The properties of carbon nanotubes. Cleaning carbon nanotubes

Ministry of Education and Science of the Russian Federation

Federal State Institution of Higher Professional Education

Russian University of Chemical Technology. D. I. Mendeleev

Faculty of oil and gas chemistry and polymeric materials

Department of Chemical Technology Carbon Materials

Practice Report

on the topic carbon nanotubes and nanovolkna

Performed: Marinin S. D.

Checked: Doctor of Chemical Sciences, Buchakina T. V.

Moscow, 2013

Introduction

Nanotechnology sphere is considered worldwide key theme for the technologies of the XXI century. The possibilities of their versatile use in such areas of the economy as the production of semiconductors, medicine, sensory equipment, ecology, automotive industry, building materials, biotechnology, chemistry, aircraft and cosmonautics, engineering and textile industry, carry a huge growth potential. The use of nanotechnology products will save on raw materials and energy consumption, reduce emissions into the atmosphere and thereby contribute to the sustainable development of the economy.

Developments in the field of nanotechnology is engaged in a new interdisciplinary area - Nanoscience, one of the directions of which is nanochemistry. Nanochemistry arose at the junction of centuries, when it seemed that everything was open in chemistry, everything was clear and the acquired knowledge acquired for the benefit of society.

Chemists always knew and well understood the value of atoms and molecules as major "bricks" of a huge chemical foundation. At the same time, the development of new research methods, such as electron microscopy, highly selective mass spectroscopy, in combination with special methods of preparation of samples made it possible to obtain information about particles containing small, less than a hundred, number of atoms.

In such particles, about 1 nm (10-9 m is just a millimeter, divided by a million), unusual, difficult chemical properties are detected.

The most famous and understandable for most people are the following such nanostructures, such as fullerenes, graphene, carbon nanotubes and nanofibers. All of them consist of carbon atoms related to each other, but the form will differ significantly. Grafen is a plane, monolayer, "bedspread" from carbon atoms in SP 2 hybridization. Fullerenes are closed polygons, something resembling a soccer ball. Nanotubes - cylindrical hollow bulk bodies. Nanofolokna can be cones, cylinders, bowls. In my work, I will try to illuminate non-nanotubes and nanofibers.

The structure of nanotubes and nanovolokon

What is carbon nanotubes? Carbon nanotubes are a carbon material, which is cylindrical structures with a diameter of a few nanometers consisting of graphite planes rolled into the tube. The graphite plane is a continuous hexagonal mesh with carbon atoms in the vertices of hexagons. Carbon nanotubes can differ in length, diameter, chirality (symmetry of the rolled graphite plane) and by the number of layers. Chirality<#"280" src="/wimg/13/doc_zip1.jpg" />

Single nanotubes. Single-layer carbon nanotubes (s) - a subspecies of carbon nanofolocon with a structure formed by the collapse of graphene into the cylinder with the connection of its sides without a seam. The collapse of graphene into the cylinder without a seam is possible only by a finite number of methods that differ in the direction of the two-dimensional vector, which connects two equivalent points on the graphene, which coincide when it is folded into the cylinder. This vector is called chirality vector single-layer carbon nanotube. Thus, single-layer carbon nanotubes differ in diameter and chirality. The diameter of single-layer nanotubes, according to experimental data, varies from ~ 0.7 nm to ~ 3-4 nm. The length of the single-layer nanotube can reach 4 cm. There are three forms of mine: Achiral types of "armchairs" (two sides of each hexagon oriented perpendicular to the axis of the CNT), ahiral type "Zigzag" (two sides of each hexagon are oriented parallel to the CNT axis) and chiral or spiral (each The side of the hexagon is located to the CNT axis at an angle, different from 0 and 90 º ). Thus, the Achiral CNTs of the "Armchairs" type characterize indexes (N, N), such as Zigzag - (n, 0), chiral - (n, m).

The number of layers in the ISD is most often not more than 10, but in some cases it reaches several tens.

Sometimes among multilayer nanotubes, two-layer nanotubes are isolated. The structure of the "Russian Matryoshka" type (Russian dolls) is a combination of coaxially nested cylindrical tubes. Another type of this structure is a combination of coaxial prisms invested in each other. Finally, the latter of the above structures resembles a scroll (Scroll). For all structures in Fig. Characteristic of the distance between adjacent graphene layers, close to 0.34 nm, inherent in the distance between adjacent planes of crystalline graphite<#"128" src="/wimg/13/doc_zip3.jpg" />

Russian Matryoshka Roll Paper Masha

Carbon nanofibers (UNV) are a class of such materials in which the curved graphene layers or nanocons are folded in the form of a one-dimensional thread, whose internal structure can be characterized by an angle α between the graphene layers and the fiber axis. One of the common differences is noted between the two main types of fibers: "Christmas tree", with tightly laid conical graphene layers and large α, and "bamboo", with cylindrical cup-like graphene layers and small α, which are more similar to multi-layer carbon nanotubes<#"228" src="/wimg/13/doc_zip4.jpg" />

a - nanofiber "Column coins";

b - nanofiber "Christmas-tree structures" (stack of cones, "fish bone");

in - nanofiber "Stack of cups" ("lamp lamps");

mr. Nanotube "Russian Matryoshka";

d - bamboo nanofibre;

e - nanofibers with spherical sections;

well - nanofibre with polyhedric sections

The separation of carbon nanotubes into a separate subspecies is due to the fact that their properties differ significantly for the better from the properties of other types of carbon nanofolocon. This is explained by the fact that the graphene layer forms the wall of nanotubes along its entire length, has high tensile strength, heat and electrical conductivity. In contrast to this carbon nanofibers when moving along the wall there are transitions from one graphene layer to another. The presence of interlayer contacts and high defectiveness of the NanOnolocone structure significantly worsens their physical characteristics.

History

It is difficult to talk about the history of nanotubes and nanofolocon separately, because these products often accompany each other during synthesis. One of the first data on the preparation of carbon nanofolocone is likely to be patent from 1889 to obtain tubular forms of carbon, formed during the pyrolysis of the mixture of CH4 and H2 in the iron crucible with Hughes and Chambers. They used a mixture of methane and hydrogen for the cultivation of carbon filaments by pyrolysis of gas with subsequent deposition of carbon. Speaking about obtaining these fibers for sure, it became possible much later when it became possible to study their structure using an electron microscope. The first observation of carbon nanofolocon with the help of electron microscopy was made in the early 1950s by Soviet scientists Radushekevich and Lukyanovich, who published an article in the Soviet journal of physical chemistry, which showed hollow graphite carbon fibers, which accounted for 50 nanometers in diameter. In the early 1970s, Japanese researchers Koyam and Endo managed to obtain carbon fiber by precipitation from the gas phase (VGCF) with a diameter of 1 μm and more than 1 mm long. Later, in the early 1980s, Tibbets in the US and Benissad in France continued to improve the process of obtaining carbon fibers (VGCF). In the US, deeper studies dedicated to the synthesis and properties of these materials for practical application were carried out by R. Terry K. Baker and were motivated by the need to suppress the growth of carbon nanofolocon due to the constant problems caused by the accumulation of material in various commercial processes, especially in the field of oil refining . The first attempt to commercialize carbon fibers grown from the gas phase was undertaken by the Japanese company Nikosso in 1991 under the brand name Grasker, in the same year Idymi published his famous article reporting on the opening of carbon nanotubes<#"justify">Obtaining

Currently, mainly syntheses based on pyrolysis of hydrocarbons and sublimation and demublimations of graphite are used.

electric arc method
radiation heating (use of solar hubs or laser radiation),
laser thermal
heating by electronic or ion beam,
reducing plasma
resistive heating.

Many of these options have their own varieties. Hierarchy Part of the variants of the electric arc method is shown in the diagram:

Currently, the thermal spraying of graphite electrodes in the arc discharge plasma is the most common. The synthesis process is carried out in a chamber filled with helium under a pressure of about 500 mm Hg. Art. When the plasma is burning, there is an intense thermal evaporation of the anode, while the precipitate is formed on the end surface of the cathode, in which carbon nanotubes are formed. The maximum number of nanotubes is formed when the plasma current is minimal and its density is about 100 A / cm2. In experimental installations, the voltage between the electrodes is about 15-25 V, the discharge current is several dozen amps, the distance between the edges of the graphite electrodes is 1-2 mm. In the process of synthesis, about 90% of the mass of the anode is deposited on the cathode. The resulting numerous nanotubes have a length of about 40 microns. They grow on a cathode perpendicular to the flat surface of its end and are collected in cylindrical beams with a diameter of about 50 μm.

