Benutzer:Drahkrub/Übersetzung
Graphitoxid, früher auch Graphitsäure, ist eine nichtstöchiometrische Verbindung aus den chemischen Elementen Kohlenstoff, Sauerstoff und Wasserstoff, die aus Graphit durch die Einwirkung starker Oxidantien gebildet wird. Bei einem Verhältnis von C:0 zwischen 2,1 bis 2,9 (höchstmögliche Oxidationsstufe) bildet sie einen gelben Feststoff mit einer Schichtenstruktur wie Graphit wenn auch größeren und unregelmäßigen Abständen zwischen den Schichten.[1]
Graphitoxid dispergiert in basischen Lösungen zu Graphenoxid, benannt analog zu Graphen, der einlagigen Form von Graphit.[2]
Aus Graphenoxid kann ein hochfester, papierähnlicher Werkstoff hergestellt werden, der in jüngster Zeit als mögliches Zwischenprodukt für die Herstellung von Graphen interessant wurde. Allerdings (Stand 2010) zeigt auf diesem Weg hergestelltes Graphen noch zahlreiche chemische und strukturelle Unregelmäßigkeiten.
Geschichte und Darstellung
Die erste Darstellung von Graphitoxid gelang 1859 dem britischen Chemiker Benjamin Collins Brodie jr., der Graphit mit einer Mischung aus Kaliumchlorat und rauchender Salpetersäure behandelte.[3] Schneller und ungefährlicher bei einer verbesserten Ausbeute ist das 1957 von William S. Hummers and Richard E. Offeman beschriebene Verfahren; sie verwendeten eine Mischung aus Schwefelsäure H2SO4, Natriumnitrat NaNO3, und Kaliumpermanganat KMnO4. Diese Methode ist bis heute (Stand 2009) im Einsatz.[1]
In jüngster Zeit wurde eine Mischung aus H2SO4 und KMnO4 benutzt, um Kohlenstoffnanoröhren in Längsrichtung aufzuschneiden, dabei entstehen mikroskopisch kleine, flache Graphenbänder mit einer Breite von wenigen Atomen, die an den Enden eine Kappe aus Sauerstoffatomen (=O) oder Hydroxylgruppen tragen (-OH).[4]
Struktur
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 Å) 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 Å 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.
Anwendungen
Graphenherstellung
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 cm2/(V·s) for holes and 0.5 to 30 cm2/(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]
Verwandte Materialien
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.
Einzelnachweise
- ↑ 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 Referenzfehler: Ungültiges
<ref>-Tag. Der Name „humm“ wurde mehrere Male mit einem unterschiedlichen Inhalt definiert. - ↑ 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
- ↑ Benjamin C. Brodie (1859), On the Atomic Weight of Graphite. Proceedings of the Royal Society of London, volume 10, S. 249.
- ↑ 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
- ↑ 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
- ↑ 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
- ↑ 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
- ↑ 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
- ↑ http://www.youtube.com/watch?v=bl45J6iw3tE
- ↑ 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
- ↑ a b c d e f C. Gomez-Navarro et al. (2007). Nano Letters, volume 7, issue 11, page 3499 doi:10.1021/nl072090c
- ↑ 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