Applications of Carbon Nanotubes

The exceptional qualities of single-wall Carbon Nanotubes (CNTs), including their stiffness, strength, toughness, and extremely high thermal and electrical conductivity, are the result of the unique nature of its carbon combined with the molecular perfection. It is the only element in the periodic table that has an extended network of connections with itself. This leads to the first known molecule with metallic-type electrical conductivity, where each delocalized pi-electron provided by its donor atom is free to wander about the entire structure rather than staying with its donor atom. Moreover, the high-frequency carbon-carbon bond vibrations provide an intrinsic heat conductivity that is higher than even that of diamond.

A. Electronic Application of CNTs

1. Substitute for Traditional Materials

A lot of attention has been paid to carbon nanotube enabled nanocomposites as a very appealing substitute for traditional composite materials because of their mechanical, electrical, thermal, barrier, and chemical characteristics, like electrical conductivity, enhanced tensile strength, better heat deflection temperature, or flame retardancy. These materials claim to provide improved breaking strength and wear resistance, antistatic qualities, and weight savings. Advanced carbon nanotube composites, for example, are thought to be able to lower the weight of spaceships and airplanes by as much as 30%. Sports items (bike frames, tennis rackets, hockey sticks, golf clubs and balls, skis, kayaks, sports arrows) are already made of these composite materials.

2. In Catalysis

The remarkable surface area of carbon nanotubes and their capacity to bind almost any type of chemical species to their sidewalls are what make them so appealing for use in catalysis. Although CNTs have already been employed as catalysts in a number of pertinent chemical reactions, it can be challenging to regulate their catalytic activity.

3. In Transistors

Semiconducting single-walled carbon nanotubes are still seen as strong contenders for the next generation of ultra-scaled, high-performance thin-film transistors and opto-electronic devices that will replace silicon electronics, even in light of the emergence of graphene and other two-dimensional (2D) materials. Whether CNT transistors at sub-10 nm widths can provide performance advantages over silicon is one of the key questions.

Regarding the question of whether CNT transistors would continue to exhibit remarkable performance at extraordinarily scaled lengths, the nanoelectronics community has been divided on the subject. Some contended, and the limited theoretical investigations supported this view, that the very small effective mass of the carriers would lead to a tunneling phenomenon that would cause the devices to break down at about 15 nm.

Conversely, some individuals persisted in their belief that the incredibly thin single-walled carbon nanotube body, measuring just 1 nm in diameter, would enable superior transistor performance even in the sub-10 nm region.

Researchers have only produced encouraging experimental findings thus far, and there are still many obstacles to overcome before CNT transistors can be successfully integrated into large-scale chip production.

4. Good Thermal Conductivity

Outstanding mechanical, electrical, and heat conductivity qualities are possessed by CNTs. They are most likely the best conceivable electron field emitter. Since they are pure carbon polymers, they may be created and altered utilizing the well-known and incredibly complex chemistry of carbon. This provides the chance to modify their structure and maximize their solubility and dispersion. These exceptional qualities make CNTs potentially useful for a variety of purposes.

5. Field Emission Applications

For the gadget to function, the material supplies a strong source of electron beam. One of the better examples is the field emission scanning electron microscope (FESEM). Numerous substances function as sources of field emissions and are well-known for having good field emissions at low fields. High current density, high enhancement factor, strong stability, and low turn on electric field are all linked to CNTs. These characteristics allow the CNTs to be utilized in a variety of field emission display technologies.

6. Conductive Plastics

Plastics have made great strides in structural applications, but not in areas requiring electrical conductivity since they are excellent electrical insulators.

By adding conductive additives to plastics, such as carbon black and bigger graphite fibers (the kind used to produce tennis rackets and golf clubs), this weakness can be ruled out. However, the loading needed to provide the appropriate conductivity using conventional fillers is usually substantial, resulting in hefty components and, more noticeably, plastic parts with severely compromised structural qualities. It is commonly known that when fibre particle aspect ratio increases, the loading is necessary to get specific conductivity. Because they have the largest aspect ratio of any carbon fiber, CNTs are ideal for this purpose. Additionally, even at extremely low loadings, their innate desire to form ropes provides incredibly lengthy conductive channels.

7. Energy Storage

According to research, CNTs are the carbon material with the largest reversible capacity for application in lithium-ion batteries. Furthermore, CNTs are currently being promoted for use as supercapacitor electrode materials and are good materials for such applications.

