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Graphite oxide


From Wikipedia, the free encyclopedia

Contents

[hide ]

* 1 History and preparation 
* 2 Structure 
* 3 Applications 
o 3.1 Graphene manufacture 
o 3.2 Related materials 
* 4 References 
* 5 See also 

*Graphite oxide*, formerly called *graphitic oxide* or *graphitic acid*,
is a compound of carbon , oxygen , and hydrogen in variable ratios,
obtained by treating graphite with strong oxidizers . The maximally
oxidized bulk product is yellow solid with C:O ratio between 2.1 and 2.9,
that retains the layer structure of graphite but with a much larger and
irregular spacing.^[1]


The bulk material disperses in basic solutions to yield monomolecular
sheets, known as *graphene oxide* by analogy to graphene , the
single-layer form of graphite.^[2] Graphene oxide sheets have been used to
prepare a strong paper-like material, and have recently attracted
substantial interest as a possible intermediate for the manufacture of
graphene. However, as of 2010 this goal remains elusive since graphene
obtained by this route still has many chemical and structural defects.


[edit ] History and preparation

Graphite oxide was first prepared by Oxford chemist Benjamin C. Brodie in
1859, by treating graphite with a mixture of potassium chlorate and fuming
nitric acid .^[3] In 1957 Hummers and Offeman developed a safer, quicker,
and more efficient process, using a mixture of sulfuric acid H_2 SO_4 ,
sodium nitrate NaNO_3 , and potassium permanganate KMnO_4 , which is still
widely used (as of 2009).^[1]

Recently a mixture of H_2 SO_4 and KMnO_4 has been used to cut open carbon
nanotubes lengthwise, resulting in microscopic flat ribbons of graphene, a
few atoms wide, with the edges "capped" by oxygen atoms (=O) or hydroxyl
groups (-OH).^[4] .


[edit ] Structure

The structure and properties of graphite oxide depend on particular
synthesis method and degree of oxidation. It typically preserves the layer
structure of the parent graphite, but the layers are buckled and the
interlayer spacing is about two times larger (~7 Ã…) than that of
graphite. Strictly speaking "oxide" is an incorrect but historically
established name. Besides oxigen epoxide groups (bridging oxygen atoms),
other functional groups experimentally found are: carbonyl (=CO), hydroxyl
(-OH), phenol groups attached to both sides.^[5] ^[6] There is evidence of
"buckling" (deviation from planarity) of the layers. The detailed
structure is still not understood due to the strong disorder and irregular
packing of the layers.

Graphene oxide layers are about 1.1 ± 0.2 nm thick ^[5] ^[6] . Scanning
tunneling microscopy shows the presence of local regions where oxygen
atoms are arranged in a rectangular pattern with lattice constant 0.27 nm
× 0.41 nm ^[6] ^[7] The edges of each layer are terminated with carboxyl
and carbonyl groups.^[5] X-ray photoelectron spectroscopy shows the
presence of carbon atoms in non-oxygenated ring contexts (284.8 eV), in
C-O (286.2 eV), in C=O (287.8 eV) and in O-C=O (289.0 eV).^[8]

Graphite oxide is easily hydrated, resulting in a distinct increase of the
inter-planar distance (up to 12 Ã… in saturated state). Additional water
is also incorporated into interlayer space due to high pressure induced
effects. The bulk product absorbs moisture from ambient air proportionally
to humidity. Complete removal of water from the structure seems difficult
since heating at 60–80 °C results in partial decomposition and
degradation of the material.

Graphite oxide exfoliates and decomposes when rapidly heated at moderately
high temperatures (~280–300 °C) with formation of finely dispersed
amorphous carbon, somewhat similar to activated carbon .



Exfoliation of graphite oxide at high temperature, screenshots from video
available here:^[9] Exfoliation results in tenfold increase fo sample
volume and formation of carbon powder with grains of few graphene layers
thickness.^[10]


[edit ] Applications


[edit ] Graphene manufacture

Graphite oxide has attracted much interest recently as a possible route
for the large-scale production and manipulation of graphene , a material
with extraordinary electronic properties. Graphite oxide itself is an
insulator,^[11] almost a semiconductor , with differential conductivity
between 1 and 5×10^-3 S/cm at a bias voltage of 10 V^[11] . However,
being hydrophilic , graphene oxide disperses readily in water, breaking up
into macroscopic flakes, mostly one layer thick. In theory, chemical
reduction of these flakes would yield a suspension of graphene flakes.

