Decomposition of an azo dye in aqueous solution by combination of ultrasound and visible light

The degradation of Acid Orange 7 in aqueous solution has been investigated under the irradiation of ultrasound and visible light respectively and simultaneously. We have observed that the maximum removal percentage K increases from 4% to 35% when the ultrasonic frequency f and power P change from f = 20 KHz and P = 3 W to f = 1 MHz and P = 40 W. On the other hand, the K-value is ∼3% under the irradiation of visible light at 632 nm and 100 mW/mm2. Under the simultaneous irradiation of ultrasound (1 MHz, 40 W) and visible light (632 nm, 100 mW/mm2), the K-value reaches to ∼65%, indicating a synergistic effect of ultrasound and visible light irradiations. A simple model based on the band gap theory and cavitation theory is proposed to explain the synergistic phenomenon.