TERM PAPER OF CHEMISTRY

TOPIC: CARBON NANOTUBE Submitted to Submit by:
Mr. Balwant Singh Bhist Mr.Shailja Kant yadav
Deptt. Of CHEMISTRY Roll. No. : - A02 Sec: - RC5911 REG NO.:-10905256

ACKNOWLEDGEMENT
I take this opportunity to present my vote of thanks to all those guidepost who really acted as lightening pillars to enlighten our way throughout this project that has led to successful and satisfactory completion of this study. I would express my sincere gratitude to my parents for trusting and investing in me and my future and providing for all my needs and requirements.

I also express my deep sense of gratitude to my teacher, Mr. Balwant Singh Bhist – Department of Chemistry, Lovely Professional University for her constant guidance and kind support throughout this project. I am heartily thankful to my friends Anil Choudhary, Pratik Anand, Suresh Hembrom for helping me with their thoughtful and creative ideas and supporting me at every hour of need. Lastly a sincere thanks to all other people about whom I have not mentioned here but who were involved in any which way with this term paper. ABSTRACT

Carbon nanofibers and nanotubes are promising to revolutionise several fields in material science and are a major component of nanotechnology. Further market development will depend on material availability at reasonable prices. Nanotubes have a wide range of unexplored potential applications in various technological areas such as aerospace, energy, automobile, medicine, or chemical industry, in which they can be used as gas adsorbents, templates, actuators, composite reinforcements, catalyst supports, probes, chemical sensors, nanopipes, nano-reactors etc. In this paper, recent research on carbon nanotube composites are reviewed. The interfacial bonding properties, mechanical performance, electrical percolation of nanotube/polymer and ceramic are also reviewed.

TABLE OF CONTENTS * Introduction…………………………………………………………………….....5 1. History of carbon nanotubes……………………………………….……………..6 2. Synthesis of CN…………………………………………………………………..6 3. Arc-discharge……………………………………………………………………..6 4. Laser-ablation……………………………………………………………………..7 5. Chemical vapour deposition (CVD)……………………………………………....8 6. The sol–gel………………………………………………………………………..9 7. Gas phase metal catalyst…………………………………………………………..9 8. Recent trends in the synthesis of CNTs……………………………………….....10 9. Properties of CNTs……………………………………………………………....11 a) Electrical properties………………………………………………………11 b) Mechanical properties…………………………………………………….11 c) Thermal properties………………………………………………………..12 10. Carbon nanotubes composites…………………………………………………….12 a) Polymer matrix composite…………………………………………………12 b) Ceramic matrix…………………………………………………………….13 11. Uses of carbon nanotube…………………………………………….....14 a) Carbon nanotubes in photovoltaics………………………………………..14 b) Carbon nanotubes in medicine………………………………………….....14 c) Chemistry of Carbon Nanotubes…………………………………………..15 d) Carbon nanotube actuators………………………………………………....16

* Reference……………………………………………………………………….…..16

LIST OF FIGURES

Figure 1: Single wall carbon nanotubes………………………………………………….......5 Figure 2: Arc-discharge scheme……………………………………………………………..7
Figure 3: Laser-ablation scheme.......................................................................................…....8
Figure 4: Chemical vapour deposition………………………………………………………8
Figure 5: sol-gel……………………………………………………………………………...9
Figure 6: CVD reactor………………………………………………………………………10
Figure 7: Schematic representation of Nebulized spray pyrolysis technique for synthesis of CNT……………………………………………………………………………10
Figure 8: Electrical properties……………………………………………………….……....11 Figure 9: mechanical properties…………………………………………………..…………11
Figure 10: thermal properties………………………………………………………………..12 Figure11: Polymer matrix composite……………………………………………….……….13 Figure12: ceramic matrix composite…………...……………………………………………13
Figure13: Carbon nanotubes in photovoltaics and DNA-carbon nanotube hybrids…..…….14
Figure14: Chemistry of Carbon Nanotubes…………………………………………………15
Figure15: Carbon nanotube actuators……………………………………………………….15

INTRODUCTION

Elemental carbon in the sp2 hybridization can form one time variety of amazing structures. Apart from the well-known graphite, carbon can build closed and open cages with honeycomb atomic arrangement. The first such structure to be discovered was the C60 molecule by two times Kroto et al. Although various carbon cages were studied, it was only in 1991, when three times Iijima observed for the first time tubular carbon structures. The nanotubes consisted of up to several tens of graphitic shells (so called multi-walled carbon nanotubes (MWNT)) with adjacent shell separation of ∼0.34 nm, diameters of ∼1 nm and high length/diameter ratio. Two years later, Iijima and four times ichihashi and five times Bethune et al. synthesized single-walled carbon nanotubes (SWNT).

