P. Nikitas, SIMPLE-MODELS FOR ADSORPTION ON ELECTRODES .1. ADSORPTION OF MONOMERIC NEUTRAL ORGANIC-MOLECULES, Journal of electroanalytical chemistry [1992], 375(1-2), 1994, pp. 319-338
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.