High ionic strength electrokinetics of anatase in the presence of multivalent inorganic ions

Shifts in the IEP of anatase induced by various combinations of 1:1 electrolytes (at concentration of 0.5 mol dm−3) and multivalent ions (concentrations in millimolar range) were studied. The high ionic strength enhanced the shift in the IEP of anatase to high pH induced by specific adsorption of barium and suppressed the shift in the IEP of anatase to low pH induced by specific adsorption of phosphate. The ζ potential of anatase at pH 3–5 is nearly zero in the presence of 0.01 mol dm−3 of sulfate at low ionic strength, but it assumes a positive value as high as 15 mV in the presence of 0.5 mol dm−3 NaI at otherwise the same conditions. Apparently, the contribution of 1:1 electrolytes to the surface charging at high ionic strengths is not mere neutralisation of the proton charge.