Nanotubes

Nanotubes have high hardness and heat resistance, as well as excellent electrical conductivity and superconductivity at low temperatures. Carbon nanotubes are the most widely used nanotube materials. Each carbon atom on the tube is sp² hybridized and combined with each other by a carbon-carbon σ bond to form a honeycomb structure composed of hexagons.

Figure 1. Structure of carbon nanotubes

Applications:

When the material scale is reduced to the nanometer level, it will produce completely invisible or particularly excellent performance on the macroscale, and will produce self-assembly effects, small size effects, surface effects, and quantum effects. Because nanotubes are hollow tubes with large internal surface area and stable properties, they are widely used in energy storage, gas storage, adsorption, catalysis and other fields.

• Gas storage: The hollow part of the nanotube is a very good micro-container, which can adsorb various molecules of suitable size and inner diameter, and can store various gases including hydrogen. Hydrogen can be filled in the form of liquid or solid inside the nanotube and the second-class pores between the nanotube bundles. Pure nanotubes with high surface activity are conducive to hydrogen storage.
• Electronic field: Nanotubes can be used as wires and switch box memory elements in microelectronic devices. In addition, the nanotube has good conductivity, which can avoid the negative influence of the electrode material on the battery due to resistance polarization. Therefore, using nanotube as cathode material is beneficial to improve the discharge capacity, cycle life and dynamic performance of lithium battery.
• Biomedical field: The hollow tube body of nanotubes can contain bio-specific molecules and drugs, and its excellent cell-penetrating properties make it useful as a carrier to transport bioactive molecules and drugs into cells or tissues. Carbon nanotubes are insoluble in any solvent, while functional modification can improve the solubility and biocompatibility of carbon nanotubes, so they can carry proteins, peptides, nucleic acids, drugs and other molecules. As carriers in cancer therapy, bioengineering, gene therapy and other fields, they are showing excellent application prospects.
• Catalyst carrier: Nanotubes are ideal catalyst carrier materials because of their small size, large specific surface area, different bond states on the surface and the interior of the particles, and incomplete coordination of surface atoms. The research of carbon nanotubes as catalyst support materials mainly focuses on the method of loading active components on the nanotubes, the influence of the electrical properties of the nanotubes on the catalysis, the influence of the unique tubular structure of the nanotubes on the catalysis, and the influence of the hydrogen storage properties of the nanotubes on the catalysis.

Production Processes:

• Arc method: This method is in a reaction chamber filled with a certain pressure of inert gas, in which a pure graphite electrode is used as the cathode, and a graphite electrode filled with catalyst is used as the anode. With high temperature caused by the arc, the raw material of nanotubes can be prepared by structural rearrangement and deposition under the action of a catalyst.
• Chemical vapor deposition method: This method is to gasify the raw materials and crack the nanotubes under the action of a catalyst. The nanotubes prepared by this method have good quality, high purity, uniform tube diameter distribution, and clean tube walls, and are particularly suitable for preparing nanotube reinforced metal composite materials.

References:

1. C. N. R. Rao and Manashi Nath. Inorganic nanotubes [J]. Dalton Trans., 2003, 1-24.
2. Richard K. F. Lee, Barry J. Cox and James M. Hill. The geometric structure of single-walled nanotubes [J]. Nanoscale, 2010, 2, 859–872.
3. Marco Serra, Raul Arenal and Reshef Tenne. An overview of the recent advances in inorganic nanotubes [J]. Nanoscale, 2019, 11, 8073–8090.