Enhanced free-radical generation by shrinking microbubbles using a copper catalyst.

Free-radicals are generated by collapsing microbubbles in aqueous solutions; however, the concentration is too low to be of practical use. In this study, copper was found to enhance the generation of hydroxyl radicals from collapsing oxygen microbubbles under acidic conditions through electron-spin-resonance spectroscopy analysis. Moreover, the degradation of polyvinyl alcohol, which is not decomposed even by ozone, was also observed during the collapse of the air microbubbles. These findings greatly increase the potential of the microbubble-collapse technique for use in the field of wastewater treatment.