An interesting area of modern membrane science is the development of "smart" membranes, which can affect the transport properties of selected components via external tuning. When the target components are ions, such a tuning can be realized with the help of electric field created by the conductive pore surface. We have proposed in this work a mathematical model of ions transport in a cylindrical nanopore with the electronic charge at the conductive surface and the chemical charge, which is separated from the surface by the Stern layer. The model is based on one-dimensional equations for potential, ion concentrations, and pressure in the diffuse layer. It is applied for describing the membrane potential at zero current, which characterizes the type and strength of ionic selectivity. It is shown that the change of surface potential in the direction from negative to positive results in the continuous change of pore selectivity from cation to anion. The decrease in the Stern layer capacitance and increase in the pore radius lead to the decrease in ionic selectivity. The presence of positive (negative) chemical charge causes the shift of potential value, at which the selectivity is switched, in the direction of negative (positive) values. At this value of potential, the membrane becomes non-selective, the diffusive flux of ions reaches maximum, and the osmotic flow ceases. The suggested model provides a qualitative and quantitative description of experimental results on switchable selectivity of tracketched membranes modified by the gold coating.
The impact of potential applied to the conductive surface of nanoporous membrane on the membrane potential at zero current is investigated theoretically on the basis of two–dimensional Space–charge model. The membrane separates two reservoirs with different salt concentrations. It is shown that the variation of applied potential from negative to positive values results in the continuous change of membrane selectivity from cation to anion. For equal ion diffusion coefficients, the dependence of membrane potential on the applied potential is an odd function, while for different ion diffusion coefficients it is shifted along the applied potential axis due to contribution of diffusion potential enhanced by the induced charge effect. The decrease of pore radius results in the increase of ionic selectivity and steep transition between cation– selective and anion–selective states when the applied potential is changing
Mesostructured carbon material CMK-3 for electrodes of electrochemical capacitors was obtained by the method of template synthesis. In order to increase the capacitance characteristics, impregnation of metal ions (Co, Ni, and Cu) into the structure of mesoporous carbon CMK-3 was carried out. The structure of the obtained materials was studied by X-ray diffraction and gas adsorption. The study by TEM showed that highly dispersed, nanosized particles are metal oxides Co, Ni and Cu with the size of 30-50 nm. The particles are uniformly distributed inside the carbon material. Electrochemical characteristics were studied in aqueous electrolytes (1M KCl and 1M KOH). It has been established that the impregnation of metal ions increases in the specific capacity of the mesoporous carbon material by about 30 % (from 110 to 156 F/g) in KOH
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