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Influence of Reaction Intermediates on the Oscillation in the Concentration of insitu formed Hydrogen peroxide during the Photocatalytic Degradation of Phenol Pollutant in Water on Semiconductor Oxides

Author Affiliations

  • 1 School of Environmental Studies, Cochin University of Science and Technology, Kochi 682022, INDIA

Res. J. Recent Sci., Volume 2, Issue (ISC-2012), Pages 82-89, February,2 (2013)

Abstract

Phenols are common pollutants in many petrochemical industry wastewaters. Due to the stability of the aromatic ring their destruction requires extreme conditions. Photocatalysis using semiconductor oxides as catalysts is found to be an effective Advanced Oxidation Process (AOP) for the mineralisation of phenol. The degradation proceeds through the formation of various intermediates which eventually get mineralized to yield CO2 and H2O. The intermediates identified are hydroquinone, catechol, and benzoquinone which are formed by the interaction of photogenerated OH radicals with phenol. These intermediates do not accumulate beyond a particular concentration even though the phenol degradation continues unabated. The insitu formed H2O2 concentration increases and decreases periodically in a wave like fashion indicating concurrent formation and decomposition. Externally added H2O2 enhances the degradation rate of phenol initially due to the generation of more reactive OH radicals by inhibiting the recombination of photogenerated electrons and holes as well as by its own self decomposition. Externally added catechol and hydroquinone inhibit the degradation of phenol initially. However their influence on the fate of H2O2 is not quite significant. The study also shows that the formation/decomposition of H2O2 is concentration dependent and after the initial build up, the formation or decomposition takes precedence depending on the concentration and composition of the reaction system. Possible reasons for the observed phenomenon are analysed and a mechanism is proposed.

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