The comparative study on the rapid decolorization of azo, anthraquinone and triphenylmethane dyes by zero-valent iron

The comparative study was carried out for the decolorization of three kinds of dyes: azo dye, Reactive Brilliant Red K-2G (RBR); anthraquinone dye, Reactive Brilliant Blue KN-R (RBB); and triphenylmethane dye, Malachite Green (MG) from aqueous solution by zero-valent iron (ZVI) as an effective reductant. ZVI was synthesized with a modified method of reduction in liquid phase, in which the macromolecule stabilizer polyvinylpyrrolidone was added. The effects of solution pH, ZVI dosage and initial dye concentration on the decolorization were investigated. The results showed that pH value had little effect on dye decolorization. With increasing dosage of ZVI, decolorization efficiency increased, but reduction capacity and reaction time showed descending trends. High decolorization efficiency (95.74–99.22%) was achieved within 2 min for 698.24 mg/L for RBR, 10 min for 691.69 mg/L for RBB and 30 min for 686.10 mg/L for MG at optimal pH. The first-order kinetic model was found to fit the experimental data well. The UV–vis spectra and FTIR spectra analysis indicated that chromophores of dyes were destroyed and some functional groups such as amino and aromatic ring were transformed in the decolorization process. ZVI was proved to be a universal and efficient reductant for rapid decolorization of the three dyes.

► Comparative study was carried out for decolorization of three kinds of dyes by zero-valent iron (ZVI).
► The dyes included: azo dye, anthraquinone dye and triphenylmethane dye.
► Decolorization of the three dyes by ZVI was independent of solution pH value.
► Decolorization of the three dyes by ZVI followed first-order kinetic models.
► ZVI was proved to be a universal and efficient reductant for rapid decolorization of the three dyes.