The oxidized graphite powder (20 g) was put into cold (0 °C) concentrated
H2SO4 (460 mL). KMnO4 (60 g) was added gradually with
stirring and cooling, so that the temperature of the mixture
was not allowed to reach 20 °C. The mixture was then stirred
at 35 °C for 2 h, and distilled water (920 mL) was added.