Mechanistic approach to intensification of sonochemical degradation of phenol

This paper addresses the matter of intensification of the sonochemical degradation of phenol from mechanistic point of view by coupling the experimental results to a mathematical model that takes into account essential physics and chemistry of cavitation bubbles. We assess the relative influence of extent of radical production by the cavitation bubbles and radical scavenging (or conservation) on the overall degradation of phenol. We have used a molecular species (oxygen) and an ionic species (Fe2+ ions) for scavenging of radicals produced by cavitation bubbles. Four different gases, viz. argon, oxygen, nitrogen and air have been used to provide cavitation nuclei in the bulk medium. It is revealed that sonochemical degradation of phenol is governed by the extent of radical scavenging, both inside and outside the bubble. Phenomenon of radical scavenging influences the probability of interaction between the phenol molecules and radicals. The extent of degradation in the presence of Fe2+ ions has been much higher. This result has been attributed to higher reactivity and uniform concentration of the Fe2+ ions in the medium, as a result of which they can effectively scavenge the radicals generated by cavitation bubbles.