Understanding the mechanism of monolayer adsorption from isotherm

A new approach for understanding the mechanism of monolayer adsorption is proposed. The Langmuir model, which does not take into account sorbate-sorbate bonds, is the most common one for interpreting monolayer adsorption.When using it, the assumption about the absence of sorbate-sorbate interactions between the sorbate molecules of the first layer is never checked. However, the sorbate-sorbate interactions can make an important contribution to the adsorption energy at physical adsorption. In this case, the formation of sorbate clusters in first layer is an energetically preferable process compared to the process of individual molecules adsorption. The monolayer cluster adsorption model, which takes into account sorbate-sorbate interactions, was introduced in our previous works. In present work, based on the experimental isotherms analysis, a criterion for the mechanism of monolayer adsorption (cluster or adsorption of individual molecules) is proposed. Examples are given of the this criterion application to the study of the mechanism of carbon dioxide adsorption by IRMOF-6, IRMOF-11 and IRMOF-1, ethane by highly activated carbon Saran and methane by mica. This work develops a new approach to the interpretation of monolayer adsorption mechanism.