Graphene oxide (GO) powder was prepared from graphite flakes using modified Hummers method
[1-2]. Briefly, 5 g of graphite (Sigma-Aldrich, cat # 332461, ~ 150 μm) and 3.75 g of NaNO3 were
placed in a flask. Then, 375 cm3 of H2SO4 was added while stirring in an ice-water bath, and 25 g
of KMnO4 were slowly added for 1 h. Stirring was continued for 2 h in the ice-water bath, the ice
15 bath was then removed and the mixture was stirred at room temperature until it became pasty
brownish and then diluted with slowly addition of 250 cm3 deionized water. The reaction
temperature was rapid increased to 98°C, and the colour changed to brown colour after 2 hours.
Finally, 15 cm3 of 30 wt% aqueous solution of H2O2 was added to complete oxidation. The ions of
oxidant and other inorganic impurity were removed by repeating cycle of centrifugation, removal
20 of the supernatant liquid, and redispersing the solid using 3 wt% HCl aqueous solution. After
filtration, the solid was dispersed again in water using ultrasonication for 2 h and centrifuged at
6000 rpm for 30 min to remove the multilayered species.
PIL of poly(1-vinyl-3-ethylimidazolium) salts bearing the bis(trifluoromethylsulfonyl)amide anion
(NTf2- or CF3SO2-N-SO2CF3) was synthesized according to a previously reported procedure [3,