Electroacoustic study of titania at high concentrations of 1-2, 2-1 and 2-2 electrolytes

The electrokinetic potentials of titania were studied over a pH range 3–9 in the presence of alkali metal sulfates, alkaline earth metal chlorides and MgSO4 at concentrations up to 1 mol dm−3 by means of the electroacoustic method. The electrokinetic potentials measured at concentrations of 0.1 mol dm−3 or higher of 1-2, 2-1 and 2-2 electrolytes were rather insensitive to the pH, and no IEP was observed. Positive electrokinetic potentials were observed in the presence of alkaline earth metal chlorides and negative electrokinetic potentials were observed in the presence of alkali metal sulfates and MgSO4. This result is consistent with specific adsorption of alkaline earth metal cations and of sulfate anion on titania, which is also observed at lower ionic strengths. The present results indicate that the electrokinetic potential does not cease at ionic strengths of about 1 mol dm−3, as it might be expected from extrapolation of the trends observed at lower ionic strengths.