Materials. GO was synthesized from natural graphite
powder (325 mesh, GAK-2, Ukraine) by the method of Hummers
and Offeman.18 It was found that, prior to the GO
preparation according to ref 18, an additional graphite oxidation
procedure was needed. Otherwise, incompletely oxidized
graphite-core/GO-shell particles were always observed in the
final product. The graphite powder (20 g) was put into an 80
°C solution of concentrated H2SO4 (30 mL), K2S2O8 (10 g), and
P2O5 (10 g). The resultant dark blue mixture was thermally
isolated and allowed to cool to room temperature over a period
of 6 h. The mixture was then carefully diluted with distilled
water, filtered, and washed on the filter until the rinse water
pH became neutral. The product was dried in air at ambient
temperature overnight. This preoxidized graphite was then
subjected to oxidation by Hummers’ method. The oxidized
graphite powder (20 g) was put into cold (0 °C) concentrated
H2SO4 (460 mL). KMnO4 (60 g) was added gradually with
stirring and cooling, so that the temperature of the mixture
was not allowed to reach 20 °C. The mixture was then stirred
at 35 °C for 2 h, and distilled water (920 mL) was added. In
15 min, the reaction was terminated by the addition of a large
amount of distilled water (2.8 L) and 30% H2O2 solution (50
mL), after which the color of the mixture changed to bright
yellow. The mixture was filtered and washed with 1:10 HCl
solution (5 L) in order to remove metal ions. The GO product
was suspended in distilled water to give a viscous, brown, 2%
dispersion, which was subjected to dialysis to completely
remove metal ions and acids. The resulting 0.5% w/v GO
dispersion, which is stable for a period of years, was used to
prepare exfoliated GO.
Materials. GO was synthesized from natural graphite
powder (325 mesh, GAK-2, Ukraine) by the method of Hummers
and Offeman.18 It was found that, prior to the GO
preparation according to ref 18, an additional graphite oxidation
procedure was needed. Otherwise, incompletely oxidized
graphite-core/GO-shell particles were always observed in the
final product. The graphite powder (20 g) was put into an 80
°C solution of concentrated H2SO4 (30 mL), K2S2O8 (10 g), and
P2O5 (10 g). The resultant dark blue mixture was thermally
isolated and allowed to cool to room temperature over a period
of 6 h. The mixture was then carefully diluted with distilled
water, filtered, and washed on the filter until the rinse water
pH became neutral. The product was dried in air at ambient
temperature overnight. This preoxidized graphite was then
subjected to oxidation by Hummers’ method. The oxidized
graphite powder (20 g) was put into cold (0 °C) concentrated
H2SO4 (460 mL). KMnO4 (60 g) was added gradually with
stirring and cooling, so that the temperature of the mixture
was not allowed to reach 20 °C. The mixture was then stirred
at 35 °C for 2 h, and distilled water (920 mL) was added. In
15 min, the reaction was terminated by the addition of a large
amount of distilled water (2.8 L) and 30% H2O2 solution (50
mL), after which the color of the mixture changed to bright
yellow. The mixture was filtered and washed with 1:10 HCl
solution (5 L) in order to remove metal ions. The GO product
was suspended in distilled water to give a viscous, brown, 2%
dispersion, which was subjected to dialysis to completely
remove metal ions and acids. The resulting 0.5% w/v GO
dispersion, which is stable for a period of years, was used to
prepare exfoliated GO.
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