Biomedical Engineering Reference
In-Depth Information
nanoparticles has also been suggested: (i) spherical or compact particles; (ii) high aspect
ratio particles; (iii) complex nonspherical particles; (iv) compositionally heterogeneous
particles - core surface variation; (v) compositionally heterogeneous particles - distributed
variation; (vi) homogeneous agglomerates; (vii) heterogeneous agglomerates; (viii) active
particles; and (ix) multifunctional particles [27]. The newer and much more detailed
classification received recommendation from the European Joint Research Centre [28].
Another possible classification is based on composition/type of nanomaterials. This
method of classification is very broadly used. The following list represents the major classes
of the nanomaterials usually considered:
carbon nanomaterials
●
metal nanomaterials
●
oxide nanomaterials
●
inorganic nanotubes
●
quantum dots
●
macromolecules
●
Interestingly, very few chemical elements and their compounds contribute towards the
majority of nanomaterials used in industrial and commercial applications. The most impor-
tant are: Ag (54%), C (17%), Ti/TiO2 (10%), silica (7%), Zn/ZnO (6%), and Au (6%) [29].
Carbon Nanomaterials
Carbon-based nanomaterials provide a diverse starting point for various industrial applica-
tions. Many of these materials are also used in basic research that might yield varied
commercial products in near future.
The discovery of fullerene - C
60
molecule - is possibly one of the most fascinating accounts
displaying results of collaboration by interdisciplinary and multinational groups in basic
research during the latter decades of the twentieth century [30-32]. For the first time, C
60
,
which is the most important representative of the fullerene family, was fully characterized by
this research. It opened the way to bulk production of fullerenes in research laboratories and
industrial plants. Interestingly, only after the discovery of C
60
did it become obvious that
fullerenes do exist in nature [33]. Fullerenes can be discovered wherever a large concentration
of carbon exists and also where excess energy is available. This requirement applies not only
to various sites on Earth but also to interstellar locations [34], near to carbon stars. It has
now been recognized that C
60
is the most abundant fullerene: its larger analogs, such as C
70
,
C
76
, C
78
, C
84
, and C
90
, are also present in nature, but in smaller quantities [32].
For millennia, diamond, graphite, and amorphous carbon had been considered the only
three allotropes of carbon. Remarkably, during the past few decades this knowledge had
been questioned and proved incorrect. Intensive work on carbon compounds during this
period has resulted in the number of known forms of carbon doubling. This fast acceler-
ating advancement was initiated in 1985 by the discovery of a new allotrope of carbon called
fullerene, a soccer-ball-shape molecule containing 60 carbon atoms [35]. Soon after, in 1991,
Iijima reported the existence of another carbon form - carbon nanotubes (CNTs) - that are
spin-off products of fullerenes [36]. The next report, published 13 years later, announced a
new breakthrough discovery of vital consequence for nanotechnology - the isolation of
graphene, a single atomic layer of graphite [37]. The nanocarbon field of research is the only
area of science where two Nobel Prize awards have been presented for work related to the
same element. First, in 1996, the Nobel Prize for Chemistry was awarded to Robert F. Curl,
Sir Harold W. Kroto, and Richard E. Smalley “
for their discovery of fullerenes
.” Fourteen
