Graphite oxide

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Structural proposal from 1998 with functional groups . A: epoxy bridges , B: hydroxyl groups , C: carboxy groups in pairs on the edge .

Graphite oxide , formerly also graphitic acid , is a non-stoichiometric compound of the chemical elements carbon , oxygen and hydrogen ; it can be obtained from graphite under the action of strong oxidants . In its maximally oxidized form, graphite oxide forms a yellow solid; the ratio of carbon to oxygen ranges from 2.1: 1 to 2.9: 1. Graphite oxide has a layer structure comparable to graphite, although the distances between the molecular planes are larger and more irregular.

In basic solutions graphite oxide breaks down into flakes with a monomolecular layer thickness, which are referred to as graphene oxide (based on graphene , the single-layer form of graphite). Graphene oxide can be used to produce a high-strength paper-like material, graphene oxide paper , which has recently become of interest as a possible intermediate product in graphene production. However (as of 2010) graphene produced in this way still shows numerous chemical and structural irregularities.

History and representation

The British chemist Benjamin Collins Brodie Jr. was the first to prepare graphite oxide in 1859 . who treated graphite with a mixture of potassium chlorate and fuming nitric acid . The process described in 1957 by William S. Hummers and Richard E. Offeman is faster and less dangerous, with a higher yield; they used a mixture of sulfuric acid H 2 SO 4 , sodium nitrate NaNO 3 , and potassium permanganate KMnO 4 . This method is still in use today (as of 2013).

Recently, a mixture of H 2 SO 4 and KMnO 4 has been used to cut carbon nanotubes lengthways, resulting in microscopic, flat graphene ribbons with a width of a few atoms with a cap made of oxygen atoms (= O) or hydroxyl groups at the ends wear (-OH).

structure

The structure and properties of the graphite oxide are determined by the synthesis method used and the degree of oxidation achieved. The layer structure of the graphite used is typically retained, but the layers are irregular in terms of their planarity and are up to twice as spaced (approximately 0.7  nm ) as graphite. Contrary to what the historically established name graphite oxide suggests, it is not an oxide in the strict sense of the word . In addition to epoxide - the following functional groups were also found experimentally : carbonyl - (= CO), hydroxy - (-OH), sulfuric acid ester (-OSO 3 H) and endoperoxides (-O 2 -).

The exact structure is not yet understood in detail due to the variable spacing between the layers and the overall poor order. The distance between the graphene oxide layers is 1.1 ± 0.2 nm. Images taken with a scanning tunneling microscope reveal regions in which oxygen atoms are arranged in a rectangular pattern with a lattice constant of 0.27 nm × 0.41 nm. The edges of each layer are bounded by carboxy groups and carbonyl groups. By means of X-ray - photoelectron spectroscopy can be shown that carbon atoms in rings without oxygen (284.8  eV are present) (see, 286.2 eV for C-O, 287.8 eV for C = O and 289.0 eV for O C = O).

Graphite oxide absorbs water very easily, which significantly increases the distance between the individual levels (up to 1.2 nm in the saturated state). At higher pressures, additional water is built into the space between the individual layers. The graphite oxide mass stores moisture from the ambient air in proportion to the air humidity. Complete drying appears difficult since heating to 60-80 ° C leads to partial decomposition of the material.

Rapid heating to 280–300 ° C causes graphite oxide to decompose ( exfoliation ), producing a finely divided, amorphous carbon powder , comparable to activated carbon .

Applications

Cleavage ( exfoliation ) of graphite oxide at high temperature. The sample volume increases tenfold and a carbon powder is formed that contains flakes of graphene, the thickness of which is only a few molecular layers.

Graphene production

In the 2000s, graphite oxide became interesting as a possible precursor for the production of graphene on a large scale. Graphite oxide is an insulator ; with a differential electrical conductivity of 5 · 10 −3 S · cm −1 ; with a bias of 10V it is almost a semiconductor .

See also

Web links

Individual evidence

  1. ↑ Heyong Hea, Jacek Klinowskia, Michael Forsterb, Anton Lerf: A new structural model for graphite oxide . In: Chemical Physics Letters. Volume 287, Issues 1-2, 1998, pp. 53-56, doi: 10.1016 / S0009-2614 (98) 00144-4 .
  2. ^ A b William S. Hummers Jr., Richard E. Offeman: Preparation of Graphitic Oxide. In: J. American Chemical Society. 80, No. 6, 1958, pp. 1339-1339, doi: 10.1021 / ja01539a017 .
  3. ↑ Daniel R. Dreyer, Sungjin Park, Christopher W. Bielawski, Rodney S. Ruoff: The chemistry of graphene oxide . In: Chemical Society Reviews . 39, 2010, pp. 228-240, doi: 10.1039 / b917103g .
  4. ^ Benjamin C. Brodie: On the Atomic Weight of Graphite . In: Proceedings of the Royal Society of London. 10, 1859, p. 249, JSTOR 108699 .
  5. ↑ 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 . In: Nature. 458, April 16, 2009, pp. 872-876, doi: 10.1038 / nature07872 .
  6. ↑ HP Boehm , W. Scholz: Investigations on Graphitoxyd, IV. Comparison of the presentation methods for graphitoxyd . In: Justus Liebig's Annals of Chemistry. 691, 1966, pp. 1-8. doi: 10.1002 / jlac.19666910102 .
  7. ↑ A. Lerf et al. : Structure of graphite oxide revisited. In: Journal Of Physical Chemistry B. 102, No. 23, 1998, pp. 4477-4482, doi: 10.1021 / jp9731821 .
  8. ↑ a b c H. C. Schniepp et al. : Functionalized Single Graphene Sheets Derived from Splitting Graphite Oxide. In: American J. of Physical Chemistry, Series B. 110, 2009, p. 8535, doi: 10.1021 / jp060936f .
  9. ↑ a b c D. Pandey, R. Reifenberger, R. Piner: Scanning probe microscopy study of exfoliated oxidized graphene sheets . In: Surface Science. 602, No. 9, 2008, pp. 1607-1613, doi: 10.1016 / j.susc.2008.02.025 .
  10. ↑ Daniel R. Dreyer, Sungjin Park, Christopher W. Bielawski, Rodney S. Ruoff: The chemistry of graphene oxide . In: Chemical Society Reviews . tape 39 , no. 1 , December 14, 2009, p. 228-240 , doi : 10.1039 / b917103g .
  11. ^ Siegfried Eigler, Christoph Dotzer, Ferdinand Hof, Walter Bauer, Andreas Hirsch: Sulfur Species in Graphene Oxide . In: Chemistry - A European Journal . tape 19 , no. 29 , July 15, 2013, p. 9490–9496 , doi : 10.1002 / chem.201300387 ( wiley.com [accessed May 14, 2019]).
  12. ↑ KA Mkhoyan et al. : Atomic and Electronic Structure of Graphene Oxide. Nano letters. 9, No. 3, 2009, pp. 1058-1063, doi: 10.1021 / nl8034256 .
  13. ↑ AV Talyzin et al. : Nanocarbons by High-Temperature Decomposition of Graphite Oxide at Various Pressures. In: J. Phys. Chem. C. 113, No. 26, 2008, pp. 11279-11284, doi: 10.1021 / jp9016272 .
  14. ↑ a b C. Gomez-Navarro et al. : Electronic Transport Properties of Individual Chemically Reduced Graphene Oxide Sheets . In: Nano Letters. 7, No. 11, 2007, p. 3499, doi: 10.1021 / nl072090c .