Graphite Oxide - Structure

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 (~0.7 nm) than that of graphite. Strictly speaking "oxide" is an incorrect but historically established name. Besides oxygen epoxide groups (bridging oxygen atoms), other functional groups experimentally found are: carbonyl (=CO), hydroxyl (-OH), phenol groups attached to both sides. There is evidence of "buckling" (deviation from planarity), folding and cracking of graphene oxide sheets upon deposition of the layers on a choice of substrate. 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. 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 The edges of each layer are terminated with carboxyl and carbonyl groups. 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).

Graphite oxide is easily hydrated, resulting in a distinct increase of the inter-planar distance (up to 1.2 nm 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. Similar to water, graphite oxide also easily incorporates other polar solvents, e.g. alcohols. Separation of graphite oxide layers is proportional to the size of alcohol molecule; additional monolayer is inserted into the structure at high pressure conditions.

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.