Fe(lll)-enhanced sonochemical degradation of methylene blue in aqueous solution

The sonochemical degradation rate of Methylene Blue (MB) is markedly increased in the presence of Fe(Ill), a rather inexpensive reagent for the application of sonochemistry to wastewater treatment. The effect of Fe(lll) is due to a sonochemically induced Fenton reaction, where both reactants (Fe(ll) and H2O2) are sonochemically synthesized. Hydroperoxide/superoxide, generated upon sonochemical processes in aerated solution, is a key species involved in both Fe(lll) reduction to Fe(ll) and in the production of H2O2. The Fenton reaction between Fe(ll) and H2O2 then produces hydroxyl radicals, enhancing the degradation of MB. A further enhancement of the degradation of the substrate in the presence of Fe(lll) takes place upon addition of H2O2, which is likely to favor the Fenton process. Interestingly, H2O2 alone, in the absence of Fe(lll), has a very limited effect on the sonochemical degradation rate.