On the kinetics of xanthine adsorption at the mercury ∣ electrolyte interface

The short-term and long-term capacity–time dependence of xanthine in 0.2 M NaCl at 35 °C inside the potential region of the capacity pit was measured at the mercury ∣ electrolyte interface. The short-term capacity–time dependence can be described well theoretically by 2D instantaneous nucleation with a constant growth rate and, for potentials near the more negative pit edge, with 2D nucleation according to an exponential law with a constant growth rate. The long-term capacity–time dependence corresponding to secondary adsorption can be modelled well by 1D instantaneous nucleation with a diffusion controlled growth rate. This mechanism refers to the formation of linear surface molecular stacks. The potential dependence of the overall nucleation and growth rate constant for the short-term and long-term capacity–time dependences will be discussed on the basis of the potential dependence of the interfacial supersaturation.