Nanotube bundles regularly cover the surface of the cathode, forming a cellular structure. The content of nanotubes in the carbon sediment is about 60%. For the separation of components, the resulting precipitate is placed in methanol and treated with ultrasound. As a result, a suspension is obtained, which after adding water is subjected to separation in the centrifuge. Large particles stick to the walls of the centrifuge, and the nanotubes remain floating in the suspension. Then the nanotubes are washed in nitric acid and dried in a gaseous stream of oxygen and hydrogen in a ratio of 1: 4 at a temperature of 750 0 C for 5 minutes. As a result of this treatment, a light porous material is obtained consisting of numerous nanotubes with an average diameter of 20 nm and 10 microns. While the maximum reached nanofolk length is 1 cm.

Pyrolysis of hydrocarbons

According to the choice of initial reagents and methods of processes, this group has a significantly larger number of options than the methods of sublimation and demublimations of graphite. It provides a clearer control of the process of formation of the CNT, is largely suitable for large-scale production and allows not only carbon nanomaterials themselves, but also certain structures on substrates, macroscopic fibers, consisting of nanotubes, as well as composite materials, in particular, modified by carbontening CNTs Carbon fibers and carbon paper, ceramic composites. Using the recently developed nanospheric lithography, it was possible to obtain photon crystals from CNT. In this way, you can select the CNT of a certain diameter and length.

The advantages of the pyrolytic method, in addition, it is possible to implement it for matrix synthesis, for example, using porous membranes from aluminum oxide or molecular sieves. Using aluminum oxide, it is possible to obtain branched CNTs and membranes from CNT. The main disadvantages of the matrix method are the high cost of many matrices, their small sizes and the need to use active reagents and harsh conditions for dissolving matrices.

More often than others for the synthesis of CNT and UNV are the processes of pyrolysis of three hydrocarbons: methane, acetylene and benzene, as well as thermal decomposition (disproportionation) of CO. Methane, as well as carbon monoxide, is not inclined to decomposition at low temperatures (a noncatalithic decomposition of methane begins at ~ 900 about C), which allows to synthesize an ount with a relatively small amount of amorphous carbon impurity. Carbon oxide does not decompose at low temperatures for another reason: kinetic. The difference in behavior of various substances is visible in fig. 94.

The advantages of methane in front of other hydrocarbons and carbon oxide include the fact that its pyrolysis with the formation of CNT or UNV is combined with the release of 2 and can be used in already operating production 2.

Catalysts

Catalysts for the formation of the formation of CNT and UNV are FE, CO and NI; Promotors that are entered into smaller quantities are predominantly MO, W or CR (less often - V, Mn, Pt and Pd), catalyst carriers - non-volatile oxides and metal hydroxides (MG, Ca, Al, La, Si, Ti, Zr) , solid solutions, some salts and minerals (carbonates, spinels, perovskites, hydrotalcite, natural clays, diatomites), molecular sieve (in particular, zeolites), silica gel, aerogel, alumogel, porous Si and amorphous C. With this V, CR, Mo, W, Mn and, probably, some other metals in the conditions of pyrolysis are in the form of compounds - oxides, carbides, metallites, etc.

Noble metals (PD, RU, PDSE), alloys (Mishmetal, Permallah, Nichrome, Monel, Stainless Steel, CO-V, Fe - CR, Fe - SN, Fe - Ni-CR, Fe - Ni- can be used as catalysts. C, CO-FE-NI, solid alloy CO-WC et al.), COSI 2 and COGE. 2, Lani. 5, MMNI 5 (MM - Mishmetal), Zr alloys and other hydride-forming metals. On the contrary, AU and AG inhibit the formation of CNT.

Catalysts can be applied to silicon covered with a thin oxide film, Germany, some types of glass and substrates from other materials.

The ideal carrier of catalysts is porous silicon, obtained by electrochemical etching of single crystal silicon in a solution of a certain composition. Porous silicon may contain micropores (< 2 нм), мезопоры и макропоры (> 100 nm). Traditional methods are used to obtain catalysts:

mixing (less often sintering) powders;
spraying or electrochemical precipitation of metals on the substrate followed by the transformation of a solid thin film to the islands of nano-sizes (the layer-by-layer sputtering of several metals is also used;
chemical precipitation from the gas phase;
dipping substrate to the solution;
applying suspension with catalyst particles for a substrate;
applying a solution on a rotating substrate;
impregnation of inert powders salts;
coexipation of oxides or hydroxides;
ion exchange;
colloidal methods (sol-gel process, reverse micelles method);
thermal decomposition of salts;
burning metal nitrates.

In addition to the two groups described above, a large number of other methods for obtaining CNT have been developed. You can classify them according to used carbon sources. The initial compounds are: graphite and other forms of solid carbon, organic compounds, inorganic compounds, organometallic connections. Graphite can be turned into a CNT in a few ways: intense ball bearings with subsequent high-temperature annealing; electrolysis of molten salts; splitting into separate graphene sheets and subsequent spontaneous twisting of these sheets. Amorphous carbon can be converted to CNT when processing in hydrothermal conditions. From carbon black (soot), CNT was obtained with high-temperature transformation in the presence of or without catalysts, as well as when interacting with water vapor under pressure. Nanotructured structures are contained in vacuum annealing products (1000 about C) films of diamond-like carbon in the presence of a catalyst. Finally, Catalytic High Temperature Transformation of Fullerite with 60 Or its treatment in hydrothermal conditions also lead to the formation of CNT.

Carbon nanotubes exist in nature. A group of Mexican researchers discovered them in oil samples extracted from a depth of 5.6 km (Velasco-Santos, 2003). The diameter of the CNT was from several nanometers to tens of nanometers, the length reached 2 microns. Some of them were filled with various nanoparticles.

Cleaning carbon nanotubes

None of the common ways to produce CNT makes it possible to allocate them in its pure form. Impurities to NT can be fullerenes, amorphous carbon, graphitized particles, catalyst particles.

destructive
non-destructive
combined.

Destructive methods use chemical reactions that can be oxidative or reducing and are based on differences in the reactivity of various carbon forms. For oxidation, either solutions of oxidants, or gaseous reagents, for recovery - hydrogen are used. Methods allow you to highlight the CNT of high purity, but are associated with loss of tubes.

Non-destructive methods include extraction, flocculation and selective precipitation, cross-current microfiltration, displacement chromatography, electrophoresis, selective interaction with organic polymers. As a rule, these methods are small and ineffective.

Properties of carbon nanotubes

Mechanical. Nanotubes, as mentioned, are extremely solid material, both on stretching and bending. Moreover, under the action of mechanical stresses exceeding the critical, nanotubes are not "ruting", but are rebuilt. Based on this property of nanotubes as high strength, it can be argued that they are the best material for the cable of the space elevator at the moment. As the results of experiments and numerical simulation show, the Young-layer nanotube module reaches the values \u200b\u200bof about 1-5 TPA, which is an order of magnitude more than steel. The graph below shows a comparison of single-layer nanotubes and high-strength steel.

1 2

The cosmic elevator for calculations must withstand the mechanical voltage of 62.5 GPa

Stretching diagram (mechanical voltage dependence σ from relative elongation ε)

To demonstrate a significant difference between the most durable at the moment by materials and carbon nanotubes, do the following mental experiment. Imagine that, as it was assumed, a certain wedge-shaped uniform structure will serve as a cable for a space elevator, consisting of the most durable materials, the diameter of the GEO (GeoStationary Earth Orbit) will be about 2 km and narrows to 1 mm at the surface Earth. In this case, the total mass will be 60 * 1010 tons. If carbon nanotubes were used as a material, the cable diameter in GEO was 0.26 mm and 0.15 mm at the surface of the Earth, in connection with which the total mass was 9.2 tons. As can be seen from the above facts, carbon nanofibers are just the material that is necessary when building a cable, the actual diameter of which will be about 0.75 m to withstand the electromagnetic system used to move the cabin of the cosmic elevator.

Electric. Due to the small size of carbon nanotubes, only in 1996 managed to directly measure their specific electrical resistance to the four-contact method.

A gold stripes were applied to the polished surface of silicon oxide in vacuo. In the interval between them, nanotubes were sprayed with a length of 2-3 microns. Then, 4 tungsten conductor with a thickness of 80 nm were applied to one of the nanotubes selected for measuring. Each of the tungsten conductors had contact with one of the gold strips. The distance between the contacts on the nanotube was from 0.3 to 1 μm. The results of the direct measurement showed that the specific resistance of nanotubes may vary in large limits - from 5.1 * 10 -6 up to 0.8 Ohm / cm. The minimum specific resistance is an order of magnitude lower than that of graphite. Most of the nanotubes have a metallic conductivity, and the smaller exhibits the properties of the semiconductor with the width of the forbidden zone from 0.1 to 0.3 eV.

French and Russian researchers (from the IPTM RAS, Chernogolovka) another property of nanotubes was opened as superconductivity. They measured the volt-ampere characteristics of a separate single-layer nanotube with a diameter of ~ 1NM, rolled into the harness of a large number of single-layer nanotubes, as well as individual multi-layer nanotubes. The superconducting current at a temperature close to 4k was observed between two superconducting metal contacts. The peculiarities of the charge transfer in the nanotube differ significantly from those that are inherent in conventional, three-dimensional conductors and, apparently, are explained by the one-dimensional transport nature.

