OVERVIEW ON THE MAJOR RESEARCH ACTIVITIES ON CARBON NANOTUBES BEING DONE IN AMERICA, EUROPE AND ASIA - Carbon Nanotubes: From Bench Chemistry to Promising Biomedical Applications - page 271

9.2.4.2 Funconalisaon of CNTs

The functionalisation of CNTs, either via covalent or non-covalent procedures,
represents a crucial step to achieve the physicochemical properties required
in almost every application. Many different methodologies have been
investigated, and the groups at the Smalley Institute have contributed to
the development of some of them. An example is given by the production of
single-walled nanotube salts and their subsequent interaction with different
molecules to yield transient radical anions that dissociate into nitrogen-
centred free radicals and halides. 113 More precisely, SWCNT salts could be
prepared by the reduction of pristine tubes ( 1 ) (Fig. 9.18) using lithium in
liquid ammonia. They subsequently react with N -bromosuccinimide (NBS)
to yield nanotubes functionalised by nitrogen-centred free radicals. Addition
of NBS to a suspension of the SWCNT salts led to NBS radical anions that
eventually produce succinimidyl radicals. When succinimidyl functionalised
SWCNTs ( 3 ) were treated with hydrazine, aminated SWCNTs ( 4 ) were
formed. Through a similar procedure, hydroxyl functionalised SWCNTs could
be prepared using SWCNT salts and then performing hydrolysis in fuming
H 2 SO 4 . As a result, the aminated and hydroxylated SWCNTs could be further
functionalised with other groups, amino acids and DNA for chemical and
biological applications.

O

O

Br

- N

-

-

N

NH 2

H 2 N-N H 2

O

Li/ NH 3

Li + Li + Li + O

1

3

SWCNT salts

4

fuming
H 2 SO 4 ,

OH

R- O- O- R

O

° C

80

O O

5

6

Figure 9.18 Scheme of functionalisation of SWCNT salts.

Another functionalisation consists in the recently reported
photohydroxylation reactions by degassing the dispersion of SWCNTs/
surfactant (e.g., sodium dodecyl sulphate, SDS). 114 The degassing method
was based on the desorption of O 2 , CO 2 and endoperoxide from the solution
and the surface of SWCNTs. In this way, solutions remained luorescent
in acidic conditions (pH 3) demonstrating that the vast majority of the O 2