Environmental Engineering Reference
In-Depth Information
unique to each other, they have shown differences in activity in many different
studies and are important to consider when choosing pyrite material for applications
[
23
,
24
,
28
,
29
].
2 Iron Pyrite Nanomaterial Synthesis
2.1 Introduction
The growth of pyrite has been an interesting topic for past geologists due to its
impact in mining, as it is the main component of creating acid mine run-off [
30
]. It
is from these papers that information can be first learned about the growth of
pyrite. There are three different mechanisms that occur to produce pyrite. One
involves iron (II) and polysulfide, the other uses FeS and S(-II), and the last is
growth of pyrite crystal growth on pyrite seeds [
31
-
35
]. It is important to note that
the first two of these reactions involve an [FeS] intermediate step. The nucleation
step of this intermediate has been proposed as the limiting reaction in the rate of
pyrite crystal formation. Figure
2
shows the proposed mechanisms of pyrite for-
mation using the two different sulfur sources. The first mechanism utilizes poly-
sulfides, while the second uses hydrogen sulfide (H
2
S). For a beautifully detailed
review of pyrite formation in nature, we direct the reader to the publication of
Rickard and Luther [
36
]. While this section is about nano-synthesis of pyrite, these
background studies are necessary to achieve better understanding of the system.
Tributsch and colleagues did a major portion of the initial studies of making use
of pyrite for solar energy conversion that deserves attention. Studies were focused
on creating thin films by first chemical vapor transportation (CVT) and then fol-
low-up studies were done using metal organic chemical vapor deposition
(MOCVD) [
37
-
41
]. It was found that they could produce pure pyrite films by
adjusting pressure, temperature, and molar concentrations of the reactants. They
could also control the preferred crystal growth and grain size by changing the
substrate on which the pyrite was grown. A great summary on their work can be
found in the review article by Ennaoui et al. [
4
].
More recently, the Wolden group has shown that pure phase pyrite thin films
can be achieved from hematite (Fe
2
O
3
) using an H
2
S plasma [
42
]. First, Fe
2
O
3
nanorods are synthesized using a chemical bath deposition (CBD) method. Then
the high sulfur activity created in plasma can be used to achieve sulfurization of
the Fe
2
O
3
. By monitoring the optical band gap and Fe:S ratio's using energy-
dispersive X-ray spectroscopy (EDAX) the transition from hematite to pyrite can
be observed. This study has shown a new technique utilizing sulfur plasma has
breathed new life into creating grown thin films.
Search WWH ::
Custom Search