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Periodic Change in the Concentration of Hydrogen peroxide Formed during the Semiconductor Mediated Sonocatalytic treatment of Wastewater: Investigations on pH Effect and Other Operational Variables

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Author Affiliations

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

Res. J. Recent Sci., Volume 2, Issue (ISC-2012), Pages 136-149, February,2 (2013)

Abstract

Hydrogen peroxide, formed in situ or externally added, is an important Reactive Oxygen Species (ROS) involved in Advanced Oxidation Processes (AOP) such as sono, photo and sonophoto catalysis being investigated as environment friendly technologies for the treatment of wastewater under ambient conditions. Among the various ROS such as .OH, HO2., O2- ., H2O2, O2 etc, H2O2 is the most stable and it serves as a reservoir of other ROS. Current investigations on the ZnO and TiO2 mediated sonocatalytic degradation of phenol pollutant in water reveal that, H2O2 formed cannot be quantitatively correlated with the degradation of the pollutant. The concentration of H2O2 varies in a wavelike fashion (oscillation) with well defined crests and troughs, indicating concurrent formation and decomposition. Both processes are sensitive to the reaction conditions and depending on the externally forced or in situ situation, either of them can predominate. The degradation of H2O2 continues for some more time even after the sonication has been put off showing that the catalyst has some residual activity. This further confirms that trapped electrons and holes have unusually longer life even after the irradiation is off. Concentration of H2O2, catalyst loading, dissolved gases, concentration of the organic pollutant, pH etc influence the oscillation. The degradation of phenol is favored in the acidic range with maximum at pH 5.5. The successive maxima and the minima in the oscillation of H2O2 concentration also are higher in the acidic range. The influence of pH on various factors leading to the oscillation in the concentration of H2O2 is unequivocally established from a number of experiments, for the first time in this paper. An appropriate mechanism to explain the complex phenomenon is also proposed.

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