A Solution Chemistry Study of Nonhydrolytic Sol−Gel Routes to Titania

The etherolysis/condensation of TiCl4 by diisopropyl ether (iPr2O) as well as the direct condensation between TiCl4 and Ti(OiPr)4 are efficient nonhydrolytic sol−gel routes to titania. A comparison of the solution chemistry of the two routes was performed by means of NMR spectroscopy. In both cases the condensation is slow at room temperature; the true precursors are titanium chloroisopropoxides in equilibrium through fast ligand-exchange reactions. The condensation takes place at 100 °C after an induction period which drastically depends upon the OiPr/Ti ratio in the reaction mixture. This behavior is related to the composition of the starting chloroisopropoxides mixture. The key species in the induction process appears to be Ti(OiPr)Cl3, which catalyzes the first condensation reactions.