Sono-, photo- and sonophotocatalytic decontamination of organic pollutants in water: studies on the lack of correlation between pollutant degradation and concurrently formed H2O2

摘要

The degradation of trace amounts of phenol in water is studied under sono-, photo- and sonophotocatalytic conditions using ZnO as a catalyst. Sonophotocatalytic degradation is more than the sum of the respective sono- and photocatalytic degradation under otherwise identical conditions, indicating synergistic effect. The degradation proceeds through many intermediates and ultimately the parent compound is mineralized. The concentration of concurrently formed H2O2 increases and decreases periodically resulting in an oscillatory behaviour. The oscillation is more pronounced in sonocatalysis in which the degradation of phenol and corresponding formation of H2O2 are slower. In photocatalysis and sonophotocatalysis, where the degradation is faster, the amount of H2O2 is relatively more and the oscillation becomes weaker and tends towards stabilization. However, in all cases the degradation of phenol continues unabated until the mineralization is complete. The stabilized concentration of H2O2 is much less than the expected amount based on the degradation of the organic pollutant. Probable causes for the phenomena are discussed.