Because of their inherent qualities, carbon nanotubes (CNTs) are the material of choice for electrodes in capacitors and batteries, two rapidly advancing technologies. CNTs have a very high surface area (~1000 m2/g), strong electrical conductivity, and-most importantly-a surface that is highly accessible to the electrolyte due to their linear design.

8. In Fuel Cell Components

They are useful as electrode catalyst supports in PEM fuel cells due to a number of characteristics, including high thermal conductivity and surface area. In addition to current collectors, they can also be employed in gas diffusion layers because of their high electrical conductivity. Because durability is crucial, carbon nanotubes (CNTs) with high strength and toughness-to-weight ratio may also be beneficial as composite parts in fuel cells used in transportation.

9. In Making Conductive Adhesives and Connectors

The precise characteristics that render carbon nanotubes (CNTs) appealing as conductive fillers for electromagnetic shielding, ESD materials, and other applications also make them appropriate for use in connectivity applications and electronics packaging, such as coaxial cables, potting compounds, adhesives, and other kinds of connectors.

10. In Molecular Electronics

A key component of nanotechnology, the concept of creating electronic circuits from molecules, the fundamental building blocks of materials, has gained momentum in the last five years. The connections between switches and other active devices become more and more crucial in any electronic circuit, but especially when sizes are reduced to the nanoscale. The best options for the connections in molecular electronics are CNTs because of their exact derivation, electrical conductivity, and geometry. Moreover, they have been demonstrated as switches.

11. CNTs as Thermal Materials

CNTs' unprecedented anisotropic thermal conductivity is paving the way for a number of heat-transfer-related applications. In electronics, more specifically sophisticated computing, where uncooled chips are now routinely beyond 100 °C, such a use can be discovered.

According to D. Walters it is a step toward producing incredibly effective heat conduits is the technology for aligned structures and ribbons of CNTs. Moreover, even at extremely low loadings, it has been shown that CNT-containing composites greatly boost their bulk heat conductivity.

12. CNTs Structural Composites

CNTs have superior mechanical qualities such strength, toughness, and stiffness in addition to their superior thermal and electrical conductivities. These characteristics open the door to a variety of uses that make use of them, such as sophisticated composites that require high values of one or more of these characteristics.

13. CNTs Fibers and Fabrics

Together with CNT composite fibers, pure CNT fibers have recently been proven and are developing quickly. Transmission line cables, body and vehicle armor, and woven textiles are just a few uses for these incredibly strong fibers.

Moreover, CNTs are used to make textiles stain-resistant. Carbon nanotube (CNT) is a very absorbing material with outstanding properties. Textile industries use carbon nanotubes (CNTs) and exhaust them in a variety of ways to create composites that are used as ballistic fabric impregnation, ballistic fabric growth, and, in the end, CNT-based fabrics. The textile industry has developed an intriguing subject for ongoing research because of carbon nanotubes (CNTs), which are thought to be a potential material for protective clothes due to their light weight, high strength, and great energy absorption capacity. CNT is a promising material for creating lightweight, multipurpose protective fabric.

The surface of the fiber covered with CNTs can thus perform multiple functions, such as being flame retardant, electrically conductive, and antimicrobial. Nanotechnology can create military-grade bulletproof suits with the aid of carbon nanotubes (CNTs).

14. CNT based Sensors

The majority of CNT-based sensors are field effect transistors (FETs); while CNT structures are strong and inert, charge transfer and chemical doping by different molecules have a significant impact on their electrical characteristics. In environmental applications, CNTs-FETs have been widely employed to detect chemicals, including greenhouse gasses.

CNTs must be functionalized in order for them to be selective for the intended analyte. The molecular recognition interactions between functionalism CNT and target analytes are the basis for several types of sensors. For instance, researchers have created flexible hydrogen sensors using single-walled carbon nanotubes embellished with palladium nanoparticles.

15. As Preservatives

Herbs that are prone to oxidation are dried using carbon nanotubes and nanohorns since they are naturally antioxidants. They are utilized in sunscreen and anti-aging cosmetics as a result of these benefits.

16. Batteries (Lithium ions batteries)

Since lithium (Li) has a low electro-negativity and can readily donate electrons, it is a useful element with unique features. As a result, it works best for producing batteries that are both lightweight and effective.

Despite the aforementioned benefits, Li's high reactivity restricts its application because it reduces the metal's efficiency. This issue can be resolved by applying CNTs and Li together. By intercalating Li ions into CNTs, an effective battery can be created. Li+ ions can move from a graphitic anode to the cathode as a result of this.

