Environmental Engineering Reference
In-Depth Information
nm and along its minor axis approximately 41.2 nm; the length-to-diameter
ratio was about two. h e single-crystalline nature of synthesized α-Fe
2
O
3
was coni rmed by the strong spots of the selected area electron dif raction
(SAED) pattern. On the basis of the results, the authors have indicated
that the reaction temperature plays a key role for varying the morphol-
ogy of the synthesized α-Fe
2
O
3
. h e sensitivity to the reaction temperature
implies that the reaction route is under kinetic rather than thermodynamic
control. h e reaction between Fe(NO
3
)
3
solution and NH
3
·H
2
O is shown in
equation:
Fe NO
(
)
+
3
NH H O
⋅
Fe OH
(
)
+
3
NH NO
(11.3)
3
3
3
3
2
3
4
3
and α-Fe
2
O
3
particles will form through a two-step phase transformation,
according to the following equation:
Fe OH
(
)
−
FeOOH
−
Fe O
(11.4)
3
2
3
Ethylene glycol will have an ef ect on preventing the Fe(OH)
3
nanopar-
ticles from agglomeration [74]. h erefore, uniform α-Fe
2
O
3
nanocrystals
were obtained at er being heated at 200-280
°
C to complete the phase
transformation.
11.5.3 Microemulsion
h e microemulsion route is presented to obtain magnetic nanoparti-
cles of dif erent sizes, of ering several advantages with respect to other
similar methods [75, 76, 77, 78]. A microemulsion can be dei ned as a
thermodynamically stable isotropic dispersion of two immiscible liquids
consisting of nanosized domains of one liquid in the other, stabilized by
an interfacial i lm of surface-active molecules. h e surfactant molecules
provide a coni nement ef ect that limits particle nucleation, growth and
agglomeration. In this method, co-precipitation occurs in tiny droplets of
water (“water pools”) embedded with surfactant molecules and homog-
enously distributed in an oil phase. h e size of these “water pools,” so
called reverse micelles, which act as micro reactors for the synthesis of the
nanoparticles, is thermodynamically dei ned by the water-to-surfactant
molar ratio [79].
In this i eld the main challenge is to create the suitable surface of mag-
netic nanoparticles in order to functionalize and allow strong interac-
tions with specii c biological components. In an ef ort to make ultrasmall,
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