The inorganic chemistry of Carbon

Carbon Nano tubes

&Graphene Graphite intercalated compounds Carbon Molecular Sieves

Fullerenes

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

University,) discovered C60, and shortly thereafter came to discover the

fullerenes. Kroto, Curl, and Smalley were awarded the 1996 Nobel

Prize in Chemistry for their roles in the discovery of this class of

molecules. C60 and other fullerenes were later noticed occurring

outside the laboratory (for example, in normal candle-soot)..

H. Kroto R. Smalley

An idea from outer space

Kroto's special interest in red giant stars 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

atoms. 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

forms graphite and diamond?

The read-out from the mass spectrometer shows

how the peaks corresponding to C60 and

C70 become more distinct when the experimental

conditions are optimized.

Fullerenes

C60 is soccer-ball-shaped or Ih with 12 pentagons and 20 hexagons. 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 fullerene 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

pentagon 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 hexagon

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

bond length values are 135.5 pm for the [6,6] bond and 146.7 pm for the [5,6] bond.

C70 (δ = 150.91, 148.36, 147.67, 145.64, and 131.15

13C NMR of C60 and C70

Preparation and purification of C60 and C70

Kratsch er’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 Argon (Kroto)

in a glass vessel (modified RB flask, Power from a transformer) . The soot formed is

scrapped and dispersed in benzene 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 metals, boron nitride has also been used

for synthesis of fullerenes )

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

How to draw a C60?

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 carbons are tricoordinate, pyramidal and all pentagons and hexagons are planar. Two types of C- C bonds are present in the molecule 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 differentiated by 13C 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)

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.

IPR IPR Not-IPR

Concept of aromaticity 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 electrons 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

a, Fullerene salts; b, exohedral adducts/derivatives; c, open-cage

fullerenes; d, quasi-fullerenes; e, heterofullerenes; f, endohedral fullerenes.

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.

Endohedral and open cage fullerenes

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 temperature and pressure 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

Molecular

Surgery!

Exohedral Fullerenes

Halogenated Fullerenes

Iodine: only

adducts

C60X6 (X=Cl, Br) Synthesis and uniqueness of structures

RuRu

Ru

COCO

CO

COCOOCOC

OC

OC

2 – Complexes of fullerenes

5- Complexes of Fullerenes

1,3-Dimethyl-2-imidazolidinone

Bucky metallocenes

Graphene is a 2D building material for different dimensionalities of carbon materials,

can be wrapped into fullerenes, rolled into nanotubes or stacked into graphite

Different dimensionalities of carbon materials

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 Sumio Iijima

Carbon Nanotubes

Nano

• Size – 10-9 m (1 nanometer)

• Border to quantum mechanics

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

What are Carbon nanotubes?

•Carbon nanotubes (CNTs) are allotropes of carbon. These cylindrical carbon molecules have interesting properties that make them potentially useful in many applications in nanotechnology, electronics, optics and other fields of materials science, as well as potential 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.

SWNT

MWNT

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

Nanotube

Diameter:

as low as 1 nm

Length:

typical few μm

High aspect ratio:

1000diameter

length

→ quasi 1D solid

The longest carbon nanotubes grown so far are over

550 mm long was reported in 2013

The shortest carbon nanotube is the organic compound

cycloparaphenylene, having 8 phenyl rings connected

through para positions which was synthesized in early

2009

Electrical Properties

• 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 band gap, otherwise the

nanotube is a moderate

semiconductor

• 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 copper

Electrical conductance depending on helicity

Mechanical Properties

Strong Like Steel

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.

Material Young's Modulus

(TPa)

Tensile Strength

(GPa)

Elongation at

Break (%)

SWNT ~1 (from 1 to 5) 13-53E 16

Armchair

SWNT 0.94T 126.2T 23.1

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

Yarn

Zhang, Atkinson and Baughman,

Science 306 (2004) 1358.

MWCNT

• Operational -196oC < T < 450oC

• Electrical conducting

• Toughness comparable to Kevlar

• No rapture in knot

Commercial

• Companies: ~ 20 worldwide - Carbon Nanotechnologies 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 Andre Geim

Graphene consists of one-atom-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 silicon. 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

Andre Geim was awarded the 2010 Nobel Prize in Physics jointly with Konstantin

Novoselov "for groundbreaking experiments regarding the two-dimensional material

graphene".

