Reducing the Toxicity of Carbon Nanotubes and Fullerenes Using Surface Modifi cation Strategy - Management of Natural Resources in a Changing Environment - page 177

discussed in current study: single-walled carbon nanotubes (SWCNTs) and
multi- walled carbon nanotubes (MWCNTs). SWCNTs are composed of a single
rolled up graphene sheet and MWCNTs are composed of a concentric arrangement
of many cylinders.
Carbon nanotubes possess high chemical and mechanical stability, which makes
it useful for different applications but due to this substitutions/modifi cations are
diffi cult and have low conversion/functionalisation rate. Derivatization of CNTs
gives products with side-wall substituents, wrapped with polymers, or with inclu-
sion of guest molecules. Several approaches have been developed including
defect functionalization, covalent functionalization of the side-walls, non-covalent
exohedral functionalization and endohedral functionalization. Most commonly used
approaches are functional group addition and surface modifi cation by compositing
with other materials (Table 2 ).
The known addition reactions of carbon nanotubes are carboxylation, anhydride
conversion, amidization, and fl uorination. These additions can potentially lead to
decreased toxicity by increasing the hydrophilic character and therefore biocompat-
ibility of the manufactured CNTs (Balasubramanian and Burghard 2005 ). However,
such modifi cations may impact on other properties, e.g., mechanical and electrical
properties (Chattopadhyay et al. 2008 ). Chemical modifi cation is examined in detail
in the following sections.

Table 2 Functional group addition and surface modifi cation for CNTs
Type of CNT Modifi cation/reagents Product References

SWCNT Carboxylation/Nitric and sulfuric acid Carboxyl

SWCNT

Zhang et al.
( 2003 )

Carboxyl-SWCNT Anhydride formation/Acid treatment SWCNT

anhydride

Sano et al.
( 2001 )

Nitrogen doped
MWCNT

Amidization/Amine groups of ferritin or
Bovine Serum Albumin (BSA)

MWCNT
ferritin or
BSA amide

Katz and
Willner ( 2004 )

Carboxyl-
functionalised
MWCNTs

Covalent modifi cation/polymeric
material grafted polyetherimide

Grafted
MWCNT

Ge et al.
( 2005 )

MWCNT Covalent modifi cation/low molecular

weight chitosan

Grafted
MWCNT

Ke et al.
( 2007 )

Polymer nanotubes
composites

Covalent attachment/polymer precursors
on the surface and the subsequent in situ
polymerization.

Grafted
nanotubes

Jia et al.
( 1999 ) and
Shaffer and
Koziol ( 2002 )

Water soluble
MWCNTs with
temperature
responsive shells

Covalent attachment of
polymers/Grafting thermosensitive
poly(Nisopropolyacrylamide)
to the side walls

Grafted
nanotubes

Guoyong et al.
( 2006 )