Reduction of Graphene Oxide Using Citrus hystrix Peels Extract for Methylene Blue Adsorption

Abstract

Kaffir lime peels extract was used as an agent for the reduction of graphene oxide (GO) into reduced graphene oxide (rGO) via a simple room temperature-dispersion process. The GO obtained from the Hummers process is dispersed in polyphenols rich extract at a varied GO-to-extract ratio of 1:1, 1:2, 1:3, and 1:4. The formation of rGO was confirmed through SEM, FTIR, XPS, XRD, and N2 sorption characterization. The restoration of C=C group and the reduction of several oxygen-containing groups confirmed the successful formation of rGO from GO. The resultant rGOs were used in the adsorption system for methylene blue uptake. The results indicated that the rGOs prepared at a GO-to-extract ratio of 1:2 had the highest adsorption capacity than rGO at other ratios. The XPS spectrum analysis of rGO 1:2 showed a higher C-C/C-O ratio than the other rGOs, indicating a higher number of adsorption sites which aid in improving the adsorption performance. The adsorption isotherm and kinetic studies were conducted to gain insight into the mechanism and rate of methylene blue uptake by the rGOs. The adsorption isotherm systems were consistent with Langmuir isotherm model with the highest adsorption capacity of 118 mg g–1 by rGO 1:2. The kinetic adsorption data are well represented by the pseudo-second order model, the adsorption equilibrium was achieved within 400 min with the overall uptake rate of 0.3 mg g–1 min–1.