Chemistry Reference
In-Depth Information
1.7
Microemulsion Route
The microemulsion method utilizes a water/oil/surfactant system
to construct numerous micro- and nanometer reactors, in which
the nanoparticles are formed. Macroscopically, microemulsion is an
optically isotropic and thermodynamically stable disperse system.
At nanometer scale, the microemulsion is heterogeneous with an
internal structure either of nanospherical droplets (micelles or
reverse micelles) or a bicontinuous phase, depending on the given
temperature as well as the ratio of different constituents. The
droplets are generally of similar size, and each small droplet could be
utilized as a micro-/nanoreactor, which promises the nanoparticles
to be prepared in a very controllable manner.
Adachi prepared ultrafine ceria nanoparticles within a reverse
microemulsion method [184]. Reverse micelles were formed in an
aqueous solution of polyoxyethylene(10) octylphenyl ether, n-hexyl
alcohol, and cyclohexane. The mean particle size obtained was
between 2.6 and 4.1 nm, exhibiting a fairly narrow size distribution.
Similar methods were adopted by Bumajad
et al
. and Sathyamurthy
et al
. to prepare nanoceria with high surface areas and good thermal
stabilities [185, 186].
Shi
et al
. employed the reverse micelle system to prepare
CeF
:Lu
3+
nanoparticles, where the emulsion was composed of CTAB,
3
3+
n
-butanol,
n
-octane, and water. The characteristics emission of Lu
was observed [187]. Ritcey
et al
. prepared
quadrilateral-shaped YF
3
nanoparticles with water in cyclohexane reverse microemulsion
under the stabilization of polyoxyethylene isooctylphenyl ether
(igepal CO520) [188]. The microemulsion was formed by mixing
aqueous YCl
and Igepal CO520 in cyclohexane under stirring, then
the aqueous solution of NH
3
HF
was added to produce the YF
4
2
3
nanoparticles within every micelle water pool. The as-obtained
nanoparticles exhibit highly uniform shapes and can self-assemble
into periodic superstructures (Fig. 1.21). Similarly, Wang
et al
.
:Yb,Tm nanobundles via the microemulsion method
using water, CTAB, cyclohexane, and 1-pentanol [189].
Cao
obtained YF
3
. developed a hydrothermal microemulsion method to
prepare LaPO
et al
nanorods/nanowiresundermildconditions
at 140°C [190]. The aspect ratio of the as-obtained nanostructures
was found to be dependent on the water/surfactant molar ratio.
Xiang
and CePO
4
4
et al
. reported the synthesis of uniform CePO
nanorods by
4
