Sensitivity of free radicals production in acoustically driven bubble to the ultrasonic frequency and nature of dissolved gases
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Date
2014
Journal Title
Journal ISSN
Volume Title
Publisher
Elsevier
Abstract
Central events of ultrasonic action are the bubbles of cavitation that can be considered as powered
microreactors within which high-energy chemistry occurs. This work presents the results of a comprehensive
numerical assessment of frequency and saturating gases effects on single bubble sonochemistry.
Computer simulations of chemical reactions occurring inside a bubble oscillating in liquid water
irradiated by an ultrasonic wave have been performed for a wide range of ultrasonic frequencies
(213–1100 kHz) under different saturating gases (O2, air, N2 and H2). For O2 and H2 bubbles, reactions
mechanism consisting in 25 reversible chemical reactions were proposed for studying the internal
bubble-chemistry whereas 73 reversible reactions were taken into account for air and N2 bubbles. The
numerical simulations have indicated that radicals such as OH, H , HO2
and O are created in the bubble
during the strong collapse. In all cases, hydroxyl radical ( OH) is the main oxidant created in the bubble.
The production rate of the oxidants decreases as the driving ultrasonic frequency increases. The
production rate of OH radical followed the order O2 > air > N2 > H2 and the order becomes more remarkable
at higher ultrasonic frequencies. The effect of ultrasonic frequency on single bubble sonochemistry
was attributed to its significant impact on the cavitation process whereas the effects of gases were
attributed to the nature of the chemistry produced in the bubble at the strong collapse. It was concluded
that, in addition to the gas solubility, the nature of the internal bubble chemistry is another parameter of
a paramount importance that controls the overall sonochemical activity in aqueous solutions.
Description
Keywords
Single-bubble sonochemistry, Computer simulations, Ultrasonic frequency, Saturating gas, OH radical