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9.4.2 Characterization of MeFe 2 O 4
MeFe 2 O 4 surface morphology analysis from TEM demonstrates the
agglomeration of many ultrafine particles with the diameter of about 20 nm. Its XRD
characterization shows broad diffraction peaks from the powder sample that precipitated
out of the solution. The CoFe 2 O 4 and MnFe 2 O 4 samples synthesized at 70 o C were
identified as pure components, while the other samples produced at 400 o C were
identified as a mixture of MeO, Fe 2 O 3 and MeFe 2 O 4 in crystalline state. Taking
MgFe 2 O 4 as an example, XRD patterns as illustrated in Figure 9.6 show that MgFe 2 O 4
particles produced at relatively lower temperature (e.g., 400 o C) contain less MgO and
Fe 2 O 3 impurities; after being heated in the air at a high temperature (e.g., 800 o C), the
mixture was continually transformed into crystalline MgFe 2 O 4 nanoparticles that
contained -Fe 2 O 3 impurity of less than 1% by weight. All the physical surface
characteristics of various magnetic nanoparticles are summarized in Table 9.1. The ratio
of cation distribution equal to 1:2 deduced from X-ray photoelectron spectroscopy (XPS)
investigation suggested the high purity of the synthesized materials, and the ratio of less
than 1:2 revealed the presence of more -Fe 2 O 3 impurity on the surface of synthesized
MeFe 2 O 4 particles, which is due to the incomplete dehydration and crystallization at
comparatively lower calcination temperature during the synthesis process. The points of
zero charge pH pzc for various magnetic nanoparticles were measured to be around 7.0-
8.0. Brunauer-Emmett-Teller (BET) results presented the comparatively higher surface
area of nanoscale particles, especially for MnFe 2 O 4 nanoparticles.
Figure 9.6 XRD patterns of synthesized MgFe 2 O 4 nanoparticles (Hu et al., 2007a)
 
 
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