Micromechanical stripping method
The graphene sheets were directly peeled off from the larger crystals with tape, and the process was repeated.
Using a material to rub with pyrolytic graphite that is expanded or introduced into defects, the surface of the bulk graphite produces flake-like crystals, and the flake-like crystals contain a single layer of graphene.
Disadvantages: Graphene has low yield, small area, difficult to control size, low efficiency, and cannot be prepared on a large scale.
2. Chemical vapor deposition
Passing one or more gaseous substances containing carbon (usually low carbon organic gases) into a vacuum reactor to decompose carbonized gas (usually a low carbon organic gas) on the surface of the substrate by high temperature The process of growing a simple substance of carbon.
Disadvantages: The hexagonal honeycomb crystal structure of graphene cannot be completely graphitized, the quality is not as good as the micro-machine stripping method, the high cost and the demanding equipment requirements limit the large-scale preparation of graphene, and the addition of catalyst to reduce graphene. purity.
3. Crystal epitaxial growth method
One is to remove Si by heating single crystal 6H-SiC to epitaxially grow graphene on the surface of SiC crystal. The graphene is in contact with the Si layer, and the conductivity of the graphene is affected by the substrate. The other is to utilize a trace amount of carbon in the metal single crystal, and the carbon in the metal is on the surface of the metal single crystal by high temperature annealing under ultra-high vacuum. Graphene is precipitated.
Disadvantages: The thickness of the graphene film is not uniform and difficult to control. The resulting graphene is closely adhered to the substrate and is difficult to peel off, which may affect the characteristics of graphene. At the same time, it needs to be grown under ultra-vacuum and high temperature conditions. The conditions are extremely harsh, the equipment requirements are high, and large-scale, controllable graphene can not be realized.
4. Graphite reduction method
Graphene oxide is generally obtained by oxidation of graphite with a strong acid. There are mainly three methods for preparing graphite oxide: Brodie method, Staudenmaier method and Hummers method, in which the Hummers method graphene dispersion needs to be ultrasonically assisted.
Features: Hummers method graphene dispersion: simple method, short time-consuming, large processing capacity, safe and pollution-free, is currently used.
5. Ultrasound assisted method
Ultrasonic graphene dispersion system uses ultrasonic assisted Hummers method to prepare graphene oxide, which is a medium containing high frequency ultrasonic vibration in liquid. Since ultrasound is a mechanical wave that is not absorbed by molecules, it causes vibrational movement of molecules during propagation. Under the effect of cavitation, that is, high temperature, high pressure, micro jet, strong vibration and other additional effects, the distance between molecules increases the average distance due to vibration, which eventually leads to molecular fragmentation. The spacing of the graphite oxide layer can be increased more effectively, and as the ultrasonic power is increased, the layer spacing of the obtained graphite oxide is expanded.
The instantaneous release of the ultrasonic pressure destroys the van der Waals force between the graphene layer and the layer, making graphene less likely to agglomerate together. Graphite oxide with larger interlayer spacing is not only beneficial to the formation of graphite oxide intercalation composites between other molecules, atoms and other intercalation layers, but also easy to be stripped into a single layer of graphite oxide, which lays a foundation for further preparation of single-layer graphene.