Also, an interesting property was detected from the University of Lausanne (Switzerland): a sharp (about two orders of magnitude) change of conductivity with a small, 5-10o, bending of a single-layer nanotube. This property can expand the scope of nanotubes. On the one hand, the nanotube turns out to be a ready-made highly sensitive transducer of mechanical oscillations into an electrical signal and back (in fact it is a multiple micron telephone tube and a diameter near the nanometer), and, on the other hand, it is a practically ready-made sensor of the smallest deformations. Such a sensor could be used in devices controlling the state of mechanical components and parts, on which the safety of people, such as passengers of trains and aircraft, and the staff of atomic and thermal power plants, etc.

Capillary. As experiments showed, the open nanotube has capillary properties. To open the nanotube, it is necessary to remove the top part - the lid. One of the removal methods is annealing nanotubes at a temperature of 850 0 C for several hours in the flow of carbon dioxide. As a result of oxidation, about 10% of all nanotubes are open. Another way to destroy the closed ends of nanotubes is an excerpt in concentrated nitric acid for 4.5 hours at a temperature of 2400 C. As a result of such a processing, 80% of nanotubes become open.

The first studies of capillary phenomena showed that the fluid penetrates into the nanotube channel if its surface tension is not higher than 200 mn / m. Therefore, solvents that have low surface tension are used to enter any substances inside the nanotubes. For example, concentrated nitric acid is used to enter the nanotube nanotubes of some metals, the surface tension of which is small (43 mn / m). Then annealing is carried out at 4000 C for 4 hours in a hydrogen atmosphere, which leads to the restoration of the metal. Thus, nanotubes containing nickel, cobalt and iron were obtained.

Along with metals, carbon nanotubes can be filled with gaseous substances, such as hydrogen in molecular form. This ability is of practical importance, for it opens up the possibility of safe hydrogen storage, which can be used as an environmentally friendly fuel in internal combustion engines. Also, scientists were able to put an entire chain of fullerenes in the nanotubes with the Hadolinium atoms already implemented in them. (see Fig. 5).

Fig. 5. Inside C60 inside a single-layer nanotube

Capillary effects and filling nanotubes

nanotube carbon pyrolysis of electric arc

Capillary phenomena in carbon nanotubes were first implemented experimentally in operation, where the effect of capillary retracting of the molten lead was observed inside the nanotubes. In this experiment, the electric arc, intended for the synthesis of nanotubes ignited between the electrodes with a diameter of 0.8 and the length of 150 cm at a voltage 30 V and a current 180 - 200 A. Forming on the surface of the cathode as a result of thermal destruction of the surface of the material of the material layer 3-4 cm was removed From the chamber and withstood for 5 hours at T \u003d 850 ° C in the flow of carbon dioxide. This operation, as a result of which the sample lost about 10% of the mass, contributed to the purification of the sample from the particles of amorphous graphite and the opening of nanotubes in the sediment. The central part of the sediment containing nanotubes was placed in ethanol and was treated with ultrasound. The oxidation product dispersed in chloroform was applied on a carbon tape with holes for observing using an electron microscope. As the observations showed, the tubes that were not subjected to processing had a seamless structure, the head of the correct shape and the diameter from 0.8 to 10 nm. As a result of oxidation, about 10% of nanotubes were with damaged caps, and part of the layers near the vertex was sodran. Designed for observations, a sample containing nanotubes was filled in vacuum by drops of molten lead, which were obtained as a result of irradiation of the metal surface with an electron beam. At the same time, on the outer surface of the nanotubes, lead droplets were observed with a size of 1 to 15 nm. Nanotubes were annealed in air at T \u003d 400 ° C (above the melting point of lead) for 30 minutes. According to the results of observations made using an electron microscope, part of the nanotubes after annealing turned out to be filled with solid material. A similar effect of filling the nanotubes was observed during irradiation of the heads of the tubes opening as a result of annealing, a powerful electron beam. With sufficiently strong irradiation, the material near the open end melts and penetrates inside. The presence of lead inside the tubes is set by X-ray diffraction methods and electron spectroscopy. The diameter of the finest lead wire was 1.5 nm. According to the results of observations, the number of filled nanotubes did not exceed 1%.

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1 Technical innovation UDC BBK 30.6 Filter based on carbon nanotubes for cleaning alcohol-containing liquids N.P. Polikarpova, I.V. Zaporotskova, TA Ermakova, P.A. Potorvods conducted experiments on cleaning alcohol-containing liquids by filtering and transmittance methods, a mass fraction of carbon nanotubes was installed, leading to the best result. A layout of a filter based on a nanomaterial concluded into the space between the layers of porous glass and its structural features are determined. Polycarpova N.P., Zaporotskova I.V., Ermakova T.A., Zaporotsky P.A., 2012 Keywords: carbon nanotubes, alcohol-containing liquid, adsorption, filter, porous glass, porous ceramics. Introduction Cleaning alcohol-containing fluids to which the food industry products are vodka, plays an important role in the process of their production. Each manufacturer is trying to use the most efficient methods for cleaning the alcohol-containing fluid from impurities and fuse oils. Suggest oils, aldehydes, mineral salts and other impurities are removed from the product by filtration using charcoal, quartz sand, silver dust, platinum filters, milk powder, egg protein. Many of the manufacturers of expensive varieties of vodka repeat cleaning repeatedly, combining various options. Each subsequent cleaning is even more eliminating the product from the sigh oil and other impurities. A double or triple degree of cleaning significantly improves taste, but also significantly increases the process of manufacturing. Currently, various methods for cleaning alcohol-containing products are used on liquor-vodka enterprises. The most common ones are cleaning with coal filters, cleaning with milk and egg proteins, "silver filtering" and cleaning with gold and precious stones. In the works of I.V. Zaporotkova and N.P. The results of theoretical calculations of the adsorption interaction of carbon nanotubes (CNT) with heavy organic alcohol molecules, which are part of alcohol-containing fluids in the form of unwanted impurities, and the possibility of their sorption on the nanotub surface is proved. This made it possible to propose an innovative method of purification of water-ethanol mixtures, which include vodka, with the help of carbon nanomaterial. As is known, graphite sorbents and charcoal purify the product from harmful impurities by 60%, milk by 70%, precious metals (silver, gold) by 75%. The use of carbon nanotubes to clean the alcohol-containing fluid from impurities by 98% as a sorbing material of carbon nanotubes. Also, the advantages of the stated filters based on CNT can be attributed: 1) high productivity of the process at low cost; 2) ten times less than the volume of the adsorbing substance; 3) the absence of side effects from the use of graphite nature adsorbents while maintaining and repeatedly increasing the activity of the process; Bulletin Volga. Series 10. SET

2 4) The possibility of selective adsorption. It should be noted that the introduction of a filter based on nanomaterials into a finished production cycle at the final stage without a fundamental change in the technological process provides almost 100% purification of the product of water-ethanolic mixtures without a significant increase in the cost of production. 1. Determination of the optimal amount of carbon nanomaterial for cleaning liquids before proceeding directly to laboratory experiments on cleaning alcohol-containing liquids (vodok domestic production), it was necessary to determine the optimal number of nanomaterial leading to the desired effect of a high purification. As an object of research, Vodka "Let's drink for" was chosen, relating to the class of conventional vodka low cost. The fluid studies were carried out by the titrimetric method until the minimum mass of nanotubes was revealed, necessary for efficient purification of 50 ml of vodka. The selection was carried out by the method "from greater to the smaller", the initial amount of carbon nanotubes was 1 g. The accuracy of weighing CNT was determined by the accuracy of the analytical scales used and was 0.0001 g. Reducing the number of nanotubes was carried out before fixing the moment when the alkalinity of vodka ceased to decrease. According to the norms of the GOST R "Vodka and Vodka are special. General technical conditions ", alkalinity of vodka should not exceed 2.5 3.0 ml. Before purification, the alkalinity of the selected vodka was 2.5 ml. The results of the completed titrimetric studies are presented in the table. Analysis of the results showed that the transmission of alcohol-containing liquid through a filter with carbon nanotubes reduces alkalinity indicator by an average of 98% (by 2.45 ml). The minimum amount of the required nanomaterial is 0.001 g, since, with a decrease in this amount, alkalinity increases sharply, and with more its decrease is slightly reduced. 2. Selection of material for creating a carbon nanotube-based filter shell in the production of vodka as filters can be used as filters with porous glass, such as Schotta filters and ceramic filters. These porous materials can also be used as materials for creating a carbon nanotube filter shell. Consider the features of these materials. Porous glass Glass-like porous material with spongy structure and silicon oxide content of SiO 2 is about 96% (mass.). Porous glass is the result of thermal and chemical processing of glass special composition. Porous glasses can be obtained only from glass with a sufficiently high content of Na 2 O, in which the coexisting phases after long thermal processing form the frame-of-performing frames. A necessary condition for obtaining porous glasses is also the content in the source glasses of at least 40% (mass) of silicon dioxide, ensuring education in the glass of the continuous spatial grid of SiO 2. Glass filters are plates from crushed and fused glass. For their manufacture, glass is grinding in the ball mills and sieved using a set of sieves. The glass powder sin the heating in the furnace in metal or ceramic forms. The obtained plates are soldered into the tubes, glasses, funnels, crucible and other dishes from the glass of the same composition. Through such plates, hot solutions, concentrated acids and diluted alkalis, can be filtered, since such filters are resistant to the action of aggressive media. Filtering plates are distinguished by porosity. Depending on the amount of pores, several filters classes are manufactured. Glass filters, or so-called Schotta filters, are produced by the following types: 1 Pore size is MCM, used to work with large-crystal precipitation; 7 6 N.P. Polycarpova et al. Filter based on carbon nanotubes

