Azo dyes are potent water pollutants with high eco-toxicity and detrimental human health impacts. Indiscriminate disposal of azo dye-containing wastewater has become a severe environmental issue because of its persistence and stability to natural degradation. As conventional wastewater treatment processes fail to remove azo dyes from the environment, researchers have given keen attention and strenuous efforts to tackle this issue. This study, therefore, focused on the fabrication of a nanocomposite by integrating nano-zero valent zinc (nZVZ) and reduced graphene oxide (rGO) using a novel electrochemical method for the adsorptive degradation of azo dyes. nZVZ-rGO nanocomposite was synthesized by in-situ electrochemical reduction of Zn2+ ions on rGO using a two-electrode system. Batch experiments were performed to evaluate influential parameters such as contact time, pH, nanocomposite dosage, initial dye concentration, and dissolved inorganic anions on methyl orange dye removal. Physiochemical characterization results of the scanning electron microscopy, energy dispersive spectroscopy, transmission electron microscopy, X-ray photoelectron spectroscopy, and X-ray diffractometry confirmed the successful synthesis of nZVZ particles on rGO with an average metal-loading of 4%. The Methyl orange (MO) dye degradation performance of the nanocomposite was investigated by using UV-Visible adsorption measurements. The maximum MO dye removal efficiency (RE%) was recorded as 99.6% at 80 minutes contact time, 1 g/L adsorbent dosage, and 25 ppm initial dye concentration. The optimized pH was 6 and the dye RE% significantly decreased at extreme pH values. Moreover, the dye RE% was decreased with increasing MO concentration. A noticeable reduction in RE% resulted from the presence of anions such as Cl-, SO42-, and CO32- in the aqueous system. Furthermore, adsorption isotherm and kinetic models were developed using experimental data. The adsorptive degradation process of MO obeys the Freundlich isotherm model (R2=0.9619) suggesting a multilayer adsorption mechanism. The Pseudo-second-order model (R2=0.9999) was the applicable kinetic model. Results of the UV-Visible spectroscopy, high-performance liquid chromatography, and Fourier transform infrared spectroscopy provided promising evidence of the degradation of MO by NZVZ-rGO. In conclusion, results revealed that the nZVZ-rGO nanocomposite is capable of successfully degrading MO in aqueous solutions.

Synthesis of nano-zero valent zinc/reduced graphene oxide nanocomposite using a novel electrodeposition technique for the adsorptive degradation of toxic azo dyes: A case study on removal of methyl orange

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