Photochemical oxidation of an azo dye in aqueous solutions by UV/H2O2 process

Advanced oxidation process (AOP) employing hydrogen peroxide with UV light has been found to be very effective method that is capable of transformation refractory non biodegradable and/or toxic organic compounds into harmless end products such as carbon dioxide and water. The UV/H2O2 oxidation process is characterized by generation of a very powerful oxidizing species, namely hydroxyl radicals. The aim of the present work is to study of the kinetics and mechanism of the photochemical oxidation of a synthetic dye with UV/H2O2 process. Choice of the present model based on its similarity of chemical structure with commercial importance dyes. The primary analysis was performed by recording the spectral changes of aqueous solutions of the dye under the following conditions (i) direct photolysis of the dye solution with light of wave length of 298 nm., (ii) thermal reaction between the dye and H2O2 in dark, and (iii) photolysis of the dye solution containing H2O2. The results demonstrate that, direct photolysis of the dye is not negligible but is very slow; the thermal reaction of the dye and H2O2 in dark is negligible. However the combination of both H2O2 and UV light enhanced both decolourisation and degradation processes. The effect of reaction pH, applied H2O2 dose and irradiation wavelength has been studied. The results indicate that the reaction is more efficient in alkaline medium. Also, the rate of photoreaction is inversely proportional with irradiation wavelength. Moreover the addition of potassium ferrioxalate generally enhanced the photochemical conversion. The kinetics and mechanism of investigated reaction have been postulated.