3 2 pore size is an μm, used to work with medium-grayscale precipitation; 3 pore size is MKM, used to work with small crystalline precipitation; 4 Pore size is 4 10 microns, used to work with very small crystalline precipitation. Ceramic membranes are porous ceramic filters of fine purification, made by sintering of metal-ceramic materials, such as aluminum oxide, titanium dioxide or zirconium (Fig. 1), with ultrahigh temperatures. Ceramic membranes usually have an asymmetric structure supporting the active membrane layer (Fig. 2). Porous ceramics consists of related particles of about the same size, which creates a homogeneous, permeable material that provides winding channels for fluid flow. Most often for the manufacture of filters are used silica and alumina, although the possibilities of choosing the material, size and form are almost unlimited. Ceramic filters are usually classified on the average pore diameter or / permeability. The average pore diameter is the average minimum pore diameter, measured in microns. Ceramic filter membranes dimensions: - Microfiltration: 1.2 μm 0.5 μm 0.2 μm 0.1 mkm; - Ultrafiltration: 50 nm 20 nm. Macroporous materials provide mechanical stability, while the active membrane layer provides separation: microfiltration, ultrafiltration, nanofiltration. Ceramic membrane filters always operate in tangential filtering mode with optimal hydrodynamic modes. The turbid liquid passes through the membrane layer inside the single or multichannel membrane at high speed. Under the action of transmembrane pressure (TMD) micromolecule and water pass vertically through the membrane layer, forming a flow of permeate. Weighted substances and high molecular compounds are delayed inside the membrane forming a concentrate flow. Thus, the purification of contaminated liquids occurs. Ceramic membranes allow the physical method to divide the mixtures of the components without the use of additives. The introduction of a carbon nanotube material system may further increase the effectiveness of such a filter. 3. Filter layout based on carbon nanotubes in a porous glass shell to create a filter layout through which the vertical transmission of the alcohol-containing fluid was carried out (Fig. 3), glass shotta filters made from porous glass with carbon nanotubes obtained on carbon nanomaterial were used Installation CVDOMNA according to the method described in I. V. Zavodsky. The filter part of the filters used is a glass porous substance Fig. 1. Porous ceramics Fig. 2. Ceramic filter Bulletin Volga. Series 10. SET

4 with a membrane size of 4 10 microns. For a pre-layout, two Scotta filters of different diameters were used, which docked each other, forming a closed filtering system. Between the plates of glass, the sizes of the pores were 4 10 microns, the layer of carbon nanotubes was placed. The enlarged image of the porous glass is shown in Figure 4. To ensure closetness, carbon nanotubes were additionally placed between the layers of filter paper. The studied product vodka "drink for" freely vertically proceeded through the filter created in this way under the action of gravity. The amount of filtering carbon nanomaterial and the volume of the alcohol-containing fluid flowing through the manufacturer was selected in accordance with the results obtained earlier: 0.001 g of CNT for cleaning 50 ml of vodka. These types of filters turned out to be sufficiently effective to provide free leakage through them a water-ethanol mixture without penetration through the glass of carbon nanomaterial, which can be explained by random position position in the block. Further studies of the quality of the product purified using molecular spectroscopy methods and liquid chromatography (Fig. 5, 6) were confirmed by a high degree of purification of vodka from impurities of high molecular weight alcohols of fusion oils: there are no peaks relating to these alcohols on the spectra. The results of the titration of vodka "drink for" by various amounts of carbon nanotubes. 3. The layout of the filter with plates of porous glass rice. 4. View of a glass plate with pores of 4 10 μm with an increase in X N.P. Polycarpova et al. Filter based on carbon nanotubes

5 transmission,% wave number, cm -1 Fig. 5. IR spectra vodka "drink for": red spectrum before cleaning; The purple spectrum after cleaning through the transmission through a filter with carbon nanotubes and the conclusion made experimental studies proved that the processing of water-ethanol mixture with carbon nanotubes helps to reduce the content of the seawous oils and other impurity substances, keeping b Fig. 6. Chromatograms of vodka "drink for": a) before cleaning; b) After cleaning through the transmission through a filter with carbon nanotubes, the content of the main utility component of the ethyl alcohol product. The created and tested layout of the carbon nanotubes filter, enclosed in the shell of porous glass, can be used as a basis for creating an industrial filter. Further research Bulletin Volga. Series 10. SET

6 will be directed to the creation of a filter layout with a ceramic shell, smaller than the pore size (compared with the pores of the glass shell) can provide better protection of the product being cleaned from carbon nanoparticles. References 1. Berkman, A. S. Porous permeable ceramics / A. S. Berkman. M.: Gosstroyisdat, p. 2. Vasilyev, V. P. Analytical chemistry. Tutrimetric and gravimetric analysis methods: Textbook / V. P. Vasilyev. M.: Drop, p. 3. Harmash, E. P. Ceramic membranes for ultra-and microfiltration / E. P. Garmash, Yu. N. Kryuchkov, V. P. Pavlikov // Glass and ceramics with GOST R vodka and vodka special. General specifications. State Standard of the Russian Federation. M.: State Standard of Russia, p. 5. Zaporotsky, I.V. Perspective nanomaterials based on carbon / I. V. Zaporotsky, L. V. Kolitov, V. V. Kozlov // Vestn. Volgogr. State un-ta. Ser. 10, Innovative activity with Zaporotskova, I. V. Sorption activity of carbon nanotubes as the basis of the innovative technology for the purification of water-ethanol mixtures / I. V. Zaporotsky, N. P. Zaporotsky, T. A. Ermakova // Vestn. Volgogr. State un-ta. Ser. 10, innovative activity with Zaporotskova, I.V. Carbon and non-trade nanomaterials and composite structures based on them: the structure and electronic properties / I. V. Zaporotsky. Volgograd: from the Volga, p. 8. Study of the effect of carbon nanotube on the process of cleaning alcohol-containing liquids / I. V. Zaporotsky [et al.] // Vestn. Volgogr. State un-ta. Ser. 10, innovative activities with Casitsyn, L. A. The use of UV, IC, NMR spectroscopy in organic chemistry: studies. Manual for universities / L. A. Kazitsyn, N. B. Kompyskaya. M.: Higher. Shk., s. 10. Sychev, S. N. Highly efficient liquid chromatography as a method for determining the falsification and safety of products / S. N. Sychev, V. A. Gavrilina, R. S. Murzalevskaya. M.: Delhi Print, p. 11. Chemical encyclopedia / Ed. I. L. Knunanya. M.: Soviet Encyclopedia, Dresselhaus, M. S. / M. S. Dresselhaus, G. Dresselhaus, P. Avouris // Carbon Nanotubes: Synthesis, Structure, Properties, and Application. Springer-Verlag, p. 13. Zaporotskova, I. V. Active Properties of Nanotubular Carbon Structures With Respect to Heavy Organic Molecules / I. V. Zaporotskova // Nanoscience & Nanotechnology-2011: Book of Abstract. Frascati National Laboratories Infn. Frascati, Sept, Frascati: Infn, P Zaporotskova, N. P. INVESTIGATION OF CARBON NANOTUBE ACTIVITY TO Heavy Organic Molecules / N. P. Zaporotskova, I. V. Zaporotskova, T. A. Ermakova // Fullerenes and Atomic Clusters. ABSTRACTS OF INVITED LECTURES & CONTIBUTED PAPERS. St.-Peterburg, July 4 8, St. Petersburg., P The Filter On The Basis of Carbon Nanotubes for Purification of Alcohol-Containing Liquids N.P. POLIKARPOVA, I.V. Zaporotskova, T.A. Ermakova, P.A. ZapoRotskov Experiments on Purification of Alcohol-Containing Liquids Are Made, The Mass Fractions of Carbon Nanotubes Leading To the Best Result is esstablished. The Filter Model On The Basis Of A Nanomaterial Concluded in Space Between Layers of Porous Glass Is Created, and Its Constructional Features Are Defined. Key Words: Carbon Nanotubes, Alcohol-Containing Liquids, AdSorption, Filter, Porous Glass, Porous Ceramics. 8 0 N.P. Polycarpova et al. Filter based on carbon nanotubes

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Cleaning carbon nanotubes

None of the common ways to produce CNT makes it possible to allocate them in its pure form. Impurities to NT can be fullerenes, amorphous carbon, graphitized particles, catalyst particles.

