Environmental Engineering Reference
In-Depth Information
Hu
et al.
[97] have synthesized various types of magnetic nanoparticles
that were prepared by chemical co-precipitation method and used for the
removal of Cr(VI) from synthetic electroplating wastewater. h e size of
these magnetic nanoparticles was measured using transmission electron
microscopy (TEM) and found to be about 20 nm. h e adsorption of Cr(VI)
was investigated in batch mode in acidic medium using 5g/L of dif erent
magnetic nanoparticles. h e Cr(VI) removal performances were compared
and the adsorption capacities followed the order: MnFe
2
O
4
> MgFe
2
O
4
>
ZnFe
2
O
4
> CuFe
2
O
4
> NiFe
2
O
4
> CoFe
2
O
4
. h e points of zero charge pHpzc
for various magnetic nanoparticles were measured to be around 7.0-8.0.
h e MnFe
2
O
4
showed a very high BET surface area in comparison to other
synthesized ferrite nanoparticles. h e equilibrium time for Cr uptake by
MnFe
2
O
4
, MgFe
2
O
4
, ZnFe
2
O
4
, CuFe
2
O
4
, NiFe
2
O
4
and CoFe
2
O
4
nanoparticles
is 5, 45, 30, 20, 15 and 60 min, respectively. It was clear that Cr adsorption
onto MnFe
2
O
4
particles reached equilibrium in the shortest time compared
to the other ferrites, which was due to the rapid redox reaction that occurred
between the Cr species and the external adsorbent surface. h e adsorption
of Cr(VI) onto MeFe2O4 nanoparticles is highly pH-dependent; hence the
desorption of Cr(VI) can be accomplished by increasing the solution pH.
An 0.01M of NaOH revealed the highest desorption ei ciency compared to
other concentrations of NaOH or the same concentration of other eluents
such as NaHCO
3
, Na
2
CO
3
and Na
3
PO
4
. Among all the ferrite nanoparticles,
CoFe
2
O
4
showed higher desorption ei ciency (98.1%).
Water-soluble hollow spherical Fe
3
O
4
nanocages with high saturation
magnetization were prepared in a one-pot reaction by sol-gel method [98],
and subsequent annealing to synthesize the maghemite (γ-Fe
2
O
3
) nanocages
with similar nanostructures was also performed. Figure 11.1a,b displays the
TEM images of the Fe
3
O
4
and γ- Fe
2
O
3
nanocages. It was found that the Fe
3
O
4
nanocages had a hollow structure and the overall diameter of the nanocages
is around 100 nm, which indicated an oriented aggregation of small Fe
3
O
4
nanoparticles. It has been observed that the shape and size of the γ-Fe
2
O
3
nanocages are similar to those of Fe
3
O
4
nanocages. However, the size of the
central hole of the nanocages becomes smaller at er annealing, owing to the
thermal dif usion of the small nanoparticles. h e SAED pattern in the insets
of Figure 11.1a,b reveals the polycrystal-like feature of the samples, and their
pattern agrees well with the structure planes of iron oxide nanocages. When
FeSO
4
and KOH are mixed together, the solution generates Fe(OH)
2
gels;
subsequently, upon addition of KNO
3
to this mixture, many small magnet-
ite nanoparticles (Figure 11.1c) were formed through homogeneous nucle-
ation. In contrast, if the Gla was not added, these small magnetite nanocages
neither demonstrate obvious growth nor do they aggregate, due to the gel
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