The p.z.c. and i.e.p. of γ-Al 2O 3 and TiO 2

Abstract

Abstracto(1)The point of zero charge (p.z.c.) and the isoelectric point (i.e.p.) of Al2O3 and TiO2 in LiCl, KCl and CaCl2 solutions were compared.(2)KCl is a neutral electrolyte for both oxides, whereas LiCl is indifferent for TiO2 and is specifically adsorbed by Al2O3; CaCl2 is specifically adsorbed by both oxides.(3)The p.z.c. of both oxides in CaCl2 shifts 1–1.5 pH towards the low pH, whereas the i.e.p., determined in 10−3 mol l−1 solutions, almost coincides in all three electrolyte solutions.(4)The p.z.c. value principally depends on the titrations in concentrate solutions because the titration curves in dilute solutions almost coincide.for all three electrolytes.(5)Due to the fact that the titration curves in dilute solutions coincide, the i.e.p. determined in these solutions (10−3 mol l−1) remains unaltered.(6)The shift of i.e.p., due to specific adsorption, is difficult to determine, because specific adsorption manifests itself principally in concentrated solutions, which are not appropriate for i.e.p. determinations. The point of zero charge (p.z.c.) and the isoelectric point (i.e.p.) of Al2O3 and TiO2 in LiCl, KCl and CaCl2 solutions were compared. KCl is a neutral electrolyte for both oxides, whereas LiCl is indifferent for TiO2 and is specifically adsorbed by Al2O3; CaCl2 is specifically adsorbed by both oxides. The p.z.c. of both oxides in CaCl2 shifts 1–1.5 pH towards the low pH, whereas the i.e.p., determined in 10−3 mol l−1 solutions, almost coincides in all three electrolyte solutions. The p.z.c. value principally depends on the titrations in concentrate solutions because the titration curves in dilute solutions almost coincide.for all three electrolytes. Due to the fact that the titration curves in dilute solutions coincide, the i.e.p. determined in these solutions (10−3 mol l−1) remains unaltered. The shift of i.e.p., due to specific adsorption, is difficult to determine, because specific adsorption manifests itself principally in concentrated solutions, which are not appropriate for i.e.p. determinations.