Dresden 2026 – wissenschaftliches Programm

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O: Fachverband Oberflächenphysik

O 36: Focus Session: Mineral-water interfaces II

O 36.5: Vortrag

Dienstag, 10. März 2026, 12:00–12:15, HSZ/0403

Water Organization and Speciation at the Calcite (10.4)-Water Interface at High pH — •Tobias Dickbreder¹, Frank Heberling², and Ellen H. G. Backus¹ — ¹Institute of Physical Chemistry, Faculty of Chemistry, University of Vienna, Vienna, Austria. — ²Institute for Nuclear Waste Disposal, Karlsruhe Institute of Technology, Eggenstein-Leopoldshafen, Germany

Calcite dissolution and precipitation are central for various environmental processes including the geological carbonate-silicate cycle, buffering of sea- and freshwater pH values and biomineralization. Since these processes take place at the calcite-water interface, the structure and properties of the interface between water and the most stable calcite (10.4) surface have been well studied. Despite this effort the protonation state of surface-bound water and interfacial carbonate groups remains poorly understood, because dissolution and carbonate buffering complicate studying calcite de-/protonation experimentally.

Here, we apply vibrational sum frequency generation (SFG) spectroscopy to directly assess the water species present at the calcite-water interface. As reported previously, the SFG spectrum at neutral pH is almost featureless due to the opposite orientation of the first two water layers [1]. At very high pH, however, we observe the emergence of spectral features suggesting surface charging and the presence of interfacial hydroxyl groups. Our study, thus, confirms the presence of hydroxyl groups at the calcite-water interface, facilitating the development of more-accurate models of the calcite-water interface.

[1] Söngen et al., J. Phys. Chem. Lett. 12 (2021), 7605 - 7611.

Keywords: Sum frequency generation (SFG); Mineral-water interface; Surface hydroxyl groups; Calcite (10.4)