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in the spinel phase to be determined while the elementary analysis gives the Co/Fe
ratio in the composites. Then, the thermogravimetric measurements bring an
approximate amount of metal in the composite. Finally, the refinement of both
zero-field and in-field low temperature Mössbauer spectra provides the amount
of metallic Fe, the amount of Fe 2+ and Fe 3+ in tetrahedral and octahedral sites of
the spinel phase, and consequently the Co content in the metallic part, the Co 2 þ
content in the spinel phase and the amount of vacancies [ 88 ]. In addition error bars
on each of these parameters can be estimated, as detailed in [ 88 ].
The study of the functionalization of nanoparticles by molecules requires a
good knowledge of both the structure and the chemical nature of the surface state
but the chemical procedure may influence on the density of grafting, the chemical
and structural evolution of the surface and the chemical bonding at the interface
defined by the molecule and the nanoparticulate substrate. It is important to
emphasize that the characterization of the chemical bonding is crucial in order to
make the functionalized nanoparticles useful and suitable for some biomedical
applications as drug delivery. Some relevant information can be obtained by
comparing Mössbauer spectra recorded in the same conditions on nanoparticles
before and after functionalization, combined to further spectroscopic techniques.
A first illustration is given by the efficient coating of bisphosphonates onto iron
oxide nanoparticles as ferrofluids. From transmission electron microscopy, the core
size of as-prepared nanoparticles is estimated at about 5 nm while the hyperfine
structure is consistent with the presence of superparamagnetic relaxation phe-
nomena, that to confirm the size and the non aggregated assembly of nanoparticles.
As is illustrated in Fig. 4.11 , the comparison of the 77 K hyperfine structures
Fig. 4.11 77 K Mössbauer
spectra of iron oxide
nanoparticles before and after
coating of bisphosphonates
[ 89 ]
-10
-5
0
5
10
AF TER
1,000
0,998
77 K
BEFORE
1,000
0,995
-10
-5
0
5
10
V [mm/s]
 
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