High-quality preparation of graphene oxide via the Hummers' method: Understanding the roles of the intercalator, oxidant, and graphite particle size

The Hummers' method, in which concentrated sulfuric acid (H2SO4) acts as the intercalator and potassium permanganate serves as the oxidant, is a commonly used method to prepare graphene oxide (GO). The amounts of intercalator and oxidant along with the particle size of graphite are important factors that affect the structure and properties of GO. In this study, Fourier-transform infrared spectroscopy, X-ray diffraction, Raman spectroscopy, ultraviolet–visible spectroscopy, scanning electron microscopy, dynamic light scattering, X-ray photoelectron spectroscopy, thermogravimetric analysis, and atomic force microscopy were used to characterize the effects of these factors on the structure and properties of GO. The results show that the amount of intercalator and oxidant clearly affect the types of oxygen-containing functional groups in the GO structure along with the oxidation degree of GO. Increasing the dosages of intercalator and oxidant can improve the oxidation degree of GO, facilitating the preparation of typical GO. Sodium nitrate (NaNO3) has a synergistic effect with H2SO4 during the process of graphite oxidation, which is helpful for the intercalation and oxidation of graphite. Increasing the oxidation degree of graphite can increase the interlayer spacing, which is conducive to the exfoliation of GO. However, the use of excessive NaNO3 is not conducive to improving GO oxidation. The effect of graphite particle size on GO interlayer spacing is greater than that of NaNO3. The obtained results provide a reference for the preparation of GO with controllable structure.