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Home , Allotropes of carbon, Carbon black, Carbon nanofoam, Carbon nanotube, Nanofoam, Radialene

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Carbon Nano tubes Carbon Molecular Sieves intercalated compounds &

Fullerenes

In 1985, Harold Kroto (Sussex), Robert Curl and , (Rice

University,) discovered C60, and shortly thereafter came to discover the . Kroto, Curl, and Smalley were awarded the 1996 Nobel Prize in Chemistry for their roles in the discovery of this class of H. Kroto R. Smalley . C60 and other fullerenes were later noticed occurring outside the laboratory (for example, in normal candle-).. Fullerenes An idea from Kroto's special interest in red giant rich in carbon led to the discovery of the fullerenes. For years, he had had the idea that long- chained molecules of carbon could form near such giant stars. To mimic this special environment in a laboratory, Curl suggested contact with Smalley who had built an apparatus which could evaporate and analyze almost any material with a laser beam. During the crucial week in Houston in 1985 the Nobel laureates, together with their younger co- workers J. R. Heath and J. C. O'Brien, starting from graphite, managed to produce clusters of carbon consisting mainly of 60 or 70 carbon . These clusters proved to be stable and more interesting than long-chained molecules of carbon. Two questions immediately arose. How are these clusters built? Does a new form of carbon exist besides the two well-known The read-out from the mass spectrometer shows forms graphite and ? how the peaks corresponding to C60 and C70 become more distinct when the experimental conditions are optimized. C60 is soccer-ball-shaped or Ih with 12 and 20 . According to Euler's theorem these 12 pentagons are required for closure of the carbon network consisting

of n hexagons and C60 is the first stable because it is the smallest possible to obey this rule (higher ones C 180, 540). In this structure none of the pentagons make

contact with each other. Both C60 and its relative C70 obey this so-called isolated rule (IPR). Non-IPR fullerenes have thus far only been isolated as endohedral

fullerenes such as Tb3N@C84

The double bonds in fullerene are not all the same. Two groups can be identified: 30 so- called [6,6] double bonds connect two hexagons and 60 [5,6] bonds connect a and a pentagon. Of the two the [6,6] bonds are shorter with more double-bond character and therefore a hexagon is often represented as a cyclohexatriene and a pentagon as a pentalene or [5]radialene. In other words, although the carbon atoms in fullerene are all conjugated the superstructure is not a super aromatic compound. The X-ray diffraction values are 135.5 pm for the [6,6] bond and 146.7 pm for the [5,6] bond. 13C NMR of C60 and C70

C70 (δ = 150.91, 148.36, 147.67, 145.64, and 131.15 Preparation and purification of C60 and C70

Kratscher’s methodology for preparation of fullerenes is the one widely used currently which has been modified by various workers to increase yields. It was Kroto again who separated C60 and C70 for the first time in pure forms. Graphite electrodes are evaporated in an atmosphere of ~ 100 torr of Helium (Kratschmer) or 50 -100 torr of (Kroto) in a glass vessel (modified RB flask, Power from a transformer) . The soot formed is scrapped and dispersed in whereupon a wine red solution is obtained. This is filtered from the insoluble solids and concentrated . This mixture of C60 and C70 is then run on an alumina column using hexane as eluant. The magneta colored C60 elutes out first followed by the port wine colored C70. In a typical case the ratio of C60 to C70 will be 5:1. Solid pure C60 will be mustard colored [UV 596, 604, 625nm] and C70 will be red [600, 617, 644 nm]. (laser vaporization of graphite and graphite doped with other elements and compounds such as lanthanide , nitride has also been used for synthesis of fullerenes ) How to draw a C60?

step 1 step 2 step 3 step 4 step 5 ( no double bonds in pentagons)

The structure of C60 can be specifically described as having 12 pentagons and 20 hexagons with the pentagons sharing no common edge and the hexagons sharing edges with another hexagon or a pentagon. All the are tricoordinate, pyramidal and all pentagons and hexagons are planar. Two types of C- C bonds are present in the with differing bond lengths, 1.388 Å for a 6,6 bond (common for two hexagons) and 1.432 Å for a 5,6 bond (common for a hexagon and a pentagon ).

