Natural graphite

GO was prepared by the oxidation of purified natural graphite (Sinopharm Chemical Reagent Co., Ltd.) based on the improved Hummer’s method⁴⁸ . A 500-mesh graphite flake (3 g) was dissolved in 100 mL concentrated sulfuric acid (95%) in an ice bath under magnetic stirring (100 rpm). Then, potassium permanganate (13.5 g) was added slowly to prevent the temperature from going over 20 °C. The reaction continued for 1 h at 40 °C with vigorously stirring (800 rpm). Then, 750 mL of water was added slowly and the solution was stirred at 90 °C for 30 min. After the addition of 500 mL of deionized water, the cooled acid mixture was further treated with a hydrogen peroxide solution (800 mL, 5%). The mixture was washed with distilled water and 300 mL of hydrochloric acid (10%) followed by repeated washing with ethanol. The resultant bright yellow suspension was purified by repeated centrifugation and washed with distilled water and ethanol until reaching pH 7.0. Finally, the filtrate liquid was air dried overnight and sonicated for 30 min to exfoliate it to create the GO dispersion.