Apply three groups of COIN cleaning methods:

destructive

non-destructive

combined.

Properties of carbon nanotubes

1 - cosmic lift cable for calculations must withstand the mechanical voltage of 62.5 GPa

2 - tensile diagram (dependence of mechanical voltage from relative elongation E)

Electric. Due to the small size of carbon nanotubes, only in 1996 managed to directly measure their specific electrical resistance to the four-contact method.

A gold stripes were applied to the polished surface of silicon oxide in vacuo. In the interval between them, nanotubes were sprayed with a length of 2-3 microns. Then, 4 tungsten conductor with a thickness of 80 nm were applied to one of the nanotubes selected for measuring. Each of the tungsten conductors had contact with one of the gold strips. The distance between the contacts on the nanotube was from 0.3 to 1 μm. The results of the direct measurement showed that the specific resistance of the nanotube may vary in significant limits - from 5.1 * 10 -6 to 0.8 ohms / cm. The minimum specific resistance is an order of magnitude lower than that of graphite. Most of the nanotubes have a metallic conductivity, and the smaller exhibits the properties of the semiconductor with the width of the forbidden zone from 0.1 to 0.3 eV.

Capillary. As experiments showed, the open nanotube has capillary properties. To open the nanotube, it is necessary to remove the top part - the lid. One of the removal methods consists in annealing nanotubes at a temperature of 850 0 C for several hours in the flow of carbon dioxide. As a result of oxidation, about 10% of all nanotubes are open. Another way to destroy the closed ends of nanotubes is an excerpt in concentrated nitric acid for 4.5 hours at a temperature of 2400 C. As a result of such a processing, 80% of nanotubes become open.

Along with metals, carbon nanotubes can be filled with gaseous substances, such as hydrogen in molecular form. This ability is of practical importance, for it opens up the possibility of safe hydrogen storage, which can be used as an environmentally friendly fuel in internal combustion engines. Also, scientists were able to put an entire chain of fullerenes inside the nanotubes with already implemented in them atoms of the gadolinium (see Fig. 5).

Fig. five. Inside C60 inside a single-layer nanotube

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Introduction

Nanotechnology is the science of the manufacture and properties of the elements of the technique at the atomic and molecular level - everyone is now "on the hearing". Nanopribals and nationars from such elements from the field of fantasy are already moving into modern life. And part of this science is the rapidly growing branch of nanotube and fullerene studies, attracted hundreds of research groups of physicists, chemists and materials scientists.

The problem of creating nanostructures with specified properties and controlled dimensions is among the most important problems of the XXI century. Its solution revolutionizes electronics, materials science, mechanics, chemistry, medicine and biology.

Carbon nanotrubs (CNT) are unique macromolecular systems. Their very small nanometer diameter and large micron length indicate that they are closest in their structure to the ideal one-dimensional (ID) systems. Therefore, CNT is ideal objects to verify the theory of quantum phenomena, in particular, quantum vehicles in low-dimensional solid-state systems. They are chemically and thermally stable at least 2000 K, have excellent thermal conductivity, unique strength and mechanical characteristics.

The simplicity of nanotube structure allows you to develop theoretical models of structures of them. Therefore, new unexpected applications are waiting for CNT in the future, especially this applies to biology (manipulating molecules inside the cell, artificial neural networks, nanomechanical memory, etc.).

1. Single-layer nanotruba

1.1 Opening

In early 1993, several groups of scientists stated that alien materials could be placed in carbon nanoparticles or nanotrubs when using modified electrodes during arc evaporation. Rodni Ruoff Group from California and Yakhachi Saito Group from Japan received Capsulated LAC 2 crystals when working with electrodes, languid lanthanas, while Suppan Seraphin with colleagues reported that YC2 could be implemented in nanotruba using electrodes containing yttrium. This work has opened a whole new area based on nanoparticles and nanotrubs as "molecular containers", but it also indirectly led to a completely different discovery with equivalent applications.

Donald Betuun and his colleagues from California IBM Almaden Research Center in San Louis are very interested in the articles of Ruoff and others. This group worked on magnetic materials in their applications to memorizing information and believed that the ferromagnetic transition metal crystallites encapsulated into carbon shells can be very valuable in this area. In such materials, the croexulated metal particles must maintain their magnetic moments and at the same time be chemically and magnetically isolated from their neighbors. For several years, this IBM group worked on the "Eshehetral Fullerenes"; Fullerenes containing inside a small number of metal atoms. But large clusters or crystals inside fullerene-like cells could present the greatest practical interest. Therefore, Betuun decided to try to carry out some experiments on arc evaporation, using electrodes impregnated with ferromagnetic transition metal metal, cobalt and nickel. However, the result of this experiment was not the one that was expected. First of all, the soot obtained during the arc evaporation was not similar to the usual material produced under the arc evaporation of pure graphite. The soot layers were swallowed like a web from the walls of the chamber, while the material besieged on the walls had a rubber texture and could be considered stripes. When Betuun and his colleague Robert Beers checked this strange new material using a high-resolution electron microscopy, they were amazed, finding that it contained a set of nanotube with the walls into one atomic layer. These beautiful pipes were confused with amorphous soot and metal particles or metal carbide supporting this material in this form, which corresponded to its strange texture. This work was accepted for printing in Nature and appeared in June 1993. Micrographs from this article are shown in Figure 1.1.

Figure 1.1 - snapshots from the work of Betuun et al., Showing single-layer carbon nanotrubs obtained with joint evaporation of graphite and cobalt. Pipes have diameters about 1.2 nm.

Regardless of the American group, Sumio-Iidji and Tyoshyry Ichikhai from NEC laboratories in Japan were also experimented with arc evaporation using modified electrodes. In addition, they were interested in the influence of the change in the atmosphere inside the arc evaporation chamber. Like Bethune and his colleagues, they discovered that under certain conditions it turns out a completely different type of soot different from the one that is usually formed under arc evaporation. For this study, Japanese scientists have implemented iron in their electrodes and a mixture of methane and argon was used as an atmosphere instead of helium. When checking the high-resolution electron microscopy, it was found that the material of such arc evaporation contained very well-wonderful nanotrons, stretching like threads between the clusters of an amorphous material or metal particles. Single-layer nanotrises differ from those that are obtained in continuous arc evaporation, a very narrow distribution of diameters. In the case of "ordinary" pipes, the inner diameter has a range from 1.5 to 15 nm, and external - from 2.5 to 30 nm. On the other hand, single-layer nanotters are all very close diameters. In the material of Betuun and his colleagues, the nanotrubs had diameters 1.2 (± 0.1) nm, while the Ichihashi is found that the pipe diameters range from 0.7 to 1.6 nm with a middle of about 1.05 nm. Like the pipes obtained with the usual arc evaporation, all single-layer nanotrubs were closed with caps, and there was no evidence of the presence of particles of the metal catalyst at the ends of these pipes. Nevertheless, it is believed that the growth of single-layer nanotube is substantially catalytic.

1.2 Follow-up work on single-layer nanotrubam

Following the initial fundamental study, Donald Betuun and his colleagues from IBM in San Jose in the Commonwealth with scientists from the California Institute of Technology, the Polytechnic Institute and Virginia State University conducted a series of research on the preparation of single-layer nanotube, using a mass of "catalysts". In one of the first episodes, they showed that the addition of sulfur and cobalt to the anode (or in the form of pure S, or COS) led to the appearance of nanotube with a wider range of diameters than when receiving with one cobalt. Thus, single-layer nanotrubs with dimers from 1 to 6 nm were obtained when sulfur was found in the cathode, compared with 1-2 nm in the case of pure cobalt. Subsequently, it was shown that bismuth and lead could similarly contribute to the formation of large-diameter pipes.

In 1997, the French group showed that with arc evaporation, a high yield of nanotube can be achieved. Their method was similar to the original technique of Betuun and his colleagues, but they used a slightly different reactor geometry. Also, a mixture of nickel / yttrium was used as a catalyst, and not preferred by the Bethune group cobalt. It was found that the largest number of nanotube was formed in the "collar" around the cathode deposit, which was approximately 20% of the total mass of the evaporated material. Fully pipe output was estimated at 70-90%. The study of the material "collar" electron microscopy of high resolution showed the presence of many beams from pipes with a dimension of about 1.4 nm. Such a yield and type of pipes obtained are similar to the "burning" samples of the Smallli group using laser evaporation.

