Environmental Engineering Reference
In-Depth Information
Table 9.1
Magnetization, BET surface area and metal ratio for MeFe
2
O
4
.
Saturation
Moment (emu)
Me:Fe
(from XPS)
BET Surface
Area (m
2
/g)
MeFe
2
O
4
pH
zpc
CoFe
2
O
4
3.7
7.9
1: 2.0
55.1
MgFe
2
O
4
1.1
8.3
1: 2.5
70.3
ZnFe
2
O
4
1.2
8.2
1: 2.4
79.6
NiFe
2
O
4
2.2
8.0
1: 2.1
101.2
CuFe
2
O
4
3.2
8.5
1: 2.2
93.8
MnFe
2
O
4
4.6
6.8
1: 2.1
204.0
The superparamagnetic properties of the MeFe
2
O
4
nanoparticles were verified by
the magnetization curve measured by vibrating sample magnetometer (VSM). The
hysteresis loop from VSM measurements presents the saturation magnetization and
coercivity of the material under an applied magnetic field. It is observed from Table 9.1
that the magnetic properties of the MnFe
2
O
4
nanoparticles are the strongest compared to
the other MeFe
2
O
4
, while the MgFe
2
O
4
nanoparticles possesses the weakest magnetic
properties. The large saturation magnetization of magnetic particles makes them very
susceptible to the magnetic field, and therefore makes the separation of the solid and
liquid phases easy. These measurements indicated that the co-precipitation method
produced MeFe
2
O
4
particles that have magnetic properties very similar to bulk values
(Snelling, 1988). To investigate the effect of ratio of metals and calcination temperature
on the magnetic properties, the magnetism of various Mg
x
Cu
1-x
Fe
2
O
4
produced by
varying metal ratios or heating temperature during the synthesizing process was
measured. Typical plots of magnetization versus applied magnetic field (M-H loop) of
the Mg
x
Cu
1-x
Fe
2
O
4
synthesized particles at 400
o
C are shown in Figure 9.7a. The
magnetization curve exhibits zero remanence and coercivity, and follows the Langevin
function (Chantrell et al., 1978), which proves that these magnetic particles have
superparamagnetic properties.
By comparing their saturation moments, Mg
0.2
Cu
0.8
Fe
2
O
4
illustrated the strongest
magnetic properties; while Mg
0.9
Cu
0.1
Fe
2
O
4
demonstrated the weakest magnetic
properties. Hence, the magnetic properties for various Mg
x
Cu
1-x
Fe
2
O
4
increased with the
increase in the content of Cu. The hysteresis loops of different MgFe
2
O
4
particles
synthesized at 400, 600, 800, and 900
o
C are shown in Figure 9.7b. It was found that the
magnetic properties of MgFe
2
O
4
particles increased with increasing the calcination
temperature.
9.4.3 Characterization of Surface-Coated -Fe
2
O
3
-FeOOH was considered for the surface coating material since it is
comparatively amorphous and possible to cover the crystalline nanoparticles. To
determine the optimal mass of -FeOOH coating on the magnetic nanoparticles, various
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