engleski

Oxidation-reduction processes of lead (II) in the presence of surface active substances

Oxido-reduction processes of lead (II) in the presence of surface active substances Z.Kozarac, B.Ćosović and P.Orlović-Leko It is known that surface active substances influence electrochemical processes at the mercury electrode mainly by reducing the rate of electrode reaction. Interest in the study of these phenomena is continuously increasing, both from the theoretical and practical viewpoint. Since mass-and charge transfer processes at the covered electrode surface depend on porosity of the adsorbed layer and possible interaction between electroactive species and adsorbed molecules, observed adsorption effects are indicative of the structure of the adsorbed layer as well as of the mechanisms of the exchange reactions at interfaces. Different electroactive species can be used as electrochemical probes which are a promising tool for a simple characterization of the structure and characteristics of adsorbed layers at the mercury electrode. Electrochemical processes of lead(II) ion are used as the probe of choice in this study. Investigations were done in wide concentration range of surfactants from region of trace amounts to micellar concentrations.To study interfacial phenomena at low surface concentrations it is necessary to use a suitable and sensitive technique enabling registration of the smallest changes in the kinetics of the electrode reaction at the stationary electrode after a prior accumulation of surface active substances at a convenient, selected potential, so that the oxido-reduction process occurs at the electrode surface which is partly or completely covered by surfactant molecules. Study of adsorption phenomena and charge transfer processes at charged electrodes can also open new possibilities for simulation of interfacial phenomena at natuiral phase boundaries. Model surfactants ( nonionic and ionic detergents, albumin and lecithin) used in these studies were taken as representative compounds of different classes of surface active constituents in natural and polluted waters. Studies were performed using the phase sensitive alternating current voltammetry. The adsorption of surface active substances was determined in the basis of capacitance measurements (out of phase)signal.The influence of adsorbed layers on the cathodic and anodic processes of lead was followed by measuring Faradaic current (in phase measurements)after accumulation at the potentials of -0.2 and -0.6V vs.Ag/AgCl.The kinetic parameters the rate constant ks and the transfer coefficient  of the electrode reaction will be estimated from the shape and height of the corresponding a.c. voltammogram using theoretical curves obtained by digital simulation.

lead ; inhibition ; surface active substances ; ac voltammetry

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