Synthesis of nano zero valent zinc-reduced graphene oxide nanocomposite using a novel electrochemical technique for the adsorptive degradation of methyl orange

Abstract

Indiscriminate disposal of effluent contaminated with persistent azo dyes has become a significant environmental issue. Since the conventional wastewater treatment processes are ineffective in removing azo dyes completely, many studies are currently being focused on finding effective methods to degrade azo dyes. We herein report a novel in-situ synthesis of a nanocomposite with nano-zero valent zinc (nZVZ) and reduced graphene oxide (rGO) that can effectively remove methyl orange, an azo dye, from an aqueous solution via adsorptive degradation. nZVZ-rGO nanocomposite was synthesized by electrochemical reduction of Zn2+ ions on rGO. The presence of nZVZ particles on rGO with an average metal-loading of 4% was confirmed by SEM-EDS, TEM, XPS and XRD results. Batch experiments showed that a maximum removal efficiency of 99.6% of methyl orange can be achieved with 25mgL-1 initial dye concentration and by optimizing the pH, nanocomposite dosage and contact time. However, a noticeable reduction in removal efficiency was observed in the presence of anions such as Cl-, SO42- and CO32-. The degradation of methyl orange was monitored using UV-Visible spectroscopy, HPLC and FTIR spectroscopy. The peaks corresponding to -N=N- group, –C-N bond and –SO3Na group have completely disappeared in the product spectrum of FTIR analysis, indicating the degradation of methyl orange. The adsorptive degradation process of methyl orange obeys the Sips model (R2=0.9820) indicating a complex heterogenous adsorption mechanism while the kinetic model was shown to be pseudo-second-order model (R2=0.9999).