Synergistic effects of high-frequency ultrasound on photocatalytic degradation of aldehydes and their intermediates using TiO2 suspension in water

The degradation of model substances, benzaldehyde (C6H5CHO) and formaldehyde (HCHO), were investigated under various conditions, namely, ultrasound (US) irradiation, TiO2 photocatalysis with UV irradiation (UV/TiO2), and the combination of sonophotocatalysis and UV irradiation (US/UV/TiO2), in order to clarify the synergistic effects between US and UV/TiO2. US and UV/TiO2 primarily contribute to the degradation of highly hydrophobic and hydrophilic substances, respectively. However, the degradation rate was found to depend on the chemical properties and concentration of not only the substances initially present, but also their decomposition intermediates. Here, the essential information for accurately evaluating the synergistic effects on reaction rate under US/UV/TiO2 conditions is reported, with a focus on the behavior of decomposition intermediates.