Dissolution Of Silver Research Articles

An electrochemical DNA hybridization detection assay based on a silver nanoparticle label.

A novel, sensitive electrochemical DNA hybridization detection assay, using silver nanoparticles as the oligonucleotide labeling tag, is described. The assay relies on the hybridization of the target DNA with the silver nanoparticle-oligonucleotide DNA probe, followed by the release of the silver metal atoms anchored on the hybrids by oxidative metal dissolution and the indirect determination of the solubilized Ag(I) ions by anodic stripping voltammetry (ASV) at a carbon fiber ultramicroelectrode. The influence of the relevant experimental variables, including the surface coverage of the target oligonucleotide, the duration of the silver dissolution steps and the parameters of the electrochemical stripping measurement of the silver(I) ions, is examined and optimized. The combination of the remarkable sensitivity of the stripping metal analysis at the microelectrode with the large number of silver(I) ions released from each DNA hybrid allows detection at levels as low as 0.5 pmol L(-1) of the target oligonucleotides.

The study of photo- and thermally-induced diffusion and dissolution of Ag in As 30S 70 amorphous films and its reaction products

Kinetics of photo- and thermally-induced diffusion and dissolution (PIDD and TIDD) of silver in a-As 30S 70 films were measured by monitoring the change in thickness of the undoped chalcogenide using a modified computer-controlled reflectivity technique. Silver-concentration profiles during photo- and thermally-induced solid-state reactions were traced by means of Rutherford backscattering spectroscopy (RBS). The enthalpy of photo- and thermally-induced reactions was measured by means of differential photocalorimetry and quasi-isothermal temperature-modulated differential scanning calorimetry (DSC), which are shown to be connected with the chemical reaction: Ag+As 3S 7=AgAsS 2+As 2S 5.

Reversible control of silver nanoparticle generation and dissolution in soda-lime silicate glass through x-ray irradiation and heat treatment

Reversible generation and dissolution of 3 nm silver particles in a glass containing only silver ions are repeatedly achieved through a combination of x-ray radiation and heat treatment. X-ray irradiation and 400 °C heat treatment induce a yellow color, whereas heating at 500 °C can change the glass to colorless again. X-ray irradiation produces large amounts of silver atoms and defects, mainly nonbridging oxygen hole centers (NBOs), in glass. Heating at 400 °C accelerates the aggregation of silver atoms into forming silver particles. The NBOs can continuously oxidize the silver atoms of particles into silver ions at higher temperature, leading to dissolution of the silver particles.

Interaction of high-power excimer-laser pulses with soda-lime silicate glass containing ion-implanted metal nanoparticles

Silver nanoparticles have been synthesised by ion implantation in soda-lime silicate glass at 60 keV at a dose of 7.0×10 16 ion/cm 2 with a current density of 10 μA/cm 2 at a temperature of 50°C. The size distribution of the metal particles was monitored by optical transmittance and reflectance registered from both the implant and rear face of the samples, together with atomic force microscopy measurements and Rutherford backscattering spectroscopy. The differences between the data indicate the asymmetry in the size distribution with depth. Annealing of the glasses was made by pulses from a high-power KrF excimer laser. Pulsed laser treatment has been used at a wavelength of 248 nm and a pulse length of 25 ns. The laser was partially focused on the sample area to yield a pulse fluence, of 200 mJ/cm 2. Several pulses of the equal energy density were accumulated in the same area of the sample. Changes induced by pulsed laser exposure suggest that there are both reductions in average size of the silver nanoparticles, and some longer range dissolution of silver into the glass. The treatments have reduced, but not removed evidence for a non-symmetric depth distribution of the silver particles. The present work discusses the possibilities of metal regrowth changes for control and modification of metal nanoparticle sizes.

Kinetics of electrochemical reactions on the Ag(Hg)/Ag4RbI5 interface

The electrochemical behaviour of the Ag(Hg)/Ag4RbI5 interface is investigated by a potentiostatic pulse method. It is found that the rate-determining step of the electrode reaction is electron transfer with an exchange current density of 68 mA cm–2 and a transfer coefficient of approximately 0.45. The order of the electrochemical reaction for silver oxidation is estimated from polarization investigations of silver amalgam in various concentrations. From this it is deduced that the mercury is ionized and is implanted in the electrolyte together with silver under anodic polarization: 15Ag+85Hg–100e–→15Ag++85Hg+. From comparison of the electrochemical behaviour of the Ag(Hg)/Ag4RbI5 and Ag/Ag4RbI5 interfaces it is concluded that the rate of anodic silver dissolution on the Ag/Ag4RbI5 interface is limited by crystallization effects.

