Page 405 - Environmental Nanotechnology Applications and Impacts of Nanomaterials

388 Environmental Applications of Nanomaterials

(Bayliss, 1977) and greigite (Fe S ) (Skinner et al., 1964), 2.24 Å for mar-
3 4
casite (FeS ) (Wyckoff, 1963), 2.26 Å for chalcopyrite (CuFeS ) (Hall and
2
2
Stewart, 1973). This result implies that 40% !10% of Fe atoms are bound
to S atoms at 2.21 Å. By taking into account the size and the crystal struc-
ture of the maghemite nanoparticles, we estimate that 40 percent of the
Fe atoms are in the surface layer. Therefore, it appears that almost all of
the surface Fe atoms are affected by the DMSAthrough inner sphere com-
plexes (Auffan et al., 2006). The stability of the DMSA coating layer was
investigated in a highly competitive medium rich in inorganic salt, sugar,
and proteins (IS ≈ 0.2 M; pH 7.4). Similar EXAFS experiments, as pre-
viously reported, have been performed at the Fe K-edge. They revealed the
stability of the DMSA coating and its nondesorption from the surface of
the maghemite nanoparticles even in a competitive solution. The effi-
ciency of DMSA-coated maghemite nanoparticles to treat arsenic con-
taminated water was evaluated using a typical adsorption isotherm
experiment. The maximum sorption capacity of arsenic was found to be
5 2 1
of the order of 2.5 10 mol m (or 4.6 mmol g of maghemite or ~15 As
2
atoms/nm ). This value is comparatively higher than previously reported
for maghemite nanoparticles alone without any coating.
All these results show that the functionalization of the surface of
inorganic nanoparticles offer excellent opportunities for selective
removal of a wide array of target compounds from polluted water. As
illustrated, the combination of iron oxide nanoparticles with an organic
compound surface provides advantages for water treatment processes
that cannot be attained separately by the inorganic nanoparticles
or organic compounds alone: pollutant specificity, fastest adsorption/
desorption rates, and magnetic removal (Cumbal et al., 2003).

Concluding Remarks
In recent years, serious problems with water contamination have pro-
duced high demands to improve methods for contaminant treatment in
water and liquid waste, along with controlling water-treatment residuals.
This chapter has shown that oxide nanoparticles ( 20 nm) have the poten-
tial to be an efficient system to remove contaminants from solution due to
their high surface area, small diffusion resistance, high reactivity, and high
affinity to adsorbates. This chapter also shows that a lot of opportunities
can exist for a variety of hybrid organic/inorganic oxide nanomaterials in
the field of water and liquid waste treatment. The hybrid nanomaterials
can be created with specific coatings that are selective for contaminants,
such as DMSA with its affinity for As, Cd, or Pb. The superparamagnetic
properties of iron oxide nanoparticles might allow for the removal of
nanoparticles from water or liquid waste using a magnetic field. Also, the
well-defined crystalline structure makes it possible to regenerate the sur-
face for reuse along with not creating residuals. These unique properties