Synthesis of TiO₂ sol in a neutral solution using TiCl₄ as a precursor and H₂O₂ as an oxidizing agent

Nanosize TiO₂ thin film on glass substrate was obtained through dip-coating method using TiO₂ sol. Suspended nanosize TiO₂ sols with anatase structure in aqueous solution were synthesized by sol-gel method using TiCl₄ as a precursor. TiCl₄ was reacted with an aqueous solution of NH₄OH to form Ti(OH)₄, and H₂O₂ was then added to form peroxo titanic acid. It was further heated in water and converted to TiO₂. The effects of the preparation parameters, viz., pH value of the Ti(OH)₄ gel, concentration of H₂O₂, and heating temperature and time, on the properties of the TiO₂ sol were investigated. The materials were characterized by X-ray diffraction, Fourier transform-infrared spectroscopy, and transmission electron microscopy. The results showed that the primary TiO₂ particles were rhombus with the major axis ca. 10 nm and minor axis ca. 4 nm, and were in anatase structure. The sol was excellent in dispersibility and was stable in neutral and even slight basic conditions for at least 2 years without causing agglomeration. The best preparation condition was optimized with the pH value of Ti(OH)₄ gel at 8, H₂O₂/TiO₂ mole ratio of 2, and heating at 97 °C for 8 h. The transparent adherent TiO₂ film on glass substrates exhibits strong hydrophilicity after illuminating with ultraviolet light and it can be used as an efficient photocatalyst.