Mechanism of Oxidization of Graphite to Graphene Oxide by the Hummers Method

The mechanism of oxidizing reaction in the preparation of graphene oxide (GO) by a chemical oxidation method remains unclear. The main oxidant of graphite oxide has not been determined. Here, we show a new mechanism in which Mn₂O₇, the main oxidant, is heated to decompose oxygen atoms and react with graphite. The whole preparation process constitutes of four distinct independent steps, different from the three steps of literature registration, and each step has its own chemical oxidation reaction. In the first step, concentrated sulfuric acid and nitric acid are intercalated between graphite layers in the form of a molecular thermal motion to produce HNO₃-H₂SO₄-GIC. In the second step, Mn₂O₇ is intercalated between graphite layers in the molecular convection-diffusion to Mn₂O₇-H₂SO₄-GIC. In the third step, Mn₂O₇ is decomposed by heat. Oxygen atoms are generated to oxidize the defects in the graphite layer to PGO. This discovery is the latest and most important. In the fourth step, PGO is purified with deionized water, hydrogen peroxide, and hydrochloric acid to GO. Optical microscopy, ultraviolet-visible spectroscopy, Fourier transform infrared spectroscopy, X-ray diffraction spectrometry, and scanning electron microscopy analytical evidence was used for confirming Mn₂O₇ as the main oxidant and the structure of GO. This work provides a more plausible explanation for the mechanism of oxidizing reaction in the preparation of GO by a chemical oxidation method.