Surface Charge and Conductance in Dispersions of Titania in Nonaqueous and Mixed Solvents

The nature and speciation of ions, and their affinities to mineral surfaces are well-known for aqueous solutions, and less well-known for mixed water-organic and nonaqueous solutions. Weak acids show strong preferential adsorption of anions on titania, and support a high negative surface charge on titania particles in organic solvents in spite of the very low degree of dissociation of these acids. The interaction between solutions of weak acids in organic solvents and titania particles results in enhanced electrical conductance with respect to the original solutions (in the absence of titania). This phenomenon is explained in terms of surface-induced electrolytic dissociation of weak acids. In mixed water-organic solvents the conductance behavior gradually shifts from water-like behavior (titania depresses the conductance) to opposite behavior (titania enhances the conductance). A quantitative model was proposed to explain the complex effect of the electrolyte and titania concentration on the conductance of the dispersion and zeta potential of the particles.