Effect of ultrasound on the kinetics of reduction of hexacyanoferrate(III) by thiosulfate ions mediated by ruthenium dioxide hydrate

Abstract

Ultrasound promotes the reduction of hexacyanoferrate(III) by thiosulfate ions mediated by RuO 2· xH 2O under diffusion-controlled conditions. There is a strong correlation between the measured first-order rate constant and the absorbance of the dispersion, which, in turn, is closely related to the specific surface area of the catalyst. The enhancement in rate with ultrasonic irradiation appears to be largely associated with the dispersive action of the ultrasound on the aggregated particles of RuO 2· xH 2O. The rate of reaction increases with increasing %duty cycle and ultrasonic intensity. The measured overall activation energies for the reaction with and without ultrasound, i.e. 18±1 and 20 ± 1 kJ mol −1, respectively, are very similar to those expected for a diffusion-controlled reaction. The homogeneous reaction is not promoted by ultrasound.