Nanotechnology for domestic water purification - Nanotechnology in Eco-efficient Construction - page 369

ppb's by continuous fi ltration of contaminated water through these fi lters.
Then, the fi lters loaded with pollutants were effectively regenerated by
treatment with acetonitrile.
In another work, Arkas et al. (2006) developed a method that permits
removal of organic pollutants by employing a simple fi ltration step, which
can be easily scaled up. They used the long-alkyl chain functionalized poly-
propylene imine dendrimers, polyethylene imine hyperbranched polymers
and β -cyclodextrin derivatives which are completely insoluble in water.

16.4.3 Metal-containing nanoparticles

Metal and metal oxide nanoparticles have been studied extensively for
water treatment applications. Most notable among the metal nanoparticles
are the noble metals (such as silver and gold which are treated as famous
biocides) and nano zero-valent iron (NZVI) used for treatment of water
containing pesticides. Among metal oxides, oxides of iron, aluminium, zinc,
magnesium and titanium have been made use of signifi cantly in groundwa-
ter remediation. We fi rst discuss the category of metals and then case studies
pertaining to metal oxides are discussed.

Zero-valent iron (ZVI)

Among the popular nanosorbents at the present time, the most exploited
is the nano ZVI having applications ranging from removal of halogenated
organics, arsenic, nitrate and heavy metals. Nanoparticles could provide
very high fl exibility for both in situ and ex situ remediations. They can also
be anchored onto a solid matrix such as carbon, zeolite or membrane for
enhanced treatment of water. ZVI removes aqueous contaminants by
reductive dechlorination, in the case of chlorinated solvents or by reducing
them to an insoluble form, in the case of aqueous metal ions.
Different material and engineering aspects of ZVI nanoparticles used for
removal of environmental pollutants were discussed by Li et al. (2006b).
These nanoparticles were used for separation and immobilization of Cr
(VI) and Pb (II) from aqueous solution by reduction of chromium to Cr
(III) and Pb to Pb (0) (Ponder et al. , 2000). Nanopowder of ZVI was used
for the removal of nitrate in water (Choe et al. , 2000). Nanoscale ZVI was
employed by Lowry and Johnson (2004) for dechlorination of polychlori-
nated biphenyl (PCB) to lower-chlorinated products under ambient condi-
tions. It was demonstrated that nano-sized ZVI oxidizes organic compounds
in the presence of oxygen (Feitz et al. , 2005). The high surface area of
nanoscale ZVI may allow for more effi cient generation of oxidants. A
decrease in reactivity is expected with the build-up of iron oxides on the
surface, particularly at high pH.

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