ZETA-POTENTIAL OF ANATASE (TIO2) IN MIXED-SOLVENTS

The replacement of water with mixed solvents (aqueous methanol and ethanol, up to 30% wt.) does not change the surface charge density dependence on the pH of anatase suspensions in 10(-3)-10(-1) mol dm-3 KCl solutions. The negative zeta-potentials are decreased and the isoelectric point is shifted towards higher pH values in systems containing 10(-1) mol dm-3 KCl, LiCl, CsCl, or KI in 30% ethanol/water or 30% methanol water mixtures as compared to pure aqueous systems. The effect is observed only at a sufficiently high ionic strength and alcohol concentration and is similar to that previously found for silica. The charge of anatase can be reversed by BaCl2 and K2SO4 in aqueous and mixed solvent systems. Finally, analogous phenomena were observed with uniform yttria particles dispersed in ethanol water mixtures in the presence of 10(-1) mol dm-3 KCl.