Specific influence of univalent cations on the ionization of alumina-coated TiO2 particles and on the adsorption of poly (acrylic) acid

A surface counterion titration method was used to monitor the interaction of monovalents cations (Li+, Na+, TMA(+)) with the surface of alumina-coated TiO2 particles in concentrated media at different pH and electrolyte concentrations. This method allows measuring separately the negative and positive contribution to the surface charge. It showed that Cl- and TMA(+) are indifferent ions, but Li+ and Na+ specifically adsorb on the non-ionized alumina surface sites. The binding sequence of cations is Li+ > Na+ > TMA(+) at all ionic strengths investigated and is consistent with the structure-making and structure-breaking model developed a few decades ago. Polyacrylic acid (PAA) previously neutralized with the corresponding hydroxide (LiOH, NaOH, TMAOH) has been adsorbed on the alumina surface at different pH. The polymer counterion has a significant influence on the polymer adsorption. The sequence of the surface coverage as a function of the polymer counterion follows the order Li-PAA > Na-PAA > TMA-PAA. The much higher surface coverage with Li-PAA and Na-PAA compared to TMA-PAA is explained by the specific adsorption of Li-PAA and Na-PAA on the nonionized alumina surface sites, the same way LiCl and NaCl do. (C) 2003 Published by Elsevier Inc.