Simulation of adsorption, desorption, and exchange kinetics of mixtures on planar surfaces. 1. Kinetic-diffusion-controlled adsorption and desorption for one-component mixtures

摘要

The quantitative theory for the kinetic-diffusion-controlled adsorption and desorption onto planar substrates has been developed. A power series representation of the adsorption and desorption valid for short times and an asymptotic representation valid for long times are given for systems obeying any adsorption isotherms. For the diffusion-controlled adsorption and desorption the analytical solutions over a wide range of time are found for one-component mixtures satisfying arbitrary adsorption isotherms by using the consistent time scale (CTS) approach. It is shown that the relaxation function F(t) may be applied to describe the adsorption and desorption processes over a wide range of times. The equation in the form of F(t) = log[T-0/Gamma(t) - 1] = n log(t/t(rel)) describes the kinetic-diffusion-controlled adsorption and desorption processes for arbitrary adsorption isotherms. The analytical analysis is shown to be asymptotical. The correlation n equals 0.5 for long times for different adsorption isotherms (linear, Langmuir, and nonlinear). Simple formulas are derived to calculate the parameters n, t(rel), and D* (effective diffusion coefficient in the adsorbed layer) and also the times of establishment of the equilibrium states for the adsorption and desorption processes obeying arbitrary adsorption isotherms. [References: 18]