Adsorption Of Silver Ions Research Articles

The kinetics of formation and transformation of silver atoms on solid surfaces subjected to ionizing irradiation

The paper discusses the results obtained in ESR-assisted studies of the kinetics of formation and transformation of silver atoms generated by γ-irradiation of silver-containing carriers. Three types of dependences have been established: (1) extreme; (2) saturation curves and (3) step-like. All the kinetic curves display, after a definite period of time, stable concentrations of adsorbed silver atoms per unit of the surface at a given temperature. Depending on the temperature of the experiment, the composition and nature of the carrier, the number of adsorbed silver ions, the irradiation dose and conditions of the experiment, a stable concentration of silver atoms at a given temperature may be equal to, higher or lower than the number of silver atoms measured immediately after γ-irradiation at a temperature of liquid nitrogen. A kinetic scheme is proposed to explain the obtained curves. The model suggests that the silver atoms adsorbed on the surface, as well as those formed after γ-irradiation, are bonded to the surface by various energies, which are related to heterogeneity of the carrier surface.

A simple method for the quantitative determination of preferential adsorption of silver ions at anionic micellar surfaces: An ESR study of γ-irradiated silver perchlorate in sodium dodecyl sulfate

Gamma-irradiation at 77 K of sodium dodecyl sulfate (SDS) micellar solution with added silver perchlorate exhibits ESR spectra of silver atoms trapped in the bulk aqueous phase with a substantial decrease in yield when compared to a frozen homogenous aqueous sample. A micellar solution of Kryptofix-22 crown ether with a long alkyl chain which is known to complex all silver ions failed to yield atomic silver at 77 K after irradiation. This can be interpreted that silver ions associated with micelles in the frozen state don't react with radiation-produced electrons. Then the ratio of the atomic silver yield in micellar media to that in homogeneous aqueous media reflects the fraction of silver ions in the bulk aqueous phase that are not associated with micelles. It is observed that 84% of the silver ions is associated with 0.1 M SDS micelles and the equilibrium constant K was calculated to be 10,500 M -1.

Correlation of catalytic activity with the amount of sulphhydryl groups in molybdenum hydrodesulphurization catalysts

The adsorption of silver ions from a pyridine solution of silver nitrate onto nine commercial sulphided hydrodesulphurization catalysts was studied. The amount of sulphhydryl groups SH was determined on the basis of the amount of protons liberated in this reaction. The reaction of catalysts with silver ions was compared with their activity in thiophene hydrodesulphurization under pressure. A dependence was found between the amount of silver ions adsorbed and the rate constant of thiophene hydrodesulphurization. For cobalt-molybdenum catalysts, a relationship exists between this constant and the amount of sulphhydryl groups. It was ascertained that the catalysts which are most active in the thiophene desulphurization probably contain, in sulphided state, a part of cobalt (nickel) in the form of sulphides.

Sulfhydryl groups on the surface of molybdenum desulfurization catalysts

The adsorption of silver ions from a pyridine solution of silver nitrate onto a cobalt-molybdenum desulfurization catalyst, molybdenum disulfide and alumina was studied. Alumina, the cobalt-molybdenum catalysts, both oxidic and reduced with hydrogen, did not react with silver nitrate. The sulfided cobalt-molybdenum catalyst and sulfided or reduced molybdenum disulfide adsorbed silver ions and the equivalent amount of protons was liberated. This process is ascribed to the presence of sulfhydryl (SH) groups on their surfaces. On this assumption, it was found that the sulfided cobalt-molybdenum catalyst contained 0.320 mmol of SH groups in 1 g, which represents about 9% of monolayer coverage. For the reduced molybdenum disulfide, the value of 0.086 mmol of SH groups in 1 g was found, which is about 24% of a monolayer. The content of sulfhydryl groups in the reduced molybdenum disulfide was not increased after sulfiding.

Adsorption of the silver ion on soda-glass—I

A study of the adsorption of silver ions on soda-glass, using a radiochemical technique, has been made, and the effects of time and temperature investigated. A simple kinetic treatment allows estimation of the rate constants for the adsorption and desorption processes.

Positional distribution of fatty acids in the triglyceride classes of milk fat.

A sample of milk fat was fractionated into high, medium and low molecular weight triglycerides by silicic acid column chromatography. Each fraction was further separated by silver ion adsorption thin-layer chromatography into triglyceride class which were subjected to stereospecific analysis. Trans-monoene fatty acids were incorporated into triglycerides in the same manner as their cis-isomer. The specific positional distribution for fatty acids in intact mild fat triglycerides was not always maintained in the molecular weight fractions or in the various classes of unsaturation. The significance of these findings is discussed in relation to biosynthetic mechanisms for milk fat synthesis.

