title: Influence of Microbubbles on Free Radical Generation by Ultrasound in Aqueous Solution: Dependence of Ultrasound Frequency.
abstract: The influence of microbubbles on sonochemical efficiencies has been investigated under 28, 45, and 100 kHz ultrasound irradiation. For the 28 and 100 kHz ultrasound frequencies, microbubbles suppressed the I3(-) formation from KI solution as well as the 7-hydroxycoumarin formation from coumarin solution caused by the ultrasonic irradiation. On the other hand, for the 45 kHz ultrasound frequency, microbubbles enhanced the I3(-) formation from KI solution as well as 7-hydroxycoumarin formation from coumarin solution caused by the ultrasonic irradiation. Detection of H2O2 after the irradiation of ultrasound in the presence or absence of microbubbles was also performed, and it was found that H2O2 formation was enhanced only when microbubbles were introduced under the 45 kHz ultrasonic irradiation, which was in good agreement with the results of KI oxidation dosimetry measurements and of coumarin fluorescent probe measurements. Based on these present results, plausible mechanisms that explain the dependence of the ultrasound frequency on the enhancement and suppression of free radical formation in the presence of MBs were proposed.
authors.affiliation: Department of Materials Engineering, Nagaoka National College of Technology , Nishi-Katakai, Nagaoka, 940-2188, Japan.
authors.forename: Nanae
authors.initials: N
authors.lastname: Masuda
authors.affiliation: Department of Materials Engineering, Nagaoka National College of Technology , Nishi-Katakai, Nagaoka, 940-2188, Japan.
authors.forename: Aya
authors.initials: A
authors.lastname: Maruyama
authors.affiliation: Aura-tec Co., Ltd. 1725-2 Tsubuku-honmachi, Kurume, Fukuoka 830-0047, Japan.
authors.forename: Toshihiko
authors.initials: T
authors.lastname: Eguchi
authors.affiliation: Environment Management Research Institute, AIST , Tsukuba, Ibaraki 305-8569, Japan.
authors.forename: Tsutomu
authors.initials: T
authors.lastname: Hirakawa
authors.affiliation: Department of Materials Engineering, Nagaoka National College of Technology , Nishi-Katakai, Nagaoka, 940-2188, Japan.
authors.forename: Yoshinori
authors.initials: Y
authors.lastname: Murakami