Res. Chem. Intermed.
, Vol. 30, No. 7-8, pp. 685–701 (2004)
Also available online - www.vsppub.com
, JOE Z. SOSTARIC
and PETER RIESZ
Radiation Biology Branch, National Cancer Institute, NIH, Bethesda, MD 20892-1002, USA
Department of Food Science, The Volcani Center, Agricultural Organization,
P. O. B. 6 Bet Dagan 50250, Israel
Received 25 February 2004; accepted 25 April 2004
Abstract—Sonochemistry and photochemistry are initiated by high-energy transient species, which
may be prone to mutual interaction. Electronic excitation of solutes by energy transfer from high
energy species generated in collapsing bubbles is already supported by experimental evidence. The
rates of photochemical reactions can be affected by ultrasound-induced mixing of liquids caused by
microstreaming near pulsating cavitation bubbles and shockwaves due to bubble collapse. This may
not only improve light absorption but also modify the pathway of reaction by increasing the contact
between reagents. Finally, one may speculate about a potentially new chemistry of photoexcited
solutes under the extreme conditions inside cavitation microreactors. This work reviews research on
the excitation of solutes by sonoluminescence, the combined effects of ultrasound and light on liquid
systems and the effect of ultrasound on photocatalytic reactions.
Keywords: Sonoluminescence; solute excitation; photochemistry.
Ultrasound is a mechanical wave of frequencies from approximately 20 kHz to
1 GHz. It propagates through liquids with a velocity of about 1000–1600 m/s and
wavelength range from micrometers to centimeters; consequently the acoustic ﬁeld
cannot couple directly with the molecular energy levels. However, its interaction
with bulk liquid is accompanied by the unique phenomenon of cavitation which
leads to an enormous concentration and conversion of the diffuse sound energy.
Historically, cavitation has been classiﬁed into two types, non-inertial and inertial.
Non-inertial cavitation bubbles oscillate about an equilibrium radius and often
persist for many acoustic cycles. As a result of these oscillations, streaming of
surrounding liquid occurs, mixing the medium. Inertial cavitation bubbles grow to
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