The interaction of linear polyphosphates with titanium dioxide surfaces

Abstract

The interaction of linear polyphosphates of the general formula [P_nO_3n+1]⁽ⁿ⁺²⁾⁻ with the surface of titanium dioxide and silica has been studied as a function of pH. Both equilibrium and kinetic aspects of the interaction were addressed, using in situ infrared spectroscopy, electrical double layer, ion chromatography, rheological and adsorption investigations. Orthophosphate is adsorbed on to the titania surface over a wide pH range as two kinds of species, a bridging bidentate surface complex and an electrostatically adsorbed orthophosphate ion. The linear polyphosphates behave in a similar fashion, with adsorption driven by combined electrostatic and chemical contributions. There is no detectable interaction between the linear polyphosphates and the surface of silica at any pH investigated. Linear polyphosphates with larger n displace lower molar mass species from the titanium dioxide surface.