Synthesis and characterization of maghemite nanoparticles dispersed within silica matrix / Ang Bee Chin
Generally, this study comprises of 3 stages. Firstly, pure maghemite nanoparticles were synthesized within 10nm size range. Secondly, the nanoparticles were encapsulated into the silica xerogel matrix to minimize agglomeration and aggregation by producing nanocomposites. Finally, the surface area...
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| Format: | Thesis |
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2011
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| Online Access: | http://studentsrepo.um.edu.my/8013/ http://studentsrepo.um.edu.my/8013/1/Full_report_(Subl).pdf |
| Summary: | Generally, this study comprises of 3 stages. Firstly, pure maghemite
nanoparticles were synthesized within 10nm size range. Secondly, the nanoparticles
were encapsulated into the silica xerogel matrix to minimize agglomeration and
aggregation by producing nanocomposites. Finally, the surface area of the
nanocomposites was increased by modifying the matrix into silica particulate form. The
nanoparticles and nanocomposites were characterized using XRD, TGA, TEM, BET,
DLS and AGM.
In stage I, the effects of varying the FeCl2 concentration on the properties of
magnetic nanoparticles produced by Massart’s procedure were investigated. The lattice
parameters of the samples obtained from XRD analysis revealed that the nanoparticles
formed were maghemites (γ-Fe2O3). The magnetization curves showed no hysteresis,
indicating that the particles were superparamagnetic. The crystallite, magnetic and
physical sizes were similar, indicating that the particles were monocrystals. When the
FeCl2 concentration increased from 0.1 to 1.0M, the size of as-synthesized maghemite
nanoparticles decreased. However, when the FeCl2 concentration was increased further,
the size of as-synthesized maghemite nanoparticles increased. This indicates that a very
low or a very high FeCl2 concentration leads to the formation of larger particles. In
addition, agglomeration and aggregation occurred for most samples. Superparamagnetic
maghemite nanoparticles with the smallest size were chosen to proceed to stage II and
stage III.
Maghemite-silica xerogel nanocomposites were produced by dispersing the assynthesized
maghemite nanoparticles into silica xerogel by sol-gel technique. The phase analysis performed using XRD confirmed that the encapsulated nanoparticles were
maghemites. TEM micrographs showed that the maghemite nanoparticles were
spherical and homogeneously incorporated into the silica xerogel matrix. The surface
area of the nanocomposites was less than 40m2/g. This was probably due to the fact that
majority of the pores in the silica gel were filled by as-synthesized maghemite
nanoparticles. Reduction in average crystallite size of dispersed maghemite particles
was observed after the encapsulation process compared to as-synthesized maghemite
nanoparticles. However, increasing the weight ratio of Fe2O3/SiO2 in nanocomposites
caused an increase in average crystallite size of embedded maghemite nanoparticles.
Maghemite-silica particulate nanocomposites were prepared by a modified solgel
process. The purpose of changing the matrix from xerogel to particulate form was to
increase the surface area and retain its properties. It is a promising alternative technique
for fabricating nanocomposites because it is simple, manufacturable, inexpensive, fast,
can be prepared at room temperature and its ability to control the composition,
crystalline distribution and properties of maghemite nanoparticles and nanocomposites.
Moreover, no surfactant or other unnecessary precursor was involved. The HRTEM
micrograph revealed that the embedded particle (core) was with the presence of atomic
interspaces indicating that the particles were crystalline and covered with a noncrystalline
material. The EELS result showed the presence of Fe-L3 signals, which
proves that the embedded particles were iron-based compounds. In stage III, a very high
surface area was attained for the produced nanocomposites (360 – 390 m2/g), compared
with those of stage II. This enhances the sensitivity and the reactivity of the
nanocomposites.
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