Changing the composition of Ag–As–S amorphous films using photo-induced solid state reaction

The technique of step-by-step optically-induced solid state reaction of Ag into As 33S 67 amorphous films, which has allowed the design of films with known silver concentrations, is reported. The host, As 33S 67 films, were photo-doped by consecutive dissolution of a 10 nm layer of silver, which resulted in a single layer film of optical quality as measured by optical transmissivity. The silver concentration of the samples ranged between 1 and 41 at.%. Such Ag containing films cannot be prepared directly by vacuum evaporation from AgAsS glasses due to the phase separation during evaporation process. We analyzed the affect of the silver doping in the host material on optical, thermal properties, and its structure by means of optical spectroscopy, temperature-modulated differential scanning calorimetry, and Raman spectroscopy, respectively. Optically-induced silver dissolution led to a formation of the solid solutions in above mentioned concentration range, connected with a decrease of –S–S– bonds due to their solid state reaction with migrating silver ions. The films with a silver content close to 25 at.% had the structure of stoichiometric AgAsS 2. There is evidence of As–As bond formation in photo-doped materials with a silver content >40 at.%. Results of all analytical techniques we used have helped to understand the processes taking place during silver photo-dissolution.

Electrochemical Behavior of Silver in 1-Ethyl-3-methylimidazolium Tetrafluoroborate Molten Salt

A room-temperature molten salt, 1-ethyl-3-methylimidazolium tetrafluoroborate with adequate purity was obtained simply by the reaction of 1-ethyl-3-methylimidazolium chloride and tetrafluoroboric acid. Silver tetrafluoroborate dissolves up to ∼0.2 mol dm−3 in at room temperature. Electrochemical deposition and dissolution of silver on a platinum electrode were found possible in containing The reduction of monovalent silver species is electrochemically irreversible, the rate constant being estimated to be cm s−1. The diffusion coefficient of Ag(I) is calculated to be cm2 s−1, suggesting that Ag(I) exists as a substantially bare cation in © 2001 The Electrochemical Society. All rights reserved.

A spectroelectrochemical investigation of the influence of sodium diisobutyldithiophosphinate on silver dissolution in aqueous cyanide

Polarization studies have been carried out to determine the influence of diisobutyldithiophosphinate (DIBDTPI) on the dissolution of silver in cyanide solutions at pH 11. DIBDTPI was found to inhibit dissolution at concentrations similar to those used when this compound is applied as a flotation collector. The inhibition efficiency in 10−2 mol dm−3 CN− was found to increase with increase in DIBDTPI concentration in the range 10−6–10−4 mol dm−3, and with increase in time of exposure of the silver to the DIBDTPI solution. The inhibition efficiency found for 10−4 mol dm−3 DIBDTPI in quiescent 10−2 mol dm−3 CN− solution at 23 °C was 64.6% and 95.0% for exposure times of 10 min and 2 h, respectively. These values are significantly less than those found previously for 2-mercaptobenzothiazole under the same conditions. Surface enhanced Raman spectroscopy showed that inhibition was associated with adsorption of DIBDTPI displacing cyanide from the silver surface. Voltammetry at 0.5 mV s−1 indicated that adsorption of DIBDTPI involves charge transfer.

Kinetics of the Dissolution of Silver in Thiocarbamide Solutions

The dependence of the rate of solution of silver on the pH of the solution, the ratio of the iron(III) and thiocarbamide concentrations, and the temperature has been determined. The rate constants for the solution of silver (ki = 2.3·10−4 to 9.6·10−4s−1) at temperatures from 283-298 K have been calculated and from the temperature dependence of the rate constant the activation energies have been calculated: 68.84 kJ/mol for kinetic control of the rate of solution and 26.06 kJ/mol in the adsorption inhibition region.

