3. Introduction
• Materials in which a single unit is sized (in at least one dimension)
between 1 to 100 nm (the usual definition of nanoscale).
• Classification of Nanomaterials
1. One dimension in nanoscale(Other two dimensions are extended)
• Thin films
• Surface Coatings
2. Two dimensions in nanoscale(Other one dimension is extended)
• Nanowires
• Nanotubes
3. Three dimensions in nanoscale
• Nanoparticles
• Quantum dots
4. Carbon Nanotubes
Carbon nanotubes are allotropes of
carbon with a cylindrical nanostructure.
These cylindrical carbon material have
unusual properties, which are valuable
for nanotechnology, electronics, optics
and other fields of material science and
technology.
5. Structure
Nanotubes are members of fullerene
structure family. Their name is derived from
their long, hollow structure with walls
formed by one-atom-thick sheets of carbon,
called graphene.
Carbon nanotubes can be obtained by
rolling a graphene sheet in a specific
direction, maintaining the circumference of
the cross-section.
Nanotubes are categorized as –
single-walled carbon nanotubes (SWCNTs)~
1nm
multi-walled carbon nanotubes (MWCNTs)
6. The (n,m) nanotube naming scheme can be thought of as a vector (Ch) in an infinite graphene sheet
that describes how to "roll up" the graphene sheet to make the nanotube.
7. Properties
1. Mechanical : The carbon nanotubes are highly elastic. The Young’s
modulus is a measure of the elasticity. The Young’ modulus for carbon
nanotubes is about 1800 GPa whereas it is about 210 GPa for steel.
Carbon nanotubes exhibit large strength in tension. They are about
ten times stronger than steel.
2. Electrical : The electrical properties of carbon nanotubes depends on
their diameter. They show electrical properties ranging from
semiconductors to those of good conductors. The energy gap decreases
as diameter of CNT is increased. Due to very low resistivity, the heat
dissipation in the CNT is very small and hence they can carry much larger
currents than the metals.
8. Properties
3. Thermal Conductivity: Carbon nanotubes are very good conductors
of heat. Their thermal conductivity is more than twice that of
diamond. The thermal conductivity also varies with direction. The
conductivity is very good along the axis of the tube and very low in
a perpendicular direction.
4. Chemical : CNT’s are chemically more inert compared to other
forms of carbon.
9. Synthesis
• There are three method using which we can
produce carbon nanotubes.
1. ARC DISCHARGE METHOD :-
The carbon arc discharge method, first utilized
for creating C60 fullerenes, is one of the most
common and easiest way to create CNTs.
The method makes CNTs through arc-
vaporization of two carbon rods situated end to
end in a location that is filled with low pressure
and inert gas. The discharge evaporates the
surface of one of the carbon electrodes, and
creates a tiny rod-shaped deposit on the opposing
electrode.
The technique creates a complicated mixture of
components. It also requires additional
purification to isolate the CNTs from the soot.
10. Synthesis Cntd.
2. LASER ABLATION:-
A high power laser was used to vaporize carbon
from a graphite target at high temperature. Both
MWNTs and SWNTs can be produced with this
technique.
The laser is focused onto a carbon targets
containing 1.2 % of cobalt/nickel with 98.8 % of
graphite composite that is placed in a 1200°C
quartz tube furnace under the argon atmosphere
(~500 Torr).
The diameter distribution of SWNTs from this
method varies about 1.0 - 1.6 nm. Carbon
nanotubes produced by laser ablation were purer
(up to 90 % purity) than those produced in the arc
discharge process
11. 3. CHEMICAL VAPOUR DEPOSITION (CVD):-
CVD technique can be achieved by taking a
carbon source in the gas phase and using an
energy source, such as plasma or a resistively
heated coil, to transfer energy to a gaseous
carbon molecule.
The hydrocarbons flow through the quartz
tube being in an oven at a high temperature (~
720 C). At high temperature, the hydrocarbons
are broken to be the hydrogen carbon bond,
producing pure carbon molecules. Then, the
carbon will diffuse toward the substrate,
which is heated and coated with a catalyst.
This method can produce both MWNTs and
SWNTs depending on the temperature
12. Functionalization
The main problem with the majority of popular synthetis methods is that they
produce samples yielding a mixture of various diameters and chiralities of
nanotubes that are normally contaminated with metallic and amorphous
impurities. However, to exploit as much as possible of their properties, most of
time they requires the functionalization.
Such as changing the surface properties to make it soluble in different media
or attaching functional groups or polymer chains.
Functionalization possibilities for SWNTs:
Covalent functionalization
Non-Covalent functionalization
13. 1. Covalent functionalization:-
Covalent functionalization of single-walled carbon
nanotubes (SWNTs) has significantly expanded the
utility of the nanotube structure. Covalent sidewall
functionalization has been employed to increase the
solubility of these materials, which allows for the
manipulation and processing of these otherwise
insoluble nanotubes.
Several SWNT sidewall functionalization
methodologies now exist, and they all have one thing in
common: a highly reactive intermediate is necessary to
attack the carbon nanotubes.
