1, mechanical stripping method
Mechanical stripping method is a method to obtain graphene thin-layer materials by using the friction and relative motion between objects and graphene. The method is simple to operate, and the obtained graphene usually keeps a complete crystal structure. In 2004, two British scientists used transparent tape to peel off natural graphite layer by layer to obtain graphene, which was also classified as mechanical stripping method. This method was once considered to be inefficient and unable to mass production.
In recent years, the industry has made a lot of research and development innovations in the production methods of graphene. At present, several companies in Xiamen, Guangdong and other provinces and cities have overcome the production bottleneck of low-cost large-scale preparation of graphene, using mechanical stripping method to industrially produce graphene with low cost and high quality.
2. Redox method
Oxidation-reduction method is to oxidize natural graphite by using chemical reagents such as sulfuric acid and nitric acid and oxidants such as potassium permanganate and hydrogen peroxide, increase the spacing between graphite layers, and insert oxides between graphite layers to prepare GraphiteOxide. Then, the reactant is washed with water, and the washed solid is dried at low temperature to prepare graphite oxide powder. Graphene oxide was prepared by peeling graphite oxide powder by physical peeling and high temperature expansion. Finally, graphene oxide was reduced by chemical method to obtain graphene (RGO). This method is simple to operate, with high yield, but low product quality [13]. Oxidation-reduction method uses strong acids such as sulfuric acid and nitric acid, which is dangerous and requires a lot of water for cleaning, which brings great environmental pollution.
Graphene prepared by redox method contains rich oxygen-containing functional groups and is easy to modify. However, when reducing graphene oxide, it is difficult to control the oxygen content of graphene after reduction, and graphene oxide will be continuously reduced under the influence of the sun, high temperature in the carriage and other external factors, so the quality of graphene products produced by redox method is often inconsistent from batch to batch, which makes it difficult to control the quality.
At present, many people confuse the concepts of graphite oxide, graphene oxide and reduced graphene oxide. Graphite oxide is brown and is a polymer of graphite and oxide. Graphene oxide is a product obtained by peeling graphite oxide to a single layer, a double layer or an oligo layer, and contains a large number of oxygen-containing groups, so graphene oxide is non-conductive and has active properties, which will continuously reduce and release gases such as sulfur dioxide during use, especially during high-temperature material processing. The product after reducing graphene oxide can be called graphene (reduced graphene oxide).
3. (silicon carbide) SiC epitaxial method
SiC epitaxial method is to sublimate silicon atoms away from materials and reconstruct the remaining C atoms by self-assembly in ultra-high vacuum and high temperature environment, thus obtaining graphene based on SiC substrate. High-quality graphene can be obtained by this method, but this method requires higher equipment.
Post time: Jan-25-2021