Environmental Engineering Reference
In-Depth Information
Table 7.2 Characteristics of Fe
3
O
4
nanoparticles prepared by solution combustion synthesis [
25
]
(powder 1) and co-precipitation (powder 2), respectively
Powder
no.
H
c
(kA/m)
1 Fe
3
O
4
10 106 15-20 55.3 3.3 3.0
2 Fe
3
O
4
9 98 10-15 61.3 0.8 0.5
D
XRD
crystallite size,
S
BET
specific surface area,
D
TEM
particle size from TEM,
M
s
saturation
magnetization,
M
r
remanent magnetization,
H
c
coercivity
XRD phase
composition
D
XRD
(nm)
S
BET
(m
2
/g)
D
TEM
(nm)
M
s
(emu/g)
M
r
(emu/g)
One can easily notice that that the two powders are very similar in terms of phase
composition (single-phase Fe
3
O
4
), crystallite size, and specific surface area and
particle size.
Considering the magnetic properties of the resulted powders one may notice that
the saturation magnetization of the sample prepared by combustion synthesis is
slightly smaller than the sample prepared by co-precipitation (Table
7.2
). At the
same time, the remnant magnetization and the coercivity of combustion synthesized
Fe
3
O
4
are a little bit larger than the co-precipitated Fe
3
O
4
, yet very close to the
superparamagnetic behavior.
7.3.2.2 Structural Characteristics of Colloidal Suspensions Based
on Fe
3
O
4
Nanoparticles
After coating the nanoparticles with a double layer of oleic acid, the stabilized
nanoparticles were dispersed in phosphate buffer saline (PBS), leading to two sets
of stable colloidal fluids, termed 1F (deriving from powder 1) and 2F (deriving from
powder 2). TEM analysis conducted on samples 1F and 2F, evidenced that the
actual size of combustion synthesized Fe
3
O
4
nanoparticles is around 15-20 nm
(Fig.
7.3
), whilst the co-precipitated magnetite particles have 10-15 nm. Both types
of nanoparticles have a sphere-like shape.
The intensity distribution of particle size revealed that the colloidal suspension
deriving from combustion synthesized magnetite (sample 1F) has virtually a single
family of particles and an average hydrodynamic diameter of 107 nm (Fig.
7.2
). On
the other hand, the colloidal suspension deriving from the co-precipitated magnetite
(sample 2F) has a bimodal particle size distribution, which suggests the presence of
two populations of particles (Fig.
7.4
).
The average hydrodynamic diameter of sample 2F (61 nm) is smaller when
compared to sample 1F. However, in both cases, the hydrodynamic diameter is
larger than the core size of Fe
3
O
4
nanoparticles observed in TEM images (Fig.
7.3
),
which is probably due to the presence of oleic acid double layer as well as the
possible aggregate formation.
