| Abstract: |
Adsorption of hydrogen and hydroxyl ions on a nonporous pyrogenic silica was determined by potentiometric titration in LiCl, KCl, and CsCl electrolytes over the pH range 1.8–9.0. No evidence of hydrogen ion adsorption was found. The sequence of counterion adsorption was Cs+ > K+ > Li+. An attempt was made to increase the extent of surface hydration of this silica by treatment in aqueous solution. This product had the same properties as untreated silica, except for slightly lower charge densities above pH 6. This difference was attributed to adsorption of impurities during treatment rather than to any significant effect of hydration state. Charge densities were found to be somewhat higher than those reported for precipitated silica, but much lower than those reported for microporous silica. Differential capacitance curves indicate the counterions for precipitated silica to be further away from the surface. It is suggested that Cs+, classed as a structure breaker in aqueous solution, is better able than Li+ to penetrate any structured water phase existing at the silica surface, in accordance with observed adsorbabilities. |
