The present work is focused on the elucidation of the detailed mechanism of Cu(II) species on TiO₂ surface, which is of paramount importance for the preparation of a composite material “Cu²⁺/TiO₂” used as catalyst, with desired properties.

The study took place by means of potentiometric titrations, adsorption edges and adsorption isotherms of Cu²⁺/TiO₂ suspensions at 25^oC. At first, the most appropriate electrolyte was selected (KNO₃) and the pH range, where Cu²⁺ species do not precipitate, was identified. It was illustrated that the point of zero charge (pzc) and surface charge (σ^o) can easily be determined by two potentiometric titration curves, one for a suspension and another for the respective blank solution. It was found that an increase in the pH value brings about an increase to the negatively charged groups of the surface, thus increasing the adsorption of the positively charged Cu²⁺ ions. Moreover, at relatively low pH values (pH<pzc), where the surface is positively charged, an appreciable adsorption of Cu²⁺ species was found. This indicates that not only electrostatic adsorption takes place, but the copper species are deposited on the TiO₂ surface through coordination and hydrogen bonds as well. Furthermore, it was found that the ionic strength does not affect the adsorption. Finally, an increment at the pH value results in an increase in the adsorption constant and in a decrease in the lateral interaction energy (table 1).

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