An electrochemical investigation of the suppression of silver dissolution in aqueous cyanide by 2-mercaptobenzothiazole

Triangular potential sweep voltammetry, potentiokinetic generation of polarization curves, and coupon corrosion tests have been carried out to determine the influence of 2-mercaptobenzothiazole (MBT) on the dissolution of silver in cyanide solutions at pH 11. MBT has been shown to be an effective inhibitor for silver dissolution at concentrations similar to those used when MBT is applied as a flotation collector. The inhibition efficiency (i.e., [1 – the ratio of the corrosion rates in the presence and absence of MBT], expressed as a percentage) in 10−2 and 10−3 mol dm−3 CN was found to increase with increase in MBT concentration in the range 10−6 to 10−4 mol dm−3, and with increase in time of exposure of the silver to the MBT solution. The inhibition efficiency found for 10−4 mol dm−3 MBT in quiescent 10−2 mol dm−3 CN− solution at 23 °C was 98.9%, 99.4% and 99.99% for exposure times of 10 min, 2 h and 5 days, respectively. Surface enhanced Raman spectroscopy showed that inhibition was associated with adsorption of MBT displacing cyanide from the silver surface.

Effect of silver dissolution on electrical properties of As2S3

The paper reports the effect of dissolution of silver into the chalcogenide As2S3. The conductivity of As2S3 decreases with doping at lower temperatures. The a.c. conductivity is proportional to Ωs for undoped as well as doped samples. The value of the frequency exponent “s” increases with doping. On the other hand, the dielectric constant of As2S3 also increases with doping and the effect is quite prominent at higher temperatures. A new structural model together with the correlated barrier hopping model has been used to explain these results. © 2001 Kluwer Academic Publishers

Electrooxidation of Silver in the Presence of Some Amino Acids

Data on the influence the solution's ionic composition and amino acids (histidine, methionine) have on the anodic dissolution of silver are presented. The dissolution is most effective in intensively agitated nitrate solutions containing methionine in excess of 0.05 M (current efficiency reaches 75%). By analogy with the gold dissolution, acceleration of the silver dissolution is attributed to oxidized methionine complexing with metals.

Kinetic Investigation of Reaction Between Metallic Silver and Nitric Acid Solutions

In this study, the reaction kinetics between metallic silver and nitric acid solutions was investigated by taking into consideration the parameters of temperature, solid-to-liquid ratio, stirring speed, nitric acid concentration, particle size and addition of sodium nitrite. It was determined that the dissolution rate of the process increased with decreasing particle size and solid-to-liquid ratio, and increasing nitric acid concentration, reaction temperature and the amount of the sodium nitrite in the solution. In addition, it was observed that the stirring speed had more effect on the dissolution rate at low stirring speeds than at high stirring speeds. In the present study, the examination of shrinking core models of fluid-solid systems showed that the dissolution of metallic silver in the nitric acid solutions was controlled by the reaction on the surface. A semiempirical model, which represented well the process, was developed by statistical methods. The activation energy of the process was found to be 57.66 kJ mol–1.

Kinetic Investigation of Reaction Between Metallic Silver and Nitric Acid Solutions

In this study, the reaction kinetics between metallic silver and nitric acid solutions was investigated by taking into consideration the parameters of temperature, solid-to-liquid ratio, stirring speed, nitric acid concentration, particle size and addition of sodium nitrite. It was determined that the dissolution rate of the process increased with decreasing particle size and solid-to-liquid ratio, and increasing nitric acid concentration, reaction temperature and the amount of the sodium nitrite in the solution. In addition, it was observed that the stirring speed had more effect on the dissolution rate at low stirring speeds than at high stirring speeds. In the present study, the examination of shrinking core models of fluid-solid systems showed that the dissolution of metallic silver in the nitric acid solutions was controlled by the reaction on the surface. A semiempirical model, which represented well the process, was developed by statistical methods. The activation energy of the process was found to be 57.66 kJ mol–1.

