Synthesis of graphene oxide: A refined approach

The conventional method for preparing graphene oxide (GO) relies on the use of corrosive acids namely concentrated H₂SO₄, HNO₃, and H₃PO₄ as well as aggressive oxidizing agents such as KMnO₄ and KClO₄. The application of heat further exacerbates the preparation, promoting the release of harmful acidic NO_x and ClO₂ fumes. The formation of the by-product Mn₂O₇ could also increase the risk of explosion. A safe(r) and shorter method of preparation of GO has been a challenge for many researchers. This study presents a method of preparing GO, that reduces risks by eliminating the need for heating and shortening the oxidation step. This method utilises mixtures of concentrated H₂SO₄ and KMnO₄ with graphite thus eliminating the release of toxic fumes.

Characterization studies revealed that the graphite precursor with an average lateral flake size of 15.06 ±1.87 µm was successfully oxidized to GO and subsequently exfoliated to thinner sheets. The resulting GO exhibited a reduced average lateral sheet size of 10.22 0.62 µm and comprised approximately 10 layers, indicating that the precursor material is polycrystalline. Comprehensive XPS analysis revealed that the oxygen content and chemical states of carbon in the synthesized GO was comparable to that of commercially available GO, with similar distribution of oxygen functionalities. In the in-house produced GO, the predominant functional group was found to be the C-O bond corresponding to the epoxy group, followed by the ester and acid anhydride functional groups. Furthermore, the decrease in the percentage of sp² hybridized carbon in GO to 45.52 %—measured using X-ray induced Auger spectroscopy—confirms the successful oxidation of the precursor, which initially exhibited 80.21 % sp² character in graphite.