New Paper: Electrochemistry of Sulfide-Modified Nano Zerovalent Iron

[PGT]

Several projects have recently led us to investigate the effects of
sulfide on reactivity of zerovalent iron (ZVI). In this study, the
sulfide was introduced during the synthesis of nano ZVI (nZVI), with
the primary goal of making a material with improved performance in
remediation applications. However, this paper is focused on
fundamental aspects of how the presence of S(II) alters the reactivity
nZVI, not contaminant degradation. The methods used are mainly
electrochemical and are organized into a protocol that should be
useful in future characterizations of the redox reactivity of other
fine-grained materials.

~~~~~~~~~~~~~~~~~~~~~~

Turcio-Ortega, D., D. Fan, P. G. Tratnyek, E.-J. Kim, and Y.-S. Chang.
2012. Reactivity of Fe/FeS nanoparticles: Electrolyte composition
effects on corrosion electrochemistry. Environ. Sci. Technol. 46(22):
12484-12492.

Zerovalent iron nanoparticles (Fe0 NPs or nZVI) synthesized by
reductive precipitation in aqueous solution (Fe/FeO) differ in
composition and reactivity from the NPs obtained by reductive
precipitation in the presence of a S-source such as dithionite (Fe/
FeS). To compare the redox properties of these types of NPs under a
range of environmentally relevant solution conditions, stationary
powder disk electrodes (PDEs) made from Fe/FeO and Fe/FeS were
characterized using a series of complementary electrochemical
techniques: open-circuit chronopotentiometry (CP), linear polarization
resistance (LPR), electrochemical impedance spectroscopy (EIS), and
linear sweep voltammetry (LSV). The passive films on these materials
equilibrate within minutes of first immersion and do not show further
breakdown until >1 day of exposure. During this period, the potentials
and currents measured by LPR and LSV suggest that Fe/FeS undergoes
more rapid corrosion and is more strongly influence by solution
chemical conditions than Fe/FeO. Chloride containing media were
strongly activating and natural organic matter (NOM) was mildly
passivating for both materials. These effects were also seen in the
impedance data obtained by EIS, and equivalent circuit modeling of the
electrodes composed of these powders suggested that the higher
reactivity of Fe/FeS is due to greater abundance of defects in its
passive film.

DOI: http://pubs.acs.org/doi/abs/10.1021/es303422w