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

The etherolysis/condensation of TiCl 4 by diisopropyl ether ( i Pr 2 O) as well as the direct condensation between TiCl 4 and Ti(O i Pr) 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 O i Pr/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(O i Pr)Cl 3, which catalyzes the first condensation reactions.