Berlin 2018 – scientific programme

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O: Fachverband Oberflächenphysik

O 8: Solid-liquid interfaces: Structure, Spectroscopy I

O 8.4: Talk

Monday, March 12, 2018, 11:15–11:30, MA 144

Determination of the surface charge of the water-rutile (110) surface at low and high pH — •Shumei Sun, Mischa Bonn, and Ellen Backus — Max Planck Institute for Polymer Research, Ackermannweg 10, 55128 Mainz, Germany

We have used visible-infrared sum-frequency generation spectroscopy (SFG) to reveal the surface charge of the rutile (110) surface in contact with water of different pH. The surface is positively and negatively charged at pH3 and pH11, respectively, through protonation and deprotonation reactions. Phase-resolved SFG experiments show that under influence of the charged surface water molecules orient themselves with the hydrogen atoms towards (basic solution) or away from (acidic solution) the TiO2 surface. By combining a recently developed theoretical framework and salt concentration-dependent SFG measurements, we are able to near quantitatively evaluate the surface charge density at pH3 and pH11. The results reveal that the surface charge density of TiO2/pH11 is one order of magnitude smaller than that of TiO2/pH3. Moreover, by increasing the pH above 11, the surface charge is not increasing anymore.