Degradation of azo dye direct sky blue 5B by sonication combined with zero-valent iron

The degradation of azo dye direct sky blue 5B by sonication combined with zero-valent iron (US-Fe-0)was investigated and an evident synergistic effect was observed. The synergetic effect is mainly due to the increase of (OH)-O-center dot radical concentration from Fenton's reaction. The (OH)-O-center dot radical concentrations in sole sonication and US-Fe-0 process were detected by using terephthalic acid as a fluorescent probe and found that (OH)-O-center dot radicals were generated continuously during sonication and the production of (OH)-O-center dot radicals in US-Fe-0 process was much higher than that in sole sonication. The degradation of direct sky blue 5B followed a pseudo-first-order kinetics and the degradation rate constants were found to be 0.0206 and 0.169 min(-1) with sole sonication and US-Fe-0 process respectively. It was also found that the degradation ratio of direct sky blue 5B increased with the increase of zero-valent iron dosage and decrease of pH value of the dye aqueous solution. The degradation mechanism of direct sky blue 5B with US-Fe-0 process was discussed by the changes of UV-Vis spectrogram of the dye during degradation. The dramatic changes of UV spectra showed a disappearance of both azo and aromatic groups during the degradation. (C) 2011 Elsevier B.V. All rights reserved.