Titanoxane-siloxane eight-membered rings as precursors of anatase/silica and rutile/silica materials

The eight-membered titanium containing siloxane rings (TiX2)(2)O-4(SiBu2t)(2) (X = Cl 1, Br 2 or I 3) are efficient single-source precursors to homogeneous titania-silica material. The ceramic conversions which occur pyrolytically at about 550 degrees C give a mixture of TiO2-SiO2 materials. Differential thermal and thermogravimetric analysis, X-ray diffraction, vibrational spectroscopy as well as scanning electron microscopy were used to characterise the materials. It was found that the nature of the halogen atoms play a crucial role in the thermal transformation. Thus, after thermal treatment, silica mixed with anatase is obtained from 1 and 3, whereas silica mixed with rutile is obtained from the brominated precursor 2. The thermal evolution of 1 studied by using Raman and infrared spectroscopies confirms the inhibiting effect of SiO2 on the anatase-rutile phase transformation. The molecular route to oxide materials described could represent an alternative to the sol-gel process and may offer certain advantages.