At the end of 1993, Shekhar submasoni from Dujna in Willmington, Delave, in collaboration with researchers from SPI International described the receipt of single-layer nanotube in another way. These scientists were used arc evaporation using electrodes with ghadolinium filling, and collected soot from the reactor walls. Together with large quantities of amorphous carbon, soot contained structures of the "marine hedgehog" type, which contained single-layer nanotrubs growing on relatively large particles of the carbide of the gadoline (with typical dimensions in tens of nanometers). Such pipes were shorter than those obtained with the metals of the iron group, but had the same range of diameters. The subsequent study showed that radial single-layer nanotrubs could be formed on a plurality of other metals, including lanthanis and yttrium. Figure 1.2, taken from the work of saito with colleagues, shows a typical image of single-layer nanotube, growing radially from a particle containing a lanthanum. In contrast to metals of the iron group, rare earth elements are not known as catalysts for obtaining multilayer nanotubes, therefore it is quite surprising to form pipes on them. The fact of the growth of pipes on relatively large particles assumes that such a mechanism for growth is different. It was assumed that the growth of pipes on the surfaces of particles may include the isolated of the deranged carbon atoms from the inside of carbide particles. Note that the radial growth of multilayer pipes from catalytic particles was observed many years ago by Baker and others.

So far discussed methods for obtaining single-layer nanotubes included arc evaporation using modified electrodes. The work of Smallli and his colleagues showed that single-layer nanotrubs can also be synthesized with the help of a purely catalytic method. The catalyst used by the molybdenum particles of several nanometers in diameter was located on aluminum. It was all placed in the inside of the pipe-shaped furnace, through which carbon monoxide was passed at a temperature of 1200 ° C. This temperature is much higher commonly used during the catalytic production of nanotube, which can explain why single-layer is raised than multilayer nanotrubs.

Catalytically cooked single-layer pipes had a number of interesting features that distinguished them from pipes synthesized with arc evaporation. First, the catalytic pipes usually had small metal particles attached to the end, as well as the multi-layer pipes obtained during catalysis. There was also a wide range of particle diameters (approximately 1-5 nm), and it seemed that the diameter of each pipe was determined by the diameter of the corresponding particle of the catalyst. Finally, catalytically formed single-layer pipes were usually rather isolated than collected in bundles, as it happens in the case of pipes synthesized with arc evaporation.

These observations gave the possibility of Smallli with colleagues to offer a growth mechanism for catalytically formed pipes, which includes the initial formation of a single-handed hat (called by them, the Jewish name of the tubeette), followed by the growth of this hat with a separation from catalytic particles, subsequently leaving the pipe. This mechanism is completely different from their proposed for the growth of single-layer pipes with laser evaporation.

Figure 1.2 - Single-layer nanotrons growing on a lanthanum particle

Figure 1.3 - TEM images of samples from "harnesses" of single-layer nanotube (a)

An image of a low resolution showing a large number of harnesses, (b) micrograph high resolution of an individual harness shown along its axis.

1.3 nanotube "harnesses"

From the discovery in 1985 in Raisa C60, the Smallli group focused on the use of lasers in the synthesis of fullerene-like materials. In 1995, they reported on the development of laser synthesis technology, which allowed them to obtain single-layer nanotrises with high yield. Subsequent improvements of this method led to the production of single-layer nanotube with unusually homogeneous diameters. The best output of homogeneous single-layer nanotube was obtained at a catalytic mixture composed of equal parts of CO and NI, and a double pulse was used to ensure a more even evaporation of such a target.

Several micrographs of the material obtained by this technology are shown in Figure 1.3. In general appearance, it is very similar to the material obtained by arc evaporation. However, individual pipes tend to form "harnesses" or extended bundles, which consist of individual pipes of the same diameter. Sometimes it was possible to detect the harnesses, which took place closely from the direction of the electron beam, so that it was possible to see them "in the end", as in Figure 1.3 (b). In addition to electron microscopy, the Smallli with colleagues conducted X-ray diffraction dimensions on "burning" samples in collaboration with John Fisher and its co-authors from Pennsylvanian State University. Well-defined reflections from a two-dimensional lattice, confirming the fact that the pipes had the same diameters. A good agreement was found with experimental data under the assumption that the nanotube diameter is equal to 1.38 nm with an error ± 0.02 nm. It was found that Van der Waals gap between the pipes is 0.315 nm, similar to crystalline from 60. From the RD studies, it was concluded that these harnesses consist mainly from (10.10) chair nanotube. It was obviously confirmed by the measurements of the electronic beam electronic nanodiffraction, so that it was possible to see them "in the end", as in Figure 1.3 (b).

2. Nanotube growth theory

2.1 General comments

Initially, it is important to consider the effect on the growth of the structure of the pipe. In his article in Nature 1991, IIMI indicated that the helicoidal structure seems to be more preferable, since such pipes have a repeating step on the growing end. This assumption illustrated in Figure 2. is very similar to the appearance of a screw dislocation on the surface of the crystal. Charming and zigzag nanotrubs do not have such a structure preferred for growth, and should require the re-nucleation of a new hexagon ring. This suggests that spiral nanotes should be more often observed than chapal or zigzagne, although currently experimental evidence is not enough to confirm this.

Figure 2. - Figure of two concentric spiral pipes, showing the presence of steps in the growing ends (5)

Further, there is a very important question for a growth mechanism - do the growing pipes have closed or open ends? An early model of nanotube growth proposed for the first time, endo and meek, preferred a mechanism with a closed end. They assumed that carbon atoms can be inserted into the closed fullerene surface to seats in the vicinity of the Pentagonal Rings, followed by the transition to an equilibrium state, which results in continuous extrusion of the initial fullerene. In support of this idea, the endo and meekly quoted the demonstration of Ulmer with colleagues that C 60 and C 70 can obviously grow into large fullerenes when adding small carbon fragments.

While the mechanism, endo-meek ensures a plausible explanation of the growth of single-layer nanotube, it remains a serious problem for explaining multi-layer growth. With its consideration, the Endo model and meek suggest that multilayer growth can be carried out "epitaxial". If this is so, then it seems there is no obvious reason why the second layer does not start growing immediately after the initial fullerene is formed, and as soon as the second layer becomes closed, any further extrusion of the inner tube should become impossible. But it is not in freaks with the observation that most of the pipes are multi-layer throughout its length. Such a model also has difficulties in explaining the structures to somewhat departments. For these reasons, the endo-meek mechanism of growth with a closed ending was not widely accepted.

The conclusion that the growth mechanism should occur with the open end of the pipe, in some way more preferable. As Richard Smallli said, "if we learned since 1984-1985, something about how carbon condenses, this is what open sheets must be happy to connect Pentagons to exclude chatting connections." The problem of pipes remaining with an open end under conditions favorable for its closure, one of those problems that considered a number of authors.

2.2 Why nanotruba remain open during growth

Some authors, especially smilled with colleagues, assumed that the electric field in the arc could play an important role in the preservation of pipes opened during growth. If more correctly, it should have helped to understand why nanotrubs never find in soot condensed on the walls of the arc evaporation chamber. However, the calculations showed that the open end energy reduction of the open end is not enough to stable an open configuration, with the exception of unreal high fields. Therefore, an elegant model was developed, in which the atom "point is welded" between layers, helping stabilizing the formation of an open end, and not its closure.

Confirmation of this idea was the experiments on the closure of individual multilayer nanotube when the voltage difference is applied and without it. Such a model can help understand the growth of nanotube in the arc, but cannot approach the case of the growth of pipes where strong electrical fields are not present. This led some authors to the assumption that some interactions between the combined concentric pipes can be essential to stabilize open pipes.

A detailed analysis of the interaction of two combined pipes was performed by Jean-Christoph's Charlier with colleagues of molecular dynamics. They reviewed (10.0) the pipe inside (18.0) pipes and found that bridging bonds are formed between the ends of two pipes. It was found that at high temperatures (3000 K), the configuration of sticking binding structures continuously fluctuates. It was assumed that the fluctuating structure should create active places for adsorption and the introduction of new carbon atoms, thus contributing to the growth of the pipe.

The problem of such the theory is that it cannot explain the growth of single-axis pipes of a large diameter in thermal exposure to fullerene sage. In general, at present, the complete explanation of the growth of open nanotubes does not seem to exist.

2.3 Properties of arc plasma

Most of the growth models of nanotube, discussed earlier, suggest that the pipes are born and grow in the plasma of the arc. However, some authors considered the physical condition of the plasma itself and its role in the formation of nanotube. The most detailed discussion of this problem was conducted by Evgeny Gamaleem, an expert on plasma physics, and Thomas Ebbene (30, 31). This is a comprehensive problem, and here is only a brief summary.

