Surface charge of silica determined using X-ray photoelectron spectroscopy

Here an approach to determine absolute surface charge densities of powder solid samples in an inert electrolyte solution using X-ray photoelectron spectroscopy (XPS) is presented. The surface charge due to the potential determining ions was obtained by determining the surface densities, using XPS, of the counterions and co-ions that were taken up by the solid from an electrolyte solution. The approach is demonstrated using results for dispersions consisted of SiO2 colloids in 20 mM NaCl and 100 mM KCI electrolyte solutions with a pH between similar to9 and similar to2. The work has shown that the surface charge density determined by XPS is in good agreement with potentiometric titration experiments in the pH interval investigated, where the former technique may provide constraints for determining unambiguously the absolute surface charge density. (C) 2004 Published by Elsevier B.V.