B. CNTs Biomedical Applications:

Even while research on CNTs for biomedical applications is still in its early stages, there is a lot of promise. Since carbon makes up a large portion of the human body, it is generally thought to be a relatively biocompatible substance.

Since it has been shown that cells can grow on CNTs, it appears that they have no harmful effects on cells. Additionally, the cells do not stick to the CNTs, creating opportunities for coatings for prosthetics and anti-fouling coatings for ships.

Biomedical uses for functionalized (chemically modified) CNT sidewalls include vascular stents and the development and regeneration of neurons. Additionally, it has been shown that a single DNA strand may be joined to a nanotube, which can then be successfully put into a cell.

1. Air and Water Filtration

CNT-based water and air filtration systems have already been created by a number of businesses and researchers. According to reports, these filters have the ability to eliminate the majority of bacteria in addition to obstructing the smallest particles. This is an additional field where CNTs have already seen commercialization and items are currently on the market.

2. Ceramic Applications

CNT has up to five times the fracture toughness (ability to not crack under stress) of conventional alumina. The material's electrical conductivity is seven times higher than that of previous ceramics manufactured using nanotubes. It is a popular material for thermal barrier coatings owing to its intriguing thermal properties, which include transmitting heat in one direction along the alignment of the nanotubes and reflecting heat at right angles to the nanotubes.

3. Carrier for Drug Delivery

The spherical aggregates of CNTs with a desultory horn-like structure are called carbon nanohorns, or CNHs for short. CNTs and CNHs have been proposed by numerous studies as possible medication delivery system carriers. Graphite layers bound by van der Waals forces have the ability to slide and are therefore useful as lubricants or glidants in the tablet-making process.

4. Genetic Engineering

CNTs and CNHs are utilized in genetic engineering to frame-up genes and atoms for the creation of tissue engineering, proteomics, and bioimaging genomes. By joining its particular nucleotides, the open DNA (single stranded) winds around the SWNT and accounts for changes in its electrostatic behaviour. CNTs are employed in cancer treatment and genetic condition treatment as gene carriers due to their cylindrical form. They were demonstrated as a vector in gene therapy using this type of carbon nanotube.

5. Artificial Implants

The body reacts negatively to implants with post-rehabilitation pain, but tiny nanotubes and nanohorns that bind to other proteins and amino acids delay rejection. Furthermore, they can be employed as implants in the form of prosthetic joints without causing host rejection. Because they are stacked/grouped in the structure of bone, contain calcium, and have a high tensile strength, carbon nanotubes can function as a substitute for bone.

6. Biosensors

The biomedical sector will take CNT-incorporated sensors to completely transform a variety of industries, most notably the biomedical sector. One example is the glucose sensing application, which requires diabetic individuals to assess and regulate their blood sugar levels by consistent self-tests. Monitoring radiation exposure in hazardous environments, such as nuclear power plants and reactors, chemical laboratories, and industrial settings, is another example.

The primary goal in each of these situations is to determine the level of exposure at each step so that the right course of action may be taken. When it comes to monitoring blood sugar, temperature, pulse, and diagnosing illnesses, CNT-based nanosensors are incredibly useful as embedded sensors. The most effective carrier of bioactive materials, such as drugs, DNA, and proteins, is carbon nanotubes, or CNTs.

Other Medical Applications of CNT's

Because of the unique qualities and traits of CNTs, researchers are able to explore new frontiers in nanomedicine. It has previously been established that SWNTs and MWNTs provide safe and efficient substitutes for earlier drug delivery techniques. They have the ability to cross membranes and deliver vaccinations, nucleic acids, and therapeutic medications far inside the cell to their substrate targets. They function as perfect non-hazardous carriers, which occasionally boost the drug's solubility for increased effectiveness and safety. Overall, CNT research has indicated that they have a very bright future in medicine.

Toxicity of CNTs and its Control

Owing to the exceptional physical and chemical characteristics of carbon nanotubes (CNTs), their application in industry has garnered significant attention. However, there exist several challenges associated with their utilization, particularly those pertaining to their toxicity.

Contrary impacts on human health are possible with CNTs, especially in the pulmonary system, which is the main site of exposure. It takes specific actions to reduce the toxicity of CNTs. Oxidative stress and inflammation are other effects of excessive exposure to CNT dust.

C. Optoelectronic and Photonic Applications

1. CNTs in Solar Cells

Additionally, CNTs have uses in solar cells. Solar panels are a prime application for them. Strong UV/Vis-NIR absorption properties of CNTs make them more beneficial for solar application. Several research organizations have claimed that using CNTs improves solar cell efficiency. According to reports, CNTs have been used to develop solar cells at the New Jersey Institute of Technology. This mixture has produced structures that resemble snakes and are useful for trapping electrons.

