Characterization of the surface of rutile by nitrogen and water vapour adsorption

Abstract

From nitrogen and water-vapour adsorption experiments the surface of pure rutile calcined at 450° has been characterized. Evidence for micropores which fill with nitrogen and water at very low pressure, was obtained from t plots for nitrogen adsorption in the multilayer region. Water-vapour adsorption isotherms determined at 25° after outgassing at various temperatures up to 470°, show an increasing level of adsorption reaching a constant value for temperatures >200°. Molecular water remains on the surface after outgassing at temperatures <200°. Rehydroxylation of surfaces containing only isolated OH groups does not occur to any significant extent at room temperature. Quantitative analysis of the water-vapour adsorption isotherms indicates that the surface contains equal proportions of hydroxylated and non-hydroxylated regions. Application of the B.E.T. theory to nitrogen adsorption on the molecular water free surface, and to water-vapour adsorption data leads to erroneous values for the monolayer volumes.