Environmental Engineering Reference
In-Depth Information
Zhang et al. proposed a simple method for preparing octahedral Fe
3
O
4
nanoparticles [33].
In this system, tetracosane and Fe(OA)
3
were used as the reaction media and precursor,
respectively. OAm was used as both the surfactant and the reducing agent. The size of the
obtained octahedral nanoparticles is 21 ± 2 nm. These octahedrons can also self-assemble
into oriented superstructures as a result of their anisotropic shapes. Solvothermal pro-
cesses have also been applied for fabricating highly crystallized Fe
3
O
4
nanoparticles by
Qi and coworkers [41]. In this system, the growth of the (111) facet is hindered because of
the absorption of hydroxyl on the (111) facet, and thus the spherical shape of the Fe
3
O
4
can
be diverted to truncated octahedral particles and octahedral particles with some residual
amorphous particles (Figure 14.3).
As mentioned above, since the (110) facet has the highest surface energy, magnetite nano-
crystals enclosed by the (110) plane are dificult to fabricate. Nevertheless, Li's group have
prepared rhombic dodecahedral (RD) Fe
3
O
4
nanocrystals by using a microwave-assisted
route in the presence of ionic liquid (IL) [C
12
Py]
+
[ClO
4
]
−
[42]. ILs can be used to alter the sur-
face condition of the Fe
3
O
4
nanocrystals, and hexamethylenetetraamine/phenol adsorbed
on (110) planes is favorable for the crystal growth along the [100] direction. Therefore, RD
Fe
3
O
4
nanocrystals enclosed by twelve (110) lakes can be obtained.
When the growth rate along the <111> direction is faster than that of the <100> direc-
tion, nanocubes can be formed for exposing distinct surfaces [43]. Yang et al. synthesized
monodispersed Fe
3
O
4
nanocubes with controllable sizes of 6-30 nm, by using Fe(acac)
3
as a
precursor; benzyl ether as a solvent; and 1,2-hexadecanediol, OA, and OAm as surfactants
(Figure 14.4a through c) [44]. OA controlled the size of nanoparticles owing to its carbox-
ylic group binding selectively to crystal facets, and OAm affected the morphology owing
to its comparatively weak and isotropic binding to the facets. When replacing Fe(acac)
3
wit h Fe(OA)
3
, the stabilizer of sodium oleate (NaOL) could lead to nanocubes, potas-
sium oleate (KOL) could generate a mixture of nanocubes with other morphologies, and
dibutylammonium oleate (DBAOL) and OA could lead to spherical nanoparticles (Figure
14.4e through f) [45]. In addition, monodisperse Fe
3
O
4
nanocubes can also be obtained
(a)
(b)
300 nm
500 nm
(c)
(d)
2 µm
4 µm
FIGURE 14.3
Morphology of Fe
3
O
4
nanoparticles. Concentrations of NaOH (mol/L) are (a, b) 0, (c) 0.5, and (d) 0.7. (Modiied
from Qi H, Chen Q, Wang M et al.,
The Journal of Physical Chemistry C
,
113, 17301, 2009.)