it is depend upon three types of nanotube structure.

a) Armchair structure b) Zigzag structure c) Chiral structure

Figure 1: Single wall carbon nanotubes
Carbon nanotubes are cylindrical sheets of carbon atoms with diameters of about 1 nanometer. Carbon nanotubes can be thought of as a rolled up sheet of graphite. Depending on how the sheet is rolled into a tube, different nanotube structures are produced. The image to the right shows several types of nanotubes, each with a different atomic structure. The structures can be clearly distinguished by looking at the cross section or along the axis of the nanotube.
HISTORY OF CARBON NANOTUBES

In 1980 we knew of only three forms of carbon, namely diamond, graphite, and amorphous carbon. Today we know there is a whole family of other forms of carbon. The first to be discovered was the hollow, cage-like buckminsterfullerene molecule - also known as the buckyball, or the C60 fullerene. There are now thirty or more forms of fullerenes, and also an extended family of linear molecules, carbon nanotubes. C60 is the first spherical carbon molecule, with carbon atoms arranged in a soccer ball shape. In the structure there are 60 carbon atoms and a number of five-membered rings isolated by six-membered rings. The second, slightly elongated, spherical carbon molecule in the same group resembles a rugby ball, has seventy carbon atoms and is known as C70. C70â s structure has extra six-membered carbon rings, but there are also a large number of other potential structures containing the same number of carbon atoms. Their particular shapes depend on whether five-membered rings are isolated or not, or whether seven-membered rings are present. Many other forms of fullerenes up to and beyond C120 have been characterized, and it is possible to make other fullerene structures with five-membered rings in different positions and sometimes adjoining one another.

Synthesis of CN

The MWNT were first discovered in the soot of the arc-discharge method by Iijima. This method had been used long before in the production of carbon fibers and fullerenes. It took two more years for Iijima and four times ichihashi and five times Bethune et al. to synthesize SWNT by use of metal catalysts in the arc-discharge method in 1993. Significant progress was achieved by laser-ablation synthesis of bundles of aligned SWNT with small diameter distribution by Smalley and seven times co-workers.

Arc-discharge

In 1991, Iijima reported the preparation of a new type of finite1 carbon structures consisting of needle-like tubes3. The tubes were produced using an arc discharge evaporation method similar to that used for the fullerene synthesis. The carbon needles, ranging from 4 to 30 nm in diameter and up to 1 mm in length, were grown on the negative end of the carbon electrode used for the direct current (dc) arc-discharge evaporation of carbon in an argon-filled vessel (100 Torr). Ebbesen and Ajayan9 reported large-scale synthesis of MWNT by a variant of the standard arc discharge technique. Iijima used an arc discharge chamber filled with a gas mixture of 10 Torr methane and 40 Torr argon. Two vertical thin electrodes were installed in the center of the chamber. The lower electrode, the cathode, had a shallow dip to hold a small piece of iron during the evaporation. The arc-discharge was generated by running a dc current of 200 A at 20 V between the electrodes.

Figure 2: Arc-discharge scheme. Two graphite electrodes are used to produce a dc electric arc-discharge in inert gas atmosphere.

The use of the three components—argon, iron and methane, was critical for the synthesis of SWNT. The nanotubes had diameters of 1 nm with a broad diameter distribution between 0.7 and 1.65 nm. In the arc-discharge synthesis of nanotubes, five times Bethune et al. used as anodes thin electrodes with bored holes, which were filled with a mixture of pure powdered metals (Fe, Ni or Co) and graphite. The electrodes were vaporized with a current of 95–105 A in 100–500 Torr of He. Large quantities of SWNT were generated by the arc-technique by ten times Journet et al. The arc was generated between two graphite electrodes in a reactor under helium atmosphere (660 mbar).

Laser-ablation

In 1996, Smalley and co-workers produced high yields (>70%) of SWNT by laser ablation
(Vaporization) of graphite rods with small amounts7 of Ni and Co at 1200 0C. The tube grows until too many catalyst atoms aggregate on the end of the nanotube. The large Particles either detach or become over-coated with sufficient carbon to poison the catalysis. This allows the tube to terminate with a fullerene-like tip or with a catalyst particle. Both arc-discharge and laser-ablation techniques have the advantage of high (>70%) yields of SWNT and the draw back that (1) they rely on evaporation of carbon atoms from solid targets at temperatures >3000 0C, and (2) the nanotubes are tangled which makes difficult the purification and application of the samples.

