Preparation of TiO2 Sol Using TiCl4 as a Precursor

A titanium dioxide sol with narrow particle size distribution was synthesized using TiCl4 as the starting material. The sol was prepared by a process where HCl was added to a gel of hydrated titanium oxide to dissolve it. The resulting aqueous titanic acid solution was heated to form titanium dioxide sol. The effects of preparation parameters were investigated. TiCl4 was slowly added to distilled water at 5°C. Aqueous solution of sodium hydroxide was added to adjust the pH of the system to 8–12. After aging for a period of time, the peptized sol was filtered and sufficiently washed. The filtered cake was repulped in water. Hydrochloric acid was slowly added to the solution with stirring. After condensation reaction and crystallization, a transparent sol with suspended TiO2 was formed. XRD results show that the crystalline phase was anatase. The suspended TiO2 particles were rhombus primary particles with the major axis ca. 20 nm and the minor axis ca. 5 nm. The TiO2 particles prepared at pH 8 had the largest surface area of 141 cm3/g and it was microporous. The compositions of the solution which yielded the smallest suspended TiO2 particles were TiO2:HCl (35% HCl) = 1:1 (molar ratio), concentration of TiO2 = 10%. Hydroxypropyl cellulose with viscosity of 150–400 cps was added as a dispersant. The sol was excellent in dispersibility and long-term stability. Transparent thin films could be obtained through dip-coating glass substrate in the sol. The dip-coating on glass can be less than three times to have one monolayer TiO2. The transparent TiO2 thin film had strong hydrophilicity after being illuminated by UV light.