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The formation of platinum nanoparticles and the transforma-
tion of
a-FeOOH to Fe3O4 can be presented by formal chemical
equations:
2ꢀ
PtðOHÞ6 þ 4eꢀ ! Pt0 þ 6OHꢀ
Pt
3
a
-FeOOH þ eꢀ ! Fe3O4 þ H2O þ OHꢀ
The source of electrons for the above mentioned reduction reac-
tions is TMAH and the products of its thermal decomposition
(methanol and trimethylamine). For the reduction of ferric iron
in
a-FeOOH to ferrous iron in Fe3O4 in this system the presence
of a platinum group metal catalyst is necessary [45,49,59,65].
Without the presence of the platinum group metal nanoparticles
the transformation of a-FeOOH to Fe3O4 in the presence of TMAH
and its thermal decomposition products has not been obtained,
even in very long hydrothermal treatments [39].
4. Conclusions
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ꢆ A strong influence of the presence of platinum(IV) ions, similar
to cations of other platinum group metals, on the formation of
iron oxides in a highly alkaline medium in the presence of tet-
ramethylammonium hydroxide was observed.
ꢆ In the presence of Pt ions lath-like
a-FeOOH particles were
formed. In their shape and size these particles were similar to
the particles in the reference sample. However, the presence
of Pt ions in the precipitation system led to the formation of
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a
-FeOOH crystallites of lower mean size. A possibility of minor
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incorporation of Pt ions into the -FeOOH structure was sug-
a
gested on the basis of Mössbauer spectroscopy and XRD results.
ꢆ A longer hydrothermal treatment led to the formation of plati-
num nanoparticles by reduction of Pt(IV) ions with TMAH and
the products of its thermal decomposition.
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ˇ
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a-FeOOH to Fe3O4 in the presence of TMAH and its thermal
decomposition products as a source of electrons necessary for
the reduction of ferric iron.
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