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Abstract
A series of titanium dioxide gels has been prepared by the oxidation of precipitated hydrous Ti(III) oxide, obtained by the addition of aqueous ammonia or ammonium carbonate to aqueous solutions of titanous chloride. The gels were dried in air at 110°C and their structures and surface properties studied with the aid of DTA, X-ray diffraction, nitrogen adsorption, and spectrophotometry. Analysis of the nitrogen isotherms has revealed that the gels exhibited a wide range of different pore structures, extending from narrow micropores to wide mesopores. The development of the gel porosity appears to have been largely controlled by the mode of removal of water ligands from the hydration sphere of the cations, enlargement of the micropore volume being obtained by the replacement of water by carbonato ligands and pore widening by increase in the pH of precipitation (over the pH range 2.3–7.1). All the gels were X-ray amorphous in their original state: some were converted directly to rutile at 500°C while others underwent the more usual transformation into the intermediate anatase form. It is postulated that the rapid removal of the water ligands can result in the formation of a defect structure which controls the development of the pore structure and also the behavior of the gels on heat treatment.
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