In contrast to C60 were all carbon atoms are identical, C70 has five different types of carbon atoms depending on the carbon environment. These are easily 13 differentiated by C NMR. C76, another fullerene whose X ray structure has been solved belongs to D2 point group, is chiral and occurs as a racemic mixture. Stability of C60

( a ) ( b) (c) IPR IPR Not-IPR

The unusual stability of C60 compared to other higher / lower fullerenes has been explained. In the structure of C60 , all the twelve pentagons are isolated from each other. Again only in C60 we can see double bonds arranged in such a way that they are located only in six membered rings and none in five membered rings. This is favored as there will be less strain on the already strained five membered rings as a result of such an arrangement. The need to avoid double bonds in pentagons largely governs the stability of fullerenes as the five membered rings with five planar hexagons around are already strained and unsaturation is going to increase the strain further. C60 has only arrangement (a) in its structure while C70 and C84 has five and six of the (b) arrangements in their structures respectively. Concept of on C60

Initially C60 was predicted to be extremely stable and aromatic. Even more than 12,500 resonance structures were proposed. The terms superaromaticity and three dimensional aromaticity were freely used to describe its structure. However the presence of strained five membered rings adjacent to benzenoid rings were overlooked. Only one structure exists for C60 which avoids having any double bonds in pentagons. The two important consequences of this finding was that a) the delocalization of in C60 is poor and so it is more reactive than expected. b) C60 is not so much an aromatic compound and the double bonds in it are isolated. This is clearly indicated by the 2 coordination shown by C60 when reacted with Vaska’s complex Chemistry of fullerenes: Different directions

30 years on from the

discovery of C60, the outstanding properties and potential applications of the synthetic carbon allotropes — fullerenes, nanotubes and graphene — overwhelmingly illustrate their unique scientific and technological importance.

a, Fullerene salts; b, exohedral adducts/derivatives; c, open-cage fullerenes; d, quasi-fullerenes; e, heterofullerenes; f, endohedral fullerenes. Endohedral and open cage fullerenes

Molecular Surgery!

The molecular surgery technique involves a series of carefully controlled chemical reactions to open up the fullerene cage and then insert the guest molecule into the fullerene cage through high and condition. It then follows up with another series of reaction to reseal the orifice while the molecule is inside. This is the technique used to synthesize all variant of dihydrogen endofullerenes Exohedral Fullerenes Halogenated Fullerenes

Iodine: only adducts C60X6 (X=Cl, Br) Synthesis and uniqueness of structures 2 – Complexes of fullerenes

OC CO OC CO OC Ru CO Ru CO OC Ru CO 5- Complexes of Fullerenes

1,3-Dimethyl-2-imidazolidinone Bucky metallocenes Different dimensionalities of carbon materials

Graphene is a 2D building material for different dimensionalities of carbon materials, can be wrapped into fullerenes, rolled into nanotubes or stacked into graphite Carbon Nanotubes

The first observation of the multiwalled carbon nanotubes was credited to Iijima. In 1993 Iijima and Donald Bethune found single walled nanotubes known as buckytubes. This helped the scientific community make more sense out of not only the potential for nanotube research, but the use and existence of fullerene.

Nanotubes discovered in the soot of arc discharge at NEC, by Japanese researcher Nano

10-9 10-6 10-3 100 103 106 109 m

• Size – 10-9 m (1 nanometer) • Border to quantum mechanics What are Carbon nanotubes?

•Carbon nanotubes (CNTs) are . These cylindrical carbon molecules have interesting properties that make them potentially useful in many applications in , , and other fields of , as well as potential SWNT uses in architectural fields.

•They exhibit extraordinary strength and unique electrical properties, and are efficient conductors of heat. Their final usage, however, may be limited by their potential toxicity.

MWNT Nanotube Three types based on style of roll formation ZIG ZAG, ARM CHAIR, CHIRAL Nanotube

High aspect ratio: Length: length 1000 typical few μm diameter

→ quasi 1D solid

The shortest is the , having 8 phenyl rings connected Diameter: through para positions which was synthesized in early as low as 1 nm 2009

The longest carbon nanotubes grown so far are over 550 mm long was reported in 2013 Electrical Properties Electrical conductance depending on helicity

• If the nanotube structure is armchair then the electrical properties are metallic • If the nanotube structure is chiral or zig zag then the electrical properties can be semiconducting with a very small , otherwise the nanotube is a moderate • In theory, metallic nanotubes (armchair) can carry an electrical current density of 4×109 A/cm2 which is more than 1,000 times greater than metals such as Mechanical Properties

Strong Like

Light Like Aluminum

Elastic Like Plastic Strength Properties • Carbon nanotubes have the strongest tensile strength of any material known. • It also has the highest modulus of elasticity. Young's Modulus Tensile Strength Elongation at Material (TPa) (GPa) Break (%) SWNT ~1 (from 1 to 5) 13-53E 16 Armchair 0.94T 126.2T 23.1 SWNT Zigzag SWNT 0.94T 94.5T 15.6-17.5 Chiral SWNT 0.92 MWNT 0.8-0.9E 150 Stainless Steel ~0.2 ~0.65-1 15-50 Kevlar ~0.15 ~3.5 ~2 KevlarT 0.25 29.6