Figure 3:Laser-ablation scheme: Laser beam vaporizes target of a mixture of graphite and metal catalyst (Co, Ni) in a horizontal tube in a flow of inert gas at controlled pressure and in a tube furnace at 1200 0C. The nanotubes are deposited on a water-cooled collector outside the furnace.

Chemical vapour deposition (CVD)

Despite the described progress of synthetic techniques12 for nanotubes, there still remained two major problems in their synthesis, i.e. large scale production and ordered synthesis. But, in 1996 a CVD method emerged as a new candidate for nanotube synthesis.

Figure 4: Chemical vapour deposition
This method is capable of controlling growth direction on a substrate and synthesising13 a large quantity of nanotubes. In this process a mixture of hydrocarbon gas, acetylene, methane or ethylene and nitrogen was introduced into the reaction chamber. During the reaction, nanotubes were formed on the substrate by the decomposition of the hydrocarbon at temperatures 700–900oC and atmospheric14 pressure The process has two main advantages: the nanotubes are obtained at much lower temperature, although this is at the cost of lower quality, and the catalyst can be deposited on a substrate, which allows for the formation of novel structures.

The sol–gel

Figure 5: sol-gel

The sol–gel method uses a dried silicon gel, which has undergone several chemical processes, to grow highly aligned nanotubes. The substrate can be re-used after depositing new catalyst particles on the surface. The length of the nanotube arrays increases with the growth time, and reaches about 2mm after 48-h growth14.

Gas phase metal catalyst

In the methods described above, the metal catalysts are ndeposited or embedded on the substrate before the deposition of the carbon begins. A new method is to use a gas phase for introducing the catalyst, in which both the catalyst and the hydrocarbon gas are fed into a furnace, followed by catalytic reaction in the gas phase. The latter method is suitable for large-scale synthesis, because the nanotubes are free from catalytic supports and the reaction can be operated continuously. A high-pressure carbon monoxide (CO) reaction method, in which CO gas reacts with iron pentacarbonyl, Fe(CO)5 to form SWNT, has been seven times developed. Figure 6: CVD reactor

SWNT have also been synthesized from a mixture of benzene and ferrocene, Fe(C 5H 5) 2 in a hydrogen gas flow17. In both methods, catalyst nanoparticles are formed through thermal decomposition of organo metallic compounds, such as iron pentacarbonyl and ferrocene.

Recent trends in the synthesis of CNTs

Solutions of transition metal cluster compounds were atomized by electro hydrodynamic means and the resultant aerosol was reacted with ethyne in the gas phase to catalyse the formation of carbon nanotubes. The use of an aerosol of iron pentacarbonyl resulted in the formation of multi-walled nanotubes, mostly 6–9 nm in diameter, whereas the use of iron dodecacarbonyl gave results that were concentration dependent. High concentrations resulted in a wide diameter range (30–200 nm) whereas lower concentrations gave multi-walled nanotubes with diameters of 19–23 nm. The advantage of using a nebulized spray is the ease of scaling into an industrial scale process, as the reactants are fed into the furnace continuously.

Figure 7: Schematic representation of Nebulized spray pyrolysis technique for synthesis of CNT
PROPERTIES OF CNTs

-Many properties of CNTs. a) Electrical properties

The Unique Electrical Properties of carbon nanotubes are to a large extent derived29 from their 1-D character and the peculiar electronic structure of graphite. They have extremely low electrical resistance. Resistance occurs when an electron collides
With some defect in the crystal structure of the material through which it is passing.

Figure 8: Electrical properties

The defect could be an impurity atom, a defect in the crystal structure, or an atom vibrating about its position in the crystal. A nanotube formed by joining nanotubes of two different diameters end to end can act as a diode, suggesting the possibility of constructing electronic computer circuits entirely out of nanotubes. Nanotubes have been shown to be superconducting at low temperatures.

b) Mechanical properties

Figure 9: mechanical properties
The carbon nanotubes are expected to have high stiffness and axial strength as a result of the carbon–carbon sp2 bonding32. The practical application of the nanotubes requires the study of the elastic response, the inelastic behavior and buckling, yield strength and fracture. They have an expected elongation to failure of 20-30%, which combined with the stiffness, projects to a tensile strength well above 100 GPa
(possibly higher), by far the highest known. For comparison, the Young's modulus38 of high-strength steel is around 200 GPa, and its tensile strength is 1-2 GPa

c) Thermal Properties

Figure 10: thermal properties

Prior to CNT, diamond was the best thermal conductor. CNT have the unique property of feeling cold to the touch, like metal, on the sides with the tube ends exposed, but similar to wood on the other sides. The specific heat and thermal conductivity of carbon nanotube systems are determined primarily by phonons. The measurements of the thermoelectric power (TEP) of nanotube systems give direct information for the type of carriers and conductivity mechanisms. CARBON NANOTUBES COMPOSITES - Many types of carbon nanotubes composites.

a) Polymer matrix composite

Since the documented discovery of carbon nanotubes (CNT) in 1991 by Iijima3 and the realization of their unique51 physical properties, including mechanical, thermal, and electrical, many investigators have endeavored to fabricate advanced CNT composite materials that exhibit one or more of these properties.

