SIMPLE-MODELS FOR ADSORPTION ON ELECTRODES .1. ADSORPTION OF MONOMERIC NEUTRAL ORGANIC-MOLECULES

Simple molecular models are developed to describe the single adsorptio n of monomer neutral organic compounds and the reorientation and coads orption processes of these substances on ideally polarized electrodes. The equilibrium properties are determined within the framework of lat tice statistics using the mean field approximation under the assumptio n of a mean electrical field acting at each site. Neglecting short-ran ge interactions, the first model for single adsorption predicts langmu irian adsorption isotherms, which are congruent only with respect to p otential, and a quadratic dependence of the Gibbs energy of adsorption on the potential. The model was tested by comparison with a variety o f experimental data and satisfactory agreement was found over a wide r ange of adsorbate concentrations and polarizations, even in cases wher e the experimental data exhibit deviations from langmuirian behaviour. Generalizations of this model to include short-range interactions, va riations of the adsorbed layer thickness and changes in the state of t he solvent molecules are examined. The model for reorientation and coa dsorption processes is also an extension of the first model. Compariso ns of its predictions with experimental data show that it describes al most quantitatively all the experimental features observed during a re orientation process of an organic adsorbate when it exhibits two disti nct polarization states on a mercury electrode. Moreover, it can provi de a satisfactory description of the coadsorption of two organic adsor bates, without using additional adjustable parameters, but from the kn own properties of their single adsorption. Thus, the models developed in this paper combine both simplicity and applicability and therefore they can be used to analyse a variety of experimental adsorption data.