Ion-Specific Interactions at a Mineral-Water Interface Revealed by Surface-Sensitive Spectroscopy under Flow Conditions

A solid surface in contact with an aqueous solution is typically charged. When put in contact with an aqueous electrolyte solution, the surface charge and composition are crucially affected by the composition of the aqueous phase due to ion-specific interactions between ions and the solid surface. In this study, we combine surface-sensitive vibrational sum frequency generation (v-SFG) spectroscopy and flow experiments to investigate ion-specific interactions at the fluorite-water interface. The flow-induced change in the concentration of dissolved ions at the surface shifts chemical equilibria and can therefore influence the surface potential, which we probe by the v-SFG intensity in the OH stretch region. By studying the v-SFG intensity and its flow-induced change for different salts, we identify charge screening and ion-specific effects, including surface adsorption.