Specific ion binding influences on surface potential of chromium oxide

다국어 초록 (Multilingual Abstract)

Colloidal force measurements as a function of pH can yield the isoelectric point (IEP) of a surface immersed in an electrolyte. Thecondition of surface charge-potential regulation imposed by the potential-dependent binding of Hþ and counter-ions at the interfacemakes a detailed analysis of the electrostatic force non-trivial. In the current study, the specic ion binding of phosphate ions on tochromium oxide has been investigated. An atomic force microscope (AFM) has been used to measure the force of interactionbetween a SiO2 sphere (. 5 m diameter) and a chromium oxide surface in aqueous media of sodium phosphate buer or sodiumchloride over the pH range 311. From the force separation proles the force at.Jump To’ is plotted over the pH range studied foreach ionic strength. As the IEP of SiO2 is around pH 2 the probe interaction with the surface measures its electrostatic properties,and hence can be used to determine the IEP. The comparison of force titration plots shows the IEP of the chrome surface decreaseswith increasing phosphate ion concentration, from around pH 8 with no phosphate ions present, down to around pH 6 at 0.01 Mionic strength phosphate buer. This indicates that there is specic ion binding of the phosphate to the chrome oxide surface. Wehave used approach of DLVO theory, together with a simple model of specic adsorption of ions at the oxidewater interface, tomodel the long range electrostatic repulsion force measured by the force separation plots at each pH and ionic strength. Bycomparing this model to the isoelectric points at several ionic strengths, we can estimate surface dissociation constants for theadsorption of protons and phosphate from the electrolyte.

참고문헌 (Reference)

1 Lide, "CRC Handbook of Chemistry and Physics" CRC Press 1991