YM is a measure of the stiffness of an elastic material TS is the maximum stress a material can take

MWCNT • Operational -196oC < T < 450oC • Electrical conducting • Toughness comparable to Kevlar • No rapture in knot

Zhang, Atkinson and Baughman, Science 306 (2004) 1358. Commercial

• Companies: ~ 20 worldwide - Carbon Inc. (CNI) - SES Research - n-Tec • Prices: - Tubes: pure SWCNT $500 / gram (CNI) MWCNT € 20-50 / gram (n-Tec)

- C60 : pure $100-200 / gram (SES Research) - Cones: Multi € 1 / gram (n-Tec)

- Gold : $10 / gram Graphene

Sir Novoselov Sir Andre Geim

Andre Geim was awarded the 2010 Nobel Prize in Physics jointly with Konstantin Novoselov "for groundbreaking experiments regarding the two-dimensional material graphene". Graphene consists of one--thick layers of carbon atoms arranged in two-dimensional hexagons, and is the thinnest material in the world, as well as one of the strongest and hardest. The material has many potential applications and is considered a superior alternative to . Geim's achievements include the discovery of a simple method for isolating single atomic layers of graphite, known as graphene using scotch tape. The team published their findings in October 2004 in Science Graphene

2 dimensional material , 1 atom thick Thinnest object: 1million times than hair Lightest object Strongest material, 300 times stronger than steel Flexible, stretchable and bendable Harder than diamond Conducts better than copper and Conducts heat better than diamond Transparent Graphene: thermal properties compared

Thermal conductivity Material W/(m·K) Silica 0.004 - 0.04 Air 0.025 Wood 0.04 - 0.4 Water (liquid) 0.6 Glass 1.1 Soil 1.5 Concrete, stone 1.7 Ice 2 Sandstone Stainless steel 12.11 ~ 45.0 Lead 35.3 Gold 318 Copper 401 Silver 429 Diamond 900 - 2320 Graphene (4840±440) - (5300±480) Preparation and characterization graphene

Preparation methods

Top-down approach Bottom up approach (From graphite) (from carbon precursors)

- Micromechanical exfoliation of - By chemical vapour graphite (Scotch tape or peel-off deposition (CVD) method) of hydrocarbon - Creation of colloidal suspensions - By epitaxial growth on from or graphite electrically intercalation compounds (GICs) insulating surfaces such as SiC - Total Organic Synthesis

Preparation methods

Top-down approach (From graphite)

Direct exfoliation of From Graphite Graphite oxide graphite intercalation method compounds Direct exfoliation of graphite

Graphene sheets ionic-liquid-modified by using graphite electrodes.

Liu, N. et al. One-step ionic-liquid-assisted electrochemical synthesis of ionicliquid- functionalized graphene sheets directly from graphite. Adv. Funct. Mater. 18, 1518–1525 (2008). Graphite intercalation compound

J. Mater. Chem. 2005, 15, 974. Graphite oxide method (Most common and high yield method)

Oxidatio Huers’ethod Graphite Oxide

H2SO4/ KMnO4 H2SO4/KClO3 Graphite Or H2SO4/HNO3 ………………. H2O

Ultrasonication (exfoliation)

Fuctionalization (for better ) Graphene Oxide monolayer or few layers

Chemical reduction to restore graphitic structures

Making composite with Chemical Vapor deposition of graphene Proposed Incredible Uses for Graphene

Scientists at Rice say graphene could Water, water everywhere and EVERY drop drinkable. MIT potentially clump together radioactive mind s have a plan for a graphene filter covered in tiny waste, making disposal is a breeze. holes just big enough to let water through and small enough to keep salt out, making salt water safe for consumption.

Touchscreens that use graphene as their conductor could be slapped onto plastic rather than glass. That would mean super thin, unbreakable touchscreens and a replacement for ITO Just a single sheet of graphene could produce headphones that have a frequency response comparable to a pair of Sennheisers, as some scientists at UC Berkeley recently showed.

