The Age of SWCNT and MWCNT innovations
SWCNT (Single-walled carbon nanotubes) and MWCNT (Multi-walled carbon nanotubes) innovations
Carbon nanotubes (CNTs) are cylindrical structures consisting of carbon atoms with unique physical, chemical and mechanical properties. They can be single-walled (SWCNT) and multi-walled (MWCNT), which causes their diverse applications in science and technology. SWCNT consist of a single layer of graphene rolled up into a tube, whereas MWCNT have several such layers nested inside each other. The differences in structure between SWCNT and MWCNT lead to different properties and applications.
Single-walled carbon nanotubes (SWCNT)
Structure and features of SWCNT
Single-walled carbon nanotubes are cylinders with a diameter of about one nanometer (Fig.1), consisting of a single layer of graphene rolled into a tube. Depending on the method of folding graphene, SWCNT can have different types of chirality: zigzag, armchair and chiral. These configurations determine their electronic properties, making them metallic or semiconductor.
Methods of obtaining SWCNT
Single-walled carbon nanotubes can be synthesized by various methods, including chemical deposition from the gas phase (CVD), arc discharge and laser ablation. CVD is the most common method where carbonaceous gas (e.g. methane) decomposes on a catalyst at high temperatures to form nanotubes. Arc discharge and laser ablation are also used, but they are less economical and require
more sophisticated equipment.
SWCNT Properties
Mechanical properties: SWCNT has the highest strength and modulus of elasticity, surpassing traditional materials such as steel and Kevlar. They are resistant to mechanical stress and deformation, which makes them ideal for use in materials requiring high strength with low weight.
Electronic properties: Depending on the chirality, single-walled carbon nanotubes can be conductors or semiconductors. Semiconductor MTPs have the potential to create nanoscale transistors that can replace silicon transistors in the future. This opens up opportunities for creating more powerful and miniaturized electronic devices.
Thermal conductivity: SWCNT have high thermal conductivity, which makes it possible to effectively remove heat in microelectronic devices, preventing them from overheating. This property is especially important for the development of new cooling systems in electronics.
Optical properties: SWCNT have unique optical properties such as photoluminescence and the ability to absorb light over a wide range of wavelengths. This makes them suitable for use in optoelectronic devices such as photodetectors and solar panels.
SWCNT is used in various fields:
Electronics: SWCNT are used to create transistors, sensors and other electronic components. They can significantly reduce the size and increase the performance of electronic devices. Examples include flexible displays, wearable devices, and transparent conductive films.
Materials: Used in composites to increase their strength and lightness SWCNT is added to polymers, metals and ceramics, improving their mechanical properties and reducing weight. This is important for the aerospace and automotive industries, where the weight of materials is critical.
Medicine: Used to create biosensors and deliver medicines. SWCNT can be functionalized for specific interaction with biomolecules, which allows them to be used for the diagnosis of diseases and targeted delivery of drugs to cells.
Energy: Used in the creation of supercapacitors and lithium-ion batteries. SWCNT increase the capacity and charging rate of such devices, which leads to the creation of more efficient and durable energy sources.
Multi-walled Carbon Nanotubes (MWCNT)
Structure and features of MWCNT
Multi-walled Carbon Nanotubes consist of several concentric layers of graphene embedded in each other (Fig. 2). The diameter of such nanotubes is much larger than that of SWCNT and can reach several tens of nanometers. The number of layers varies from two to several dozen. MWCNT may have a more complex internal structure, which affects their properties and application.
Methods of obtaining of MWCNT
Multi-walled Carbon Nanotubes can also be synthesized by CVD, arc discharge, and laser ablation methods. The process of MWCNT synthesis is similar to that of OSUNT, however, the temperature and composition of the catalysts can be adjusted to obtain multilayer structures. In particular, catalysts with larger particles are often used for the synthesis of MWCNT, which contribute to the formation of multilayer structures.
MWCNT Properties
Mechanical properties: MWCNT have high strength and resistance to deformation. They can withstand significant mechanical loads and bends, which makes them ideal for use in structural materials.
Electronic properties: Unlike SWCNT, Multi-walled Carbon Nanotubes have a more complex electronic structure, which makes them less suitable for use as transistors. However, they can be used in other electronic components where their complex structure is not a disadvantage.
Thermal conductivity: Although the thermal conductivity of MWCNT is lower than that of SWCNT, it still remains high enough for use in thermal interfaces. This allows them to be used in cooling systems where efficient heat dissipation is required.
Optical properties: MWCNT have less pronounced optical properties compared to SWCNT. However, they can still be used in devices where optical performance is not critical.
MWCNT is also widely used in various fields:
Materials: Used in composites to increase their strength and resistance to wear. MWCNT are added to various matrices to improve their mechanical characteristics and durability. This is important for the production of high-strength and durable materials in construction and mechanical engineering.
Energy: Used in the production of electrodes for batteries and supercapacitors. MWCNT provide improved conductivity and increase the capacity of energy devices, which makes it possible to create more efficient and durable batteries and capacitors.
Catalysis: MWCNT are used as catalysts in various chemical reactions. Their large surface area and unique structure make them effective catalysts for hydrogenation and oxidation reactions.
Adsorbents: Due to their large surface area, MWCNT are effectively used for the adsorption of various substances. They can be used to purify water and air from pollutants, as well as to store gases such as hydrogen.
Carbon nanotubes, both single-walled and multi-walled, are unique materials with a wide range of properties and applications. SWCNT, due to its electronic and thermal characteristics, are used in high-tech fields such as electronics and medicine. MWCNT, having high strength and stability, are widely used in the production of composite materials and energy devices.
The prospects for using CNTs include the further development of nanotechnology, the creation of new types of materials and devices, as well as the improvement of existing technologies. MWCNT can play a key role in the development of microelectronics and nanoelectronics, while MWCNT will continue to find applications in various industrial and energy projects. The development of synthesis methods and the improvement of CNT characteristics will open up new opportunities for their application in the future. It is expected that further research and innovation in the field of CNT will contribute to the creation of new technologies and materials that will change our daily lives.