Relationship between triglyceride structure and softening point of milk fat

SummaryEight samples of milk fat were selected for softening point (SP) range. They were separated into high, medium and low molecular weight triglyceride fractions by silicic acid-column chromatography to enable further separation into triglyceride classes by silver ion adsorption thin-layer chromatography. Correlation between triglyceride class content and SP was low. The molecular species composition of the triglyceride classes was determined and correlated with SP. The best correlations were between SP and some low and some high molecular weight triglycerides of the total fat and the trisaturated (SSS) triglyceride class. Correlation coefficients were determined between SP and mole percentage of individual fatty acids and groups of acids. The highest correlations were between SP and individual short chain-length fatty acids (C4–C10) and groupings of short chain-length acids (C4–C10) and groupings of long chain-length acids (C16–C20). The triglyceride class composition of a sample of milk fat was determined before and after interesterification. Interesterification increased the SP from 31·6 to 36·3 °C and produced increased amounts of both low and high and decreased amounts of medium molecular weight triglyceride molecular species in all triglyceride classes. The increases in the amounts of high molecular weight triglycerides were several times greater than the increase in the amounts of low molecular weight triglycerides.

Joint homogeneous and heterogeneous catalysis: a new synergistic effect

An increase of the order of 104 in the rate of the Menschutkin reaction was achieved at reaction sites created by the adsorption of silver ions on silver iodide or carbon surfaces.

Fast surface states activated by silver ions on a germanium-neutral electrolyte interface

The activation peculiarities and fast surface state (FSS) parameters, including the recombination centers (RC) caused by adsorption of silver ions on a germanium surface in contact with a neutral electrolyte and oriented along the three main cristallographic planes (111), (110), and (100), were investigated. It has been detected that the anisotropy of the FSS and RC parameters differs from that found earlier for a “pure” germanium surface or for gold-doped germanium under analogous conditions, but agrees with the anisotropy of the potential distribution on the Ge-electrolyte interface and is apparently governed thereby, exactly as in later cases. The surface state parameters are quite close in all cases. The singularities in the kinetics of surface state activation are associated with the higher migration capability of the silver ions under the effect of polarization. It is shown that successive adsorption of gold and silver ions does not result in the effect of neutralizing the RC which is observed on a “dry” germanium surface in such a situation.

Stability of silver–thiourea complexes in montmorillonite clay

Ion exchange adsorption of a silver–thiourea complex into sodium-, calcium- and aluminum montmorillonite at 25°C has been studied. The reversible nature of the reaction is demonstrated and the standard free energy changes for the displacement of the three ions by the silver complex are calculated. The results are, in kJ equiv.–1: –20 (Na–Ag), –20.7 (Ca–Ag) and –19 (Al–Ag). These values are consistent with values for Na–Ca and Ca–Al exchanges, found in the literature. The free energy loss for adsorption of the silver complex exceeds that for the aqueous ion by some 19 kJ equiv.–1 The enhancement of the selectivity and the coordination values of adsorbed silver ions are consistent with the following free energy changes for the successive formation of the complexes: ΔG1=–59.5, ΔG1→2=–20.3 and ΔG2→3=–7.4 kJ mol–1. Relative to the free energies of formation of these complexes in solutions, these values correspond to stabilization of the complex containing one thiourea molecule and destabilization of that containing three.

Ion-selective electrode study of trace silver ion adsorption on selected surfaces

Ion-selective electrode study of trace silver ion adsorption on selected surfaces

Methods for the isolation and characterization of constituents of natural products: XI. Preparation of the 2,4-dinitrophenylhydrazone derivatives of fatty acid esters of glycolaldehyde and separation of an homologous series by thin-layer partition chromatography

An homologous series of the 2,4-dinitrophenylhydrazone derivatives of the glycolaldehyde esters of fatty acids have been prepared. The derivatives are all solids having an absorption maximum at 350 mμ (CHCl 3) and a molar extinction coefficient near 20,000. Neutral and alkaline thin-layer partition chromatographic procedures and a thin-layer, silver-ion adsorption system are described for resolving the derivatives.

