Nontronite as natural source and growth template for (nano)maghemite [γ-Fe2O3] and (nano)Wüstite [Fe1−xO]

Nontronite as natural source and growth template for (nano)maghemite [γ-Fe2O3] and... Nontronites are iron-rich dioctahedral smectites that serve as a natural source of nanomaghemite and nanowüstite, which are industrial minerals widely used to develop biomedicine and semiconductor applications. The integration of various bulk analytical techniques and computational calculations to study the structure of nontronites show that their contents of tetrahedral Fe3+ surpass theoretical values. Consequently, the microstructure of nontronite has only been partially understood. Three nontronites (NAu-1 and NAu-2 from South Australia) and NG-1 (Högen Hagen, Germany) were studied as received using high-resolution techniques, namely, High-Resolution Scanning and Transmission Electron Microscopy coupled with Energy Dispersive X-ray Spectroscopy (HRSEM and HRTEM-EDS), and Electron Spin Resonance Spectroscopy (ESR). Nontronite surfaces contained abundant nanodomains (predominantly ≤ 2-nm in diameter), homogeneously distributed, mostly circular in shape, discrete, crystalline, and composed by a single phase. Nanodomains were found invariably associated to nontronite surfaces, mostly embedded although loosely bound at times. Noteworthy were nanodomains showing non-round contours, a signature of halted growth. However, nanodomain abundance related to the tetrahedral Fe (or unit cell formulae). If theoretical contents of tetrahedral Fe in nontronite were higher (NAu-2, NG-1) then the nanodomains were found to be less abundant and more heterogeneous in size and shape. Acquired Miller diffraction indexes for Fe nanodomains confirmed the presence of maghemite [γ-Fe2O3] and wüstite [Fe1−xO]. Most remarkably, wüstite, a highly-reduced mineral remained stable under oxic conditions, so the small size of wüstite and its interactions with nontronite surfaces inhibited the oxidation of structural Fe by atmospheric oxygen. Finally, we specuate that mineral microregions containing nanomaghemite and nanowüstite may form a Fe mixed valence system showing electronic and magnetic properties resembling those characteristic of Fe(II)-Fe(III) minerals. http://www.deepdyve.com/assets/images/DeepDyve-Logo-lg.png Applied Clay Science Elsevier

Nontronite as natural source and growth template for (nano)maghemite [γ-Fe2O3] and (nano)Wüstite [Fe1−xO]

Loading next page...
 
/lp/elsevier/nontronite-as-natural-source-and-growth-template-for-nano-maghemite-lvT6WpG7ek
Publisher
Elsevier
Copyright
Copyright © 2018 Elsevier B.V.
ISSN
0169-1317
eISSN
1872-9053
D.O.I.
10.1016/j.clay.2018.02.009
Publisher site
See Article on Publisher Site

Abstract

Nontronites are iron-rich dioctahedral smectites that serve as a natural source of nanomaghemite and nanowüstite, which are industrial minerals widely used to develop biomedicine and semiconductor applications. The integration of various bulk analytical techniques and computational calculations to study the structure of nontronites show that their contents of tetrahedral Fe3+ surpass theoretical values. Consequently, the microstructure of nontronite has only been partially understood. Three nontronites (NAu-1 and NAu-2 from South Australia) and NG-1 (Högen Hagen, Germany) were studied as received using high-resolution techniques, namely, High-Resolution Scanning and Transmission Electron Microscopy coupled with Energy Dispersive X-ray Spectroscopy (HRSEM and HRTEM-EDS), and Electron Spin Resonance Spectroscopy (ESR). Nontronite surfaces contained abundant nanodomains (predominantly ≤ 2-nm in diameter), homogeneously distributed, mostly circular in shape, discrete, crystalline, and composed by a single phase. Nanodomains were found invariably associated to nontronite surfaces, mostly embedded although loosely bound at times. Noteworthy were nanodomains showing non-round contours, a signature of halted growth. However, nanodomain abundance related to the tetrahedral Fe (or unit cell formulae). If theoretical contents of tetrahedral Fe in nontronite were higher (NAu-2, NG-1) then the nanodomains were found to be less abundant and more heterogeneous in size and shape. Acquired Miller diffraction indexes for Fe nanodomains confirmed the presence of maghemite [γ-Fe2O3] and wüstite [Fe1−xO]. Most remarkably, wüstite, a highly-reduced mineral remained stable under oxic conditions, so the small size of wüstite and its interactions with nontronite surfaces inhibited the oxidation of structural Fe by atmospheric oxygen. Finally, we specuate that mineral microregions containing nanomaghemite and nanowüstite may form a Fe mixed valence system showing electronic and magnetic properties resembling those characteristic of Fe(II)-Fe(III) minerals.

Journal

Applied Clay ScienceElsevier

Published: May 1, 2018

References

You’re reading a free preview. Subscribe to read the entire article.


DeepDyve is your
personal research library

It’s your single place to instantly
discover and read the research
that matters to you.

Enjoy affordable access to
over 18 million articles from more than
15,000 peer-reviewed journals.

All for just $49/month

Explore the DeepDyve Library

Search

Query the DeepDyve database, plus search all of PubMed and Google Scholar seamlessly

Organize

Save any article or search result from DeepDyve, PubMed, and Google Scholar... all in one place.

Access

Get unlimited, online access to over 18 million full-text articles from more than 15,000 scientific journals.

Your journals are on DeepDyve

Read from thousands of the leading scholarly journals from SpringerNature, Elsevier, Wiley-Blackwell, Oxford University Press and more.

All the latest content is available, no embargo periods.

See the journals in your area

DeepDyve

Freelancer

DeepDyve

Pro

Price

FREE

$49/month
$360/year

Save searches from
Google Scholar,
PubMed

Create lists to
organize your research

Export lists, citations

Read DeepDyve articles

Abstract access only

Unlimited access to over
18 million full-text articles

Print

20 pages / month

PDF Discount

20% off