Development of dispersed-type sonophotocatalytic process using piezoelectric effect caused by ultrasonic resonance

Recently, degradation of persistent organic pollutants (POPs) with low biodegradability in the environment and in industrial and municipal wastewaters has gained importance. In this study, a dispersed-type sonophotocatalysis (SP) process, which is a combination of sonolysis and photocatalysis with dispersed light sources, has been proposed for the effective and energy-efficient degradation of POPs. In this method, the piezoelectric effect caused by ultrasonic resonance in a piezoelectric element is used for producing luminescence in a LED. A luminescent device composed of eight UV-LEDs and a piezoelectric element was designed for dispersion of UV light in water; this device was confirmed to show luminescence under ultrasonic irradiation. Sonophotocatalytic degradation experiments were carried out using several such devices, and the results were compared with those obtained in sonolysis, photocatalysis, and fixed-type SP. The comparison showed that the degradation rate constants in fixed-type and dispersed-type SP were larger than the sum of the rate constants obtained for sonolysis and photocatalysis; further, the synergetic effect caused by the combination of sonolysis and photocatalysis was 7.5% and 18% in fixed-type and dispersed-type SP, respectively.