Applications of carbon nanotubes

Nanotubes are not new, but not many people understand the scope of their applications. In order to make more people know the specific applications of carbon nanotubes, they are summarized as follows:

Carbon nanotube concept

Carbon nanotubes, also known as buckytubes, belong to the Fuller carbon system, which is composed of a single or multiple layers of graphite sheets curled into seamless nanotubes. Each layer of carbon nanotube is a cylindrical surface consisting of a hexagonal plane formed by the complete bonding of carbon atoms with three surrounding carbon atoms by SPZ hybridization. Since the diameter of the carbon tube is generally between 1 and 30 mm, and the length can reach several meters, and the aspect ratio is between 100 and 1000, it can be regarded as a one-dimensional quantum wire. According to the different number of carbon atom layers in carbon nanometer tubes, carbon nanotubes can be roughly divided into two types: single-walled carbon nanotubes SWNI's) and multi-walled carbon nanotubes (MWNTs)< SWNTs are composed of a single layer of carbon atoms, and their structure has good symmetry and uniformity. MWNTs are composed of many cylindrical carbon tubes with the same shaft sleeve. The number of layers is between 2 and 50, and the spacing between layers is 0.34 run, which is the same amount of distance as the distance between layers of carbon atoms in graphite.

The history of carbon nanotubes:

The development of carbon nanotubes is as follows: in 1991, Japanese scientists discovered carbon nanotubes; In 1992, researchers found that carbon nanotubes exhibit the special electrical conductivity of a semiconductor or a good conductor depending on the structure of the tube wall. In 1995, scientists studied and confirmed its excellent field emission performance. In 1996, Chinese scientists realized large-area directional growth of carbon nanotubes. In 1998, researchers used carbon nanotubes as the cathode of electron tubes. In 1998, scientists used carbon nanotubes as room-temperature field effect transistors. In 1999, a South Korean research group made a carbon nanotube cathode color display sample tube; In 2000, Japanese scientists made a high-brightness carbon nanotube field emission display sample tube.

Uses of carbon nanotubes:

The use of nanometer is very wide, in the introduction is impossible to face the mask, the main application areas are summarized as follows.

First, energy - representative of hydrogen storage materials and nanocarbon fiber batteries

Hydrogen storage material

Tsinghua University's Carbon Nanomaterials Research Group has discovered a modified carbon nanotube that can store hydrogen, which could be used as a material for hydrogen batteries, a new clean energy source. Our team has systematically studied the electrochemical hydrogen storage properties of directional carbon nanotubes, and found that the nanotubes have many novel mechanical, electrical, thermal and optical properties, especially when mixed with copper powder. The research team used carbon nanotubes as electrodes to conduct constant current charge-discharge electrochemical experiments. The results show that the hydrogen storage capacity of directional MWCNT electrode with copper mixed powder is 10 times that of graphite electrode, and 13 times that of non-directional MWCNT electrode. The specific capacitance of MWCNT electrode is up to 1625mAh/g, and the corresponding hydrogen storage capacity is 5.7wt % (mass fraction). According to the U.S. Department of Energy's (DOE) standards for vehicle hydrogen storage technology, the team's results are close to the weight and density requirements for hydrogen storage materials. The technology can be used in the manufacture of fuel cells, as a constant and stable hydrogen source. Fuel cell is a kind of power generating device which converts the chemical energy in fuel directly into electric energy by continuous electrical reaction without combustion. Among them, proton exchange membrane fuel cell (PEMFC) uses pure hydrogen as fuel, which has the advantages of low operating temperature, large output power, small size, light weight and "zero emission", and is especially suitable for transportation.

Nano-carbon battery Nano-carbon fiber battery is a new green energy developed by Chinese and American scientists after ten years of investment in manpower and material resources, new materials and new technologies. It is light in weight, only 1/10 of the weight of lead-acid battery, and 1/16 of the volume of ordinary batteries. The energy is amazing. The surface area ratio of each gram of nanocarbon fiber battery is 2000M grams, each nanomaterial is 10~30nm, and the length is 150mm. Light, sound and electricity all produce energy that is difficult to be produced by ordinary molecular materials, and the conductive resistance is close to 0, which is incomparable to any conventional batteries. The product has the characteristics of quick charging and burst power, the weight ratio energy can be between 170Wh/kg~230Wh/kg, and the volume ratio energy can be between 500W~1000W/L, charge and discharge can be up to more than 1000 times, life as long as 10 years. The price is half that of lithium-ion batteries. It is widely used in electric vehicles, submarines, electric locomotives and other electric machinery requiring large energy storage and light weight. Its introduction is a revolution in superconductivity and energy storage science and opens up a new way for the research of electrochemical capacitors with higher performance.

