Attenuated Total Reflection FT-IR Spectroscopy to Measure Interfacial Reaction Kinetics at Silica Surfaces

Abstract

Attenuated total reflection (ATR) FT-IR spectroscopy has been adapted to measure the rates of chemical modification reactions at silica surfaces. In this method, a silicon ATR crystal is oxidized at 1000°C under dry O₂ to produce a silicon dioxide layer on the crystal surface, the thickness of which can be measured using ellipsometry. The oxidized silicon layer is then used as a model silica surface in measurements of the rates of chemical modification. A flow cell is filled with a solution of a surface active reagent. ATR infrared spectra are obtained at regular time intervals, where confinement of the intensity to the interface by total internal reflection provides a measure of local changes in concentration of species which adsorb or bind to the surface. The effect of the silicon dioxide layer on the sensitivity of measuring absorbance at the silica-solution interface is investigated. A model reaction study is carried out to determine the binding kinetics diphenylchlorosilane to silica from carbon tetrachloride solution. The technique yields both in situ kinetic and structural information about the reaction of this reagent with silica surfaces.