Nanomaterials: Properties, Preparation and Applications - Environmental and Human Health Impacts of Nanotechnology - page 35

Table 2.1 A list of material types used in the search [(material type) and (nano* or quantum)
and (synthesis or preparation)]. Some examples are given for common nanomaterials under
these classes and the total number of publications referring to these materials in this manner.
(Source - MIMAS Web of Science.)

Material type Common examples Number of hits

Oxide TiO 2

SiO 2
CeO 2
Total inc. ZnO, iron oxides, etc.

3161
1926
492
8801

Sulfi de Cadmium, zinc, lead, mercury, bismuth,

antimony, iron, indium

1248

Selenide Cadmium, zinc, lead, mercury, bismuth,

antimony, iron, indium

281

Telluride Cadmium, bismuth, antimony, iron, indium 104

Phosphide Cadmium, iron, cobalt, indium 147

Nitride Silicon, carbon, aluminium, gallium 1356

Arsenide Gallium 56

Gold Gold metal 4134

Silver Silver metal, silver sulfi de Ag 2 S 2970

Carbon nanotube Single, double and multiwalled 4513

details and distinctions. It has its roots in the defi nition for ultrafi ne particles
(SCENIHR, 2005), which is a term usually reserved for aerosol particles and
is discussed in detail in Chapter 5. However, in the case of a nanoparticle it can
be diffi cult to draw distinction between a nanoparticle and a molecule, particularly
when some molecules may be considered to have dimensions larger than some
materials which would be routinely referred to as particles. A good example of
this would be a comparison of the size of a polymer containing 1000 segments
with an end-to-end segment length of 0.3 nm in solution, which has a root mean
squared (RMS) radius of 30 nm, and a nanoparticle of silver with a diameter of
only 5 nm.
Attempts to draw distinctions between a nanoparticle and a molecule have
recently relied on connectivity and variability in composition. Nanoparticles rou-
tinely contain a range of sizes and their exact connectivity is not well defi ned,
whereas most polymer molecules and large clusters, such as polyoxometallates
(Long et al. , 2007), have a well defi ned connectivity and in the case of clusters exist
in a single size. There has, as yet, been no consensus about how the two may be
delineated. With recent advances in nanoparticle preparation and characterisation
there has even been a report of a single crystal structure of what would convention-
ally be considered a nanoparticle. This provides an example of a complete descrip-
tion of a ' nanoparticle ' s ' connectivity for a material which would be conventionally
considered a nanoparticle. In some cases the use of the terms associated with col-
loidal systems are routinely used and are a useful way of describing nanoparticles
which have been dispersed in a liquid, but this neglects those which are, for example,
embedded in a polymer or form part of an extended array of nanoparticles.