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 (50mL), 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 (50mL), 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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