Formation mechanism of nano graphitic structures during microwave catalytic graphitization of activated carbon

Catalytic graphitization of biomass-based carbon has been used to synthesize graphene nanostructures with extraordinary electrochemical properties. To further improve the structural properties of these graphene nanostructures, it is critical to gain a deeper understanding of the formation mechanism and influence of process variables on the structural features of the resulting material. Here, we report the impact of various parameters such as catalyst loading, temperature, holding time, and catalyst salt precursor on the low-temperature catalytic graphitization of activated carbon (AC). Quantitative X-ray diffraction (XRD) analysis results show that at 20 wt% catalyst loading, reaction temperature of 1400 °C, and holding time of 30 min, a complete graphitization of amorphous carbon was achieved. In situ XRD and transmission electron microscopy (TEM) results indicated that the dissolution-precipitation and metal-induced graphitization are the primary mechanisms under which graphitized carbon was formed. Furthermore, it was found that the rate of graphitization under microwave irradiation is significantly higher than conventional heating, mainly owing to the enhanced precipitation of graphitic carbon caused by both carbon saturation and temperature fluctuation of the catalyst particles.