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Pub2877.pdf

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Ultrasonics Sonochemistry 10 (2003) 203–208

Electrochemical, luminescent and photographic characterisation of cavitation

Peter R. Birkin a,*, John F. Power a, Mamdouh E. Abdelsalam a, Timothy G. Leighton b a Department of Chemistry, University of Southampton, Highfield, Southampton SO17 1BJ, UK

b ISVR, University of Southampton, Highfield, Southampton SO17 1BJ, UK Received 13 July 2002; accepted 6 December 2002

Abstract

The characterisation of a small sonochemical reactor has been performed using electrochemical, luminescent and photographic techniques. The electrochemical experiments have employed a novel flow system to determine the formation of sonochemical products (in this case hydrogen peroxide) in semi-real time with high sensitivity. The rate of production of hydrogen peroxide is reported as a function of driving pressure amplitude. The degradation of an organic molecule, specifically the organic dye amaranth, within the sonochemical cell is also reported.

www.elsevier.com/locate/ultsonch

Ó 2003 Elsevier Science B.V. All rights reserved.

Keywords: Hydrogen peroxide; Flow cell; Organic destruction; Frequency

1. Introduction

The generation of cavitation through the application of power ultrasound is an appealing way of accelerating or driving a range of physical and chemical processes [1]. The acceleration and possible alteration of mechanistic pathways are strongly associated with the unusual con- ditions produced as the result of oscillating or collapsing cavitation bubbles [2]. However because of the complex nature of this particular environment, it is often difficult to determine the extent and the actual effect of cavitation on the phenomena in question. Clearly if cavitation is to be fully exploited and developed as a useful industrial and academic technique, the understanding of the com- plex and interacting processes that occur within this unusual environment is paramount. It is with this aim in mind that the study presented here was performed.

In the study of sonochemical reactions, many diffe- rent approaches and experimental set ups have been reported. The range of different ultrasonic frequencies employed best demonstrates this variation in approach to investigating the effects of cavitation on chemical

* Corresponding author. Fax: +44-23-80-593781. E-mail address: prb2@soton.ac.uk (P.R. Birkin).

processes [3–9]. Frequency ranges from >1 MHz to 20 kHz can be found as well as differing experimental arrangements such as Ôultrasonic hornÕ or Ôultrasonic reactorÕ approaches. However, in many cases the char- acterisation and consideration of the spatial and tem- poral nature of the sound field that operates within these environments is lacking. This is unfortunate as without this consideration accurate explanations of the experi- mental findings are difficult to achieve. It is suggested here that an understanding of the acoustics of the sono- chemical reactor is paramount to the appropriate ex- planation of experimental results.

In the study reported here an electrochemical ap- proach to the detection of a sonochemical product (in this case hydrogen peroxide) has been employed within a small cylindrical sonochemical reactor. The electro- chemical detection of hydrogen peroxide is routinely performed in the assaying of enzymatic reactions and the investigation of the mechanism of oxygen electro- reduction [10,11]. However, in order to combine electrochemical detection of hydrogen peroxide with the sonochemical system, the technique must satisfy a number of criteria. First, the electrochemical technique must be sensitive enough to detect the low levels of hydrogen peroxide expected. As an example Sato et al. have reported hydrogen peroxide production rates of

1350-4177/03/$ - see front matter Ó 2003 Elsevier Science B.V. All rights reserved. doi:10.1016/S1350-4177(02)00155-4

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