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I.Yu. Popova, V.I. Kiselev, V.I. Lobyshev
Physics Department, Moscow State University, Russia
Investigation of biological activity of anolytes and catholytes produced by diaphragm electrolysis of aqueous solutions excites enormous interest [1]. Diaphragm divides the electrolyzer into two compartment anode and cathode and prevents mixing of electrolysis products. Therefore catholyte and anolyte have different physicochemical properties and posses different action on biological objects. It is known that catholyte obtained by electrolysis of aqueous chloride solutions stimulates activity of biological cells while anolyte inhibits their development [1]. It was shown [2] that oxidizers forming in anolyte cause the depressive action. The anolyte solutions containing strong oxidizers, for example potassium hypochloride, are used in medicine and other technologies [1]. Although anolyte and catholyte have a lot of practical application the nature of the processes occurring during the electrolysis and leading to its biological activity are investigated insufficiently.
Physicochemical properties (pH, electroconductivity, redox-potential) of catholyte and anolyte produced by diaphragm electrolysis were investigated. Distilled water, pure water from Milli-Q (Millipore) device and aqueous solutions of potassium chloride were used. These parameters were studied as a function of several treatment conditions. At any case the pH value of catholyte is displaced to alkaline region while the pH value of anolyte is displaced to acid region, anolyte redox-potential is greater than catholyte redox-potential. However the changes of conductivity depend on ionic composition of aqueous solution. Under electrolysis of NaCl solution conductivity of anolyte increases and anolyte conductivity becomes greater than that of catholyte. On the contrary under electrolysis of distilled water conductivity of catholyte increases so as conductivity of anolyte is less than that of catholyte. Under electrolysis of pure water anolyte conductivity increases as well as in the case of salt solutions. The values of investigated parameters depend on several conditions including diaphragm properties. The distinction of catholyte and anolyte properties are stored for a long time since they are placed into separated vessels.
The value of pH, electroconductivity and redox-potential are investigated as a function of time, current strength and concentration of NaCl. It is determined that the values of pH in catholyte and anolyte achieve limiting values. During the electrolysis the limiting values increase in proportion of salt concentration. The obtained dependencies are practically linear in the range of small concentration (2×10-5-10-3 mol/l) of salt. Concentrations of H+ ions in anolyte and OH- ions in catholyte approximately correspond to salt concentration in solution. Under subsequent increase of salt concentration (more than 10-3 mol/l) the incline of corresponding curves decreases. The data obtained show that the value of maximum pH gradient between catholyte and anolyte is limited by the quantity of co-ions in aqueous solution. However the data does not allow to confirm or to disprove the hypothesis [3] that pH and conductivity changes under the electrolysis of distilled water is a result of changing of water itself and influence of any admixtures may be neglected.
During the electrolysis there was measured potential difference (U) by probe electrodes between neighboring points in both anode and cathode compartment. It is determined that the average value and the shape of U(t) are different in anode and cathode compartments. Under the electrolysis of distilled water the U value in anolyte is more than U in catholyte and the average values (normalized on a value of the passing current) correlate with the final values of anolyte and catholyte conductivity. Under the electrolysis of NaCl solutions and pure water the U value in anolyte is less than that in catholyte that correlates with the larger value of final anolyte conductivity.
The U value changes sharply during 10-30 min after the beginning of the electrolysis, depending the initial conductivity value. The U(t) dependence in anolyte and catholyte is different. In case of distilled and pure water, in addition to slow change of U, high-frequency fluctuations are observed in catholyte while they are negligible in anolyte. The U(t) dependence changes with the increase of salt concentration. Already at c[NaCl]=2×10-5mol/l high-frequency fluctuations of U value both in catholyte and anolyte appear, but at c[NaCl]=(4-6)×10-4 mol/l those fluctuations disappear in anolyte again.
Action of catholyte and anolyte produced by electrolysis of distilled water on root growth of Tradescantia Viridis and development of duckweed is studied. In both cases more active development of biological objects in anolyte than at catholyte is observed.
On the contrary the anolyte depresses development duckweed while using NaCl solution but catholyte stimulates its development. The experimental data obtained in solutions are in agreement with the literature data which assert that anolyte have depressive properties.
Opposite sign of the effect in salt solution and distilled water is not clear and lead to the necessity of a new outlook on the causes of biological activity of aqueous solutions obtained by diaphragm electrolizer.
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