Graphene oxide (GO), also referred to as graphite/graphitic oxide, is obtained by treating graphite with oxidisers, and results in a compound of carbon, oxygen, and hydrogen in variable ratios.
The structure and properties of GO are much dependent on the particular synthesis method and degree of oxidation. With buckled layers and an interlayer spacing almost two times larger (~0.7 nm) than that of graphite, it typically still preserves the layer structure of the parent graphite.
Graphite oxides demonstrate considerable variations of properties depending on degree of oxidation and synthesis method.[9] For example, temperature point of explosive exfoliation is generally higher for graphite oxide prepared by Brodie method compared to Hummers graphite oxide, the difference is up to 100 degrees with the same heating rates.[10] Hydration and solvation properties of Brodie and Hummers graphite oxides are also remarkably different.
GO absorbs moisture proportionally to humidity and swells in liquid water. GO membranes are vacuum-tight and impermeable to nitrogen and oxygen, but permeable to water vapours. The ability to absorb water by GO depends on the particular synthesis method and also shows a strong temperature dependence.
GO is considered as an electrical insulator for the disruption of its sp2 bonding networks. However, by manipulating the content of oxygen-containing groups through either chemical or physical reduction methods, the electrical and optical properties of GO can be dynamically tuned. To increase the conductivity, oxygen groups are removed by reduction reactions to reinstall the delocalised hexagonal lattice structure. One of the advantages GO has over graphene is that it can be easily dispersed in water and other polar organic solvents. In this way, GO can be dispersed in a solvent and reduced in situ, resulting in potentially monodispersed graphene particles.
Due to its unique structure, GO can be functionalised in many ways for desired applications, such as optoelectronics, drug delivery, chemical sensors, membrane filtration, flexible electronics, solar cells and more.
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. He reported synthesis of "paper-like foils" with 0.05 mm thickness. In 1957 Hummers and Offeman developed a safer, quicker, and more efficient process called Hummers' method, using a mixture of sulfuric acid H2SO4, sodium nitrate NaNO3, and potassium permanganate KMnO4, which is still widely used, often with some modifications.