Surface processes in silver and gold cyanidation

Rate processes for silver and gold cyanidation are controlled by a series of coupled electrochemical reactions. These include anodic metal dissolution and oxygen reduction. This study demonstrates basic differences between silver and gold dissolution both in reference to the metal and the accompanying oxygen discharge. The kinetics of oxygen reduction are compared for silver and gold. At a fixed voltage, the cathodic current for gold is less than that of silver except at large negative potentials where the kinetics are oxygen diffusion-limited. A mathematical model is presented for oxygen reduction based upon two paths: one path with peroxide formation followed by alternate catalytic decomposition and desorption, and a second path with continued peroxide reduction to hydroxyl ions. The model permits separate calculations of the first and second waves of oxygen reduction. Based upon mixed potential models, silver dissolution is shown to be controlled by both the first and second waves of oxygen reduction with the number of electrons approaching four for high cyanide concentrations. Gold dissolution is controlled by surface reactions with mixed potentials associated mainly with the first wave of oxygen control and limited to two-electron transfer. The model permits an evaluation of the number of electrons which may be transferred for a given potential and shows this number is voltage-dependent. Silver dissolution is shown to include both diffusion or mixed diffusion plus charge transfer kinetics, influenced by the degree of agitation and both oxygen and cyanide concentration-dependent. Gold dissolution kinetics are controlled by crystal-dissolution overpotentials and are independent of agitation. Models of oxygen discharge and metal dissolution are used to explain observed characteristics and kinetics of silver and gold leaching.

THE CHEMISTRY OF PHOTOGRAPHY IN FULL DAYLIGHT

Photography, the daughter of art, is also considered the well-bred child of science. From its very beginnings, the new visual art fully utilized the most advanced scientific discoveries pertinent to its development; particularly those occurring in the field of chemistry. The most notable advantage of photographic chemistry, in relation to chemical education, is found in its unique scope, which combines interesting inorganic, organic and physical chemistry with a powerful visual communication medium of tremendous social importance. Chemical educators dwelled on both the theoretical and the experimental aspects of photographic chemistry. Yet the proposed experiments do not involve the magical process of image development. In the present work, methods involving the rehalogenating bleaching of black and white photographs are presented and also experiments for the “development” of the bleached image in full daylight. The chemical topics that can be covered by such experiments range from the dissolution of metallic silver in dilute nitric acid to the reduction of silver ions using common organic reducing agents. [Chem. Educ. Res. Pract. Eur.: 2000, 1, 175-177]

Anodic dissolution of silver in ultrasonic field

Anodic dissolution of silver in ultrasonic field

Potentiodynamic growth of anodic silver chromate layers

Silver passivation is studied in sodium chromate aqueous solutions. It is shown that the active–passive transition involves active metal dissolution followed by the precipitation of a poorly-conducting layer of silver chromate that passivates the electrode. The potentiodynamic current–potential behavior is adequately described by using the layer-pore-resistance model (LPRM). The agreement between experimental and theoretical curves is excellent and allows us to demonstrate that, after the first stages that involve active dissolution of silver and nucleation of the film, the growth of the passive layer is mainly controlled by the resistance of the electrolyte in the pores of the layer. After passivation, further growth of the film occurs under diffusion control.

Modification of size distribution of ion implanted silver nanoparticles in sodium silicate glass using laser and thermal annealing

Silver nanoparticles have been synthesised by ion implantation in soda–lime silicate glass at 60 keV to a dose of 7.0×1016 ion/cm2 and a current density of 10 μA/cm2. The size distribution of the metal particles was monitored by optical transmittance and reflectance registered from both the implant and rear face of the samples. The differences between the data indicate the asymmetry in the size distribution with depth. Changes induced by furnace and pulsed laser beam thermal treatments are different and suggest there are both reductions in size of the larger silver nanoparticles, and some longer range dissolution of silver into the glass. A combination of furnace heating followed by laser pulses can influence regrowth, with evidence for a narrower size distribution. The present study discusses the possibilities of such changes for control and modification of metal nanoparticle sizes. Sizes were estimated in the framework of the Mie plasma resonance theory.

Reduction of the size of the implanted silver nanoparticles in float glass during excimer laser annealing

Silver nanoparticles have been synthesised by ion implantation in float glass at 60 keV to a dose of 7.0×10 16 ion/cm 2 and a current density of 10 μA/cm 2 at a temperature of 50°C. The size distribution of the metal particles was controlled by monitoring optical transmittance and reflectance together with atomic force microscopy measurements and Rutherford backscattering spectroscopy. A reduction in size of large silver nanoparticles and some dissolution of silver into the glass network has been made by pulse annealing with a high-power KrF excimer laser. The present study explores the possibilities of controlled size formation of metal nanoparticles within an insulator. Explanations of the observed modifications are proposed.