Surface charge of anatase and alumina in mixed solvents

Heavy water (up to 50%) does not affect the surface charge density of oxide s. The absolute value of negative surface charge of anatase and alumina dec reases, when water is replaced by dimethylsulfoxide (DMSO)-water mixtures. The relative decrease of the negative surface charge of these oxides in the presence of DMSO is independent of the nature and concentration of the sup porting electrolyte. In contrast, the positive branch of the charging curve s of alumina is insensitive to DMSO admixtures, and for anatase, the positi ve charge even increases when DMSO concentration increases. Dioxane causes a shift of the pzc of alumina to lower pH values, especially at low ionic s trengths, but the effect of dioxane on the surface charge density is rather insignificant when alumina carries a high negative or high positive surfac e charge. (C) 1999 Elsevier Science B.V. All rights reserved.