Green synthesis of nanoscale zero-valent iron using a grape seed extract as a stabilizing agent and the application for quick decolorization of azo and anthraquinone dyes

Grape seed-coated nanoscale zero-valent iron (GS-NZVI) was synthesized using grape seed extract as the stabilizing agent, and it was used to degrade Reactive Brilliant Red K-2G (RBR, azo dye) and Reactive Brilliant Blue KN-R (RBB anthraquinone dye). The GS-NZVI was characterized by scanning electron microscopy (SEM), X-ray energy-dispersive spectrometry (EDS), transmission electron microscopy (TEM), dynamic light scattering (DLS), X-ray diffraction (XRD), Brunauer-Emmett-Teller isotherm (BET) and Fourier transform infrared spectroscopy (FTIR). The grape seed extract played the role of a stabilizing agent to protect GS-NZVI from agglomeration and oxidation. Based on the decolorization efficiency and cost saving, the optimal grape seed extract concentration for GS-NZVI synthesis was 0.2 wt%. The effects of dye solution pH, GS-NZVI dosage and initial dye concentration on dye decolorization were investigated. The solution pH had little effect on dye decolorization. According to decolorization efficiency, reduction capacity and reaction time, the optimal GS-NZVI dosage was 2.0 g L-1. The decolorization efficiency (96.08-98.22%) was achieved within 7 min with an initial RBR concentration ranging from 500 to 2000 mg L-1; and decolorization efficiency of 97.45-99.08% was achieved within 17.5 min with an initial RBB concentration ranging from 250 to 1000 mg L-1. The kinetic analysis demonstrated that the first-order kinetic model was more suitable to describe the decolorization processes of RBR and RBB dyes. The UV-vis spectra showed that the chromophores of the dyes and some functional groups were destroyed by GS-NZVI. GS-NZVI has good application prospects because of its low-cost, eco-friendly synthesis and significantly high decolorization efficiency.