Partial reduction can be achieved by treating the suspended graphene oxide
with hydrazine hydrate at 100 °C for 24 hours^[8] , or by exposing
graphene oxide to hydrogen plasma for a few seconds,^[11] or by exposure
to a strong pulse of light, such as that of a Xenon flash .^[12] However,
the conductivity of the graphene obtained by this route is below 10
S/cm,^[12] and the charge mobility is between 2 to 200 cm^2 /(V·s) for
holes and 0.5 to 30 cm^2 /(V·s) for electrons.^[11] These values are much
greater than the oxide's, but still a few orders of magnitude lower than
those of pristine graphene.^[11] Inspection with the atomic force
microscope shows that the oxygen bonds distort the carbon layer, creating
a pronounced intrinsic roughness in the oxide layers which persists after
reduction. These defects also show up in Raman spectrum of graphene
oxide.^[11]



[edit ] Related materials

Dispersed graphene oxide flakes can also be sifted out of the dispersion
(as in paper manufacture ) and pressed to make an exceedingly strong
graphene oxide paper .


[edit ] References

1. ^ ^/*a*/ ^/*b*/ William S. Hummers Jr., and Richard E. Offeman (1958)
/Preparation of Graphitic Oxide./ J. American Chemical Society, volume 80
issue 6, pages 1339–1339. doi :10.1021/ja01539a017

2. *^ * Daniel R. Dreyer, Sungjin Park, Christopher W. Bielawski and
Rodney S. Ruoff (2010), /The chemistry of graphene oxide/. Chemical
Society Reviews, volume 39, pages 228-240 doi :10.1039/b917103g

3. *^ * Benjamin C. Brodie (1859), /On the Atomic Weight of Graphite/ .
Proceedings of the Royal Society of London, volume 10, page 249. 4. *^ *
Dmitry V. Kosynkin, Amanda L. Higginbotham, Alexander Sinitskii, Jay R.
Lomeda, Ayrat Dimiev, B. Katherine Price, James M. Tour: /Longitudinal
unzipping of carbon nanotubes to form graphene nanoribbons/. Nature,
volume 458, p. 872--876 (16 April 2009). doi :10.1038/nature07872

5. ^ ^/*a*/ ^/*b*/ ^/*c*/ H. C. Schniepp /et al./ (2006) /Functionalized
Single Graphene Sheets Derived from Splitting Graphite Oxide./ American J.
of Physical Chemistry, series B, volume 110, page 8535. doi
:10.1021/jp060936f

6. ^ ^/*a*/ ^/*b*/ ^/*c*/ D. Pandey /et al./ (2008), /Scanning probe
microscopy study of exfoliated oxidized graphene sheets/. Surface Science,
volume 602 issue 9, page 1607-1613. doi :10.1016/j.susc.2008.02.025

7. *^ * K. A. Mkhoyan /et al./ (2009) /Atomic and Electronic Structure of
Graphene-Oxide./ Nano Letters, volume 9 issue 3, pages 1058-1063. doi
:10.1021/nl8034256

8. ^ ^/*a*/ ^/*b*/ S. Stankovich /et al./ (2006), /Stable aqueous
dispersions of graphitic nanoplatelets via the reduction of exfoliated
graphite oxide in the presence of poly(sodium 4-styrenesulfonate./ J.
Material Chemistry, volume 16, page 155. doi :10.1039/b512799h

9. *^ * http://www.youtube.com/watch?v=bl45J6iw3tE 10. *^ * A. V. Talyzin
/et al./ Nanocarbons by High-Temperature Decomposition of Graphite Oxide
at Various Pressures, J. Phys. Chem. C, 2009, 113 (26), pp 11279–11284
doi :10.1021/jp9016272

11. ^ ^/*a*/ ^/*b*/ ^/*c*/ ^/*d*/ ^/*e*/ ^/*f*/ C. Gomez-Navarro /et al./
(2007). Nano Letters, volume 7, issue 11, page 3499 doi :10.1021/nl072090c

12. ^ ^/*a*/ ^/*b*/ Laura J. Cote, Rodolfo Cruz-Silva, and Jiaxing Huang
(2009), /Flash Reduction and Patterning of Graphite Oxide and Its Polymer
Composite/. Journal of the American Chemical Society, volume 131, pages
11027–11032 doi :10.1021/ja902348k



[edit ] See also

* Oxocarbon