Biomedical Engineering Reference
In-Depth Information
Figure 12.4
Schematic illustration of the procedure for the
synthesis of uniform and water-dispersible iron
oxide nanocapsules.
300 ml of ammonium hydroxide (30 wt%) was added to a solution containing 5 l
ethanol and 500 ml deionized water. After being precoated with polyvinylpyrrol-
idone ( PVP ), the as - prepared
-FeOOH nanoparticles were dispersed in the solu-
tion. TEOS (7 ml) was then added to the mixture solution at room temperature,
with vigorous stirring, and the mixture was held at room temperature for 10 h with
constant stirring to yield the uniform silica shell/
β
- FeOOH core nanocomposite;
this was then isolated by centrifugation and washed with water. The composite
was heated to 500 °C under an air atmosphere, and the temperature maintained
for 5 h to produce the silica shell/hollow hematite nanostructures. The formation
of a hollow structure was due to the formation of pores in the
β
β
- FeOOH particles
at low temperature (
200 °C) that merge, at higher temperatures, to form single
large pores leading to the generation of nanocapsules. This was demonstrated by
TEM analyses during the annealing process, and confi rmed by thermogravimetric
and differential thermal analyses; these showed a weight loss associated with a
simultaneous endothermic process between 160 and 330 °C, due to the thermal
dehydroxylation of
≤
- Fe
2
O
3
).
In order to obtain magnetite nanocapsules, the silica shell/hollow hematite
nanostructures were further heated at 500 ° C for 10 h under a fl ow of H
2
/Ar (10/90,
v/v). The iron oxide/silica nanostructures were immersed in 0.1
M
of NaOH
solution with sonication for 5 h to remove the silica shell (for 1 g of nanocomposite,
250 ml
β
- FeOOH forming hematite (
α
of
0.1
M
NaOH was added). All ions in the resultant suspensions
