Characterizing the silica/water interface is critical to understand numerous geochemical, environmental and industrial processes. Many of these processes depend on the surface charge density and thus on the acid-base equilibria of the silica/water interface. Using the Eisenthal group's ?(3) technique of second harmonic generation spectroscopy, we recently observed that these acid-base equilibria are largely specific to the ions present in the aqueous phase. Consistent with previous observations that anions exhibit more pronounced ion specific effects, herein we present how the acid-base behavior of the silica/water interface varies quantitatively depending on what halide ions are present.  Chloride, bromide, and iodide, with both sodium and potassium co-ions, demonstrated very different acid-base behavior that eventually led to different effective pKa values for the silica/water interface. The fraction of deprotonation of the surface silanol groups at a certain pH and its specificity to the halide ions will also be discussed.

Halide specific effects on the acid-base equilibria of the silica/water interface studied by second harmonic generation spectroscopy

243rd National Meeting (2012)

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