School of Earth and Environment
Research Experience Placements Scheme (‘REP’)
Ni-doped Iron Sulfides: Formation and Structure
Supervisors: Dr Adriana Matamoros-Veloza (SEE), Dr Michael Ward (Materials),
Dr Rik Drummond-Brydson (Materials), Professor Liane G. Benning (SEE)
10 weeks placement
Poorly ordered iron sulphide (FeS) phases are potential synthetic catalysts for CO2 conversion into
small organic molecules. This is particularly true when FeS forms in the presence of dopants (i.e. Ni,
Co) because it is anticipated that these phases may be used in reducing the noxious effects of CO 2
to the climatic change.1-4 Amorphous FeS phases are believed to be important precursors to the
more crystalline FeS minerals like mackinawite and greigite. However, we have absolutely no
quantitative information about the nature and structure of amorphous FeS phases both in the pure
state or when formed in the presence of dopants. There is also a dearth of data about the kinetics
and mechanisms of the first stages of formation, and we do not know if during these initial stages
additional intermediate, short-lived phases evolve, as demonstrated in other mineral systems.5-6
In this project we aim to study the first stages of formation of Ni-doped FeS, and to identify the
intermediate phases and mechanisms occurring prior the formation of mackinawite. We will follow
the reaction using two synthesis methods: (1) a stepwise titration of Ni/Fe(II) with Na2S in under an
O2 free atmosphere, while monitoring pH and redox potential using a highly controlled reactor
system; (2) simple diffusion of sulphide onto a Ni/Fe(II) solution also under anaerobic conditions. For
both methods, in-situ measurements of changes in absorbance using Ultraviolet Visible
Spectroscopy and the formation of particles using Dynamic Light Scattering will be collected. Tests
to find a suitable wavelength to record the formation of the amorphous FeS phases at the pH
conditions of the diffusion experiments will be required. Samples will be collected as a function of
pH, and after filtration and drying they will be characterized by X-ray diffraction, transmission
electron microscopy and Fourier transform infrared spectroscopy.
This is an ambitious project and we are looking for a student who after receiving adequate training is
keen to perform the synthesis reactions under O2 free controlled conditions and is interested in
gaining hands-on experience in the use of new instruments for the characterization of solid and
solution samples both in the Cohen Laboratories in Earth Sciences but also at the Leeds Electron
Microscopy And Spectroscopy Centre, where s/he will learn about characterization of solids at the
micro-scale. The student will not just learn about methods of synthesis and characterization of solid
and liquid samples but also have the opportunity to improve his/her communication and writing
skills.
Data from this project will complement other synchrotron data and help gain a quantitative
understanding of the kinetics and mechanisms of nucleation, growth and aggregation of Ni-doped
FeS particles.
[1] Cairns-Smith et al (1992) Origins of Life and Evolution in the Biosphere 22, 161. [2] Russell & Martin (2004) Trends
Biochem. Sci., 29, 358. [3] Russell et al (1994) J. Mol. Evol.,39, 231. [4] Russell & Hall (1997) J. Geog. Soc. Lond., 154,
377. [5] Penn & Banfield (1998) Science 281, 969. [6] Rodriguez-Blanco et al Nanoscale (2011) doi: 0.1039/C0NR00589D.