Scalable Synthesis of Graphene Oxide

Typically, flake graphite (10 g), KMnO₄ (6 g) and K₂FeO₄ (4 g) as the oxidants, and boric acid (0.01 g) as a stabilizer were first dispersed in 100 mL of concentrated sulfuric acid in a vessel and stirred for 1.5 h at less than 5 °C. After the addition of another KMnO₄ (5 g), the vessel was transferred into a water bath at about 35 °C and stirred for another 3 h to complete the deep oxidation. Next, as 250 mL of deionized water was slowly added, the temperature was adjusted to 95 °C and held for 15 minutes, when the diluted suspension turned brown, indicating the hydrolysis and absolute exfoliation of intercalated graphite oxide. Finally, this brown suspension was further treated with 12 mL H₂O₂ (30%) to reduce the residual oxidants and intermediates to soluble sulfate, then centrifuged at 10000 rpm for 20 min to remove the residual graphite, and washed with 1 mol/L HCl and deionized water repeatedly, producing the terminal GO (designated GO2). For comparison, another GO (designated GO1) was synthesized following Kovtyukhova improved Hummers method20 , except two of little modification: (1) the ingredients were adjusted slightly, as shown in Table S1; (2) both preoxidation and oxidation time was set at 4 hours.