Chemical Effects of Ultrasound on Aqueous Solutions. Formation of Hydroxyl Radicals and Hydrogen Atoms

Article abstract of DOI:10.1021/j100231a020

Direct evidence for the formation of <*>OH and <*>H in the cavitation bubbles produced by ultrasound in argon-saturated aqueous solutions is presented.The methods of spin trapping with 5,5-dimethyl-1-pyrroline 1-oxide(DMPO), 4-<<(1,1-dimethylethyl)imino>methyl>-1-methylpyridinium N-oxide (PYBN), and 2-methyl-N-(4-pyridinylmethylene)-2-propanamine N,N'-dioxide (POBN) combined with ESR were used for the detection of <*>OH and <*>H.With either DMPO or PYBN, the OH and H spin adducts were obtained, and with POBN, the H adduct was observed.These results were confirmed by sonolysis of D2O solutions containing the same spin traps.By studying the competition reactions for <*>OH and <*>H between the spin traps, DMPO and POBN, and <*>OH and <*>H scavengers , we obtained further verification for the formation of <*>OH and <*>H.Sonolysis of aqueous solutions containing DMPO POBN in the presence of air suppressed formation of H adducts but not that of OH-DMPO.The unusually large effects of acetone and MNP on the spin adduct yields could be explained either by the scavenging of radicals in the gas phase of the cavitation bubbles or by preventing the collapse of the gas bubbles during cavitation and thus reducing radical formation.From the results of the present work, it was inferred that <*>OH and <*>H are formed in the cavitation bubbles.