Preparation of TiO<sub>2</sub> Sols with High Solid Contents by Sol Gel Method

Abstract

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.