Citrus macroptera Peel Extract Mediated Facile Synthesis of Reduced Graphene Oxide and Its Application for Adsorption of Methylene Blue

Graphene and its derivatives have become one of the hottest research topics in the field of carbon nanomaterials. Reduced graphene oxide (rGO) is the reduced form of graphene oxide (GO) having separated a few layers with a trace number of functionalities. Sustainable synthesis of reduced graphene oxide (rGO) is in significant demand due to its extraordinary properties and potential applications in various fields. In this study, a green and facile strategy is reported for the synthesis of reduced graphene oxide (rGO) by the reduction of graphene oxide (GO) using Citrus macroptera peel extract as the green reducing agent. To optimize the synthetic conditions, the authors carried out the reactions by changing different reaction parameters, namely, time, temperature, pH, and concentration of plant extract. After that, the optimum condition was employed to prepare the most efficient material for further study. The synthesized material was characterized by UV-Vis spectrophotometry, FT-IR spectroscopy, X-ray Diffraction (XRD), Scanning Electron Microscopy (SEM), Energy Dispersive X-ray (EDX) analysis, and Thermogravimetric (TG) analysis. The effective elimination of oxygen-containing functionalities in GO was confirmed by the UV-Vis, FT-IR, and XRD analysis. The restoration of the C=C group and the reduction of several oxygen-containing groups confirmed the successful formation of rGO by the successful reduction of GO. The SEM confirmed the successful formation of exfoliated and separated few layers of rGO nano-sheets. Methylene Blue (MB) was taken as a model dye to carry out the adsorption efficacy of the obtained rGO. The dye removal activity and adsorption efficiency were monitored by UV-Vis spectroscopy. To study the kinetics of the adsorption of MB on rGO, four models, namely pseudo-first-order, pseudo-second-order, Boyd, and intra-particle diffusion (IPD) were employed and found as obtained data is best fitted with the pseudo-second-order kinetic model and for isotherm study, three distinct models were employed, namely, Langmuir, Freundlich and Temkin isotherm model and found that the Langmuir model is best fitted with a high adsorption capacity of 112.31 mg/g. This result indicates the homogeneous surface of rGO for mono-layered adsorption. In addition, kinetics and thermodynamic analyses demonstrated that the adsorption of MB onto rGO can be treated as a chemisorption mechanism which can be described by the enhanced surface area of obtained rGO, H-bonding, electrostatic, and π − π interactions as all these things are correlated with the adsorptive removal of Methylene Blue (MB) dye. It is expected that the green approach could be a suitable alternative to a chemical method and synthesized rGO could be a promising material to treat industrial wastewater via a profitable approach. This green approach having great potential provides a new prospect for the large-scale production of rGO in an eco-friendly and cost-effective manner.

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