Infrared study of adsorption in situ at the liquid/solid interface. IV. The utility of internal reflection techniques

Abstract

Experiments were carried out to explore the feasibility of using internal reflection spectroscopy to study adsorption phenomena in situ at the liquid/solid interface. To test the methods, stearic acid was adsorbed from CCl 4 solution directly onto the surfaces of Ge and Al 2O 3 internal reflection prisms which acted as adsorbents. Infrared spectra of the adsorbed layer were measured with a Beckman IR-12 and also a Digilab FTS-14 Fourier transform spectrometer. It was possible to follow the build-up of the adsorbed layer as function of time and, with solutions of various concentrations, to note changes in the total adsorption as function of concentration. The maximum amount adsorbed was about 0.3 monolayer with solutions in the 10 −4–10 −2 M range. The lowest coverage observed was about 0.03 monolayer. Some information about the orientation of the adsorbed species could be obtained through the use of polarized radiation. Although the method is restricted to adsorbates which can be fashioned into internal reflection elements, the techniques are suitable for obtaining information about kinetics of adsorption and desorption, adsorption isotherms, adsorbate-adsorbent perturbations, the orientation and structure of the absorded layer, and chemisorption.