Interfacial interactions between aqueous solutions of 4,4'-bipyridyl and mercury

Abstract

From analysis of electrocapillary curves obtained by drop-time measurements with spindle-type capillary and the method of controlled convection the data on reversible equilibrium adsorption of 4,4'-bipyridyl on mercury from aqueous 0·1M solutions of Na2SO4 and H2SO4 were obtained. In neutral solution 4,4'-bipyridyl is strongly adsorbed: at potential of maximum adsorption the Langmuir coefficient β = 1.4 . 102 m3 mol-1 and Γm = 1.8 . 10-6 mol m-2; in acid solution the adsorption of the doubly protonated 4,4'-bipyridylium cation is weaker and its potential dependence goes through a minimum. The increase of adsorption of the bipyridylium cation and a simultaneous increase of negative charge with increasing negative potential are explained by charge transfer in adsorbed state. The electroreduction of 4,4'-bipyridyl is preceded by formation at the electrode surface of a layer of sparingly soluble salt of the bipyridyl cation radical.