Effect of temperature and alcohols in the preparation of titania nanoparticles from alkoxides

We report on the formation of titania (TiO₂) colloids via the hydrolysis and condensation of alkoxides under a large excess of water. This process is characterized by a rapid precipitation of large aggregates, followed by a slow peptization (deaggregation) induced by the presence of nitric acid. We find that the hydrolysis temperature and the length of the alkoxy group have a minor effect on the size of the peptized colloid. In contrast, the particle size is sensitive to the peptization temperature and exhibits a minimum at 50°C. The presence of alcohols inhibits peptization and results in both larger colloids and longer peptization treatments. The smallest size (∼20 nm in diameter) is obtained when no alcohol is added to the reaction mixture. The results suggest that the formation of TiO₂ nanoparticles is controlled by colloidal interactions, whereas chemical factors (the rate of hydrolysis and condensation) have a secondary role.