CALORIMETRY OF POLY-(ACRYLIC ACID) ADSORPTION ON TIO2

The adsorption of low molecular weight poly-(acrylic acid) (PAA) from aqueous solutions on TiO2 (anatase) has been studied and at pH 10 as a function of the electrolyte type and concentration. At low pH an exot hermic heat of adsorption is found but at high pH in CaCl2 and NaCl so lutions heat is consumed during adsorption. This endothermic effect is related to specific interactions between the cations and the TiO2 sur face. If a Ca-salt is used the endothermic effect also originates from Ca2+ PAA interactions. The most likely driving force for PAA adsorpti on on TiO2 at high pH is the entropy gain by the release of hydration water of specifically interacting ions. (C) 1994 Academic Press, Inc.