Decolorization kinetics and mechanisms of commercial dyes by H2O2/iron powder system

The oxidation kinetics and mechanisms of Reactive Red 120, Direct Blue 160, and Acid Blue 40 by H2O2/iron powder system were investigated in a well-mixed batch reactor. Optimal pH ranged from 2.0 to 3.0 depending upon the dye molecular structure and the iron dissolution rate. The optimal ratio of H2O2 to iron metal was 0.001 M to 1.0 g/L. The initial oxidation rates were obtained according to pseudo-first-order kinetics. Dye molecular structure is an important factor that influences decolorization kinetics. The results suggest that the structure chromophore including Azo bonds are the primary target oxidized by H2O2/Fe powder system. The less substituted anthraquinone ring in Acid Blue 40 is more readily to be destroyed than the Azo dyes. Dimerization may take place at high concentration of Acid Blue 40, which decreases the decolorization efficiency. In addition, the color change during decolorization processes may also result from the dye complexes with the iron species. As a result, H2O2/iron powder system is better than the Fenton s reagent system, e.g., H2O2Fe2+, due to the continuous dissolution of iron powder and the dye adsorption on the iron powder, despite the fact that Fentonʹs reaction was the major process contributing to decolorization.