Sir Novoselov

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 electricity better than copper and silver

Conducts heat better than diamond

Transparent

Graphene

Material Thermal conductivity W/(m·K)

Silica Aerogel 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)

Graphene: thermal properties compared

Preparation and characterization graphene

Preparation methods

Top-down approach (From graphite)

Bottom up approach (from carbon precursors)

- By chemical vapour deposition (CVD) of hydrocarbon - By epitaxial growth on electrically insulating surfaces such as SiC - Total Organic Synthesis

- Micromechanical exfoliation of graphite (Scotch tape or peel-off method) - Creation of colloidal suspensions from graphite oxide or graphite intercalation compounds (GICs)

Top-down approach (From graphite)

Graphite oxide method

From Graphite intercalation compounds

Direct exfoliation of graphite

Preparation methods

Graphene sheets ionic-liquid-modified by electrochemistry

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).

Direct exfoliation of graphite

J. Mater. Chem. 2005, 15, 974.

Graphite intercalation compound

Graphite oxide method (Most common and high yield method)

Graphite

Oxidatio Hu ers’ ethod

H2SO4/ KMnO4

H2SO4/KClO3

Or H2SO4/HNO3

………………. H2O

Ultrasonication (exfoliation)

Graphite Oxide

Graphene Oxide monolayer or few layers

Fuctionalization (for better dispersion)

Making composite with polymers

Chemical reduction to restore graphitic structures

Chemical Vapor deposition of graphene

Proposed Incredible Uses for Graphene

Scientists at Rice say graphene could

potentially clump together radioactive

waste, making disposal is a breeze.

Water, water everywhere and EVERY drop drinkable. MIT

mind s have a plan for a graphene filter covered in tiny

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.

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 black 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.

Graphite Intercalation Compounds

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 .

Application of Molecular Sieving

Carbon

Molecular Sieving Carbon is widely used for gas separation. One of the most typical applications is nitrogen PSA

(Pressure Swing Adsorption). Nitrogen PSA is using velocity separation, which makes use of the difference of adsorption velocity between nitrogen and oxygen. The performance 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.

Molecular Sieving Carbon (MSC) or Carbon Molecular Sieves (CMS)

Activated carbon is generally used for gas and liquid adsorption has well developed micro and transitional pores of 10 to 500 angstrom in pore diameter. On the other hand, Molecular Sieving

Carbon has only uniform supermicro pores of less than 10 angstrom (1 nm) in pore diameter.

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

Pore size = 3-4 Å

O2 (2.8×3.9 Å) N2 (3.0×4.3 Å ).

Carbon Molecular Sieves (CMS)

Preparation of CMS

Precursors

Polyimides

Polyacrylonitrile

Phenol-formaldehyde

resin

Polyfurfuryl alcohol

Pre-treatment Pyrolysis (500-1000 C) Post

Treatment

Carbon molecular sieves (CMS) and CMS membranes result

from a heat treatment under controlled atmosphere or under

vacuum of an organic polymeric precursor. During this heat

treatment ( 500-1000 C) the polymeric chains decompose

giving rise to an amorphous carbon skeleton with

interconnected pores. The pore size ( less than 1 nm) and its

network is responsible for the separation of molecules.

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.

PSA

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.

membrane

separation

MCM-48

MCM-48 after

carbonization

with sugar

catalyzed by

H2SO4

CMK-1 after

leaching out

MCM-48 with

NaOH and EtOH

Carbon molecular sieves from Zeolites

Carbon Black

Quantity wise the maximum produced carbon allotrope

Total production was around 8,100,000 metric tons in 2006. The most

common use (70%) of carbon black is as a pigment 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 toner, and other inks and

paints.

About 20% of world production goes into belts, hoses, and other non-tire

rubber goods.

Carbon black is a material produced by the incomplete combustion of heavy

petroleum products such as coal tar, ethylene cracking tar, and a small amount

from vegetable oil. Carbon black is a form of paracrystalline carbon that has a

high surface-area-to-volume ratio, albeit lower than that of activated carbon

Allotropes of carbon:

a) Diamond, b) Graphite,

c) Lonsdaleite (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. glassy carbon

L. Carbon nanobud

M. Carbon nanofoam

Etc…………