ADSORPTION-KINETICS OF A NONIONIC SURFACTANT ON THE STATIONARY MERCURY-ELECTRODE

Adsorption kinetics of the non-ionic trans-2-heptyl-5-hydroxy-1,3-dioxane (THHD) surfactant on the stationary mercury electrode was investigated by a.c. polarography (tensammetry) with 0.4 M KCl solutions used as supporting electrolyte. The experimental results obtained for various bulk surfactant concentrations were interpreted in terms of the exact numerical solutions of the governing mass-transfer equation. A good agreement between the experimental kinetic measurements and the theoretical predictions was found, especially for longer adsorption times. The equilibrium adsorption isotherm of THHD was also determined. It was proved that the experimental isotherm can be adequately described by the localized adsorption Langmuir model with K(a) = 0.15 cm (this value corresponds to DELTAG = -40 kJ mol-1). The non-localized adsorption model proved to be inadequate.