Environmental Engineering Reference
In-Depth Information
Table 8.1 Nanoparticles - categories and applications (adapted from Jortner and Rao
(2002)
Nanostructure
Example Material or Application
Fullerenes (incl. nanotubes)
Carbon
Nanowires
metals, semiconductors, oxides, sulfi des, nitrides
Quantum dots
insulators, semiconductors, metals, magnetic materials
Other nanoparticles
ceramic oxides, metals
called buckyballs and cylindrical ones are called carbon nanotubes or buckytubes.
Fullerenes are similar in structure to graphite, which is composed of stacked sheets
of linked hexagonal rings. C 60 was the fi rst fullerene discovered (Kroto et al. , 1985 )
and is known as buckminsterfullerene, after architect Buckminster Fuller' s geode-
sic domes, which the molecule resembles. Another fairly common buckminster-
fullerene is C 70 but fullerenes with 72, 76, 84 and 100 carbon atoms can also be
found.
8.2.2.2
Nanotubes
Carbon nanotubes (CNT), fi rst discovered by Iijima (1991), are a specifi c type of
fullerene. They are similar in structure to C 60 but are elongated to form tubular
structures, 1-2 nm in diameter. They can be produced with very large aspect ratios
(length/diameter) and can be more than 1 mm in length. In their simplest form,
nanotubes comprise a single layer of carbon atoms (single molecule) arranged in
a cylinder. These are known as single-wall carbon nanotubes (SWCNTs). They can
also be formed as multiple concentric tubes (multi-wall carbon nanotubes,
MWCNTs) having diameters signifi cantly greater, up to 20 nm, and length greater
than 1 mm.
CNTs have great tensile strength and are considered to be 100 times stronger
than steel whilst being only one sixth of its weight, thus making them potentially
the strongest, smallest fi bre known. They also exhibit high conductivity, high specifi c
surface area, unique electronic properties and potentially high molecular adsorp-
tion capacity (Maynard et al. , 2004). Applications that are currently being investi-
gated include polymer composites (conductive and structural fi ller), electromagnetic
shielding, electron fi eld emitters (fl at panel displays), super capacitors, batteries,
hydrogen storage and structural composites.
From an occupational health perspective, thinking of nanotubes as a single group
of materials is overly simplistic. In practice they can exist in a wide variety of forms
including single and multi-walled, they may appear straight and relatively rigid, or
they may become twisted into ropes and balls. They may also be functionalised with
a wide range of molecules. However, the large aspect ratios of CNTs, their durabil-
ity and the desire to produce bulk quantities make them of particular interest. These
properties provide parallels to other durable inorganic fi bres, such as asbestos, that
are known to cause signifi cant adverse health effects when inhaled.
 
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