Green Reduction of Graphene Oxide using Kaffir Lime Peel Extract (Citrus hystrix) and Its Application as Adsorbent for Methylene Blue

Green reduction of graphene oxide (GO) by phytochemicals was explored using the aqueous extract of kaffir lime peels. The research methods included preparation of extracts, preparation of GO, preparation and characterization of reduced-GO (RGO) using Fourier Transform Infrared (FTIR), X-ray diffraction (XRD), and UV-Vis spectroscopy, as well as methylene blue (MB) adsorption test using RGO. The RGO characterization showed that GO was successfully reduced by a C=C group restoration. The MB adsorption kinetics profile in RGO is more suitable for the pseudo-second-order model, whereas for the adsorption isotherm it is more suitable for the Langmuir model with a maximum adsorption capacity (q(max)) of 276.06 mg/g at room temperature. The best ratio of GO: kaffir lime peel extract used to prepare RGO was at a ratio of 1: 2. Based on the ΔG, ΔH, and ΔS values, the adsorption of RGO-MB was defined as spontaneous and endothermic process. The results promise the potential application of RGO derived via green route to remove cationic dye in wastewater.