Second, the field of composite materials

The ratio of length to diameter is a key factor in determining the strength of a high-strength carbon fiber. At present, material engineers hope to obtain a length to diameter ratio of at least 20∶1. However, even in the nanometer lengths available today, nanotubes are thousands of times larger than their diameters, thus being called "fibres". They are 100 times stronger than steel, but only one-sixth as heavy. They are so tiny that 50,000 of them are the width of a human hair.

Catalytic Fiber and Membrane Industries and its team have injected or coated carbon nanotubes with vanadium oxide, an important catalyst used in the sulphuric acid industry and petrochemical industry. Sometimes vanadium oxide can reach the gaps in the graphite layer of the nanotube wall. Oxidize the carbon tubes with oxygen, leaving ultrafine fibres, made entirely of vanadium oxide, in the shape of nanotubes. This vanadium oxide, which is made into nanofibers, has a very high surface area, which greatly enhances its catalytic effect. In addition to vanadium oxide, carbon nanotubes can also be used as carriers for other metals and metal oxide catalysts, which can greatly improve the efficiency of catalysts. The oriented membrane made of carbon nanotube "array" can be used as a field emission device, and can also be made into a filter membrane. Because the membrane is also nanometer, it can filter some molecules and viruses, so that the ultrafiltration membrane enters a new world.

Nano high efficiency, energy saving, environmental protection gas combustion catalyst, the oil supply or by the air filter into the pump into the gasoline engine, resulted in the mixing amount of oil and gas in the cylinder (100 nm) oxide particles with nanometer particle size small, the contact surface area larger (1 g nano material surface area of about 100 m2), when the contact area is larger, higher surface energy, These surface atoms are in a serious Vacancy state, so their activity becomes extremely high, which will affect the substances in contact with them, make them more active, and have very good electrical susceptibility. Then, through the intake and compression stroke of the gasoline engine, these nano oxide particles themselves are charged or charged due to high pressure. The gasoline engine cylinder is filled with hundreds of millions of dust ignition ignition ignition point, can reach the full combustion of gasoline in an instant, reduce the carbon deposit in the cylinder block, so that the vehicle dynamic performance is improved, the engine power is enhanced, fuel saving, improve exhaust pollution emissions. At the same time, increase horsepower, reduce fuel consumption, become energy saving, environmental protection and green products, maintenance and extend the engine life.

A team of American and Australian scientists has begun producing ultra-thin and ultra-strong materials with unique properties that can be used in a variety of fields, from home appliances to artificial muscles and space sails. That, according to a paper published in the new issue of Science, is using carbon nanotubes, hollow synthetic cylinders the size of individual molecules, as ribbons.

Nanotechnology has been in the field for decades and carbon nanotubes have long been developed, but before that no one had been able to weave nanotubes into fabrics. Now scientists at the University of Texas in the United States and the Industrial Research Institute in Australia have announced a major breakthrough: they have developed a device that can use nanotubes to produce strips about seven centimeters wide, at a rate of 14 meters per minute.

Scientists have confirmed that the material has unique properties that make it stronger than steel or any plastic, transparent and flexible, and gives off light when heated. The nanotube fabric, which the researchers estimate weighs just 77 kilograms per square mile (258 hectares), has shown solar-cell properties in laboratory conditions: it generates electricity when exposed to sunlight.

Inventors and observers are confident that commercial applications for nanotube fabrics will not be long off. Dr Andrew Baron, a chemist at Rice University in Houston, believes the next stage of the miracle fabric could be used to produce lighter and stronger racing car shells that could also act as batteries.

3. Applications in the electronic field

WASHINGTON, Sept. 19 (ScienceDaily) -- Antennas made from carbon nanotubes can pick up light waves in the same way that antennas pick up radio waves, U.S. scientists have found. In an antenna receiving radio waves, the size of the antenna corresponds to the wavelength or a fraction of the wavelength of the incident radio wave. Radio waves can excite electrons into an electric current. This response to, amplification and modulation of radio waves is the basis of radio and television broadcasting, enabling the transmission of sound and image. In the case of light waves, which have wavelengths of several hundred nanometers, it is difficult to respond to, amplify, and modulate. However, according to a report just published in Applied Physics Letters, a team of scientists at Boston College in the US, led by Chinese-American scientist Yang Wang, have now used carbon nanotubes to observe a basic antenna effect on visible light, where incident visible light causes the nanotubes to generate a weak current. According to Wang, they would like to measure these weak currents directly, but that would require 1015 Hertz "nano-diodes" capable of handling optical frequencies and oscillating electric pulses, but they are not yet available. A good result for the future, they say, would be the observation of secondary radiation emitted by a weak current. Carbon nanotubes not only respond to incident light as dipole antennas, but they also exhibit polarization effects; When the incident light is polarized at a right Angle to the direction of the nanotube, the response disappears.

