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In-Depth Information
(b)
(c)
(a)
Figure 2.20
(a) Proposed silanization model of nanoparticles with exposed
amine functional groups; (b) TEM image of amine functionalized
Tb-doped γ-Fe
nanocrystals; inset: well-dispersed amine
functionalized nanocrystals in water [84]; (b) TEM images of
silica-coated PVP/NaYF
O
2
3
:Yb, Er nanocrystals [94].
4
2.3.5
Hollow Rare Earth Nanostructures
Fabrication of hollow structures has drawn considerable interests
due to a wide range of potential applications, including drug and gene
delivery, photonics, catalysis, cosmetics, hydrogen production and
storage, and as rechargeable batteries [95]. The large void fraction
in hollow structures has been successfully used to encapsulate and
control the release of sensitive materials such as drugs, cosmetics,
and DNA. Methods developed for the fabrication of hollow structures
for a range of materials include chemical vapor deposition or epitaxy
[96], layer-by-layer technique [97], sacrificed templated or template
engaged replacement reaction [98, 99], microemulsion [100], and
polymer/surfactant micellar templating [101].
Rare earth materials as hollow nanoparticles have been reported
in the form of spherical, fullerene-like, and nanotube structures. Li
et al
. [102, 103] synthesized a number of rare earth hydroxide and
fluoride fullerene-like nanoparticles containing single or multiple
cavities (RE = Y, Yb, Tm, Er, Ho, Dy, Tb, Gd, Eu, Sm, Nd, Pr, La). Figure
2.21 shows some of the representative TEM images of the different
rare earths hollow nanospheres and nanotubes. By controlling the
reaction temperature and pH of the solution, they could selectively
synthesize hydroxide nanowires, nanosheets, and nanotubes.
Again, dehydration, sulfuration, and fluoridation of the hydroxide
nanotubes resulted in oxide, oxysulfide, and oxyfluoride nanowires,
nanosheets, and nanotubes. TEM image of an yttrium oxysulfide
is shown in Fig. 2.21d. In another study, Ma
et al
. [104] reported
hollow nanosphere by microwave hydrothermal process (Fig.
2.22a). These hollow nanospheres were proposed as drug carrier, or
as lubricant additives in catalysis.
PrF
3
