抄録
Recently, it has been reported that photocatalytic reaction drived using ultrasonic (US) irradiation
even under dark condition, and this reaction has been known as sonocatalytic reaction. However, its reaction
mechanism has not become clear in detail. In this study, we evaluated the removal ratio of organic compounds
in water phase based on sonocatalytic activity with 50 kHz US irradiation under dark condition. In order to
clarify the influences of TiO2 crystal structure, physical properties of target compounds, and H2O2 addition on
the removal ratio, three crystal types of TiO2 and two different aldehydes, such as benzaldehyde (C6H5CHO)
and formaldehyde (HCHO), were used for the degradation experiments. In case of TiO2 (P25) suspension with
US irradiation under dark condition (US/P25), removal ratios of both aldehydes increased 10 % approximately.
On the other hand, the effects of crystal structure and particle size of TiO2 were evaluated by comparing US/P25
with US/ST21 and US/ST21 with US/ST01, respectively. When smaller size TiO2 particles including rutile type
structure (P25) were used, the removal ratio of C6H5CHO improved slightly whereas the removal ratio of HCHO
did not change in contrast. It was estimated that sonocatalytic reaction can be occurred in hydrophobic field
near the cavitation bubble. Furthermore, it has been reported that OH radicals formation was influenced by
H2O2 addition, and depended on TiO2 structure. Therefore, we also investigated the effect of H2O2 addition on
removal ratio by US/P25 and US/ST21. As a result, by H2O2 addition, removal ratio of HCHO was enhanced
by US/P25 and reduced by US/ST21. However, removal ratio of C6H5CHO was reduced by both US/P25 and
US/ST21. The different behavior in H2O2 addition means that TiO2 characteristics contribute to sonocatalyst
reaction.
