Environmental Engineering Reference
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prepare ZnO/PbS heterostructured functional nanocomposite based on
Pb
2+
sorbed ZnO. In brief, ZnO nanosheets prepared via a hydrothermal
approach were used to adsorb Pb
2+
and then hydrothermally treated in
aqueous solution containing sulfur source.
9.2.5
Nano Aluminum Oxides
Alumina (Al
2
O
3
) is a well-explored adsorbent for heavy metals. Chang
et al.
prepared [54] nanosized γ-Al
2
O
3
by sol-gel method and employed
it as solid phase extraction material for separation/preconcentration of
trace metal ions. Sorption ability of γ-Al
2
O
3
towards heavy metals
can
be enhanced by chemical or physical modii cation of γ-Al
2
O
3
nanopar-
ticles with certain functional groups containing some donor atoms
such as oxygen, nitrogen, sulfur and phosphorus [55, 56]. h e removal
mechanism is changed on the immobilization of modii er at the surface
of alumina. h e target metals are not only removed by adsorption on
the surface of the alumina but also by a surface attraction or chemi-
cal interaction due to modii er [56]. h e i xing of γ-mercaptopropy-
trimethoxysilane (γ-MPTMS) on the surface of γ-Al
2
O
3
would enhance
the desorption capacity of γ-Al
2
O
3
towards Cu, Hg, Au and Pd ions [57].
It was found that the γ- Al2O3 tends to be amorphous due to the forma-
tion of the chemical bond of Si-O-Al. h e adsorption of metal ions onto
γ-MPTMS-modii ed nano alumina was governed by three mechanisms:
(1) metal ions adsorbed through the ai nity of -SH, (2) the hydroly-
zation of metal ions, and (3) electrostatic adsorption. h e i rst mecha-
nism plays a dominant role in acidic medium, while in basic solutions,
the hydrolyzation and the electrostatic interactions are the signii cant
forces of attraction. Sodium dodecyl sulfate-coated nano γ-Al
2
O
3
was
modii ed with 2, 4-dinitrophenylhydrazine (DNPH) as a solid-phase
adsorbent for removal of trace Pb(II), Cr(III), Cd(II), Ni(II), Co(II)
and Mn(II). h e SEM image showed that naked alumina nanoparticles
had a mean diameter of 53 nm, while that of the modii ed ones were
in the range of 68-87 nm [58]. h e BET surface area decreased from
42.62 m
2
/g to 30.38 m
2
/g at er modii cation due to the bulk size of the
organic ligand [59-61]. h e sorption isotherms were better described
by Freundlich model for Mn(II), Pb(II), Cr(III) and Cd(II) ions and by
Langmuir model for Ni(II) and Co(II) ions. h e maximum adsorption
capacity values of the modii ed alumina nanoparticles (q
m
, calculated
from Langmuir equation) toward Cr(III), Cd(II) and Pb(II) ions from
multiple-metal solution (mixture of six metal ions) were 100.0, 83.33
and 100.0 mg/g, respectively [62].
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