A study of graphenes prepared by different methods: characterization, properties and solubilization.

A study of graphenes prepared by different methods: characterization, properties and solubilization.

K. S. Subrahmanyam, S. R. C. Vivekchand, A. Govindaraj and C. N. R. Rao

J. Mater. Chem., 2008, 18, 1517 - 1523

This paper is from a special theme issue in Journal of Materials Chemistry on carbon nanostructures; if you're in to that sort of thing, check it out here. There's also a feature article by organic "graphenes" guru Klaus Mullen in there that I'll be reviewing soon, but you should go ahead and read it yourself since it's pretty nifty. I love the concept of the paper we're reviewing today; it's a head-to-head comparison of graphene made by different methods. Unfortunately, two of the three methods they use are pretty obscure, and the authors do not test "Scotch-tape" style graphene. Fortunately (and accidentally), I've already reviewed the relavent methods.

The paper evaluates graphene made by the dreaded camphor method (they call this CD), the well-respected method of oxidizing graphite to graphene oxide (EG, since they make a big deal of exfoliating it once it's oxidized; to me that's too easy to confuse with our Scotch tape method), and the circa-2003 method of thermally converting nanodiamond (they call this DG). I'd like to point out that that last sentence is more self-referential than most Wikipedia articles, and I don't care who knows it. The authors also mention graphene made from arc evaporation of SiC, but only take TEM images of it.

Anyway, this is an amazing amount of data, so I'll just break this down by characterization method and skip the barely-mentioned TEM.

X-Ray Diffraction (XRD): Gives number of layers (two of the samples gave two different sets of layered structures) and size of the crystallites:
CG: 51 layers, 6.1 nm crystallites
EG: 3 and 16 layers, 4.7 nm crystallites
DG: 6 and 87 layers, 5.0 nm crystallites

AFM: Also number of layers:
CG: 20
EG: 3-6
DG: 3-6

Raman: Gives multiple sizes of crystallites, in nm:
CG: 7, 10, 12
EG: 4, 6, 7
DG: 3, 4, 5

Magnetic susceptibility, in emu g^-1:
CG: No (publishable) data
EG: -3.5*10^-6
DG:-4.4*10^-6 (both EG and DG show Curie behavior, which I can't find a good summary for)

TGA: supposedly gives the oxidation temperature, but I think in the graphene oxide (EG) case it might better reflect the decarboxylation temperature (in degrees C):
CG: 730
EG: 520
DG: 700

Surface Area (in m^2 g^-1)
CG: 46
EG: 925
DG: 520
Lit value for single-layer graphene: 2600

Hydrogen Uptake (at low pressure and temp, then high pressure and temp, in wt%):
CG: No data
EG: 1.38, 3.1
DG: 0.68, 2.5 (these are comparable with carbon nanotubes)
Department of Energy Target: 6.0

Electrochem:
CG: acts like basal plane of graphite
EG, DG: better kinetics than CG

Supercapacitor measurements, in F g^-1:
CG: No data
EG: 117 (supposedly good)
DG: 35


Then they chemically modified these things with the nitric/sulfuric treatment or with an amidation treatment to make them more soluble.

Well, there you have it folks. I'm frankly blown away that they put all of this data into one paper, and although I wish they would have included the epitaxial "Scotch tape" graphene, it was interesting to see that the nanodiamond (DG) sample had properties similar to the graphene oxide. If you're making graphene and want to see how your samples compare- here's a whole battery of tests to match up to. Expect this paper to get a lot of citations in the future.

Also, the camphor graphene pretty much sucked. Told you.



Subrahmanyam, K.S., Vivekchand, S.R., Govindaraj, A., Rao, C.N. (2008). A study of graphenes prepared by different methods: characterization, properties and solubilization. Journal of Materials Chemistry, 18(13), 1517. DOI: 10.1039/b716536f