L’graphite oxide, formerly called graphitic oxide or graphitic acid, is an inorganic compound of carbon, oxygen and hydrogen in varying atomic ratios. It is obtained by processing the graphite (Graphite is a mineral which is, with diamond, lonsdaleite and chaoite, one…) with strong oxidants. The most oxidized product is the solid yellow (There are (at least) five definitions of yellow that refer to roughly the same…) with a C:O ratio between 2.1 and 2.9 which retains the layer structure of graphite but with much wider and irregular interlayer spaces.
The solid compound disperses in basic solutions producing monomolecular layers, known asoxide graphene (This article should not be confused with the article grapheme.) by analogy with graphene, the monolayer form of graphite. Graphene oxide was used to prepare a species (In the life sciences, the species (from the Latin species, “type”…) of paper (Paper (from the Latin papyrus) is a material made from fibers…) very strong and has recently attracted considerable interest as a possible intermediate for the manufacture of graphene. However, this objective remains difficult to achieve since the graphene obtained by this method has many chemical and structural defects.
History and preparation
L’graphite oxide (Graphite oxide, formerly called graphitic oxide or graphitic acid, is a…) was originally prepared by the chemist (A chemist is a scientist who studies chemistry, i.e. the science of…) from Oxford, Benjamin C. Brodie (in) in 1859, by treating graphite with a solution of potassium chlorate (Potassium chlorate is a chemical compound with the formula KClO3. When pure, it is…) in L’nitric acid (Nitric acid, sometimes called nitric acid, is a liquid chemical compound…) smoking. In 1957, William S. Hummers and Richard E. Offeman developed a safer, faster, and more effective method using a mixed (A mixture is an association of two or more solid, liquid or gaseous substances…) ofsulfuric acid (Sulfuric acid (formerly called oil of vitriol or vitriol) is a compound…)H2N/A4of nitrate (Nitrates (formerly called nitre, often synonymous with saltpeter) are the salts of…) of sodium (Sodium is a chemical element, symbol Na and atomic number 11. It is a…)NaNO3 and of Potassium permanganate (Potassium permanganate is an inorganic salt with the chemical formula KMnO4. It is composed…)KMnO4which is still widely used in 2010. In 2009, a mixture of H2N/A4 and KMNO4 was used to open in the meaning (SENS (Strategies for Engineered Negligible Senescence) is a scientific project which aims to…) of the length (The length of an object is the distance between its two furthest extremities…) nanotubes of carbon (Carbon is a chemical element of the family of crystallogens, symbol C,…) which produces microscopic flat ribbons of graphene of a few atoms (An atom (from the Greek ατομος, atomos, “that one cannot…) wide and whose edges are “capped” by atoms ofoxygen (Oxygen is a chemical element of the family of chalcogens, of…) (=O) or hydroxyl groups (–OH).
Graphite oxide has generated a lot of interest as a possible route for the large-scale production and manipulation of graphene, a material (A material is a material of natural or artificial origin that man shapes…) with extraordinary electronic properties. Graphene oxide is itself a insulating (An insulator is a material that prevents the exchange of energy between two systems….)almost a semiconductor (A semiconductor is a material that has the electrical characteristics of a…)with a differential conductivity between 1 and 5×10-3 S/cm at a voltage of 10 V. However, being highly hydrophilic, graphene oxide disperses very well in thewater (Water is a ubiquitous chemical compound on Earth, essential for all…) and breaks up into macroscopic flakes, most one layer thick. In theory (The word theory comes from the Greek word theorein, which means “to contemplate, to observe,…)the chemical reduction of these flakes would give a suspension (The act of suspending particles In chemistry, suspension designates a dispersion of…) of graphene flakes.
A partial reduction can be obtained by treating the dispersed graphene oxide, with hydrate ofhydrazine (Hydrazine (or Diazene), with chemical formula N2H4 and formula…)H2N–NH2 at 100°C for 24 hours (Time is a unit of measurement:) or by exposure to a strong light pulse such as that from a camera flash. However, the graphene obtained with this method is below 10 S/cm and the mobility of charge (The payload represents what is actually…) is between 2 and 200 cm2/(V s) for holes and between 0.5 and 30 cm2/(V s) for electrons. These values are much larger than those of the oxide but they are still a few orders of magnitude lower than those of pristine graphene. Inspections at atomic force microscope (The atomic force microscope (or AFM for atomic force microscope) is a derivative of the microscope…) of graphene oxide show that the bridging oxygens distort the carbon layer, creating a pronounced intrinsic roughness in the layers that persists after reduction. These defects are also highlighted in the Raman spectrum of graphene oxide.
The structure and properties of graphite oxide depend on the particular synthesis method and the degree (The word degree has several meanings, it is notably used in fields…) of oxidation. It generally retains the layer structure of graphite, but the layers are hazy and the interlayer spacing is about twice as large (~0.7nm (7 Å)) as that of graphite. Strictly speaking, the term “oxide” is incorrect, but it has established itself historically. In addition to epoxide (oxygen atom bridging) groups, other functional groups found experimentally are carbonyl (The carbonyl function, C=O, where a carbon atom is connected to an oxygen atom by a…) (=CO), hydroxyl (-OH) and phenol groups attached on both sides. There is evidence of “deformation” (deviation from flatness) of the layers. The detailed structure is not yet understood due to the strong disorder and irregular stacking of the layers.
The graphene oxide layers are 1.1 ± 0.2 nm thick. The microscopy (Microscopy is the observation of a sample (placed in a microscopic preparation…) at tunnel effect (The tunnel effect refers to the property that a quantum object has of crossing…) shows the presence of local regions where the oxygen atoms are arranged in a regular rectangular arrangement with lattice parameters of 0.27 nm × 0.41 nm. The edges of each layer are finished with groups carboxyl (In organic chemistry, a carboxyl group is a functional group composed of an atom of…) and carbonyl. The photoelectron spectrometry X (X-ray photoelectron spectrometry, or X-ray induced photoelectron spectrometry…) shows the presence of carbon atoms included in the aromatic and non-oxygenated rings (284.8 eV), of C–O (286.2 eV), of C=O (287.8 eV) and of OC=O ( 289.0 eV).
Graphite oxide hydrates readily, leading to a visible increase in interlayer distance (up to 1.2 nm (12 Å) in the saturated state). Additional water is also absorbed in the interlayer space, this being due to effects of high pressure (Pressure is a fundamental physical notion. You can think of it as a reported force…) induced. The solid material thus absorbs thehumidity (Humidity is the presence of water or water vapor in the air or in a substance…) of the’air (Air is the mixture of gases that make up the Earth’s atmosphere. It is odorless and…) ambient in proportion to the humidity. Complete removal of water from this product is difficult even when heated to 60–80°C which leads to its decomposition (In biology, decomposition is the process by which organized bodies, whether they…) partial and its degradation.
Graphite oxide exfoliates and decomposes when rapidly heated to moderately high temperatures (~280–300°C), also forming finely divided amorphous carbon, somewhat similar to activated carbon.