AVS 60th International Symposium and Exhibition
    Ions at Aqueous Interfaces Focus Topic Monday Sessions
       Session IA+AI+BI+IS+NL+SS-MoA

Paper IA+AI+BI+IS+NL+SS-MoA6
Specific Ion Effects on Acid-Base Equilibria at the Planar Silica/Water Interface

Monday, October 28, 2013, 3:40 pm, Room 203 A

Session: Ions at Aqueous Interfaces
Presenter: J.M. Gibbs-Davis, University of Alberta, Canada
Correspondent: Click to Email
The interaction of ions with biological and environmental interfaces depends not only on their valency but also their identity. These specific ion interactions can influence other processes like deprotonation at mineral oxide interfaces. To monitor such interactions we utilized surface specific second harmonic generation (SHG) to report on changes in the surface charge density of silica in real time. We observe that the intrinsic equilibrium constant of the silanol groups is sensitive to the identity of the alkali ion. In contrast, varying the identity of the anion does not affect the intrinsic acidity of the sites but rather their mechanism of deprotonation. Specifically, positive cooperativity is observed in the deprotonation of silanol groups with increasing anion size and polarizability. These results and complementary measurements of the water structure using sum frequency generation spectroscopy will be discussed.