Abstract
The effect of ultrasound on dye degradation and the anodic behaviour of copper was studied. Dye degradation was studied by bulk sonolysis and bulk electrolysis of aqueous solutions containing three model dyes, namely Orange I, Sandolan Yellow and Indigo Carmine. The degradation of the various dyes was monitored by measuring the absorbance decay at the wavelength of maximum absorbance Amax• Sonochemical degradation was accelerated by bubbling argon and/or increasing the ultrasonic intensity. Sonochemical degradation using an 850 kHz bath was faster than degradation using a 40 kHz bath. Orange I was found to degrade faster in acidic solutions and this was due to the increased hydrophobicity of the un-dissociated dye at low pH, i.e. the dye degraded faster when the pH was adjusted to be smaller than the pKa of the dye. Electrolytic dye degradation was achieved using potassium chloride, potassium sulphate, and potassium nitrate as electrolytes. Electrochemical degradation was fastest using potassium chloride since chlorine and hence hypochlorite (bleach) were generated during electrolysis. Ultrasound was found to degas chlorine and this resulted in slow sonoelectrochemical degradation rates. This was not the case when potassium sulphate and potassium nitrate were used as electrolyte and the sonoelectrochemical process revealed a synergistic effect of ultrasound and electrochemistry during dye degradation. This synergistic effect was a result of the improved mass transport during sonication. Platinum and copper were used as electrode material and electrolysis using copper electrodes did not result in complete decolouration of the dye, i.e. the absorbance did not decrease below the limiting value of 0.8 AU.The electrochemistry of copper was studied by the anodic polarisation of a copper electrode and the effect of ultrasound upon the voltammetry and chronoamperometry of copper was established. Anodic dissolution of copper was found to be promoted by sonication. However, sonication did not prevent passivation of the electrode in the potential region E > 0.10 V (SHE) in strongly alkaline solution. The sonovoltammogram featured an unusual anodic peak during the reverse cathodic scan. Pre-sonication was found to be a method of activating the electrode surface and increasing the number of active sites. The current-time transients (CTTs) recorded during chronoamperometry in strongly alkaline solution indicated metal dissolution, crystal growth and passivation. A model for the anodic electrocrystallization was formulated and the equation developed describing the CTTs was successfully tested on the experimental data. Using this model the kinetic parameters, i.e. rate constants, were extracted and were found to be proportional to the applied electrode potential.
| Date of Award | 2003 |
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| Original language | English |
| Awarding Institution |
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| Supervisor | Phil Lorimer (Supervisor), D Walton (Supervisor) & Timothy Mason (Supervisor) |