Sono-Catalysis - Hielscher Ultrasonics0 pages

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Sonocatalysis – The effects of sound generated waves on catalytic chemistry
Power Ultrasound
During the sonication of liquids, the accoustic wavelength range between approx. 110 and
0.15 mm for frequencies of 18kHz and 10Mhz. This is significantly higher than those of
molecular dimensions, resulting in that there is between the molecules and the accoustic
field no direct coupling of chemical species. The effects of sonication are mostly generated
by the ultrasonic cavitation in liquids (picture 1). Therefore, for the ultrasound catalysis at
least one reagent in a liquid phase is necessary. Cavitation erosion on particle surfaces
generates unpassivated, highly reactive surfaces. Short periods of high temperatures and
pressures contribute to a molecular decomposition and increase the reactivity of many
chemical substances. Ultrasonic irradiation can also be used to prepare the catalysts, e.g. to
produce aggregates of fine-size particles.

Picture 1: Ultrasonically generated cavitation on the sonotrode of a 1500watts ultrasonic processor
(blue illuminated for better visibility)

The application of power ultrasound is a well-known tool to create extremely fine emulsions
and dispersions. In chemistry such extremely fine-size emulsions and dispersions are used to
enhance chemical reactions. This means that the interfacial contact area between two or
more immiscible liquids or between liquid and solid becomes dramatically enlarged and
provides thereby a better, more complete and/or faster course of the reaction. Other useful
effects, which can be achieved by ultrasonication, are the break-up of bondages and the
creation of free radicals.