Green fabrication of reduced graphene oxide decorated with Ag nanoparticles (rGO/Ag NPs) nanocomposite: A reusable catalyst for the degradation of environmental pollutants in aqueous medium

In this current work, a bio-inspired green approach has been followed to synthesize Ag nanoparticles (NPs), which were immobilized over reduced graphene oxide (rGO) as a suitable support. In the stepwise preparation of the bionanocomposite (rGO/Ag NPs) by using Menthapulegium flower extract, initially graphene oxide (GO) was reduced to rGO followed by in situ reduction of Ag+ ions to Ag NPs. In these reductions, different biomolecules such as, polyphenols, flavonoids, alkaloids, terpenoids and mild acids were employed as the natural reductant. The oxygenated functions in the aforementioned biomolecules, efficiently, assisted the capping and stabilizing the AgNPs. The as-synthesized nanocomposite was fully characterized using different techniques such as, UV-Vis spectroscopy, scanning electron microscopy (SEM), energy-dispersive X-ray spectroscopy (EDX), wavelength dispersive X-ray spectroscopy (WDX) elemental mapping, transmission electron microscopy (TEM), X-ray diffraction (XRD) and inductively coupled plasma (ICP). Diameter of the biosynthesized Ag NPs were found to be in the range of 20-25 nm. The constituent elements were found to be homogeneously dispersed as found from elemental mapping study. This novel prepared nano-composite showed excellent water dispersibility due to the hydrophilicity of biomolecules attached to them, which is essential criterion in heterogeneous catalysis. This composite was used as an effective catalyst in the reductive degradation of water contaminated by organic dyes such as methyl Orange (MO) and rhodamin B (RhB) using NaBH4 as reductive agent at room temperature. The progress of reduction was monitored by UV-Vis spectroscopy. Both the reactions followed pseudo-unimolecular kinetics and the corresponding rate constants were found being 0.098 s(-1) and 0.096 s(-1) respectively. The material was significantly robust as justified by the leaching as well as hot-filtration tests and its reusability for several times without any appreciable loss in its activity. (C) 2020 Published by Elsevier B.V.