Hamali and Ebiesen begin with the assumption that nanotrubs and nanoparticles are formed in the area of \u200b\u200bthe arc near the cathode surface. Therefore, they analyze the density and velocity of carbon vapors in the area, taking into account the temperature and properties of the arc itself in order to develop their model. They believe that in the carbon pair layer near the cathode surface there will be two groups of carbon particles with different speed distributions. This idea is central in their growth model. One group of carbon particles must have Maxwellovskoe, i.e. Isotropic speed distribution, corresponding arc temperature (~ 4000 K). Another group consists of ions accelerating in the gap between a positive spatial charge and cathode. The velocity of these carbon particles should be greater than the heat particle rate, and in this case the flow should be rather directed than isotropic. The process of forming nanotube (and nanoparticles) is considered as the implementation of a series of cycles, each of which consists of the following steps:

1. Formation of the embryo. At the beginning of the discharge process, the distribution of carbon velocities in the evaporated layer is predominantly Maxwell, and this leads to the formation of structures without any axis of symmetry, such as nanoparticles. When the current becomes more directed, open structures are beginning to be formed, which hamleles and ebiesen are considered as embryos for nanotube growth.

2. True pipes during a stable discharge. When the discharge stabilizes, the flow of carbon ions penetrates in a steam layer in the direction perpendicular to the surface of the cathode. These carbon particles will contribute to the elongation of single-layer and multilayer nanotube. Since the interaction of directional carbon particles with a solid surface should be more intense than carbon particles of the steam layer, the growth of extended structures should be prefeedled on the formation of isotropic structures. However, condensation on the cathode surface of carbon from the steam layer will contribute to the thickening of nanotube.

3. Growth and closing. Hamali and Ebiessen note that nanotrubs are often seen in the form of beams and that in the observed beam for all pipes growth and its ending occurs approximately at the same time. This allows them to assume that in the arc discharge there are instability, which can lead to a sudden ending of the growth of nanotube. Such instability can occur from an unstable movement of the cathode spot along a cathode surface or from spontaneous interrupt and arson of arc. Under such circumstances, carbon particles with Maxwellian velocity distribution will again prevail, and the condensation of such carbon will ultimately lead to the closing of the pipe with the cap and the end of growth.

2.4 Alternative models

Scientists presented a completely different theory of nanotube growth under arc evaporation. In this model, nanotrubs and nanoparticles do not grow in the plasma of the arc, and rather form on the cathode as the result of the transformation of the solid state state. Thus, the growth of nanotube is not a consequence of the operation of the electric field, but simply the result of very rapid heating to high temperatures experienced by the material deposited on the cathode during the actions of the arc. This idea was initiated by the observation of the fact that nanotrubs can be prepared by high-temperature thermal impact on fullerenery soot and provides for a two-step process of growth of nantes, in which fullerene soot is an intermediate product. The model can be generalized as follows. At the initial stages of arc evaporation, the fullerene-like material (plus fullerenes) should be condensed on the cathode, and then the condensed material must be subjected to high temperatures during the continuation of the arc process, leading to the formation of one-layer, nanotrup-containing structures initially, and then multilayer nanotube. In this two-step model, an annealing of fullerene soot is a key action. Thus, besieged on the soot reactor walls, which tests relatively weak annealing is not transformed into the pipes. On the other hand, the soot, which condenses on the cathode, should just experience a significant annealing: it will lead to the formation of pipes and nanoparticles as a solid mass. Therefore, such a model gives us the opportunity to explain the effect on the production of nanotube variables such as the cooling of the electrodes and the pressure of helium. It seems that water cooling should be essential to maintain the temperature of the cathode low to the level required to exclude the laying of pipes. Similarly, the role of helium can be explained in terms of its influence on the temperature of the cathode deposit. Since helium is a wonderful heat conductor, high pressure should lead to a decrease in the temperature of the electrode, leading to its drop in the area where the nanotube growth may occur without laying.

2.5 Growth of single-layer nanotube

First, consider the growth of single-layer nanotube in an arc evaporator. This process raises no less questions than the growth of multi-layered nanotube in the arc. Among most obvious are the following: why only single-layer nanotrubs are observed? Why is there such a narrow distribution of pipe diameters? What is the role of metal? Why are pipes grow most often in the form of beams? And again we have only a few specific answers to these questions.

One thing that seems clear is that the growth of single-layer nanotube should be significantly determined by the kinetics rather than thermodynamics, as it is expected that pipes with a very small diameter are less stable than with a large. The absence of many layers is allegedly constrained by kinitic factors. As for the role of metal, then Betuun with colleagues, and Iijias with Ichikhas assumed that individual metal atoms or their small clusters can act as growth catalysts in the vapor phase by analogy with that way in which small metal particles catalyze the growth of multilayer pipes. The participation of individual atoms or well-defined clusters should help explain the narrow-sized distributions. However, it is surprising that catalytic particles, apparently, are never observed on the tops of one-layer nanotube. Even if the catalytic particles would be separate atoms, they could be detected by high-resolution electron microscopy or scanning transmission electron microscopy (STEM). Perhaps catalytic atoms or particles will be discharged during the closing of pipes. As noted above, Betuun and colleagues showed that the addition of such elements such as sulfur to metal can strongly disrupt the distribution of pipe diameters. Further study of this phenomenon can give useful explanations of the growth mechanism.

One of several attempts to develop a detailed model of growth of single-layer nanotube was undertaken by Chingg-Hwa Kanggom and William Goddard. These researchers suggest that plenary polyane rings can serve as embrying of the formation of single-layer nanotube. It was shown that such ring structures should be dominant particles in carbon pairs whereas closed frame structures dominate with large sizes. It was postulated that carbon rings can be predecessors in the formation of fullerenes, although it remains controversial. Kiang and Goddard believes that the initial materials of the formation of single-layer nanotube are monocyclic carbon rings and gas-phase cobalt carbide clusters, possibly charged. Cobalt carbide clusters act as catalysts when connected to rings with 2 or other particles. These authors suggest that the specific conformation should affect the structure of the emerging nanotrub.

Smallli with colleagues, following their synthene nanotube "harnesses", suggested a growth mechanism, which has some similarities with Kiang and Goddard mechanism. This model is based on the assumption that all pipes have the same (10.10) chart. This structure is unique in its kind allows the disclosed hexagonal rings to be "blocked" triple bonds, although they must be substantially tense compared to their initial linear location. Then the Smallli group assumes that a separate nickel atom will be chemically adsorbed to the end of the pipe and "run" along the periphery (Figure 2.1), helping to accommodate carbon atoms on hexagonal rings. Any locally non-optimal structures, including pentagons, will be reflected, so such a pipe will continue to grow indefinitely.

Here, as well as for other mechanisms proposed for the growth of single-layer nanotube, there is no direct experimental proof.

Figure 2.1 - Illustration of a "scooter" mechanism with growth (10.10) of chair nanotube.

A number of groups of scientists in the world tried to purify nanotube samples using such methods as centrifuging, filtering and chromatography. Some of these methods include the initial preparation of colloidal suspensions of the material containing material, using surfactant agents. For example, Jean-Mark Bonard with colleagues applied an anionic surfactant for sodium dodeciclosulfate (sdn) to achieve a stable suspension of nanotube and nanoparticles in water. Initially, a filtration method was used to separate nanotube from nanoparticles, but a more successful separation was achieved simply: allowing nanotrubs to fall out in the form of flakes, leaving nanoparticles in suspension. The precipitate can, it was then to extract and continue further precipitation procedures. This not only allowed to extract nanoparticles, but also led to some division of pipes by lengths.

Another method of achieving the separation of nanotube in size is described by Duisberg with colleagues from Max - Planck of the Institute in Stuttgart and Trinity College Dublin. The separation of pipes and other material was again obtained in the acid SDN. Then the separation was carried out using the chromatography of dimensional exception (HR). This technology was widely used to separate biological macromolecules, and the authors demonstrated that it is possible to successfully separate nanotube samples on fractions with pipes of different lengths. One possible disadvantage of the use of revolt, such as SDNs, in the cleaning of nanotube is that the footprints may remain in the final product. However, Bonard with colleagues showed that it is possible to reduce the level of the SDN below 0.1% by washing.

3. Cleaning single-layer pipes

Methods for cleaning single-layer pipes were also developed, although this process requires great effort than for multilayer nanotube. In addition to a large amount of amorphous carbon, soot containing nanotruba contains both metal particles that themselves are often covered with carbon. More - the hard oxidation methods used to clean multilayer nanotubes are also destructive and for single-layer pipes.

Japanese scientists step by step described the process of consistent exclusion of various impurities. The first step turned on the washing of untreated soot by distilled water for 12 hours. Followed by filtration and drying. This procedure made it possible to remove some graphite particles and amorphous carbon. Fullerenes were washed away with toluene in the Sokklet's apparatus. Then the soot was heated to 470? With in air for 20 minutes to get rid of metal particles. Finally, the remaining soot was exposed to chlorine acid in order to dissolve metal particles. Checking the final product of electron microscopy and X-ray diffraction showed that most of the contaminants were removed, although some filled and empty nanoparticles remained in it.

