A mixture containing 0.8 g of graphite flakes and 0.4 g of sodium nitrate (NaNO3) was prepared in a round-bottom flask placed on an ice bath, which was positioned on top of a magnetic stirrer. A volume of 18.4 mL of 99% sulfuric acid (H2SO4) was gradually added to the mixture whilst slightly increasing the stirring speed. After the mixture was left to stir for 10 min, 2.4 g of potassium permanganate (KMnO4) were added very slowly. The ice bath was replaced by a distilled water bath, which allowed the temperature of the reaction to increase gradually over time. After 30 minutes, the mixture was more homogenous and became a thick, dark green paste, into which 37.5 mL of water for injections were transferred very slowly, drop by drop using a sterilised glass Pasteur pipette (Fisher Scientific, UK). During this procedure, a violent purple effervescence was observed as a result of the reaction between the water and the acidic mixture, followed by a sharp increase in temperature. When the reaction temperature reached 98ºC, the water bath was replaced by an oil bath that was pre-heated at 80-90ºC, so that the mixture could stabilise at 98ºC, not exceeding 100ºC owing to a temperature controller. The mixture was kept stirring for 30 minutes and started displaying a thicker, paste-like appearance of a dark brown/green colour, which indicated the oxidation of graphite. Then, 112.5 mL of warm water for injections (T ~ 50ºC) followed by 12.5 mL of 30% hydrogen peroxide (H2O2) were finally added in order to stop the reaction, by reducing the residual KMnO4, manganese dioxide (MnO2) and dimanganese heptoxide (Mn2O7) to soluble manganese sulfate (MnSO4) salts . Effervescence could be observed as a result of the release of carbon dioxide (CO2), confirming the termination of the reaction. The round-bottom flask was covered with aluminium foil and left to rest for 1 hour.