Production of O Radicals from Cavitation Bubbles under Ultrasound

In the present review, the production of O radicals (oxygen atoms) in acoustic cavitation is focused. According to numerical simulations of chemical reactions inside a bubble using an ODE model which has been validated through studies of single-bubble sonochemistry, not only OH radicals but also appreciable amounts of O radicals are generated inside a heated bubble at the violent collapse by thermal dissociation of water vapor and oxygen molecules. The main oxidant created inside an air bubble is O radicals when the bubble temperature is above about 6500 K for a gaseous bubble. However, the concentration and lifetime of O radicals in the liquid water around the cavitation bubbles are unknown at present. Whether O radicals play some role in sonochemical reactions in the liquid phase, which are usually thought to be dominated by OH radicals and H2O2, should be studied in the future.

Automated summary

This review focuses on the production of O radicals (oxygen atoms) in acoustic cavitation. Numerical simulations revealed that significant amounts of O radicals are generated inside a heated bubble during the violent collapse through thermal dissociation of water vapor and oxygen molecules. However, the concentration and lifetime of O radicals in the surrounding liquid water are currently unknown. Future studies should investigate the potential role of O radicals in sonochemical reactions in the liquid phase, which are traditionally believed to be dominated by OH radicals and H2O2.