D. V. Konev

Copper electrodeposition into ion-exchange materials

Electrodeposition of copper into spherical granules of ion-exchange materials KU-23 and KU-2 out of acid sulfate solutions is studied by a method of cyclic voltammetry. It is discovered that the discharge of copper ions in an ion-exchange matrix is characterized by a cathodic overvoltage that is higher than the overvoltage of the same process on a graphite substrate by 0.08 V, which is most probably connected with a limited mobility of ions localized at fixed groups [RSO3−]. The cyclic voltammogram exhibits an additional cathodic peak in the potential region corresponding to the reduction of single-charged copper ions that form as a result of their accumulation inside pores of the ion-exchange matrix during anodic dissolution of metal deposited previously. It is fixed microscopically that the process of deposition begins at the graphite substrate/ion-exchanger interface and passes into bulk upon the formation of an electron-conducting layer saturated with copper. Preliminary saturation of the ion-exchanger by copper deposited chemically facilitates uniform electrodeposition of copper over the entire volume of pores of the ion-exchange matrix.

Kinetics of oxygen reduction by nanocomposite silver-ion exchanger

It was experimentally determined that the rate of reduction of molecular oxygen from water by the nanocomposite silver-ion exchanger KU-23 is substantially lower than by copper-containing composite and takes place with substantial kinetic inhibition. The kinetic parameters of the process were determined by solving the reverse kinetic problem; it was found that this was due to a reduction in the rate constant of the reaction of silver with oxygen at virtually constant internal diffusion coefficient of molecular oxygen. The transition from kinetic to diffusion control was determined to depend on the silver particle size.

The inverse problem of the kinetics of redox sorption taking into account the size of ultradisperse metal particles in an electron-ion exchanger

The inverse kinetic problem of reducing sorption of molecular oxygen by a copper-containing electron-ion exchanger was formulated and solved taking into account the influence of the size of ultradisperse metal particles on the total rate of the process. These results were used to determine the inside diffusion coefficient of oxygen and rate constants for its interaction with disperse copper from the experimental kinetic curves. The diffusion coefficient obtained was compared with the result of an independent experiment. The kinetic parameters found were used to perform a theoretical analysis of the contributions of various factors influencing the rate of the process under consideration. The reason for the experimentally observed acceleration of the reducing sorption of oxygen by a high-dispersity electron-ion exchanger sample was shown to be an increase in the surface area of metal because of a decrease in the size of its particles and a comparatively high copper content in the surface layer of grains.

Oxygen electroreduction on a granulated layer of a copper-containing electron-ion exchanger

The reduction of dissolved oxygen from a flowing aqueous solution of sodium sulfite on a cathodically polarized granulated layer of a copper-containing electron-ion exchanger is studied. It is established that the polarizing current is distributed over the layer height nonuniformly. A peak current corresponding to the oxygen electroreduction is discovered. The peak shifts from the inlet into the granulated layer to the exit out of it, which is connected with the advance of the concentration front and with an increase in ohmic resistance due to partial oxidation of copper centers. The distribution of the polarizing current is analogous to the distribution of the limiting current of the oxygen reduction, which is determined from polarization curves. The reaching of a stationary position of the peak of the polarizing current and the oxygen reduction degree with time testifies to the onset of a stationary state, at which the current turns limiting and the balance between the arrival and electroreduction of oxygen is fulfilled.

Regard for particle size distribution in a model of the macrokinetics of the reduction of oxygen dissolved in water by a metal-ion-exchanger nanocomposite

The function of granulometric size distribution of metal particles is introduced into the equations of a mathematical model that describes the reduction of molecular oxygen from water by metal-ionexchanger nanocomposites. It is shown that the pattern and parameters of the distribution function have an effect on the behavior of the kinetic curve. It is noted that this is particularly important for systems in which small particles dominate. The calculation and analysis of changes in the metal particle size distribution curve during the process are performed using the example of a silver-sulfocation exchanger nanocomposite.

Chemical activity of silver nanoparticles in anion-exchange matrices with respect to molecular oxygen dissolved in water

New silver-containing nanocomposites different in their dispersity of metal were synthesized on the basis of strongly and weakly basic anion-exchange resins. The chemical activity of the nanocomposites with respect to oxygen dissolved in water was investigated. It was shown that silver nanoparticles in samples based on strongly basic anion exchangers and weakly basic anion exchangers in the NO3− salt form are not oxidized by oxygen; for weakly basic matrices in the free amine form, this process occurs to only a small extent. The resistance to oxygen is explained by inhibition of processes of formation of silver oxides. Nanocomposites based on strongly basic anion-exchange resins are recommended for testing as to catalytic activity.

Reductive sorption of molecular oxygen from water on silver-KU-23 sulfo-cation exchanger nanocomposites in different ionic forms

It was found that the rate of reductive sorption of molecular oxygen on dispersed silver-KU-23 sulfo-cation exchanger nanocomposites depends substantially on the ionic form (H+, Ag+, Na+ forms) of the nanocomposite. It was established that the observed dependence is due to the influence of the composition of the medium in pores of the ion-exchange matrix, which serve as nanoreactors, on the rate of the chemical reaction between silver nanoparticles and dissolved molecular oxygen.

The dynamics of reductive sorption of oxygen by a granular bed of electron-ion exchangers with different copper dispersities

The behavior of an immobile granular sorbent bed in one-component sorption in a column reactor is described in terms of the kinetic model of redox sorption taking into consideration the dispersity of metal particles, their radial distribution, peculiarities of chemical oxidation, and the relation of the overall rate of the process to the properties of the ion exchange matrix. The mathematical problem is formulated and solved numerically; the solution is analyzed theoretically in relation to the basic parameters of the sorption system. A satisfactory agreement is obtained between the experimental and calculated data on the reductive sorption of molecular oxygen from water on a copper-containing electron-ion exchanger.

Percolation effects with copper electrodeposition in ion-exchange material

The effect of preliminary doping of sulfo cation-exchange material KU-23 15/100S with a chemically deposited metal (Ag, Cu) on the rate of copper ion electroreduction is investigated. It is shown that the threshold dependence of the reaction current of copper electroreduction on the amount of doped metal is due to the formation of a single percolation cluster in an ion-exchange grain and, as a result, to the appearance of electron conductivity. It is established that preliminary doping changes the nucleation mechanism from a gradual to an instantaneous one. Results from a local X-ray spectral microanalysis provide the basis for concluding that copper electrodeposition is uniform throughout the volume of an ion-exchange grain. The average size of the copper particles formed is 100 nm.

Kinetics of the reduction of molecular oxygen from water by ultrafine copper in an ion-exchange matrix

The rate of the reduction of molecular oxygen from water with a low-capacity copper-containing electron-ion exchanger at various initial ionic forms, grain radii, and sizes of metal particles dispersed into pores. The applicability of the mixed-diffusion and diffusional-kinetic models incorporating a first-order irreversible reaction to describing the system under study was examined. The kinetic parameters of the system were determined within the framework of these models. It was found that the limiting stage of the process in the stationary mode is the internal diffusion of oxygen molecules to the redox sorbent particle. The increase in the rate of the absorption of oxygen by samples containing copper of higher dispersity was observed at the initial stage of the process and was likely associated with an increase in the surface area of the reactive interface.