Medical field and biological engineering

So-called "smart" biological nanotubes, led by Leslie Wilson and Chirus Safenia at the University of California, could one day deliver drugs inside the human body.

In the experiment, the researchers used microtubules extracted from cow brain tissue. Microtubules are nanoscale cylinders that can enter the skeleton of a cell. In the human body, microtubules perform several functions, including the transport of substances and the transmission of nerve impulses. It has been found that the self-assembly of the microtubes occurs when the negatively charged microtubes interact with the positively charged lipid membrane. Not only that, but if a voltage is applied to the solution containing these microtubes, the shape of the microtubes can be changed to open both ends or one of them. The outer diameter of the "container" is about 40 nanometers, while the inner diameter is about 16 nanometers.

Scientists believe that in the future, drugs could be placed inside biological "containers" and released wherever they are needed. The researchers have conducted a series of experiments to show that the new method is reliable and effective. However, scientists do not yet predict that "smart" biological nanotubes will be practical any time soon.

Living Molecular Components (Living Molecular Components)

In the world of biomolecules, structure and function play important roles, and cell function is maintained by filamentous proteins in the cytoplasmic fluid, known as Cytoskeleton. The cytoskeleton provides the mechanical support necessary to maintain the shape of a cell. The cytoskeleton is composed of at least three types of fibers: Microtubules, microfilaments, and Intermediate filaments. Microtubules are hollow tubules composed of A and B tubulins. The outer diameter of microtubules is 25nm, and the inner diameter is 15nm. The main function of microtubules is cell movement. The microfilaments consist of two twisted chains of Actin, 7nm in diameter, and Myosin, which are responsible for muscle contraction and cell movement. The intermediate filament, with a diameter of 8-12nm, is made of fibrin superstranded to maintain the shape of the cell. We found that the cytoskeleton structure, which is composed of almost nano units, affects the operation of whole biomolecules in such a fine composition. For example, the microtubules and microfilaments in the cytoskeleton are completed by the interaction of a protein complex called Motor molecules. The various forms of moving molecules do so by changing shape, each time releasing the free end and extending it further along the microtubules or filaments.

In the musculology of a cell, for example, the motility of an amoeba is actually a chain of molecular events. In addition, the famous "biomechanical" Flagella movement of a microorganism, in which a wave of the Flagella has the power to propel the entire organism forward, is often used as an example of a biological component as a nanomachinery. The principle is to use the sliding of microtubules, the arrangement of microtubules in flagella is a special structure of "9+2", 9 microtubules in pairs (twins) around a circle, 2 microtubules in the center are Singlet row station, the protein with A and B dimer in the microtubules in the front segment is called tubulin (42K), Dynein (400K) plays a similar role as myosin in the skeletal muscle. Tubulin and Dynein locally combine and Slide each other, causing the two fibers to shorten, so they can exert the "contraction state" of force.

Nature's mechanical principles often involve structural changes in proteins, and these work units are nanocrystalline. Such a small working machine can generate enough force to deform or move an entire microorganism, and the artificial DNA nanomechanics described in the first part should have similar potential to perform functions that nature may not have been designed to perform. Using the principle of movement and work of protein molecules, we call it "biomechanical machine system". The working principle of biomolecular components can be applied to other technology industries. How to use the tiny energy of biomolecules to transform it into huge power will be the direction of future efforts.

V. Environmental protection

The development goal of this project is to utilize the characteristics of nano dust collecting dust particles to develop new moisturizing materials, greatly improve the water retention capacity of soil, and improve the success rate and speed of greening. It is hoped that by the development and application of this new technology, the crisis of soil weathering and water loss in desertification zone can be solved effectively.

Carbon nanotubes have attracted the attention of scientists all over the world because of their special structure, peculiar mechanical, chemical and electronic properties, extremely wide application range and potential application value. The research on carbon nanotubes has become one of the important international frontiers, and Chinese scientists have made some important progress in this field. Carbon nanotubes have a very bright prospect. It is believed that in the next 10 years, with the development of carbon nanotubes application technology and products, carbon nanotubes will have a significant and profound impact on many fields, and bring great benefits to mankind.