Kinetic analysis of free radical scavenging in sonochemistry

As an advanced oxidation process, high-power ultrasound produces free radicals in aqueous solution through acoustic cavitation. Whereas radical production inside the cavitation bubble is well understood, radical scavenging outside the bubble is still unexplored quantitatively. In this study, we modeled the behavior of radicals in the scavenging process by solving the diffusion-advection-reaction equations. Using terephthalate as the scavenger, the principal reaction pathways of hydroxyl radicals are identified and the scavenging efficiency is quantified. The analysis shows that among the various reactions competing for hydroxyl radicals, the scavenging by terephthalate is in disadvantage for the small mass diffusivity. It limits the replenishment of scavengers to the reaction zone and compromises radical trapping efficiency. A parametric study puts the maximum radical trapping efficiency below 30%. Our study elucidates the key factor limiting the utilization of ultrasound-induced radicals and paves the way for future efforts to maximize the sonochemical effects.