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The Preparation Method of Graphene

wallpapers Industry 2020-08-18

The mechanical exfoliation method uses the friction and relative movement between an object and graphene to obtain a thin layer of graphene material. This method is simple to operate, and the obtained graphene usually maintains a complete crystal structure. In 2004, two British scientists used scotch tape to peel off the natural graphite layer by layer to get graphene. It was also classified as a mechanical peeling method. This method was once considered to be low in production efficiency and unable to industrialize mass production. This method can prepare micron-sized graphene, but its controllability is small, and it is difficult to achieve large-scale synthesis.

In 2016, Chinese scientists invented an efficient and straightforward green peeling technology to realize the large-scale preparation of few layers of graphene (the number of layers is 3.8±1.9) through the soft rolling transfer process between "ball-microball."

Redox method

The redox method is to oxidize natural graphite by using chemical reagents such as sulfuric acid, nitric acid, and oxidizing agents such as potassium permanganate and hydrogen peroxide increase the spacing between graphite layers and insert oxides between graphite layers to obtain graphite oxide (Graphite Oxide). Then, the reactant is washed with water, and the washed solid is dried at low temperatures to obtain graphite oxide powder. The graphite oxide powder is peeled off by physical peeling, high-temperature expansion, and other methods to obtain graphene oxide. Finally, the graphene oxide is chemically reduced to obtain graphene (RGO). This method is simple in operation and high in output, but the product quality is low. The oxidation-reduction process uses strong acids such as sulfuric acid and nitric acid, which is dangerous and requires a large amount of water for cleaning, which causes significant environmental pollution.

Graphene prepared by the redox method contains abundant oxygen-containing functional groups and is easy to modify. However, it isn't easy to control the reduced graphene's oxygen content when the graphene oxide is reduced. At the same time, the graphene oxide will be continuously reduced under the sun's influence and the high temperature in the carriage during transportation. Therefore, the redox method The quality of graphene produced is often inconsistent from batch to batch, and it isn't easy to control the quality.

Chemical vapor deposition

Chemical vapor deposition (CVD) uses carbon-containing organic gases as raw materials for vapor deposition to produce graphene films. This is the most effective way to produce graphene films. The graphene prepared by this method has extensive and high-quality characteristics, but the cost is relatively high at this stage, and the process conditions need to be further improved. Because the thickness of the graphene film is skinny, a large-area graphene film cannot be used alone and must be attached to macroscopic devices to be of value, such as touch screens, heating devices, etc.

Some scholars use the low-pressure vapor deposition method. It generates a single layer of graphene on the surface of Ir. Further research shows that this graphene structure can cross metal steps, and the continuous and micron-scale single-layer carbon structure is gradually increasing. Formed on the surface of Ir. Millimeter-level, single-crystal graphene is obtained by the method of surface segregation. Some scholars discovered Centimeter-level graphene and epitaxial growth of graphene on polycrystalline Ni film. The surface of a 300-nanometer thick Ni film was heated at 1000°C and exposed in a CH4 atmosphere at the same time. After a period of reaction Later, a large area of ​​a few layers of graphene film will be formed on the metal surface.

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Tag: Graphene