Environmental Engineering Reference
In-Depth Information
nanosilver) and metal oxides (TiO 2 , ZnO, CeO 2 , SiO 2 and Al 2 O 3 ) represent an
important group of nanomaterials. Metal oxides represent the largest number of
commercial nanomaterials. Dendrimers are highly branched, three dimensional,
nano-sized polymers with controlled structure, several chain ends on their surface
that can be tailored to perform specifi c chemical functions and a tendency to adopt
a globular shape (for more discussion about molecules, dendrimers and nanopar-
ticles, see Chapter 2). These properties have made them useful in medical chemis-
try application, for instance they can be used for drug delivery by placing drug
molecules within the cavities of their three dimensional structure (Cloninger, 2002;
Liu and Fréchet, 1999). Composites (including nanoclays) are complex structures
combining several nanoparticles or nanoparticles with larger particles.
1.9.2
Origin
Nanomaterials can be classifi ed according to their origin into manufactured, natural
or adventitious. Manufactured nanomaterials are intentionally produced due to
their particular properties such as carbon nanotubes, metals and metals oxides such
as silver and titanium dioxide (Chapter 2). In general, when nanoparticles or nano-
materials are discussed, it is these manufactured materials which are being dis-
cussed. Natural nanomaterials are naturally occurring such as viruses, aquatic and
terrestrial colloidal matter, mineral composites and ultrafi ne particulate matter
(Chapters 4 and 5). Adventitious nanomaterials are unintentionally produced and
occur as a result of industrial processes, such as diesel exhaust particles, or other
friction or airborne combustion by-products, such as from road vehicles, fossil fuel
and cooking (Chapter 5 ).
1.9.3
Size
How nanoparticles are compared to other size dependent environmentally relevant
particles that have been known for decades is shown in Figure 1.3. In aquatic
0.1
1
10
100
1000
Nano-
meters
450
dissolved
conceptual
dissolved particulate
operational
colloids
Nanoparticles
PM 0.1
Ultrafine particles
Figure 1.3 Defi nition of different sizes relevant to nanoparticles. (Reprinted from B. Nowack,
and T.D. Bucheli, Occurrence, behavior and effects of nanoparticles in the environment,
Environment. Pol. , 150 , 5-22. Copyright 2007, with permission from Elsevier.)
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