Smallli with colleagues developed a method for cleaning nanotube samples from harnesses using microfiltration. They were the first to describe the technique of using a cationic surfactant for preparing a suspension from nanotube and accompanying material in the solution, and then nanotube planting on the membrane. However, repeated filtering with the preparation of suspension after each filtering in order to achieve a significant level of cleaning, which makes such a procedure very slow and ineffective. The improved method was described in the work, where we used the processing of ultrasound, while maintaining the material in suspension during filtration and, thus, making a continuous process of filtering a large number of sample possible. In this way, it was possible to purify up to 150 mg of soot for 3-6 hours with a material containing more than 90% AUNT.

Single-layer pipes could also be cleaned when using chromotographics, Duisburg, etc. described the method similar to that used for MSNT, and showed its effectiveness for AUND.

4. Aligning nanotube samples

carbon nanotruba fullerene-like plasma

Many preparation methods described above provide samples with randomly oriented, nanotrubs. Although the pipes are often grouped into the bundles, these bundles themselves do not align one relative to the other. To measure the properties of nanotube, it would be very useful to have samples in which all pipes are aligned in one direction. Although the catalytic methods of preparation of aligned pipes have already been described, but it was also necessary to develop the technologies for aligning pipe samples after their synthesis. So, one of the first such methods was proposed in 1995 by a group of Ecol Polytechnic by the Federal Lausanne in Switzerland. They used the MSNT sample prepared by arc evaporation, which was purified by centrifugation and filtering from nanoparticles and other polluting material. Then thin films of purified nanotube were besieged on the surface of the plastic, and SEM images have shown that these pipes were leveled perpendicular to the film in such a freely precipitable state. It was found that the pipes could be aligned parallel to the surface of the sample, pre-easily gratened with teflon or aluminum foil. The authors argue that this method can make films "arbitrarily large", and they used these films to perform experiments on field emissions.

Another method of alignment nanotube is to introduce these pipes into the matrix and the subsequent extrusion of such a matrix in any way so that the pipes become aligned in the direction of the flow.

5. Control of carbon nanotube length

The technique of cutting individual single-layer nanotubes on controlled lengths is described by researchers from Delft and Rais Universities At the end of 1997, the nanotroba used was obtained by the laser evaporation by the Small group and were besieged on the surface of gold single crystals for research using scanning tunnel microscopy. When a suitable nanoteuba was identified, the scanning stopped and the PT / IR needle moved to the selected point on this pipe. Then the feedback turned off, and the voltage pulse was supplied between the edge and sample for a certain period. When the scanning resumed, a break was visible on Nanotrub if the circumcision was successful. It was demonstrated that individual pipes can be cut up to four separate positions. It was found that a critical factor in the process of cutting is the voltage rather than the current required for the cutting process of the minimum of voltage must be 4 V.

Having chopped individual nanotrubs into short lengths, the authors were able to show that the electrical properties of short pipes were different from the properties of the original nanotube. These differences were attributed to the manifestation of quantum dimensional effects.

As well as controlling the lengths of individual nanotube, it is possible to cut into short lengths and volumetric samples from single-layer nanotube. This was demonstrated in 1998 by the Smallli Group. The most effective way of obtaining samples from short pipes (they were called "fullerene tubes") is the treatment of the ultrasound of the nanotube material in the solution of sulfur and nitric acids. During this impact, it is manifested that loyal sonochemistry produces holes on pipe surfaces, which are then attacked by acids, forming open "tubes". Smallli with colleagues showed that these tubes can be sorted to various fractions by the fraction method known as fractionation in the field stream. They also finished the ends of such open nanubes by various functional groups and showed that gold particles can join fuudionic pipe ends. This work can be considered the beginning of a new organic chemistry based on carbon nanotrubs.

6. Analysis of research

The arc evaporation method of Iijima, Ebbegest and Adayayana remains undoubtedly the best technology of high-quality nanotube synthesis, but it suffers from the shortcomings. First, it is large on labor costs and requires some skill to achieve an appropriate level of reproducibility. Secondly, the output in it is quite low, since the steamed carbon is precipitated on the walls of the chamber more than on the cathode, and nanotrubs are contaminated with nanoparticles and other graphite debris. B-third, it is rather "baking" than a continuous process, and it is not easy to scalize. If nanotruba ever be used commercially on a large scale, then, apparently, you will need to use another cooking method. Progress in this direction is hampered by the lack of understanding the mechanism of the growth of pipes in the arc. Therefore, further studies should be welcomed, specially devoted to clarify the mechanism of nanotube growth.

There is another serious weakness of the method of arc evaporation and all other current technology for the preparation of multilayer nanotubes: they produce a wide range of pipe sizes and structures. And this may be a problem not only by some applications, but also a disadvantage in those areas where specific pipe structures are needed, in such as nanoelectronics. Is it possible to predict the path to which pipes with certain structures will be prepared? It may be achieved by creative use of catalysts.

The researchers are drawn to the greater homogeneity of single-axis pipes than their many-sized fellow, at least in relation to their diameters. However, the methods are directly used to synthesize one-way pipes, the methods are more complex than for multi-stone nanotube. The technique of laser evaporation, developed by the Smith group, serves to produce the best quality material with the highest output, but the high-energy lasers required for this method are not always available for a conventional laboratory. As for multilayer pipes, the path for moving forward may include catalytic methods, and today's research is encouraged in this direction. Ultimately, you can hope that the organic chemists will be able to complete the full synthesis of nanotube. However, it is necessary to keep in mind that it may be a distant perspective, since even the full Synthesis of C60 has not yet been implemented.

With that, currently, the best quality nanotrubs are obtained using methods that also produce a significant amount of polluting material, it is important to note that there are methods for removing this material. Fortunately, there has been significant progress in this area, and now there are a number of methods for removing unnecessary nanoparticles, microporous carbon and other contaminants from samples both multilayer and single-layer nanotubes. The procedures for equalizing pipes and their cuts with controlled lengths were also developed. These technologies will progress in areas where still the lack of pure and well-defined samples remains a serious problem.

Conclusion

The method of cooking nanotube, the described indie in 1991, gave a relatively weak way out, making it difficult to further study their structure and properties. An important promotion occurred in July 1992, when Thomas Ebaenes and Pullery Ageyan, working in the same Japanese laboratory as the IIMI, described the method of preparation of grams of nanotube. And again it was an unexpected discovery: trying to prepare a derivatives of fullerenes, Ebaesen and Ageyan found that the increase in helium pressure in the arc evaporation chamber dramatically improves the yield of nanotube, formed in cathode soot. The availability of nanotube in a large amount led to a huge rise in the rate of research throughout the world.

Another area involved in the early interest was the idea of \u200b\u200busing carbon nanotube and nanoparticles as "molecular containers". The milestone in this direction was a demonstration of Adayayan and the Andiya that nanotrubs can be filled with molten lead and thus be used as templates for the "nanowire". Subsequently, more controlled methods for opening and filling nanotube were developed, allowing to put inside a wide range of materials, including biological. The consequence of the opening and filling of nanotube can be amazing properties that can be applied in catalysis or in biological sensors. Filled carbon nanoparticles may also have important applications in such different areas as magnetic recording and nuclear medicine.

Maybe the largest volume of nanotube should be devoted to their electronic properties. Above theoretical work was already noted, which preceded the opening of Iijima. After a short time, after the publishing of the letter in Nature 1991, there were two other articles on the electronic properties of carbon nanotube. MIT A group of scientists and Noriaki Hamada with colleagues from the Laboratory of Iijima from Tsukuba conducted calculations of the zone structure using a hard-tone model, and demonstrated that electronic properties depend on both the structure of the pipe and its diameter. These wonderful predictions caused great interest, but an attempt to determine the electronic properties of nanotube experimentally faced with great difficulties. But only in 1996 experimental measurements were performed on separate nanotrubs, capable of confirming theoretical predictions. These results suggested that nanotrubs can become components of future nanoelectronic devices.

The determination of the mechanical properties of carbon nanotube represented impressive difficulties, but once again the experimenters took this challenge. Measurements carried out using transmission electron microscopy and atomic force showed that the mechanical characteristics of carbon nanotube may also be exceptional, as well as their electronic properties. As a result, interest in the use of nanotube in composite materials increased.

Nowadays, other possible applications of nanotube cause them interest. For example, a number of scientists explore the problem of using nanotube as an edge for scanning probe microscopy. With their oblong shape, pointed tops and high rigidity of nanotrubs were to be perfect for this purpose, and initial experiments in this area showed extremely impressive results. It was also shown that nanotruba possess the beneficial properties of field emissions that can lead to their use in flat displays. Everywhere the volume of studies of nanotube grows with astronomical speed, and their commercial applications will certainly wait long for a long time.

Bibliography

1. P. Harris, carbon nanotrubs and related structures. New materials of the XXI century - M.: Technosphere, 2003.

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The properties of carbon nanotubes. Cleaning carbon nanotubes

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Cleaning carbon nanotubes

Properties of carbon nanotubes

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