Highly oxidized and exfoliated graphene using a modified Tour approach

A comparative study of different chemical modified methods of graphene oxide (GO) synthesis is described, using natural graphite as starting material. The first one (GO-1) is an improved Hummers method without using NaNO₃. The second one (GO-2) is the reported “modified Hummers method”. The third one (GO-3) is our variation of the Tour method, in which we use a different protective agent, H₃BO₃, instead of the commonly used H₃PO₄ in the original Tour method. With GO-3 method, we are able to reduce significantly the oxidation time of graphite by increasing significantly the amount of oxidizing agent (KMnO₄). The fourth one (GO-4) is a combination of GO-2 and GO-3. The properties of GO powders were analyzed by UV–Visible spectroscopy, Fourier Transform Infrared spectroscopy, X-ray photoelectron spectroscopy, high-resolution scanning electron microscopy, high-resolution transmission electron microscopy, X-ray energy dispersive spectroscopy and X-ray diffraction. It is observed that with GO-3 method natural graphite has been highly oxidized and becomes GO with a 9.20 Å interlayer space and a carbon to oxygen ratio of about 0.8. The new protective agent has given a good exfoliation, leading double layers of graphene oxide sheets with more intact graphene basal planes. Comparing with the original Tour method, our products from GO-3 method are obtained in much less time of production and show a high-quality of GO sheets with a selected number of layers.