Overpotential phenomena at Ag/AgBr anodes in AgNO3 solutions

Overpotential at silver anodes covered with anodically-deposited AgBr layers of 9 μ thickness was measured in silver nitrate solutions of varying concentration within the current density range, 10−5–10−1 A/cm2 at 25°. The rate-determining process was suggested to be the transfer of silver ions through the AgBr/solution interface, acceleration being brought about by the increase of concentration of interstitial silver ions, Ag0+, in the layer, especially in the space charge regions. At a certain limiting current, overpotential increases rapidly and then stops at a certain maximum value indicating that a large excess of Ag0+ renders the slow process sufficiently fast. The space charge region at the metal/layer interface, which contains a very large excess of vacant sites, Ag▭−, is gradually neutralised with increasing current density. The onset of the limiting current was, therefore, attributed to an abrupt increase of Ag0+-conentration in that region as it approaches the neutral structure. Adsorbed silver ions catalyse the slow process, perhaps through the weakening of the interionic forces in the surface. At currents above the limiting value, overpotential decreases with current; this was ascribed to an increase in the roughness of the surface. In addition to the above features, the results in acidified solutions are characterised by an overpotential arrest before the limiting current is reached. Considerable decrease of overpotential was also observed at higher currents and was related to specific adsorption of H+ ions. As a result of excess adsorption, a negatively-charged space charge region is built up at the layer/solution interface. The sudden increase of Ag0+-concentration that accompanies the neutralisation of this region during anodic polarisation, leads to self-acceleration of the slow process and hence to an arrest in overpotential. The resistance of AgBr layers of 3–15 μ thickness was measured in different solutions in the current density range, 10−6–10−1 A/cm2. The results indicated the absence of pores even in 3 μ-thick layers. The resistance of the layer decreases with increase of the current density; this was attributed to the diffusion of Ag0+ and Ag▭− under the effect of concentration differences, beside their mobility in the operative electric field. Below about 5·10−4 A/cm2, diffusion is almost restricted to Ag▭− whereas at higher currents diffusion of Ag0+ predominates.

Overpotential phenomena at Ag/AgBr anodes in AgNO 3 solutions

Summary Overpotential at silver anodes covered with anodically-deposited AgBr layers of 9 μ thickness was measured in silver nitrate solutions of varying concentration within the current density range, 10 −5 –10 −1 A/cm 2 at 25°. The rate-determining process was suggested to be the transfer of silver ions through the AgBr/solution interface, acceleration being brought about by the increase of concentration of interstitial silver ions, Ag 0 + , in the layer, especially in the space charge regions. At a certain limiting current, overpotential increases rapidly and then stops at a certain maximum value indicating that a large excess of Ag 0 + renders the slow process sufficiently fast. The space charge region at the metal/layer interface, which contains a very large excess of vacant sites, Ag ▭ − , is gradually neutralised with increasing current density. The onset of the limiting current was, therefore, attributed to an abrupt increase of Ag 0 + -conentration in that region as it approaches the neutral structure. Adsorbed silver ions catalyse the slow process, perhaps through the weakening of the interionic forces in the surface. At currents above the limiting value, overpotential decreases with current; this was ascribed to an increase in the roughness of the surface. In addition to the above features, the results in acidified solutions are characterised by an overpotential arrest before the limiting current is reached. Considerable decrease of overpotential was also observed at higher currents and was related to specific adsorption of H + ions. As a result of excess adsorption, a negatively-charged space charge region is built up at the layer/solution interface. The sudden increase of Ag 0 + -concentration that accompanies the neutralisation of this region during anodic polarisation, leads to self-acceleration of the slow process and hence to an arrest in overpotential. The resistance of AgBr layers of 3–15 μ thickness was measured in different solutions in the current density range, 10 −6 –10 −1 A/cm 2 . The results indicated the absence of pores even in 3 μ-thick layers. The resistance of the layer decreases with increase of the current density; this was attributed to the diffusion of Ag 0 + and Ag ▭ − under the effect of concentration differences, beside their mobility in the operative electric field. Below about 5·10 −4 A/cm 2 , diffusion is almost restricted to Ag ▭ − whereas at higher currents diffusion of Ag 0 + predominates.

Adsorption of Silver Ion on Silver Chloride Precipitate and Its Influence on Electrical and Photochemical Properties of the Precipitate

Adsorption of Silver Ion on Silver Chloride Precipitate and Its Influence on Electrical and Photochemical Properties of the Precipitate

The isoionic point of silver iodide sols and silver bromide and bromoiodide emulsions

The isoionic points (IP) of silver bromide and iodide dispersions were measured in the presence of surface-active materials by means of the desorption of silver or halide ions on digestion, as a function of initial pAg of the dispersion. Anionic materials increased adsorption of silver ions and decreased that of halide, so that the pAg of the IP was increased. Conversely, cationic surfactants and polyethylene oxide lowered the IP. Silver bromide and bromoiodide gelatin emulsions changed their IP as a function of pH in accordance with the ionization of gelatin. The maximum amount of bromide ions desorbed on digestion of a silver bromide emulsion was about 1 milliequivalent per mole of silver bromide, corresponding to an original bromide coverage of approximately one tenth of the surface. Desorption of bromide was observed even when the surface area, as measured by dye adsorption, remained unchanged.

