Photocatalysis of a transparent titanate aqueous sol prepared from titanium tetraisopropoxide and tetramethylammonium hydroxide

Photocatalysis of a transparent titanate aqueous sol, which was prepared by mixing titanium isopropoxide and tetramethylammonium hydroxide or triethylamine, followed by diluting with water, was examined via the photo-fading of rhodamine B. An irradiation of UV light to the sol containing rhodamine B caused the colour fading by the photocatalytic reactions of the titanate colloids in the sol. The combination of the UV-irradiation with the bubbling of N2 gas accelerated the fading, whereas that with the bubbling of O2 led to the decrease in the fading rate, indicating that the fading was caused by the photocatalytic reduction with the titanate colloid, which competed with the photocatalytic reduction of the dissolved oxygen in the sol. On the other hand, the aqueous suspension of a TiO2 fine powder also exhibited a similar photo-fading of rhodamine B. However, the combination of the photoirradiation with the O2 bubbling increased the fading rate, whereas that with the N2 bubbling decreased the fading rate, indicating that the colour fading was caused by the photocatalytic oxidation of rhodamine B with the TiO2 powder. Consequently, it was found that the photocatalytic reaction mechanism of the titanate sol is different from that of the TiO2 powder. The cyclic voltammogram of the titanate sols showed that the reduction of rhodamine B adsorbed onto the titanate colloid occurred at a more positive potential than that of rhodamine B itself.