Adsorption on to lonogenic Surfaces

Abstract

Michaelis and Ehrenreich¹ were the first to suggest that the adsorption of large ions such as the organic dyes, on ionogenic surfaces, takes place by two distinct mechanisms operating simultaneously: one of an electrochemical nature, and in addition to this a ‘normal' physical adsorption. Later, Freundlich and Poser² stated explicitly that the adsorption of large positive ions on clays could be explained qualitatively by the combined effects of an irreversible ion-exchange adsorption and a reversible physical adsorption, and this idea was further elaborated by Michaelis and Rona³. It is interesting for the historian of science that this simple idea was afterwards forgotten, but was ‘rediscovered' on several occasions prior to our work. The idea of simultaneous adsorption by two different mechanisms is not mentioned by Swan and Urquhart⁴ in their comprehensive review on adsorption, or in text-books. Even Freundlich himself in his "Kapillarchemie" (1930) seems to have lost sight of the implications and usefulness of the idea, but it was formulated in different ways by Stadnikoff⁵, Fogle and Olin⁶, Hendricks⁷ and Grim et al.⁸.