Nanotechnology for domestic water purification - Nanotechnology in Eco-efficient Construction - page 365

other approaches because it has the potential to be more cost effective
(Tratnyek and Johnson, 2006). However, in situ remediation requires deliv-
ery of the treatment to the contamination and this has proven to be a major
obstacle to expanded development of in situ remediation technologies. With
respect to this issue, nanotechnology has special relevance because of the
potential for injecting nanosized (reactive or absorptive) particles into con-
taminated water. In this manner, it should be possible to create either: (i)
in situ reactive zones with nanoparticles that are relatively immobile; or (ii)
reactive nanoparticle plumes that migrate to contaminated zones if the
nanoparticles are suffi ciently mobile.
The current understanding of the basic processes involved in this technol-
ogy is still evolving and incomplete. In addition to making it diffi cult to
move forward with the engineering of full-scale implementations, these
uncertainties make it very diffi cult to assess the risks that this technology
might bear to human and/or ecological health. Recognizing this, some
groups have adopted the 'precautionary' position that in situ applications
of nanoparticles for remediation should be prohibited (The Royal Society
and The Royal Academy of Engineering, 2004), whereas others have recom-
mended, in effect, that research on all fronts should proceed in parallel
(EPA, 2005).

16.4 Types, properties and uses of nanomaterials

in water purifi cation

Nanoparticles have two key properties that make them particularly attrac-
tive as sorbents. On a mass basis, they have much larger surface areas than
bulk particles. Nanoparticles can also be functionalized with various chemi-
cal groups to increase their affi nity towards target compounds. It has been
found that the unique properties of nanoparticles enable the development
of high capacity and selective sorbents for metal ions and anionic contami-
nants. To make the discussion on the application of nanomaterials in the
fi eld of water purifi cation easy to comprehend and follow, the nanomateri-
als can be categorized under four different classes:

￿ ￿ ￿ ￿ ￿ ￿

1. zeolites
2. dendrimers
3. metal-containing nanoparticles including metal oxides
4. carbon nanotubes.

The literatures encompassing the research and development work involv-
ing these nanomaterials are cited very briefl y in the sub-sections that follow.
To make the discussion meaningful and somewhat exhaustive, at different
places (application of nanomaterials like TiO 2 nanoclays and magnetic
nanoparticles), excerpts from the Annual Review of Nano Research (Man-
soori et al. , 2008) are reproduced.