KINETICS OF SILVER – SILVER ION EXCHANGE

The kinetics of silver – silver ion exchange have been studied with etched silver foils. The results indicate that several different rates of reaction occur on a single specimen. This may be interpreted to indicate the presence of crystal faces of different orientations, each of which exchange at a given rate. Interchange of ions in solution with radioactive ions adsorbed on the metal surface was not distinguishable from exchange between ions in solution and active atoms of the metal. When adsorbed silver ions were electrodeposited, the resulting metal surface exhibited a completely heterogeneous character with respect to exchange.

The charge effect in relation to the kinetics of photographic development. I. The general effect

The view is rather widely accepted 1-:, tha t the reduction of silver ions in normal chemical (direct) development takes place at or near the interface between silver halide and silver. At the start of development, the interface is tha t between silver halide and the latent-image material (very probably silver); in the later stages of development of the individual grains, the silver involved is tha t formed by prior reduction of part of the silver halide. Once the interface is accepted as the locale of the reduction of silver ions, it remains to be decided whether or not the developing agent must be present at the interface before the reduction can occur. On the basis of what m ay be termed the catalytic hypothesis, development depends primarily upon the adsorption of silver ions to the silver and the accompanying alteration in the act ivat ion energy conditions of the reaction between the silver ions and the developing agent. An alternative view holds tha t the silver nuclei act simply as electrodes which can accept electrons from the developer at any point on the metal surface and can conduct the electrons to the interface. The per t inent experimental evidence does not allow a clear-cut decision between these views, but the trend is against the electrode hypothesis. The evidence on the adsorption of hydroquinone, in particular, seems incompatible with the electrode scheme. The kinetics of development by hydroquinone indicate tha t adsorption of the bivalent ion occurs prior to the reaction. 6 However, both direct adsorption measurements 7 and kinetic measurements 8 fall to indicate adsorption of hydroquinone to silver. The obvious implication is tha t the hydroquinone is adsorbed (as bivalent ion) to the silver bromide surface or to the interface. There is indirect evidence for the adsorption to silver bromide, 9 and it

Intensification of the latent image on photographic plates and films: II. The decomposition of hydrogen peroxide and the mechanism of latent image intensification

1. (1) It has been shown that, just as with pure alkaline and acid solutions of hydrogen peroxide and a metal catalyst, alkaline hydrogen peroxide in the presence of gelatin-silver or gelatin-silver sulphide sol, with or without the presence of soluble bromide, is much more easily decomposed than acid hydrogen peroxide under similar conditions. 2. (2) It has also been shown that both acid and alkaline solutions of hydrogen peroxide in the presence of soluble bromide react with silver sulphide, in bulk, to give sulphuric acid or a sulphate and colloidal silver bromide. 3. (3) Colloidal silver was found to dissolve to a greater or less extent in gelatin-hydrogen peroxide solution with a pII of 5.5 or less, giving rise to silver ions which when soluble bromide is also present form colloidal silver bromide. 4. (4) These facts indicate that intensification of latent image, and probably also the effect of hydrogen peroxide on sensitivity or the production of latent fog, is chemical in nature as Clark has contended and that a chemiluminescence mechanism while it has not been disproved is not necessary in order to explain the phenomenon. 5. (5) A chemical mechanism is proposed based on Hickman's recent theory of the formation of latent image by light. 6. (6) It is proposed that the bromine set free by the action of acid peroxide on the soluble bromide in the plate being very limited in quantity acts on the silver sulphide speck to form metallic silver, which in turn may be partly converted by the acid hydrogen peroxide into silver ions, and if any soluble bromide is left in the vicinity some colloidal silver bromide is formed containing on its surfaces adsorbed silver ions. It is believed that any one or all of these, metallic silver, silver ions, or colloidal silver bromide with silver ions adsorbed, produces a greater degree of developability of the grain than the original silver sulphide speck. 7. (7) This view is supported by the experimental fact that if soluble bromide is largely removed from a plate by action of silver nitrate (less than an excess), hydrogen peroxide produces very little if any intensification of latent image.