Overview of Nanoscience in the Environment - Environmental and Human Health Impacts of Nanotechnology - page 3

reduction of an aqueous solution of AuCl − using phosphorus in CS 2 (Faraday, 1857 ).
Shortly after that, in 1861, the term ' colloid ' (of which nanoparticles are the smallest
fraction) was coined by Graham (Graham, 1861).
This brief discussion shows clearly that nanoparticle usage has a long history. The
novelty today is the scale of research and industry and the ability to manipulate
and design materials at the nanoscale to create large structures with fundamentally
new properties and functions. This will lead to unprecedented understanding and
control of the properties of materials to discover novel phenomena, process and
tools. Therefore, nanotechnology will enable a wide range of discoveries in all
major scientifi c areas.

1.3 Defi nitions

Various defi nitions for nanomaterials have been given, or are actually in debate.
Most of these are based on size and imply that there is a size range between
that of molecules and bulk materials, where particles have unique properties
different than those of molecules or bulk material (Tratnyek and Johnson, 2006).
Some of these properties arise only for particles smaller than approximately
10 nm or so, where particle size approaches the length-scale of certain molecular
properties (Klabunde et al. , 1996). For instance, below 10 nm, particle specifi c
surface area increases exponentially and qualitatively similar trends apply to related
properties such as the ratio of surface/bulk atoms. Another example is that of
quantum confi nement, which arises because the band gap of semi-conducting
materials increases as particle size decreases (Klabunde et al. , 1996 ). The decrease
in haematite particle size (from 37 to 7.3 nm) greatly promotes the oxidation of
aqueous manganese (II) in the presence of molecular oxygen (Madden and
Hochella, 2005), quite separate from the surface area related effect. Small magne-
tite nanoparticles (9 nm) exhibit greater reactivity toward carbon tetrachloride
(CCl 4 ) relative to larger nanoparticles (80 nm), both on mass and surface area nor-
malized bases (Vikesland et al. , 2007). The decrease in size of ceria nanoparticle
alters the oxidation state of the nanoparticles with an increase in the fraction of
Ce 3+ at sizes less than approximately 15 nm with complete reduction of ceria par-
ticles to Ce 3+ at sizes less than approximately 3 nm (Wu et al. , 2004 ). Size dependent
inhibition of nitrifying bacteria has been observed and the inhibition was correlated
to the fraction less than approximately 5 nm in the suspension (Choi and Hu, 2008).
These properties of nanomaterials and others are discussed in more details in
Chapter 2 and 3.
Nanoscience is, however, generally defi ned more inclusively, as the scientifi c
study of materials on the nanoscale, approximately defi ned as the length scale
between 1 and 100 nm (Borm et al. , 2006b). Nanotechnology, as defi ned by the
United States National Nanotechnology Initiative, is 'the research and technology
development at the atomic, molecular or macromolecular levels, in the length scale
approximately 1-100 nm; the creation, and use of structures, devices and systems
that have novel properties and functions because of their small size; and ability to
be controlled or manipulated on the atomic scale' (NNI, 2004). The Royal Society