Graphene

Graphene

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  • Graphene

    Graphene is a new carbon nanomaterial that was first discovered in 2004. Under the action of external forces, the bonding bonds between graphene carbon atoms will be deformed and the structure is stable. Therefore, graphene has very good strength performance. Crystal lattice of graphene is carbon hexagons with stable structure, and the thermal conductivity of graphene is excellent. Due to the special structure, graphene has strong thermal stability which does not change with temperature. The ideal graphene structure is a planar hexagonal lattice, which can be seen as a layer of stripped graphite molecules. In graphene structure, each carbon atom is SP2 hybridized, and it can contribute a remaining electron to form a large π bond. The π electrons can move freely, giving graphene good electrical conductivity. Moreover, at room temperature, the electron transfer rate is much faster than ordinary conductive materials. Furthermore, graphene is only one atom thick and has a light transmittance of 97.7%, which is very transparent. From an optical point of view, graphene is a "transparent" conductor that could very well replace liquid crystal materials.

    Applications:

    • Sensor field: With the unique two-dimensional layered structure, graphene has a large specific surface area, which is necessary for making highly sensitive sensors. In addition, graphene also has a unique electronic structure. When certain gas molecules are attached to graphene, the electronic structure of graphene can be changed, resulting in rapid and significant changes in electrical conductivity.
    • An example of graphene designed as a gas sensor.Figure 1. An example of graphene designed as a gas sensor.

    • Transistor field: Graphene is a zero-gap semiconductor, showing good properties and excellent electrical conductivity. The conduction rate of electrons in graphene is much higher than that of ordinary semiconductors. Transistors made from graphene have the advantages of small, inexpensive, faster and energy conservation. In addition, graphene transistors can work well at room temperature and they can be easily designed in any structure.
    • The others: Graphene also can be used in many other fields including energy storage, supercapacitors, transparent electrodes, superconducting materials, field emission materials, composite materials and the others. For example, graphene has the advantages of small mass, high chemical stability and large specific surface area, making it the best candidate for hydrogen storage materials.

    An example of graphene used as hydrogen storage material.Figure 2. An example of graphene used as hydrogen storage material.

    Classification:

    Graphene can be divided into single-layer graphene, double-layer graphene, few-layer graphene and multi-layer graphene.

    • Single-layer graphene: Single-layer graphene refers to a two-dimensional carbon material consisting of a layer of carbon atoms that are periodically densely packed together in a benzene ring structure.
    • Double-layer graphene: Double-layer graphene refers to a two-dimensional carbon material consisting of two layers of carbon atoms stacked in a benzene ring structure.
    • Few-layer graphene: Few-layer graphene refers to a two-dimensional carbon material consisting of 3-10 layers of carbon atoms that are periodically densely packed together in a benzene ring structure.
    • Multi-layer graphene: Multi-layer graphene refers to a two-dimensional carbon material consisting of over 10 layers of carbon atoms that are periodically densely packed together in a benzene ring structure.

    References

    1. Singh S B, De M. Thermally exfoliated graphene oxide for hydrogen storage[J]. Materials Chemistry and Physics, 2019, 239:122102.
    2. Wu Y, Yao B, Yu C, et al. Optical Graphene Gas Sensors Based on Microfibers: A Review[J]. Sensors, 2018, 18(4):941.
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