Purification and treatment of polluted water by photocatalytic reaction using TiO₂ powder have been studied widely. In this case, it is necessary to separate the TiO₂ powder from the treated water. To solve this problem, studies such as TiO₂ thin film formation on glass tubes or glass plates have been performed. However, reaction efficiencies of these kinds of reactors are not sufficient because of the small surface area per reaction volume. If TiO₂ thin photocatalytic layer can be formed on surface of transparent particles with a certain size for easy handling, it will improve the surface area per volume and the utilization efficiency of lights of the reactor. Based on the background, in the previous study, we have developed a new method of TiO₂ coating on silica particles by using alkoxide method in which TiO₂ can be coated on the surface of silica particles uniformly. In this study, two different size silica particles were used for TiO₂ coating to examine the effect of particle size on TiO₂ coating and their photocatalytic activity.

The results showed that the primary particle sizes of TiO₂ which were accumulated on the silica particles were about 4 nm in average for both sizes of the silica particles after TiO₂ coating process. After calcination, the accumulated TiO₂ particles were sintered and TiO₂ coated particles were obtained. SEM observation showed that for both particle sizes TiO₂ was coated uniformly in the same way. These results indicated that the difference of particle size had a little effect on TiO₂ coating under the experimental conditions used this time.

The photocatalytic activities of the obtained TiO₂ coated particles were evaluated by the photocatalytic decomposition of 2,4-dinitrophenol (DNP). The result showed that the photocatalytic reaction rate increased with the increase of the coated TiO₂ amount for both particle size cases. However, it seemed that there would be a certain thickness of the TiO₂ coated layer above which the photocatalytic activity does not increase further even though the amount of the coated TiO₂ increases.