Ferrihydrite formation: the role of Fe13 Keggin clusters

Joshua Simon Weatherill, Katherine Morris, Pieter Bots, Tomasz M. Stawski, Arne Janssen, Liam Abrahamsen, Richard Blackham, Samuel Shaw

Research output: Contribution to journalArticle

20 Citations (Scopus)

Abstract

Ferrihydrite is the most common iron oxyhydroxide found in soil and is a key sequester of contaminants in the environment. Ferrihydrite formation is also a common component of many treatment processes for clean-up of industrial effluents. Here we characterize ferrihydrite formation during the titration of an acidic ferric nitrate solution with NaOH. In-situ SAXS measurements supported by ex situ TEM indicate that initailly Fe13 Keggin clusters (radius ~0.45 nm) form in solution at pH 0.5 - 1.5, and are persistant for at least 18 days. The Fe13 clusters begin to aggregate above ~ pH 1, initially forming highly linear structures. Above pH ~ 2 densification of the aggregates occurs in conjunction with precipiation of low molecular weight Fe(III) speices (e.g. monomers, dimers) to form mass fractal aggregates of ferrihydrite nanoparticles (~ 3 nm) in which the Fe13 Keggin motif is preserved. SAXS analysis indicates the ferrihydrite particles have a core-shell structure consisting of a Keggin center surrounded by a Fe-depleted shell, supporting the surface depleted model of ferrihydrite. Overall, we present the first direct evidence for the role of Fe13 clusters in the pathway of ferrihydrite formation during base hydrolysis, showing clear structural continuity from isolated Fe13 Keggins to the ferrihydrite particle structure. The results have direct relevance to the fundamental understanding of ferrihydrite formation in environmental, engineered and industrial processes.
LanguageEnglish
Pages9333-9342
Number of pages10
JournalEnvironmental Science and Technology
Volume50
Issue number17
Early online date2 Aug 2016
DOIs
Publication statusE-pub ahead of print - 2 Aug 2016

Fingerprint

ferrihydrite
shell
Titration
Densification
Dimers
Fractals
in situ measurement
transmission electron microscopy
Effluents
hydrolysis
Hydrolysis
Monomers
Molecular weight
Impurities
nitrate
Nanoparticles
Transmission electron microscopy
Soils
iron
pollutant

Keywords

  • ferrihydrite
  • oxyhydroxides
  • environmental contaminants

Cite this

Weatherill, J. S., Morris, K., Bots, P., Stawski, T. M., Janssen, A., Abrahamsen, L., ... Shaw, S. (2016). Ferrihydrite formation: the role of Fe13 Keggin clusters. Environmental Science and Technology, 50(17), 9333-9342. https://doi.org/10.1021/acs.est.6b02481
Weatherill, Joshua Simon ; Morris, Katherine ; Bots, Pieter ; Stawski, Tomasz M. ; Janssen, Arne ; Abrahamsen, Liam ; Blackham, Richard ; Shaw, Samuel. / Ferrihydrite formation : the role of Fe13 Keggin clusters. In: Environmental Science and Technology. 2016 ; Vol. 50, No. 17. pp. 9333-9342.
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Weatherill, JS, Morris, K, Bots, P, Stawski, TM, Janssen, A, Abrahamsen, L, Blackham, R & Shaw, S 2016, 'Ferrihydrite formation: the role of Fe13 Keggin clusters' Environmental Science and Technology, vol. 50, no. 17, pp. 9333-9342. https://doi.org/10.1021/acs.est.6b02481

Ferrihydrite formation : the role of Fe13 Keggin clusters. / Weatherill, Joshua Simon; Morris, Katherine; Bots, Pieter; Stawski, Tomasz M.; Janssen, Arne; Abrahamsen, Liam; Blackham, Richard; Shaw, Samuel.

In: Environmental Science and Technology, Vol. 50, No. 17, 02.08.2016, p. 9333-9342.

