Soluble Graphene Prepared

"Solution Properties of Graphite and Graphene"
Niyogi, S.; Bekyarova, E.; Itkis, M. E.; McWilliams, J. L.; Hamon, M. A.; Haddon, R. C. J. Am. Chem. Soc. 2006, 128, 7720-7721.
DOI: 10.1021/ja060680r

One of the pioneers of carbon nanotube chemistry, Prof. Robert Haddon, led his group to prepare organic soluble graphene, following essentially the same method he used for soluble carbon nanotubes.

It was necessary to first obtain oxidized graphite, which is partially exfoliated with plenty of carboxylic acids for functionalization. The oxidation procedure was carried out in multi-gram quantity scale. In the preparation, a commerically available graphite sample (Aldrich, 5-g) was subject to mixed acid treatment (H2SO4:HNO3 = 3:1) (cup-horn sonication for 2 h @ 40C). After standing for 4 days (Tag 1: Is it necessary stand so long?) when the dispersion turn to purple-brown, the sample was repeatedly washed with water (centrifugation/decantation), filtered through PTFE filter, and washed with ethanol.

The grayish oxidized graphite was then subject to thionyl chloride refluxation for 24 h. After removal of excess SOCl2, 10 x weight octadecylamine (ODA) was added, and the mixture was kept at 120C (ODA melt @ ~50C) for 4 days. The crude product was dispersed in hot ethanol, filtered, and washed with hot ethanol. It was then dissolved in THF, and filtered through coarse filter paper (Tag 2: I assume here the filtrate is the soluble graphene). The solubility was 0.5 mg/mL in THF. The product was also soluble in CCl4 and 1,2-dichlorobenzene.


Characterization:

UV/vis/NIR:

• Essentially featureless with a maximum @ ~4.2 eV (or ~295 nm)
• Following Beer's Law, with extinction coefficient of 40L/mol cm at 1000 nm (in comparison to the value of 400 L/mol cm for SWNTs from the same group) without obvious scattering.
• The spectra of of oxidized graphite were dominated by scattering (Tag 3: Beer's Law plot not quite meaningful?)

FT-IR:

• weak amide carbonyl @ 1653 cm-1 (carbonyl signaks of oxidized graphite seems stronger);
• C-H stretches @ ~2850-2920 cm-1.

AFM:

• Graphite crystals (Gn) feature heights of 1.5-2.5 nm
• Individual graphene sheets (G1) heights of ~0.53 nm (somewhat different from previous observations made by Novoselov, et al.; consideration of dead space between graphene and substrate)

TGA in air:

• Graphite: 800C
• Oxidized Graphite: 600C/200C (loss of functional groups)
• ODA-Gn: 300C organic loss of 7wt% (Tag 4: The small organic group percentage indicate the domination of edge-functionalization)