The effect of ultrasound upon the oxidation of thiosulphate on stainless steel and platinum electrodes.

Ultrasound was found to increase the oxidation peak current and hence the decomposition rate of thiosulphate 50-fold compared to silent conditions. The effects of the ultrasonic frequency (20 and 38 kHz) and power upon the electrochemical oxidation of thiosulphate in aqueous KCl (1 mol dm-3) at stationary stainless steel and platinum electrodes were studied chronoamperometrically and potentiostatically (at various scan rates). No sigmoidal-shaped voltammograms were observed for the redox couple S4O6(2-)/S2O3(2-) in the presence of ultrasound. However, application of ultrasound to this redox couple provided an increase in the oxidation peak current at the frequencies employed, the magnitude of which varied with concentration, scan rate and ultrasonic power. Under sonication at 20 and 38 kHz, the oxidation peak potential shifted anodically with increasing ultrasonic power. This anodic shift in potential may be due to the formation of hydroxyl radicals, changes in electrode surface composition and complex adsorption phenomena. The large increase in oxidation peak currents and the rates of decomposition of thiosulphate, in the presence of ultrasound, are explained in terms of enhanced mass transfer at the electrode due to cavitation and acoustic streaming together with microstreaming coupled with adsorption phenomena. It is also shown that changes in macroscopic temperature throughout the experiment are insufficient to cause the observed enhanced diffusion.

[1]  J. Einhorn.  Advances in sonochemistry: Edited by T.J. Mason JAI Press, 1990 , 1991 .

[2]  Evan Cooper,et al.  Mass Transport in Sonovoltammetry with Evidence of Hydrodynamic Modulation from Ultrasound , 1998 .

[3]  B. Pollet,et al.  The effect of ultrasonic frequency and intensity upon limiting currents at rotating disc and stationary electrodes , 1996 .

[4]  D. Vacco,et al.  Factors limiting the recovery, regeneration, and reuse of photographic processing solutions , 1993 .

[5]  P. Birkin,et al.  A study of the effect of ultrasound on mass transport to a microelectrode , 1996 .

[6]  Dennis C. Johnson,et al.  The Importance of Anodic Discharge of H 2 O in Anodic Oxygen‐Transfer Reactions , 1992 .

[7]  S. Glasstone,et al.  The Hydrogen Peroxide Theory of Electrolytic Oxidation. , 1939 .

[8]  C. Bernard,et al.  Sonoelectrochemistry : effects of ultrasound on voltammetric measurements at a solid electrode , 1994 .

[9]  B. Pollet,et al.  The effect of ultrasonic frequency and intensity upon electrode kinetic parameters for the Ag(S2O3)23−/Ag redox couple , 1999 .

[10]  T. Fahidy.  Elements de genie electrochimique : F. Coeuret and A. Storck Techniques et Documentation, 285FF , 1985 .

[11]  R. Compton,et al.  VOLTAMMETRY IN THE PRESENCE OF ULTRASOUND. SONOVOLTAMMETRY AND SURFACE EFFECTS , 1994 .

[12]  Allen J. Bard,et al.  Encyclopedia of Electrochemistry of the Elements , 1978 .

[13]  Richard G. Compton,et al.  Dual activation: coupling ultrasound to electrochemistry—an overview , 1997 .

[14]  S. Glasstone,et al.  The Electrolytic Oxidation of Thiosulfate in Ethylene Glycol Solution , 1943 .

[15]  J. Weiss,et al.  The influence of the electrode surface on anodic processes , 1935 .

[16]  James L. Melville,et al.  Differential Pulse and Chronoamperometric Studies of Insonated Systems: Acoustic Streaming and Cavitational Effects , 2001 .

[17]  S. Visvanathan,et al.  Electrolytic recovery of silver from colour bleach fix solution , 1993 .

[18]  Timothy J. Mason,et al.  Quantifying sonochemistry: Casting some light on a ‘black art’ , 1992 .

[19]  A. Cooley.  Silver recovery for environmental compliance in photographic processing , 1993 .