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Common methods for dispersing graphene |
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1. Mechanical exfoliation |
Graphene sheets are directly peeled off from larger crystals using adhesive tape, and this process is repeated.
Friction with a material is used to exfoliate bulk graphite, resulting in flake-like crystals that contain single-layer graphene.
Disadvantages: Low production yield, small area, difficult to control size precisely, low efficiency, and not suitable for large-scale preparation. |
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2. Chemical vapor deposition |
A gas or gases containing carbon, usually a low-carbon organic gas, is introduced into a vacuum reactor. The gas is then decomposed and carbonized at high temperatures, resulting in the growth of a carbon monolayer on the surface of a substrate.
Disadvantages: The six-membered honeycomb crystal structure of graphene cannot be completely graphitized, and its quality is not as good as that of mechanical exfoliation. The high cost and stringent equipment requirements limit its large-scale production, and a catalyst needs to be added to reduce the purity of graphene. |
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3. Epitaxial growth method |
One method is to heat single crystal 6H-SiC to remove Si, and then grow graphene epitaxially on the surface of SiC crystal. Graphene is in contact with the Si layer, and its conductivity is affected by the substrate. Another method is to use the trace carbon content in a metal single crystal. By high-temperature annealing under ultra-high vacuum conditions, carbon elements in the metal single crystal precipitate graphene on the surface of the metal single crystal.
Drawbacks: The thickness of the graphene film is uneven and difficult to control. The generated graphene is tightly attached to the substrate, which affects the characteristics of graphene. At the same time, it needs to be grown under ultra-high vacuum and high-temperature conditions, which are extremely harsh conditions. The equipment requirements are high, making it impossible to achieve large-scale, controllable preparation of graphene. |
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4. Graphene oxide reduction method |
Graphene oxide is generally obtained by strong acid oxidation of graphite. There are three main methods for preparing graphene oxide: Brodie method, Staudenmaier method, and Hummers method, in which ultrasound assistance is required for graphene dispersion in the Hummers method.
Features: Hummers method graphene dispersion: simple method, short processing time, large processing capacity, safe and pollution-free, is currently the most commonly used method. |
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5. Ultrasound-assisted method |
Ultrasonic graphene dispersion system uses ultrasound-assisted Hummers method to prepare graphene oxide, which is a high-frequency ultrasound vibration added to the liquid medium. Since ultrasound is a mechanical wave that is not absorbed by molecules, it causes molecular vibrational motion during propagation. Under cavitation effects, such as high temperature, high pressure, microjet, and strong vibration, the average distance between molecules increases due to vibration, which ultimately leads to molecular fragmentation. It can more effectively increase the interlayer spacing of graphene oxide. With the increase of ultrasound power, the interlayer spacing of the obtained graphene oxide tends to expand.
The pressure released by ultrasound instantaneously destroys the van der Waals force between graphene layers, making graphene less likely to aggregate together. Graphene oxide with larger interlayer spacing is not only conducive to the insertion of other molecules, atoms, etc. to form graphene oxide intercalated composite materials, but also easy to be peeled off into single-layer graphene oxide, laying a foundation for further preparation of single-layer graphene. |