ABSTRACT
The application of ultrasound (US) irradiation for the degradation of organic pollutants in water has been broadly described in literature in the past. The thermal decomposition of pollutants by direct pyrolysis and/or oxidation by means of the reactive radicals coming from water and oxygen dissociation in the presence of US irradiation have been proposed in literature as the main degradation mechanisms. Consequently, hydrophobic pollutants with high vapor pressure are decomposed mainly by pyrolytic degradation, whereas hydrophilic pollutants with low vapor pressure are decomposed by hydroxyl radical oxidation. However, the rate of pollutant degradation of ultrasonic irradiation is rather low to be applied in practice, especially for highly hydrophilic compounds. Hence, one strategy to enhance the degradation ef›ciency of organic pollutants in water is to combine US irradiation with the presence of a solid catalyst. The presence of solid particles provides additional nuclei for the cavitation phenomena, increasing the number of cavitation events that result in the enhancement of the degradation performance activity. Likewise, in a biphasic solid-liquid medium, irradiated by power US, the solid particle size is reduced leading to an increase of surface area with the subsequent increase rate of phase mixing and mass transfer. Nevertheless, a high amount of solids might lead to the scattering of the sound waves with the decrease in the transferred energy to the reaction medium.
