Shell-Induced Ostwald Ripening: Simultaneous Structure, Composition, and Morphology Transformations during the Creation of Hollow Iron Oxide Nanocapsules

Lei Yu, Ruixin Han, Xiahan Sang, Jue Liu, Melonie P. Thomas, Bethany M. Hudak, Amita Patel, Katharine Page, Beth S. Guiton

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36 Citations (SciVal)


The creation of nanomaterials requires simultaneous control of not only crystalline structure and composition but also crystal shape and size, or morphology, which can pose a significant synthetic challenge. Approaches to address this challenge include creating nanocrystals whose morphologies echo their underlying crystal structures, such as the growth of platelets of two-dimensional layered crystal structures, or conversely attempting to decouple the morphology from structure by converting a structure or composition after first creating crystals with a desired morphology. A particularly elegant example of this latter approach involves the topotactic conversion of a nanoparticle from one structure and composition to another, since the orientation relationship between the initial and final product allows the crystallinity and orientation to be maintained throughout the process. Here we report a mechanism for creating hollow nanostructures, illustrated via the decomposition of β-FeOOH nanorods to nanocapsules of α-Fe2O3, γ-Fe2O3, Fe3O4, and FeO, depending on the reaction conditions, while retaining single-crystallinity and the outer nanorod morphology. Using in situ TEM, we demonstrate that the nanostructured morphology of the starting material allows kinetic trapping of metastable phases with a topotactic relationship to the final thermodynamically stable phase.

Original languageEnglish
Pages (from-to)9051-9059
Number of pages9
JournalACS Nano
Issue number9
StatePublished - Sep 25 2018

Bibliographical note

Funding Information:
*E-mail: ORCID Xiahan Sang: 0000-0002-2861-6814 Jue Liu: 0000-0002-4453-910X Bethany M. Hudak: 0000-0002-4392-9237 Katharine Page: 0000-0002-9071-3383 Beth S. Guiton: 0000-0002-9478-9190 Author Contributions L.Y. designed and conducted the experiments and characterization, with contribution from R.H., X. S., M.P.T., and A.P., and B.M.H. assisted with in situ TEM heating experiments. J.L. and K.P. performed in situ XRD experiments. B.S.G. guided the research and experimental design. All authors contributed to writing and editing the manuscript. All authors have given approval to the final version of the manuscript. Funding This research was supported by National Science Foundation under DMR 1455154 (L.Y., R.H., B.S.G.), with partial salary support from OIA 1355438 (L.Y., R.H., M.P.T.) and from NASA Kentucky under NASA award no. NNX15AK28A (M.P.T.). XRD experiments and analysis (J.L. and K.P.) were funded by the Basic Energy Sciences Office of Science Early Career Award: Exploiting Small Signatures: Quantifying Nano-scale Structure and Behavior KC04062, under contract no. DE-AC05-00OR22725. Notes The authors declare no competing financial interest.

Funding Information:
STEM and in situ XRD work at ORNL was conducted at the Center for Nanophase Materials Sciences, which is a DOE Office of Science User Facility and by instrumentation provided by the U.S. DOE Office of Nuclear Energy, Fuel Cycle R&D Program, and the Nuclear Science User Facilities. The authors thank Shawn Reeves for preparing cross-sectional samples by ultramicrotomy and Dr. David A. Cullen for assistance with STEM imaging and EDS mapping. We thank John P. Selegue for assistance with TGA measurements and the Kentucky Geological Survey and the UK Electron Microscopy Center for use of their facilities for characterization.

Publisher Copyright:
© 2018 American Chemical Society.


  • Ostwald ripening
  • hollow nanorods
  • in situ TEM
  • iron oxide
  • phase transformation

ASJC Scopus subject areas

  • Materials Science (all)
  • Engineering (all)
  • Physics and Astronomy (all)


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