Research output: Contribution to journalArticle

TY - JOUR

T1 - Ferrihydrite formation

T2 - Environmental Science and Technology

AU - Weatherill, Joshua Simon

AU - Morris, Katherine

AU - Bots, Pieter

AU - Stawski, Tomasz M.

AU - Janssen, Arne

AU - Abrahamsen, Liam

AU - Blackham, Richard

AU - Shaw, Samuel

PY - 2016/8/2

Y1 - 2016/8/2

N2 - Ferrihydrite is the most common iron oxyhydroxide found in soil and is a key sequester of contaminants in the environment. Ferrihydrite formation is also a common component of many treatment processes for clean-up of industrial effluents. Here we characterize ferrihydrite formation during the titration of an acidic ferric nitrate solution with NaOH. In-situ SAXS measurements supported by ex situ TEM indicate that initailly Fe13 Keggin clusters (radius ~0.45 nm) form in solution at pH 0.5 - 1.5, and are persistant for at least 18 days. The Fe13 clusters begin to aggregate above ~ pH 1, initially forming highly linear structures. Above pH ~ 2 densification of the aggregates occurs in conjunction with precipiation of low molecular weight Fe(III) speices (e.g. monomers, dimers) to form mass fractal aggregates of ferrihydrite nanoparticles (~ 3 nm) in which the Fe13 Keggin motif is preserved. SAXS analysis indicates the ferrihydrite particles have a core-shell structure consisting of a Keggin center surrounded by a Fe-depleted shell, supporting the surface depleted model of ferrihydrite. Overall, we present the first direct evidence for the role of Fe13 clusters in the pathway of ferrihydrite formation during base hydrolysis, showing clear structural continuity from isolated Fe13 Keggins to the ferrihydrite particle structure. The results have direct relevance to the fundamental understanding of ferrihydrite formation in environmental, engineered and industrial processes.

AB - Ferrihydrite is the most common iron oxyhydroxide found in soil and is a key sequester of contaminants in the environment. Ferrihydrite formation is also a common component of many treatment processes for clean-up of industrial effluents. Here we characterize ferrihydrite formation during the titration of an acidic ferric nitrate solution with NaOH. In-situ SAXS measurements supported by ex situ TEM indicate that initailly Fe13 Keggin clusters (radius ~0.45 nm) form in solution at pH 0.5 - 1.5, and are persistant for at least 18 days. The Fe13 clusters begin to aggregate above ~ pH 1, initially forming highly linear structures. Above pH ~ 2 densification of the aggregates occurs in conjunction with precipiation of low molecular weight Fe(III) speices (e.g. monomers, dimers) to form mass fractal aggregates of ferrihydrite nanoparticles (~ 3 nm) in which the Fe13 Keggin motif is preserved. SAXS analysis indicates the ferrihydrite particles have a core-shell structure consisting of a Keggin center surrounded by a Fe-depleted shell, supporting the surface depleted model of ferrihydrite. Overall, we present the first direct evidence for the role of Fe13 clusters in the pathway of ferrihydrite formation during base hydrolysis, showing clear structural continuity from isolated Fe13 Keggins to the ferrihydrite particle structure. The results have direct relevance to the fundamental understanding of ferrihydrite formation in environmental, engineered and industrial processes.

KW - ferrihydrite

KW - oxyhydroxides

KW - environmental contaminants

UR - http://pubs.acs.org/journal/esthag

U2 - 10.1021/acs.est.6b02481

DO - 10.1021/acs.est.6b02481

M3 - Article

VL - 50

SP - 9333

EP - 9342

JO - Environmental Science and Technology

JF - Environmental Science and Technology

SN - 0013-936X

IS - 17

ER -

Weatherill JS, Morris K, Bots P, Stawski TM, Janssen A, Abrahamsen L et al. Ferrihydrite formation: the role of Fe13 Keggin clusters. Environmental Science and Technology. 2016 Aug 2;50(17):9333-9342. https://doi.org/10.1021/acs.est.6b02481