Kinetics and mechanism of the enhanced reductive degradation of nitrobenzene by elemental iron in the presence of ultrasound

Sonolysis, reduction by elemental iron (Fe-0), and a combination of the two processes were used to facilitate the degradation of nitrobenzene (NB) and aniline (AN) in water. The rates of reduction of nitrobenzene by Fe-0 are enhanced in the presence of ultrasound. The first-order rate constant, k(US),for nitrobenzene degradation by ultrasound is 1.8 x 10(-3) min(-1), while in the presence of Fe-0, the rate was found to be substantially faster. The observation of similar degradation rates for aniline in each system suggests that the sonication process was not affected by the presence of Fe-0. The observed rate enhancements for the degradation of nitrobenzene can be attributed primarily to the continuous cleaning and chemical activation of the Fe-0 surfaces by acoustic cavitation and to accelerated mass transport rates of reactants, intermediates, and products between the solution phase and the Fe-0 surface. The relative concentrations of nitrosobenzene and aniline, the principal reaction intermediates generated by Fe-0 reduction, are altered substantially in the presence of ultrasound.