2. Passive mode-locked lasers using CNT saturable absorbers

CNT-based saturable absorbers are quickly overtaking more traditional methods, like semiconductor-based saturable absorbers mirrors (SESAM) and nonlinear optical loop mirrors (NOLM), to achieve saturable absorption. SESAMs are still the most common component in commercial passively mode-locked lasers at the moment, but producing them requires clean room facilities and unique fabrication for every operating wavelength due to their complicated manufacturing process.

Conversely, CNTs demonstrate a recovery time of less than a picosecond, broadband functionality, fiber compatibility, compact size, and ease of manufacture. Moreover, the operation of CNT-based saturable absorbers can be done in either the reflection or transmission modes. Researchers are beginning to choose CNT-based devices over the more well-established SESAMs for commercial applications for a number of reasons.

3. Light Emission

When a semiconducting CNT is electrically or optically pumped, it can produce photons (photoluminescence, PL) (electroluminescence, EL). In addition to being used for biological imaging and sensing in living tissues, PL is a crucial instrument for characterizing CNTs. By injecting a hole and an electron into a single semiconducting CNT, it has been established that an ambipolar CNT-FET can function as a nanoscale light emitter based on EL. It has also been shown that semiconducting CNTs exhibit optical gain as a result of stimulated emission.

4. Nonlinearity

In CNT, saturable absorption (SA) and nonlinear refractive index change (Kerr effect), which are third-order nonlinearities, are considerable and naturally occur at a fast rate. It has been shown that CNTs can function as a very effective super absorber (SA) for passively mode-locked short-pulse fiber lasers, particularly for high repetition-rate fiber lasers with a short cavity.

5. Photovoltaics

It has been established that a single-CNT photodetector can function as a semiconducting CNT photodetector at the nanoscale. CNTs play roles in producing transparent electrodes and improving efficiency in polymer or dye-synthesized solar cells for use in solar cell applications where area-size and efficiency are crucial.

6. Display

Semiconducting carbon nanotubes (CNTs) can be an excellent electron emitter for field emission display (FED) due to their high mobility and tiny tube diameter. For flat panel displays like liquid crystal or organic EL displays, CNT-based transparent electrodes are especially helpful.

7. Transparent Conduction

Although indium tin oxide (ITO) is the most widely utilized material at the moment for transparent electrodes in solar cells and flat screens, it has certain drawbacks. Conductive CNT coatings have great optical transparency across a wide spectrum range, from the UV visible to the near-infrared, and high conductivity owing to the high mobility in CNT, making them a potential replacement.

D. Potential Applications of Carbon Nanotubes:

Carbon nanotubes have the potential to be a more affordable alternative to metal wires due to their great electrical conductivity. They are potential replacements for current computer chips due to their semiconducting qualities. Carbon nanotubes and carbon fibres will probably the reinforced nanocomposites that are expected to promote the formation of an electrical network in the composites.

Furthermore, it has been discovered that CNTs are a more eco-friendly flame-retardant addition for plastics. Paints containing micron-sized nylon stars (MWNTs) have also been proven to inhibit the growth of algae and barnacles on ship hulls, reducing biofouling. This makes MWNT-containing paints a safer option to paints containing biocide. An organic light-emitting diode (OLED) display was built by University of Tokyo researchers using a rubbery nanotube-based conductor. This OLED can compete with the devices, where weight of the device is a major issue such as kelvar.

E. Current Applications of Carbon Nanotubes:

For a while now, CNTs have been leaving a significant influence on commercial goods. Carbon nanotubes are already integrated to anti-static packaging and utilized to regulate or improve conductivity in polymers. Nowadays, structural reinforcement is the most common application for CNTs. Their great strength, light weight, and flexibility are why they are combined with other materials, such as rebar in concrete. Further, CNTs can be fabricated into thin films and bulk composite materials.

Limitations of CNTs

• Insoluble in the majority of biologically acceptable solvents (aqueous based).
• The ability to produce batches of CNTs with consistent properties that are repeatable both chemically and architecturally.
• Difficulty in keeping minimal contaminants and high quality.

Conclusion

Carbon nanotubes, or CNTs, are only one example of how nanotechnology is continuing to shine as the scientific future beacon. Compared to steel, carbon nanotubes are 100 times stronger while weighing only a sixth as much. Better than copper, they also conduct electricity and heat. When used effectively, carbon nanotubes (CNTs) are transforming material science and technology.