Facile preparation of stable aqueous titania sols for fabrication of highly active TiO2 photocatalyst films

Abstract

Highly stable aqueous titania sols were prepared via a facile process using titanium tetraisopropoxide in the co-existence of acetylacetone and acetic acid. Their co-existence efficiently suppressed the hydrolysis and condensation reaction of titanium tetraisopropoxide even in water, retaining the diameter of titania colloidal particles lower than 10 nm (average diameter d = ca. 4 nm). The titania sols possessed significantly high stability for more than 1 year and could be easily coated on various substrates such as quartz glass via a simple spin-coating method, forming highly homogeneous and transparent films. The calcinations of the coated films in the air at 600 °C produced densely packed anatase TiO₂ particles; the diameter was retained below 50 nm even after the calcinations at 900 °C without phase transition to rutile, maintaining the fairly good transparency of the films. On the other hand, the TiO₂ particles prepared on a quartz substrate from other precursors, such as titanium–peroxo-citrate complexes, were found to transform from anatase into the rutile phase at above 700 °C with a significant increase in the particle size up to ca. 200 nm. The TiO₂ films prepared from the present aqueous titania sols exhibited higher activity for photo-induced surface superhydrophilicity under UV light irradiation than those prepared from other precursors.