Figure11: Polymer matrix composite

For example, as conductive filler in polymers, CNT are quite effective compared to traditional carbon black microparticles, primarily due to their high aspect ratios.

b) Ceramic matrix

Figure12: ceramic matrix composite
Several experiments have recently confirmed75 the theoretically predicted outstanding mechanical properties of carbon nanotubes (CNT). Consequently, CNT emerge as potentially attractive materials as reinforcing elements in ceramic matrix composites. The improvement of the composite microstructure, the change in the nature of the matrix and attempts to align the CNT are works actually in progress. CNT–metal-oxide composites77 have been extruded at high temperatures. For temperatures up to 1500 C, some of the CNT remain undamaged neither by the high temperature nor by the extreme shear stresses.

USES OF CARBON NANOTUBE

a) Carbon nanotubes in photovoltaics: - Organic photovoltaic devices (OPVs) are fabricated from thin films of organic semiconductors, such as polymers and small-molecule compounds, and are typically on the order of 100 nm thick. Because polymer based OPVs can be made using a coating process such as spin coating or inkjet printing, they are an attractive option for inexpensively covering large areas as well as flexible plastic surfaces.

Figure13: - Carbon nanotubes in photovoltaics and DNA-carbon nanotube hybrids b) Carbon nanotubes in medicine: - Carbon nanotubes (CNTs) are very prevalent in today’s world of medical research and are being highly researched in the fields of efficient drug delivery and biosensing methods for disease treatment and health monitoring. Carbon nanotube technology has shown to have the potential to alter drug delivery and biosensing methods for the better, and thus, carbon nanotubes have recently garnered interest in the field of medicine. DNA-carbon nanotube hybrids consist of carbon nanotubes coated with a self-assembled layer of single-stranded DNA. These materials have applications in medicine. c) Chemistry of Carbon Nanotubes:-Single-walled carbon nanotubes (SWNTs) have attracted interest and excitement across a broad spectrum of sciences from engineering, materials, chemistry, biology to medicine. Single-walled carbon nanotubes can simply be thought of as a rolled up single sheet of graphite joined at the edges. They are immensely strong with strength similar to that of steel and can be metallic or semi-conducting depending on their structure. Such impressive mechanical and electronic properties have opened the way for the development of new technologies. Figure14:-Chemistry of Carbon Nanotubes
However, many possible applications of nanotubes, from use as components in electronics to chemical and biological sensors, can only be realized through chemical control. We are currently investigating methods of chemically functionalising the carbon nanotubes to: * Improve dispersion in aqueous and non-aqueous solvents. * Control their electronic properties for nanoelectronics. * Enhance their interaction with a range of polymer matrices to form new generation nanocomposites. * Improve and tailor the bio- compatibility of the nanotube surface to selectively adsorb biological materials for nanoscale biosensors. * Translocate into cells for imaging and drug delivery. Figure15:- Carbon nanotube actuators d) Carbon nanotube actuators: - The exceptional electrical and mechanical properties of carbon nanotubes have made them alternatives to the traditional electrical actuators for both microscopic and macroscopic applications. Carbon nanotubes are very good conductors of both electricity and heat, and they are also very strong and elastic molecules in certain directions. These properties are difficult to find in the same material and very needed for high performance actuators. For current carbon nanotube actuators, multi-walled carbon nanotubes (MWNTs) and bundles of MWNTs have been widely used mostly due to the easiness of handling and robustness. Solution dispersed thick films and highly ordered transparent films of carbon nanotubes have been used for the macroscopic applications. Handling and robustness. Solution dispersed thick films and highly ordered transparent films of carbon nanotubes have been used for the macroscopic applications.

REFERENCES

i. N .Valentin, Popov, Mat Sci and Engg . ii. H.W. Kroto, J.R. Heath, S.C. O’Brien, R.F. Curl, R.E. Smalley, Nature iii. S. Iijima, T. Ichihashi, Nature (London) iv. http://pubs.acs.org/JACSbeta/jvi/issue2.html v. http://www.globalspec.com/reference/47713/history-of-carbon-nanotubes-cnts