Electroacoustic study of adsorption of ions on anatase and zirconia from very concentrated electrolytes

The reduction of absolute values of negative ζ potentials (basic branch) of anatase with the concentration of 1 -1 salts (alkali halides, nitrates, and perchlorates) is much more pronounced than that of the positive ζ potentials (acidic branch). The extent of this effect increases in the series Cs < K < Na < Li for a given anion and CH3COO < Cl < NO3 < ClO4 < Br < I for a given cation. For sufficiently high concentrations of most lithium and sodium salts, e.g., 0.53 mol dm-3 NaI, there is no isoelectric point (iep) and the ζ potentials are positive over the entire available pH range. For potassium and cesium salts, an iep is always observed, even at very high concentrations, but it is substantially shifted toward the higher pH values. Small cations show a differentiating effect: the course of ζ(pH) curves for particular lithium and sodium salts at a given high ionic strength is very sensitive to the nature of the anion, but the effect of the nature of the anion is relatively insignificant when different potassium salts are considered. Large anions (iodide) show a differentiating effect, while smaller anions (chloride) do not. © 1996 American Chemical Society.