Green synthesis of high surface area of reduced graphene oxide via Aloe vera extract: characterization, DFT mechanistic insights, and enhanced Rhodamine B adsorption using Chitosan@EDTA@rGO composite

Abstract

Graphene oxide (GO) was synthesized from recycled graphite via the Hummers' method and reduced using a green approach involving Aloe vera extract. Response Surface Methodology (RSM) was employed to optimize the reduction temperature, extract volume, and time, targeting the maximization of the Brunauer-Emmett-Teller (BET) surface area of reduced graphene oxide (rGO). Optimal conditions (80-100 degrees C and appropriate extract volumes) enhanced the surface area, while excessive parameters led to slight restacking of the graphene layers. The resulting rGO exhibited a BET surface area of 92.33 m2/g. Furthermore, a composite material, Chitosan@EDTA@rGO, was synthesized and characterized using Fourier Transform Infrared Spectroscopy (FTIR), X-ray Diffraction (XRD), BET, and Scanning Electron Microscopy (SEM). This composite showed a significantly higher BET surface area (125.67 m2/g) and improved textural properties. Adsorption experiments for Rhodamine B (RB) removal indicated that Chitosan@EDTA@rGO followed pseudosecond-order kinetics, confirming a chemisorption mechanism. It achieved a higher adsorption capacity (153.85 mg/g) than rGO (144.93 mg/g) and reached 97.07% RB removal efficiency at pH 8, demonstrating enhanced performance and strong potential as an effective dye adsorbent. Density Functional Theory (DFT) analysis confirmed that functionalizing rGO with chitosan and EDTA introduced additional active sites, thereby increasing the adsorption energy and enhancing electronic interactions with Rhodamine B dye. The calculated adsorption energies and electronic properties corroborated the experimental findings, indicating that Chitosan@EDTA@rGO possesses a stronger binding affinity and superior charge transfer capabilities compared to rGO alone. These theoretical insights further support the composite's enhanced adsorption performance.