Experimental Studies and Theoretical Interpretation of the Calorimetric Effects Accompanying Ion Adsorption at Oxide/Electrolyte Interfaces: Application of Flow Adsorption Calorimetry
Résumé
Application of flow-adsorption calorimetry is demonstrated to measure the enthalpic effects accompanying adsorption of simple ions at oxide/electrolyte interfaces. A new kind of experiment is presented, in which calorimetric effects are recorded, accompanying the change of the concentration of the inert electrolyte at constant pH equal to the point of zero charge (PZC). It is shown that carrying out calorimetric experiments in that way decreases by one half the number of parameters that must be determined by best fitting the experimental data by theoretical expressions. The theoretical expressions applied here are essentially those developed in our previous publications, though certain theoretical aspects are discussed here more rigorously. The adsorption of NaCl on an anatase sample was selected for study. A special high-purity anatase sample was prepared, having a high surface area equal to 61.7 m2/g and a PZC value close to that of pH of distilled water. A striking difference was found between the enthalpies of proton adsorption in the absence and in the presence of Na+, Cl- ions.