Structural properties of the silver iodide-aqueous solution interface

Abstract

A survey of existing literature on the water structure around AgI particles shows that a complete description of this topic can not yet be given. In order to contribute to the knowledge of the AgI-aqueous electrolyte solution interface, the shift of the point of zero charge due to the replacement of water molecules by alcohol molecules and the influence of temperature on double layer parameters are analyzed and discussed. From the thermodynamic analysis of the temperature dependency, yielding the interfacial excess entropy η σ , and from the alcohol adsorption experiments, it is inferred that at 25°C water dipoles are not preferentially oriented at a surface charge of about −1 μC.cm −2, coinciding with the adsorption maximum of alcohols. From this point on, dipole orientation increases upon increasing positive and negative charge. However, at positive charges the effect is obscured by the structure-breaking effect of specifically adsorbed nitrate ions. At 85°C, the relation between η σ and surface charge is more pronouced than at 25°C, whereas the cation specificity has completely disappeared.