Flake graphite

Flake graphite (carbon content of 97%, moisture content of less than 0.5%, density of 1.6 g cm⁻³, flake size of 0.5 mm) was purchased from Sinopharm Chemical Reagent Co., Ltd. (Shanghai, China). Sodium chloride (AR), sodium hydroxide (AR), poly vinyl pyrrolidone (PVP) (AR), dodecyl trimethyl ammonium bromide (DTAB) (AR), sodium dodecyl benzene sulfonate (SDBS) (AR) and ethanol (AR) were all purchased from Sinopharm Chemical Reagent Co., Ltd. (Shanghai, China).
The hydroxyl radical production and graphite exfoliation apparatus was designed and manufactured by our laboratory, and the detailed device diagram is shown in Fig. 1. An analytical balance (TG328A) was purchased from Balance Instrument Factory (Shanghai, China). The pumping equipment was purchased from Guohua Electric Co. (Shanghai, China). The vacuum drying oven was purchased from Anteing Electronic Instrument Factory (Shanghai, China).

Flake graphite of chemical grade (≤30 μm) were from Sinopharm Chemical Reagent Co. Ltd., China. Styrene, ethanol and sodium p-styrene sulfonate were obtained from Kelong chemical reagent company. Cobalt nitrate hexahydrate was bought from Shanghai Macklin Biochemical Co. Ltd. All other reagents used in this study, including ethylenediamine, sodium bicarbonate, potassium persulfate, sodium chloride, sodium hydroxide, sodium nitrate, concentrated sulfuric acid, potassium permanganate, concentrate hydrochloric acid, hydrogen peroxide, absolute ethyl ethanol and carbamide were purchased from Luoyang Chemical Reagent Co. Ltd., China. All these chemicals were of analytical grade and were used without further purification. Water used in the experiments was double-distilled.

Silicon powder (200 mesh, AR, 99.9%), germanium dioxide (AR, 99.9%), flake graphite (AR, 99.9%) and gelatin (LR, 98%) were purchased from Sinopharm Chemical Reagent Co., Ltd.