Preparation of TiO2 Sols with High Solid Contents by Sol Gel Method

Titanium oxide has been extensively used as a photocatalytic material because of its excellent UV light-responsive effect, high refractive index, and high chemical stability. TiO2 in anatase phase for applications in optical or electronic devices and photocatalysis has generally been used in the form of a thin film. The aim of this study was to prepare a stable TiO2 sol with high solid content. Therefore one can use less coating time to have a mono layer of TiO2 film on the substrate. In this study, TiCl4 was slowly added to the distilled water in an ice bath. Aqueous solution of sodium hydroxide was added to adjust the pH of the solution to between 8 and 12 to form titanium hydroxide gel. After aging for a period of time, the Ti(OH)4 gel was filtered and sufficiently washed. The filtered cake was repulped in water. Hydrochloric acid, as a catalyst for polycondensation, was slowly added to the solution with stirring. After poly-condensation reaction and crystallization, a transparent suspended TiO2 sol 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 sample prepared at pH 8 had the largest BET surface area of 141 cm3/g among all samples. The best preparation condition to have the smallest TiO2 particles are Ti: H = 1: 1 (atomic ratio), 10% solid content of TiO2, and hydroxypropyl cellulose with viscosity of 150-400 cps as a surfactant. The thin film was obtained by dip-coating the glass in TiO2 sol. Since the sol had high solid content, the coating time became less. The dip-coating on glass was less than three times to have one monolayer TiO2. The transparent TiO2 thin film had super-hydrophilicity after illumination by UV light.