Preparation of expanded graphite with (NH4)2S2O8 and H2SO4 by using microwave irradiation

Background: In recent years, many researchers have paid great attention to expanded graphite (EG) due to its excellent properties and potential applications. However, the preparation of EG usually consumes a lot of chemicals and energy and generates hazardous residues, such as heavy metal containing wastewater. The main purpose of this study was to develop a green method for the preparation of EGs. Methods: (NH4)2S2O8 and H2SO4 were used for the chemical intercalation process and the microwave irradiation process was employed for the expansion of graphite intercalation compounds (GICs) to obtain EGs. The Fourier transform infrared spectroscopy (FTIR) and the scanning electron microscopy (SEM) were used to examine the changes in the material microstructures. Significant findings: The results showed that the reactant proportion of graphite : (NH4)2S2O8 : H2SO4 equal to 1 : 5 : 5.5 was the most appropriate condition to prepare GICs, and the EGs with the highest expanded volume (-267 L/kg) was obtained by treating the GICs with microwave irradiation at 500 W for 60 s. Under these conditions, the EGs had a long axial length and few breakages. Excessive levels of microwave irradiation impaired the EGs and then left a loose structure and damaged surfaces, thus greatly increasing the specific surface area.