POROUS TEXTURE OF A TITANIUM-OXIDE GEL - EVOLUTION AS A FUNCTION OF MEDIUM USED

Esterification reaction was used to prepare gels by hydrolysis of titanium isopropoxide. Depending on the acetic acid/alkoxide ratio, crystals, gels or precipitates can be obtained. The relation between theoretical and experimental hydrolysis ratio, h, has been determined using gas chromatography. The porous structure was measured in the case of a gel prepared with h(th) = 6 (h(expt) = 1.27). The infrared spectra show that acetic acid acts as bidentate ligand bridging two titanium atoms. The gel texture was measured by small angle X-ray spectroscopy. If the Scherer model is applied, the mean pore radius obtained was 2.2 nm. The mean mesopore radius, measured by thermoporometry in decane, was 2.8 nm. Thermoporometry measurements were performed in water. Pore radii evolved to a stable value of 4 nm. This can be explained by hydrolysis of organic groups present in the gel.