The silica/water interface is crucial in many geochemical, environmental, and industrial processes. The nature of these processes depends extensively on the surface charge density and thus on the acid-base equilibria of the interface. Using non-resonant second harmonic generation spectroscopy, we recently observed that the acid-base equilibria of the silica/water interface is influenced by the identity of the ions present in the aqueous phase. Herein we present the quantitative dependence of surface charge density of the silica/water interface over a broad pH range in the presence of different alkali halides. The effective pKa values for the silica/water interface change dramatically depending on the nature of the alkali halide. More polarisable anions like iodide also exhibit cooperative acid-base behavior indicating that the mechanism of deprotonation also depends on the identity of the electrolyte. The effect of the salt concentration on the effective pKa, and surface speciation of silanol groups will also be discussed.

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

244th National Meeting (2012)

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