we report chemical reduction methods for preparation of silver nanoparticles exhibiting multicolor in aqueous solutions. Depending on chemical conditions the obtained nanoparticles are different regarding size and morphology.In order to investigate the relationship between size, stability and color of silver colloids we obtained silver nanoparticles in aqueous solutions using different reducing agents. The effect of polyvinyl pyrrolidone (PVP) and polyvinyl alcohol (PVA) on stabilization of obtained silver colloids was investigated. We have also studied the effect of silver precursor and its concentration on the formation of stable silver colloids.UV-VIS spectrum for silver colloids contains a strong plasmon band near 410 nm, which confirms silver ions reduction to Ag° in the aqueous phase. The formation of metal silver was also confirmed by powder X-ray diffraction (XRD) analysis. The diameter size of silver nanoparticles was in the range from 5 nm to 100 nm     

Investigation of chemically modified barium titanate beads as surface-enhanced Raman scattering (SERS) active substrates for the detection of benzene thiol, 1,2-benzene dithiol, and rhodamine 6G

SERS active surfaces were prepared by depositing silver films using Tollen's reaction on to barium titanate beads. The SERS activity of the resulting surfaces was probed using two thiols (benzene thiol and 1,2-benzene dithiol) and rhodamine 6G. The intensity of the SERS signal for the three analytes was investigated as a function of silver deposition time. The results indicate that the SERS intensity increased with increasing thickness of the silver film until a maximum signal intensity was achieved; additional silver deposition resulted in a decrease in the SERS intensity for all of the studied molecules. SEM measurement of the Ag coated barium titanate beads, as a function of silver deposition time, indicate that maximum SERS intensity corresponded with the formation of atomic scale islands of silver nanoparticles. Complete silver coverage of the beads resulted in a decreased SERS signal and the most intense SERS signals were observed at deposition times of 30 min for the thiols and 20 min for rhodamine 6G.     

Polyethylenimine complexes with silver ions in aqueous solutions as precursors for synthesis of monodisperse silver iodide particles

The conditions of formation and composition of polyethylenimine complexes with silver ions in aqueous solutions are found. The complex is formed according to the model of a uniform distribution of ions throughout the macromolecule, and the composition of the complex may vary depending on pH of the medium. The size parameters are determined and the volume fractions of polyethylenimine macromolecular coils in solution are calculated. The synthesis of silver iodide particles is carried out under conditions where the silver ions are bound in the complex with polyethylenimine macromolecules and are distributed homogeneously over the volume of solution. The use of the polyethyleneimine complex with silver ions as a precursor of silver iodide allows the preparation of particles 1.2 nm in diameter with a narrow size distribution.     

Facile synthesis of high-concentration, stable aqueous dispersions of uniform silver nanoparticles using aniline as a reductant

A facile method was developed for preparing uniform silver nanoparticles with small particle sizes of less than 10 nm at high concentrations, in which aniline was used to reduce silver nitrate (AgNO(3)) to silver nanoparticles in the presence of dodecylbenzenesulfonic acid (DBSA) as a stabilizer. Upon the addition of excess NaOH to the DBSA-aniline-AgNO(3) (DAA) system, the formation of silver nanoparticles was almost complete in just 2 min at 90 °C (in 94% yield). The average size of those resultant silver nanoparticles was 8.9 ± 1.1 nm, and the colloids were stable for more than 1 year at ambient temperature. A possible mechanism for the formation of silver nanoparticles was proposed to be related to two factors: one was the mesoscopic structures of the DAA system in which silver ions were restricted in the dispersed phases composed of DBSA and aniline; the other was Ag(2)O nanocrystallites generated in situ that could be readily reduced by aniline to small silver nanoparticles at high concentrations.