Chemistry Reference
In-Depth Information
1.00
0.99
0.98
0.97
-10
-5
0
5
10
-10
-5
0
5
10
V (mm/s)
Fig. 4.12 Mössbauer spectra recorded at 77 K obtained on Fe oxide nanoparticle with an
average grain size of 12 nm before (in black) and after phosphatation (in red). The inset
corresponds to the spectrum resulting from the difference between the two previous ones, giving
clear evidence for a quadrupolar doublet [
41
]
observed on as-prepared and coated nanoparticles (as frozen ferrofluids) give
clearly evidence for the emergence of a quadrupolar doublet attributed to a para-
magnetic interface layer resulting from a ferric phosphate oxide phase originated
from the superficial bisphosphonate molecules, i.e. the phosphatation reaction
favors an iron-phosphate complex. The mean thickness of the paramagnetic layer is
estimated at about two atomic layers from the respective absorption areas of the
magnetic and paramagnetic components, assuming the same recoilless factors. In
addition, the magnetic contributions do not significantly differ, but that character-
istics of the coated particles exhibits slightly more broadened lines in agreement
with smaller magnetic cores.
The second example is concerned by magnetite nanoparticles in size which
have been phosphated in orthophosphoric acid [
41
]. The difference of Mössbauer
spectra as illustrated in Fig.
4.12
allows to distinguish and to identify the iron ions
involved in phosphate complexes, from the supplementary quadrupolar doublet
which is clearly observed at the center (see the inset of Fig.
4.12
). Such a feature
was previously reported by Tronc et al. for phosphate maghemite and attributed to
surface iron-phosphate complexes [
37
]. The value of the isomer shift value cor-
responding to this quadrupolar doublet indicates clearly that the phosphatation
occurs by interaction with both positively charged groups and hydroxyl sites at the
surface with Fe
3+
ions in octahedral sites. Such a result allows to suggest that the
