Study on the Preparation of GO and RGO by Chemical and Mechanical Exfoliation of Natural Graphite for the Aluminum Industry

Abstract

Aluminum is produced in chemical electrolysis by the Hall–Heroult process using carbon-based materials in electrodes (cathode and anode). The amorphous calcined petroleum coke is normally used as the carbon material. During the electrolysis of alumina, a voltage drop of about 0.15–0.25 V occurs due to the formation of gas bubbles at the anode which therefore reduces the electrolysis reaction kinetics. To improve the electrolysis efficiency, graphite material is partly used in both the cathode and anode. To further improve the efficiency of the electrolysis, the graphite may be replaced by graphene oxide (GO) and reduced graphene oxide (RGO) because of their outstanding electrical, mechanical and chemical properties. As the demand for graphene oxide and graphene is increasing daily, large-scale and economic processes should be developed to meet this challenge. This study was carried out to produce GO and RGO from natural high-purity graphite (HPG) by applying oxidation and reduction processes through chemical and mechanical exfoliation processes. In the chemical exfoliation process, multi-metal alloys of zinc, iron, aluminum and silicon are used as the reductant instead of using hazardous chemical materials. In the mechanical exfoliation process, a planetary ball mill is used to exfoliate the natural graphite by purging gaseous oxidants and reductants such as O₂ and H₂ for the oxidation of GO and the reduction of RGO, respectively. The morphology, structure and composition of HPG, GO and RGO have been characterized using different analytical techniques, such as X-ray diffraction, scanning electron microscopy, and transmission electron microscopy with selected area electron diffraction, micro-Raman spectroscopy and Fourier-transform infrared spectroscopy. The number of layers of the GO and RGO samples has been determined based on the characterization data and found to be four to five layers.