Environmental Engineering Reference
In-Depth Information
Fig. 4 TEM pictures of nucleation step to create pyrite particles and the following results of
growth steps. Reprinted with permission from [ 23 ]
(Fe 2 O 3 ) and elemental sulfur as the chalcogenide along with oleic acid (OA),
oleylamine (OLA) and CTAB, cubic structures could be obtained [ 44 ]. All com-
ponents are loaded into one flask and heated up to 290 C and kept there for 1 h
with stirring. Such a high temperature was necessary to completely convert the
hematite into pyrite, and if the temperature was raised even higher greigite (Fe 3 S 4 )
impurities were observed. Without the presence of the ligands, it was found that
that both starting material and marcasite phases were found in the particles. Par-
ticle size length was *100 nm, though the size distribution was quite large
(±25 nm, size distribution was not reported). This report earns honorable mention
due to its ability to convert iron raw material feedstock (hematite) directly to
pyrite, instead of utilizing different iron precursor where the iron likely originated
from hematite.
More recently, the Soldt group reported a unique synthetic method utilizing a
modification of the standard one pot synthesis. In their article, it was shown that by
utilizing a nucleation step FeS 2 that creates irregular nanocrystals followed by a
growth step by adding more precursors, beautiful cubic/rectangular shapes could
be obtained [ 23 ]. Figure 4 shows TEM images of the particles throughout the
synthesis. From the images it can be seen that these are the cleanest edged cubic
structures created to date. It is also the first report of cubic structures with side
lengths {50 nm, which would allow for thinner films when creating devices.
The synthetic method starts with loading FeCl 2 and sulfur powder with a ratio
of [S]/[Fe] equaling 6 along with hexadecylamine into a three-necked flask and
then purged under argon. The material is then heated up to 250C for 3 h. The end
result of this first step was irregular-shaped pure phase nanocrystals with sizes
around *30-40 nm. They deemed this step the nucleation step, which should not
be confused with the initial nucleation step that the seeds are created from which
these particles grow. These irregular particles show absorbance spectra much like
other spherical particles that have been made with a shoulder around *550 nm
with steady increase of absorbance to the blue. Nucleation step was followed by a
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