Adsorption, from electrolyte

Recent studies [6-14] on adsorption from electrolyte solutions on energetically homogeneous electrode surfaces, like the surface of the Hg electrode, show that at least for aqueous solutions the above approach should be re-examined in two respects first in what concerns the adsorption mechanism (1) and second the treatment of the intermolecular interactions at the surface solution. The adsorption mechanism (1) should be re-examined since, using a thermodynamic method proposed for the determination of the size ratio parameter ni, the value nj = 1 0.2 has been found for a variety of experimental systems, despite the fact that the adsorbate molecules can have dimensions considerably different from those of the solvent molecules [6-11]. In what concerns the intermolecular interactions, in the presence of polar molecules a significant contribution arises from the electric field across the surface solution, which is created by their dipoles [7,12-14]. Similarly, an electric field is established when ions, either from an electrolyte in the bulk solution or from impurities, penetrate the surface solution. In both cases this field is expected to have a dominant effect on the surface activities. 

Tombacz, E., Adsorption from electrolyte solutions, inAdsorption Theory, Modeling, and Analysis, Toth, J., ed., Marcel Dekker, New York, 2(X)2, p. 711. 

FIG. 1 Conceptual interaction web of adsorption from electrolyte solutions showing the mutual contribution of chemical processes and electrostatic constraints. 

Focusing on the purpose of this book, one may expect a systematic treatment of the topic s theory, modeling, and analysis given in the book title for the kind of adsorption discussed in this chapter. To give a comprehensive description of adsorption from electrolyte solutions would require a book in itself, whieh may not be interesting for the readers who have known the relevant literature. Here, I would like to point to the given chapters of excellent books Lyklema... 

Adsorption from electrolyte solutions refers to the accumulation of mostly charged species from the aqueous phase at an electrified interface between the sohd and water. Chemical species are... 

As I see, an essential problem in this field is that the complex aspect of adsorption from electrolyte solutions shown in Fig. 1 has not been widely accepted. I have hardly found a systematic analysis of all probable simultaneous equilibria in a given adsorption system in the relevant literature. In most cases the solution condition (e.g., pH)-dependent dissolution of the solid phase, the surface precipitation, and the speciation in the aqueous phase are omitted in the evaluations either without mentioning them or with reference to some reasoning. To demonsteate some outcomes, it is worth inspecting a simple case of the surface-charge titration of a common aluminum oxide in detail. 

Lamperski, S. (1997). Molecular model for anion adsorption from electrolyte of constant ionic strength. Journal of Electroanalytical Chemistry, Vol. 437,225-231. 

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