Environmental Engineering Reference
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Light Harvester
Acceptor 2
Ring molecule
Ground state
Acceptor 1
Spacer
Stopper
Excitation
Excited state
Relaxation
Ground state
Figure 2.3
A representation of a rotaxane based molecular switch. As the molecule is
excited with light an electron is transferred from the light harvester to acceptor 2. It is then
transferred to acceptor 1, thereby switching the ring molecule from one position to the other.
The switch then returns to the ground sate and the ring returns to its original position around
acceptor 2.
Current state-of-the-art from a commercial perspective is focused clearly on the
use of particulates rather than devices. This is generally due to the huge constraints
in using nano devices under non-laboratory conditions. Whilst this places some
framework for the consideration of current materials it does no necessarily exclude
the nanomachines in the future and clearly in such a rapidly changing fi eld current
proposed applications are being realised increasingly rapidly. However, in order to
focus the content of this work, further discussion are restricted to the production,
properties and use of nanoparticles.
Nanoparticles have been prepared from a wide range of materials (Table 2.1)
with a diverse range of morphologies and properties. As has already been discussed
they have already found commercial applications and some have been in use for
thousands of years. The recent interest in the application of nanotechnology has
the potential to apply a much wider range of materials in higher volume to a range
of diverse applications and therefore careful application of the technology is
needed.
2.3
Nanoparticle Architecture
The generally accepted defi nition of a nanoparticle is a particle with at least one
dimension less than 100 nm (Royal Society & The Royal Academy of Engineering,
2004 ; NIOSH, 2004 ). This defi nition, whilst workable, leaves out some important
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