Graphene could pave the way for bionic devices in living tissues that could be connected directly to your neurons. So people with spinal injuries, for example, could re-learn how to use their limbs. Graphite Intercalation Compounds

One of the best studied graphite intercalation compounds, KC8, is prepared by melting potassium over graphite powder. The potassium is absorbed into the graphite increasing the interlayer distance from 335 to 540 nm and the material changes color from to bronze. The resulting solid is pyrophoric. The composition is explained by assuming that the potassium to potassium distance is twice the distance between hexagons in the carbon framework. The bond between anionic graphite layers and potassium cations is ionic. The electrical conductivity of the material is greater than that of α-graphite.KC8 is a superconductor with a very low critical temperature Tc = 0.14 K. The gold-colored material KC8 is one of the strongest reducing agents known. It has also been used as a catalyst in polymerizations and as a coupling reagent for aryl halides to biphenyls . Molecular Sieving Carbon (MSC) or Carbon Molecular Sieves (CMS)

Dry air contains 78 % N2, 21% O2, 0.9% Ar, 0.04% CO2

Activated carbon is generally used for gas Application of Molecular Sieving and liquid has well developed Carbon micro and transitional pores of 10 to 500 Molecular Sieving Carbon is widely used angstrom in pore diameter. for gas separation. One of the most On the other hand, Molecular Sieving typical applications is nitrogen PSA Carbon has only uniform supermicro pores (Pressure Swing Adsorption). Nitrogen of less than 10 angstrom (1 nm) in pore PSA is using velocity separation, which makes use of the difference of diameter. adsorption velocity between nitrogen and oxygen. The of PSA is largely affected by the property of Molecular Sieving Carbon. It is because the difference of molecular sizes is very

small between O2 (0.28nm×0.39nm) and N2(0.30nm×0.43nm). The best Molecular Sieving Carbon for N2/O2 separation is precisely controlled so as to have

slightly larger pores than N2. This pore size control results in that the N2 is harder to adsorb and O2 is easier to adsorb. Pore size = 3-4 Å

O2 (2.8×3.9 Å) N2 (3.0×4.3 Å ). Carbon Molecular Sieves (CMS) Preparation of CMS

Carbon molecular sieves (CMS) and CMS membranes result from a heat treatment under controlled atmosphere or under of an organic polymeric precursor. During this heat treatment ( 500-1000 C) the polymeric chains decompose giving rise to an skeleton with interconnected pores. The pore size ( less than 1 nm) and its network is responsible for the separation of molecules. Precursors

Polyimides Polyacrylonitrile Phenol-formaldehyde resin Polyfurfuryl alcohol

Pre-treatment (500-1000 C) Post Treatment PSA separation

Pretreated compressed air enters the bottom of the on-line tower and follows up through the CMS. Oxygen and other trace gasses are preferentially adsorbed by the CMS, allowing nitrogen to pass through. After a pre-set time, the on-line tower automatically switches to regenerative mode, venting contaminants from the CMS. Carbon molecular sieve differs from ordinary activated carbons in that it has a much narrower range of pore openings. This allows small molecules such as oxygen to penetrate the pores and be separated from nitrogen molecules which are too large to enter the CMS. The larger molecules of nitrogen by-pass the CMS and emerge as the product gas. membrane separation

Atmospheric air contains essentially 78% nitrogen and 21% oxygen. Ordinary dry compressed air is filtered and passed through a technically advanced bundle of hollow membrane fibers where nitrogen is separated from the feed air by selective permeation. Water vapor and oxygen rapidly permeate safely to the atmosphere, while the nitrogen gas is discharged under pressure into the distribution system. Pressure, flow rate and membrane size/quantity are the main variables that affect nitrogen production. Nitrogen purity (oxygen content) is controlled by throttling the outlet from the membrane bundle(s). At a given pressure and membrane size, increasing the nitrogen flow allows more oxygen to remain in the gas stream, lowering nitrogen purity. Conversely, decreasing nitrogen flow increases purity. For a particular purity, higher air pressure to the membrane gives a higher nitrogen flow rate. Purity ranges of less than 90% to 99.9% are possible. Carbon molecular sieves from

MCM-48

MCM-48 after carbonization with sugar catalyzed by H2SO4

CMK-1 after leaching out MCM-48 with NaOH and EtOH Quantity wise the maximum produced carbon allotrope

Carbon black is a material produced by the incomplete combustion of heavy products such as tar, cracking tar, and a small amount from . Carbon black is a form of paracrystalline carbon that has a high surface-area-to-volume ratio, albeit lower than that of

Total production was around 8,100,000 metric tons in 2006. The most common use (70%) of carbon black is as a and reinforcing phase in automobile tires. Carbon black also helps conduct heat away from the tread and belt area of the tire, reducing thermal damage and increasing tire life. Carbon black particles are also employed in some radar absorbent materials and in photocopier and laser printer , and other and paints.

About 20% of world production goes into belts, hoses, and other non-tire rubber goods. Allotropes of carbon:

a) Diamond, b) Graphite, c) (meteoric graphite)

d) C60 (Buckminster fullerene or buckyball), e) C540, f) C70, g) Amorphous carbon, and h) single-walled carbon nanotube i. Graphene j. Linear Acetylenic carbon K. L. Carbon nanobud M. Carbon

Etc…………