Sonophotolytic degradation of dimethyl phthalate without catalyst: Analysis of the synergistic effect and modeling

The merits of the combined process of high-frequency ultrasound (US) and catalyst-free ultraviolet irradiation (UV) have been evaluated in this study by investigating the sonophotolytic degradation of dimethyl phthalate (DMP). A 400 kHz ultrasonic system and a photolytic system at 253.7 nm were employed individually, sequentially and simultaneously to examine the details of the processes. High UV intensities and low pH conditions enhanced the sonophotolytic degradation of DMP and a clear synergy was evident from the combination of the US and UV irradiation with a synergetic index of 2.6. The role of ultrasonically generated hydrogen peroxide was examined qualitatively and quantitatively, and its generation and photo-decomposition were found to be the principal reason for the process synergy. A novel inverted S-curve model was developed and found to successfully describe the process of sonophotolysis and DMP degradation. [Display omitted] ► Merits of the combined process of US/catalyst-free UV have been evaluated. ► A synergy effect was evident from the combination process with a synergetic index of 2.6. ► The photo-decomposition of H2O2 was the dominant reason for synergy effect. ► An inverted S-curve model was developed successfully in describing the combined process.