What is Carbon Nanotube?
Carbon nanotubes, also known as bucky tubes, are one-dimensional quantum materials with a special structure. It is mainly composed of carbon atom layers of graphite curled into cylindrical carbon tubes with small radial dimensions. The tube wall of carbon nanotubes is generally composed of carbon hexagonal rings, and some pentagonal carbon rings and heptagonal carbon rings exist in the bending parts of carbon nanotubes. The diameter of carbon tubes is generally between 1nm and 30nm, and the length can reach the micrometer level. The needle-shaped carbon tubes can be divided into single-walled carbon nanotubes and multi-walled carbon nanotubes according to the number of layers of the tube wall. As a kind of nano-scale small particles, carbon nanotubes, like other nanoparticles, exhibit small size effects, surface and interface effects and quantum size effects. These effects make carbon nanotubes have good mechanical properties, strong hardness, good electrical and thermal conductivity.
Figure 1. The structure of carbon nanotube materials
What are the Application of Carbon Nanotubes?
- Carbon Nanotubes for Composite Material Field: Since the carbon atoms in the carbon nanotubes adopt sp2 hybridization, the s orbital composition in the hybridization is relatively large, so that the carbon nanotubes have high modulus and high strength. The tensile strength of carbon nanotubes can reach 50-200GPa, which is 100 times that of steel, but the density is only 1/6 of that of steel. The elastic modulus of carbon nanotubes can reach 1TPa, which is comparable to that of diamond and about 5 times that of steel. For a carbon nanotube with a single-walled ideal structure, the tensile strength is about 800 GPa. Although the structure of carbon nanotubes is similar to that of polymer materials, its structure is much more stable than that of polymer materials. Using other materials as the matrix and carbon nanotubes to make composite materials can make the composite material show good strength, elasticity, fatigue resistance and isotropy, which greatly improves the performance of the composite material. In addition, carbon nanotubes have high thermal conductivity. As long as a small amount of carbon nanotubes are doped in the composite material, the thermal conductivity of the composite material will be greatly improved.
- Carbon Nanotubes for Electronic Field: The p electrons of carbon atoms on carbon nanotubes can form a wide range of delocalized π bonds, which give them some special electrical properties. In terms of electrical conductivity, carbon nanotubes can be metallic or semiconducting, and even different parts of the same carbon nanotube will exhibit different electrical conductivity. Antennas made of carbon nanotubes can receive light waves just like antennas that receive radio waves. Radio waves excite electrons into an electric current. This response, amplification and modulation of radio waves is the basis of radio and television broadcasting, enabling the transmission of sound and images. The nano-antenna can also be a high-efficiency solar energy converter, which can greatly improve the efficiency of converting solar energy into electricity.
- Carbon Nanotubes for New Energy Field: The hollow structure and good adsorption properties of carbon nanotubes make them suitable for use as hydrogen storage materials in the field of new energy. Hydrogen-adsorbed carbon nanotubes can be used to fabricate fuel cells and serve as a continuous and stable source of hydrogen. In addition, the super nano carbon fiber battery prepared by using carbon nanotubes is light in weight, only 1/10 of the weight of lead-acid batteries, and only 1/16 of the volume of ordinary batteries. It is widely used in electric vehicles, submarines, electric locomotives and other electric power machinery that need large energy storage and light weight.
- Deepmala Gupta, Bhasker P. Choudhary, Nakshatra B. Singh, N. S. Gajbhiye. Carbon nanotubes: an overview [J]. Emerging Mater. Res, 2013, 2(6), 299-337.