Environmental Engineering Reference
In-Depth Information
possess the capability to treat wastewater on an industrial scale and are
convenient for magnetic separation, are the most promising materials for
heavy metal removal.
Recently, Feng
et al.
synthesized monodisperse carboxyl-functionalized
superparamagnetic iron oxide nanoparticles, Fe
3
O
4
(np)-COOH [88].
Representative TEM images of the Fe
3
O
4
(np)-COOH nanoparticles depos-
ited from a water dispersion and dried under ambient conditions revealed
the presence of clearly dei ned features of an average size of ~8-17 nm with
narrow size distribution. h ey examined their ability to adsorb Cd
2+
from
aqueous solutions. h e adsorption ei ciency of the particles for Cd
2+
was on
the order of 0.17−0.20 μmol Cd/mg Fe
3
O
4
(np)-COOH, which was among
the highest reported in literature. As reported by the authors, the adsorp-
tion ei ciency of the 8 nm particles was a bit higher than that for the 17 nm
analogues. It had been clearly observed that an increase in the acidity of the
media led to desorption of Cd
2+
.
In order to provide long-term, high quality water, or to enable water
recycling, Girginova
et al.
[94] recently synthesized silica-coated magne-
tite particles for magnetic removal of Hg
2+
from water. Silica-coated mag-
netite particles derivatized with dithiocarbamate groups were evaluated
as magnetic nanodrivers to remove trace levels of Hg
2+
from aqueous
solutions using a simple external NdFeB magnet. h e authors reported
that the uptake ei ciency for Hg
2+
was signii cantly higher for the par-
ticles bearing dithiocarbamate groups at the surface (74%), as compared
to the non-derivatized silica-coated magnetite (24%). On the basis of this
study, one can suggest that this ei ciency of nanomaterials is related to
the high stability of the chelates formed between the dithiocarbamate
group and Hg
2+
.
To further facilitate the adsorption ai nity of guest molecules on nano-
materials, surface modii cation, including inorganic and organic coating,
and covalent binding, has ot en been explored to enable specii c metal
complexation. Notably, the amino-functionalized materials demonstrated
an outstanding ability to remove a wide variety of heavy metal ions such
as Cu(II), Co(II), Ni(II), Zn(II), Pb(II), Cr(VI), and Cd(II) from aqueous
solutions owing to the strong metal complexing capability of amino groups
[95]. h eSiO
2
is stable under acidic conditions and inert to redox reactions,
as compared with the organic coating materials, and hence functions as
an ideal shell composite to protect the inner magnetite core. Silica-coated
core-shell magnetite nanoparticles (Fe
3
O
4
@SiO
2
) have recently been inves-
tigated for potential environmental and biomedical applications [95]. h e
SiO
2
coating provides plenty of surface hydroxyl groups, which of ers ease
of succedent functionalization of magnetite nanoparticles.
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