Surface Speciation at Solid/Liquid Interfaces: A Vibrational Sum-Frequency Study of Acetate Adsorption at the Fluorite/Water Interface

Vibrational sum-frequency spectroscopy (VSFS) has been used to investigate the adsorption of acetate at the fluorite/water interface in situ. The bulk pH value was varied to control the composition of the liquid phase in contact with a single crystalline fluorite (CaF2) surface. Spectra were recorded in frequency regions corresponding to vibrational modes of the adsorbate and water. Quantitative information on interfacial water molecules in different states of order was obtained from the present data. Furthermore, the effect of background electrolyte concentration was studied, and it was found that surface hydroxyls play a crucial role for the oriented adsorption of acetate ions at the interface. 1