Skip to main content

Lund University Publications

LUND UNIVERSITY LIBRARIES

Structural evolution of iron forming iron oxide in a deep eutectic-solvothermal reaction

Hammond, Oliver S. ; Atri, Ria S. ; Bowron, Daniel T. ; de Campo, Liliana ; Diaz-Moreno, Sofia ; Keenan, Luke L. ; Doutch, James ; Eslava, Salvador and Edler, Karen J. LU orcid (2021) In Nanoscale 13(3). p.1723-1737
Abstract
Deep eutectic solvents (DES) and their hydrated mixtures are used for solvothermal routes towards greener functional nanomaterials. Here we present the first static structural and in situ studies of the formation of iron oxide (hematite) nanoparticles in a DES of choline chloride : urea where xurea = 0.67 (aka. reline) as an exemplar solvothermal reaction, and observe the effects of water on the reaction. The initial speciation of Fe3+ in DES solutions was measured using extended X-ray absorption fine structure (EXAFS), while the atomistic structure of the mixture was resolved from neutron and X-ray diffraction and empirical potential structure refinement (EPSR) modelling. The reaction was monitored... (More)
Deep eutectic solvents (DES) and their hydrated mixtures are used for solvothermal routes towards greener functional nanomaterials. Here we present the first static structural and in situ studies of the formation of iron oxide (hematite) nanoparticles in a DES of choline chloride : urea where xurea = 0.67 (aka. reline) as an exemplar solvothermal reaction, and observe the effects of water on the reaction. The initial speciation of Fe3+ in DES solutions was measured using extended X-ray absorption fine structure (EXAFS), while the atomistic structure of the mixture was resolved from neutron and X-ray diffraction and empirical potential structure refinement (EPSR) modelling. The reaction was monitored using in situ small-angle neutron scattering (SANS), to determine mesoscale changes, and EXAFS, to determine local rearrangements of order around iron ions. It is shown that iron salts form an octahedral [Fe(L)3(Cl)3] complex where (L) represents various O-containing ligands. Solubilised Fe3+ induced subtle structural rearrangements in the DES due to abstraction of chloride into complexes and distortion of H-bonding around complexes. EXAFS suggests the complex forms [–O–Fe–O–] oligomers by reaction with the products of thermal hydrolysis of urea, and is thus pseudo-zero-order in iron. In the hydrated DES, the reaction, nucleation and growth proceeds rapidly, whereas in the pure DES, the reaction initially proceeds quickly, but suddenly slows after 5000 s. In situ SANS and static small-angle X-ray scattering (SAXS) experiments reveal that nanoparticles spontaneously nucleate after 5000 s of reaction time in the pure DES before slow growth. Contrast effects observed in SANS measurements suggest that hydrated DES preferentially form 1D particle morphologies because of choline selectively capping surface crystal facets to direct growth along certain axes, whereas capping is restricted by the solvent structure in the pure DES. (Less)
Please use this url to cite or link to this publication:
author
; ; ; ; ; ; ; and
publishing date
type
Contribution to journal
publication status
published
subject
in
Nanoscale
volume
13
issue
3
pages
15 pages
publisher
Royal Society of Chemistry
external identifiers
  • scopus:85100233428
  • pmid:33428701
ISSN
2040-3364
DOI
10.1039/d0nr08372k
language
English
LU publication?
no
additional info
Publisher Copyright: © 2021 The Royal Society of Chemistry.
id
72592969-73ae-42ab-8acb-d0985fc85096
date added to LUP
2022-07-12 15:40:38
date last changed
2024-04-16 06:58:09
@article{72592969-73ae-42ab-8acb-d0985fc85096,
  abstract     = {{Deep eutectic solvents (DES) and their hydrated mixtures are used for solvothermal routes towards greener functional nanomaterials. Here we present the first static structural and <em>in situ</em> studies of the formation of iron oxide (hematite) nanoparticles in a DES of choline chloride : urea where <em>x</em><sub>urea</sub> = 0.67 (aka. reline) as an exemplar solvothermal reaction, and observe the effects of water on the reaction. The initial speciation of Fe<sup>3+</sup> in DES solutions was measured using extended X-ray absorption fine structure (EXAFS), while the atomistic structure of the mixture was resolved from neutron and X-ray diffraction and empirical potential structure refinement (EPSR) modelling. The reaction was monitored using <em>in situ</em> small-angle neutron scattering (SANS), to determine mesoscale changes, and EXAFS, to determine local rearrangements of order around iron ions. It is shown that iron salts form an octahedral [Fe(L)<sub>3</sub>(Cl)<sub>3</sub>] complex where (L) represents various O-containing ligands. Solubilised Fe<sup>3+</sup> induced subtle structural rearrangements in the DES due to abstraction of chloride into complexes and distortion of H-bonding around complexes. EXAFS suggests the complex forms [–O–Fe–O–] oligomers by reaction with the products of thermal hydrolysis of urea, and is thus pseudo-zero-order in iron. In the hydrated DES, the reaction, nucleation and growth proceeds rapidly, whereas in the pure DES, the reaction initially proceeds quickly, but suddenly slows after 5000 s. <em>In situ</em> SANS and static small-angle X-ray scattering (SAXS) experiments reveal that nanoparticles spontaneously nucleate after 5000 s of reaction time in the pure DES before slow growth. Contrast effects observed in SANS measurements suggest that hydrated DES preferentially form 1D particle morphologies because of choline selectively capping surface crystal facets to direct growth along certain axes, whereas capping is restricted by the solvent structure in the pure DES.}},
  author       = {{Hammond, Oliver S. and Atri, Ria S. and Bowron, Daniel T. and de Campo, Liliana and Diaz-Moreno, Sofia and Keenan, Luke L. and Doutch, James and Eslava, Salvador and Edler, Karen J.}},
  issn         = {{2040-3364}},
  language     = {{eng}},
  month        = {{01}},
  number       = {{3}},
  pages        = {{1723--1737}},
  publisher    = {{Royal Society of Chemistry}},
  series       = {{Nanoscale}},
  title        = {{Structural evolution of iron forming iron oxide in a deep eutectic-solvothermal reaction}},
  url          = {{http://dx.doi.org/10.1039/d0nr08372k}},
  doi          = {{10.1039/d0nr08372k}},
  volume       = {{13}},
  year         = {{2021}},
}