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. Th e observation of similar degradation rates for aniline in each system sugge sts that the sonication process was not affected by the presence of Fe-0. T he observed rate enhancements for the degradation of nitrobenzene can be at tributed primarily to the continuous cleaning and chemical activation of th e Fe-0 surfaces by acoustic cavitation and to accelerated mass transport ra tes of reactants, intermediates, and products between the solution phase an d the Fe-0 surface. The relative concentrations of nitrosobenzene and anili ne, the principal reaction intermediates generated by Fe-0 reduction, are a ltered substantially in the presence of ultrasound.