But, it drastically affects the electronic structure of
SWNTs and hence affects their properties.
14. Functionalization Cntd.
2. Non-covalent functionalization:-
The non-covalent interaction is based on van
der waals forces and it is controlled by
thermodynamics.
The great advantage of this type of functionality
relies upon the possibility of attaching various
groups without disturbing the electronic system
of rolled graphene sheets of CNTs.
The formation of non-covalent aggregates with
surfactants is a suitable method for dispersing
nanotubes in organic solvent.
15. Advantages Disadvantages
Extremely small and lightweight, making them
excellent replacements for metallic wires.
Extremely small, so are difficult to work with.
Are resistant to temperature changes, meaning they
function almost just as well in extreme cold as they do
in extreme heat.
Currently the process is relatively expensive to
produce the nanotubes.
Despite all the research, scientists still don’t
understand exactly how the work.
16. Applications
CNT’s can store lithium due to which they can be used in batteries. CNT’s
can also store hydrogen and hence find potential applications in fuel cells.
They are used in the tips for atomic force microscope probes.
They are being used to develop flat panel displays for television and
computer monitors.
They are used in chemical sensors to detect gases.
17. Fullerene
A fullerene is an allotrope of carbon in the form
of a hollow sphere, ellipsoid, tube, and many
other shapes. Spherical fullerenes, also referred to
as buckyballs
The first fullerene molecule (C60) was
manufactured in 1985 at Rice University.
Minute quantities of the fullerenes, in the form
of C60, C70, C76, C82 and C84 molecules, are
produced in nature, hidden in soot and formed by
lightning discharges in the atmosphere.
18. Structure of C60
A truncated icosahedron structure.
Icosahedron- A polygon with 60 vertices and 32 faces,
12 of which are pentagonal and 20 hexagonal.
A carbon atom is present at each vertex.
Valancies of each carbon atom are satisfied by two
single and one double bond.
The bonding pattern of C60 fullerene, with yellow
bonds representing double bonds and red bonds as
single bonds.
The pentagonal rings contain only single bonds; as
double bonds have a shorter bond length and lead to
instability in pentagonal ring.
19. Properties
• The molecule can act as a semiconductor, conductor and superconductor
under specific conditions.
• It is very tough and thermally stable.
• It can be compressed to lose 30% of its volume without destroying its
carbon cage structure.
20. Synthesis
1. Arc method
Fullerenes can be made by vaporizing carbon within
a gas medium.(they could form spontaneously in a
condensing carbon vapor).
An electric arc is maintained between two nearly
contacting graphite electrodes.
Most of the power is dissipated in the arc and not in
resistive heating of the rod.
The entire electrode assembly is enclosed in a
reaction kettle that is filled with ~ 100 torr pressure of
helium.
Black soot is produced, and extraction with organic
solvents yields fullerenes.
R. E. Smalley, Nobel Prize lecture,
December 7, 1996
22. Endohedral Fullerene
Atoms, molecules, or ions can be trapped inside the
cavity of a fullerene cage to form endohedral
fullerenes. H2 , N2 , and a wide variety of noble gases
and transition metal atoms have been successfully
encapsulated.
The procedure starts with a ring opening or a ring
expansion generally induced by cycloadditions or
radical-oxidation reactions in order to open a ‘hole’ in
the sphere and put in the desired species .The
reconstitution of the cage after the encapsulation is
achieved at high temperatures.
23. Exohedral fullerene
Exohedral fullerene, also called as
exofullerenes, are fullerenes that have
additional atoms, ions, or clusters attached
to their outer spheres such as-
C50Cl10
C60H8.
These materials offer the most exciting
potential for useful applications of fullerene
materials.
24. Fullerides
Fullerides are chemical compounds containing
fullerene anions. Common fullerides are derivatives
of the most common fullerenes, i.e. C60 and C70.
The scope of the area is large because multiple
charges are possible, i.e., [C60]n− (n = 1, 2...6), and all
fullerenes can be converted to fullerides. The suffix "-
ide" implies their negatively charged nature.
Fullerides have been prepared in various ways :
One of the way is treating fullerene with alkali metals to
give the alkali metal fullerides :
C60 + 2 K → K2C60
25. Carbon Peapods
• Carbon peapod is a hybrid nanomaterial consisting of
spheroidal fullerenes encapsulated within a carbon nanotube. It is named
due to their resemblance to the seedpod of the pea plant. Since the
properties of carbon peapods differ from those of nanotubes and fullerenes,
the carbon peapod can be recognized as a new type of a self-assembled
graphitic structure.
• Possible applications of nano-peapods include nanoscale lasers, single
electron transistors, and data storage devices thanks to the memory effects
and superconductivity of nano-peapods
26. Applications
Due to their extremely resilient and sturdy nature, fullerenes are being
considered for use in combat armor.
Elements can be bonded with it to create more diverse materials,
including superconductors and insulators.
It is suitable for used as a lubricant due to its spherical structure.
