A study of the SiO2-aqueous electrolyte (NaCl, CsCl) interface by X-ray photoelectron spectroscopy

摘要

The surface of amorphous silicon dioxide in NaCl and CsCl solutions with various values of ionic strength and pH is studied by X-ray photoelectron spectroscopy. Samples are prepared through the fast freezing of wet pastes prepared by the centrifugation of suspensions. It is shown that the X-ray photoelectron spectra of such samples provide experimental information on the composition of the SiO2-solution interface, the number of electrolyte ions near the solid phase surface, and its chemical modification. The sign of the charge of silicon dioxide particles can be judged from the dependence of a measured Na(Cs)/Cl atomic ratio; the controlled removal of water from the samples in the chamber of an electronic spectrometer makes it possible to directly estimate the surface potential and study the energy effects of counterion hydration using the shifts in the binding energies of the corresponding photoelectron levels. An analysis of the binding energies of Cs 3d(5/2) and Cl 2p(3/2) lines in the X-ray photoelectron spectra for the SiO2-CsCl solution interface yields additional information on the structure of the formed electrical double layer, thus making it possible to distinguish between the ions adsorbed at the surface and the counterions compensating for its charge.