(A) study on the effect of hydrothermal treatment on the photocatalytic properties of titania synthesized by sol-gel method

Abstract

The effect of hydrothermal treatment on the photocatalytic properties of titania and silica embedded titania synthesized by sol-gel process was investigated. The characterization of the prepared catalyst was carried out with XRD, TEM, SEM, FT-IR, $N_2$ Adsorption and ESR study. The photocatalytic activity of titania catalysts was investigated for the degradation of 4-chlorophenol whose concentration was measured by HPLC with UV detector. The transition from anatase phase to rutile phase was suppressed by hydrothermal treatment. When silica was embedded in titania, there was a significant decrease in the density of surface hydroxyl group, whose distributions, however, were not affected by hydrothermal treatment. It was observed that hydrothermal treatment seemed to induce the formation of paramagnetic species such as $Ti^{3+},ㆍO_2^-$ on titania surface. Hydrothermally treated sol-gel titania showed a better photo-catalytic activity for the degradation of 4-chlorophenol than the sol-gel titania without hydrothermal treatment. It was also confirmed that the incorporation of silica into titania increased the photocatalytic activity. Even if the anatase phase was believed to have a better photocatalytic activity, the rutile phase formed by calcining the hydrothermally treated sol-gel titania at a higher temperature showed no less photocatalytic activity than the anatase phase formed at a lower temperature. The enhancement of anatase phase and the formation of the active paramagnetic species by hydrothermal treatment were responsible for the greatly enhanced photocatalytic activity.