Cooperative adsorption on solid surfaces

Adsorptions are commonly of monolayer coverage of adsorbate molecules on adsorbent sites, in particular for chemisorptions, where Langmuir adsorption isotherm equation and kinetics are adequate. The Langmuir adsorption is termed ideal adsorption as the surface active centers are uniformly distributed, the molecules are of point-sizes and the interactions between adsorbate molecules and the adsorbent are uniform. However, there are more cases where Langmuir adsorption isotherm and/or kinetics are inadequate in describing the adsorption behavior. Apparent multilayer adsorption has been shown to be descriptive of both physisorptions and chemisorptions as a means of idealization to nonideal adsorptions. The deviation of adsorption isotherm and/or kinetics from (ideal) Langmuir adsorption is due to cooperative adsorption, or interactions between adsorbates or between adsorbate and adsorbent caused deviation from "uniform" interactions. The multi-layer or apparent multilayer behavior of adsorption is an excellent model to describe cooperative adsorption. Adsorption kinetics and isotherms have been derived for adsorptions without differentiating the different types of adsorptions. The simplistic approach can explain majority of the adsorption isotherms and kinetic behaviors.