Green synthesis of graphene oxide via electrochemical exfoliation and its characterization

Graphene oxide (GO) is a versatile carbon nanomaterial whose properties strongly depend on the synthesis route. In this study, an environmentally friendly electrochemical exfoliation (EE) method using 0.1 M ammonium sulfate electrolyte was developed and compared with the conventional Hummers' method (HM). The influence of electrolysis duration and purification on the structural and electrical properties of the obtained materials was systemically investigated. UV–Vis spectroscopy showed a characteristic absorption band at approximately 190 nm for electrochemically exfoliated samples, while prolonged electrolysis (8 h) resulted in the appearance of a weak shoulder near 230 nm, indicating gradual oxidation of the graphite structure. XRD analysis revealed that HM-derived GO exhibited a characteristic (001) reflection at 11.09° (d-spacing = 7.99 Å), whereas electrochemically exfoliated GO retained a broad (002) peak centered at 26.54°, corresponding to an interlayer spacing of 3.36 Å and indicating partial preservation of the graphitic structure. Raman spectroscopy demonstrated a lower defect density in electrochemically exfoliated GO, with an I_D/I_G ratio of 0.759 compared with 0.864 for HM-derived GO. FTIR spectra further confirmed the lower abundance of oxygen-containing functional groups in the electrochemically synthesized material. Electron microscopy revealed thin, transparent, wrinkled graphene-like nanosheets with significantly improved exfoliation after dialysis. Electrical resistivity measurements performed between 40 and 100 °C under laboratory air, humid atmosphere, and flowing argon demonstrated consistently lower resistivity for electrochemically exfoliated GO than for HM-derived GO, indicating higher electrical conductivity due to its lower oxidation degree and better preservation of the sp² carbon network. These results demonstrate that EE provides a simple, low-cost, and environmentally benign approach for producing conductive graphene-like materials with reduced oxygen functionalization while avoiding the hazardous oxidants required in the conventional Hummers' method.