CARBON NANOTUBES-TREATMENT AND

FUNCTIONALIZATION

BY,

LINI CLEETUS C

2ND M.Sc BPS

CBPST, KOCHI

Example Bullet Point Slide

Carbon nanotubes are fullerene-related

structures which consist of graphene

cylinders closed at either end with caps

containing pentagonal rings

CARBON NANOTUBES

SINGLE WALLED NANO TUBES Most single-walled nanotubes (SWNT) have a diameter of

close to 1 nanometer, with a tube length that can be many millions of times longer

The structure of a SWNT can be conceptualized by wrapping a one-atom-thick layer of graphite called graphene into a seamless cylinder

The way the graphene sheet is wrapped is represented by a pair of indices (n,m) called the chiral vector

The integers n and m denote the number of unit vectors along two directions in the honeycomb crystal lattice of graphene

If m = 0, the nanotubes are called "zigzag". If n = m, the nanotubes are called "armchair". Otherwise, they are called "chiral"

Zigzag (n,0)

Chiral (n,m)

MULTI WALLED NANOTUBESMulti-walled nanotubes (MWNT) consist of multiple

rolled layers (concentric tubes) of graphiteIn the Russian Doll, sheets of graphite are

arranged in concentric cylindersIn the Parchment model, a single sheet of graphite

is rolled in around itself, resembling a scroll of parchment or a rolled newspaper

TREATMENT AND FUNCTIONALIZATION

CNTs unique properties make them desirable for many different applications. However, to exploit as much as possible these properties, most of the applications require the functionalization of carbon nanotubes, such as changing the surface properties to make nanotubes soluble in different media, or attaching functional groups or polymer chains for specific utilizations of modified nanotubes

TYPES OF FUNCTIONALIZATION

Endohedral functionalization

Exohedral functionalization

Example Bullet Point SlideEndohedral functionalization; CNTs aretreated by filling their inner empty cavity with different

molecules or nano particles

Schematic representation of a SWNT filled with C60 fullerenes

Example Bullet Point SlideExohedral functionalization;

It involves grafting of molecules on the outer surface of nanotubes

Several approaches have been developed and include defect functionalization covalent functionalization and noncovalent functionalization with surfactants or polymers

The different types of exohedral functionalization can be classified via the nature of the interactions between the surface of carbon nanotubes and the functional groups or polymer chains

These interactions can rely upon covalent or non-covalent bonds.

Example Bullet Point Slide

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Functionalization possibilities for CNTs: defect functionalization

(A),

covalent sidewall functionalization (B), noncovalent

functionalization with surfactants (C) and polymer wrapping (D)

NON-COvALENT FUNCTIONALIZATION wITh SUrFACTANT Or POLYmEr

The noncovalent interaction is based on van der Waals forces or - stacking and it is controlled by thermodynamicsπ π

The great advantage of this type of functionalization relies upon the possibility of attaching various groups without disturbing the electronic system of the rolled graphene πsheets of CNTs

The formation of non-covalent aggregates with surfactants is a suitable method for dispersing individual nanotubes in aqueous or organic solvents

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Interaction of nanotubes with pyrene derivatives

Carbon nanotubes can be also wrapped with polymer chains to form supramolecular

complexes of CNTs

Different steps in PE coating of nanotubes is given below

Covalent funCtionalization

Two major groups of chemical functionalization of CNTs via covalent attachment can be distinguished, the end and “defect-group” chemistry and the sidewall functionalization

end and defeCt-side Chemistry

The functionalization via “end and defect-side” chemistry consists to graft functional group directly on the already existing defects in the structure of CNTs

Indeed, carbon nanotubes are generally described as perfect graphite sheets rolled into nanocylinders.

In reality, all CNTs present defects and can be curved

Typical defects in a SWNT

This method was used to graft amine

moieties onto carbon nanotubes via the reaction

with diamines such as triethylenetetramine,

ethylenediamine or 1,6-hexamethylenediamine

The figure shows open end of the SWNT

terminated with –COOH groups. Other

terminal groups, such as –OH, -H and =O, are also

possible

sidewall funCtionalization It involves grafting of chemical groups through reactions onto

the -conjugated skeleton of CNTsπThe reactivity of CNT sidewalls remains low and sidewall-

functionalization is only successful if a highly reactive reagent is used, whereas the nanotube caps are quite reactive due to their fullerene-like structure

Another constraint for sidewall functionalization is the tendency of CNTs to form

bundles and to limit the available nanotube surface for the grafting of chemical reagents

A large majority of covalent sidewall functionalizations is carried out in organic solvent, which allows the utilization of sonication process to improve the dispersion of CNTs and, thus, the available surface of carbon nanotubes

Schematic describing various common covalent sidewall functionalization reactions of CNTs using organic solvents

Example Bullet Point Slide

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