Oscillation in the Concentration of H2O2 during Advanced Oxidation Processes:TiO2Mediated Sonocatalytic Degradation of Phenol

Sono, photo and sonophotocatalysis are major Advanced Oxidation Processes (AOP) under intensive investigation as potential technologies for the removal of trace pollutants from water.The techniques involve the formation and participation of Reactive Oxygen Species (ROS) like . OH, HO2 . , O2 . , H2O2 etc. Among these, H2O2 is the most stable and is also a precursor for the reactive free radicals. Current investigations on the TiO2 mediated sonocatalytic degradation of phenol pollutant in water confirm our earlier findings using ZnO catalyst that H2O2 formed insitu cannot be quantitatively correlated with the degradation of the pollutant. The concentration of H2O2 formed does notincrease corresponding to phenol degradation and reaches a plateau or varies in a wave-like fashion (oscillation) with well defined crests and troughs, indicating concurrent formation and decomposition. The number of maxima and minima or their precise occurrence at any point in time is unpredictable and inconsistent, indicating the complexity of the free radical process. The influence of various reaction parameters on the oscillation are identified and investigated in detail.