Further Comments on "Engineering Shape Anisotropy of Fe3o4-Γ-Fe2o3hollow Nanoparticles for Magnetic Hyperthermia"

Author

Fernande Grandjean, Missouri University of Science and TechnologyFollow
Gary J. Long, Missouri University of Science and TechnologyFollow

Abstract

In their earlier paper, Niraula et al. (ACS Appl. Nano Mater. 2021, 4, 3148-3158) described the morphological, compositional, and magnetic properties of three different magnetite/maghemite or Fe₃O₄/γ-Fe₂O₃, hollow nanoparticles, referred to herein as nanorings, short-nanotubes, and long-nanotubes. Scanning electron microscopy indicates that these nanoparticles have lengths of 275 ± 51, 411 ± 92, and 515 ± 98 nm and outer diameters of 201 ± 55, 251 ± 46, and 229 ± 42 nm, respectively, dimensions that are all rather similar in view of their distributions, as is shown in a figure herein. Further, the lengths indicate that these nanoparticles are far larger than what are normally considered nanoparticles. Rietveld refinement of the powder X-ray diffraction patterns presumably reveals the presence of Fe₃O₄, γ-Fe₂O₃, and small amounts of α-Fe₂O₃in some of the nanoparticles; unfortunately, the lack of refinement details make the validity of these compositions at least problematic. The published iron-57 Mössbauer spectral analysis is marginal. An alternative analysis of both the reported X-ray lattice parameters and the Mössbauer spectral results for the three nanoparticles in terms of solid solutions of magnetite and maghemite, ^AFe³⁺[^BFe_1-3δ²⁺Fe_1+2δ³⁺□_δ]O₄, where □ represents a vacancy, δ= 0 corresponds to magnetite, Fe₃O₄, and δ= 0.333 corresponds to maghemite, γ-Fe₂O₃, is proposed herein. In the presence of the expected magnetite Verwey transition, the Mössbauer spectral analysis is formulated with the stoichiometry ^AFe³⁺[^BFe_2(1-3δ)^2.5+Fe_5δ³⁺□_δ]O₄, and as far as we can tell, this model is consistent with the Rietveld X-ray diffraction analysis. The values of δ= 0.28(2) and 0.30(1) obtained from the X-ray diffraction and Mössbauer spectral analyses, respectively, indicate that the composition of the nanoparticles is very close to γ-Fe₂O₃, in contrast to the earlier conclusion. During the course of this reformulation, numerous errors in the mathematical expressions, and in some cases their subsequent misuse, have been discovered and corrected herein whenever possible.

Recommended Citation

F. Grandjean and G. J. Long, "Further Comments on "Engineering Shape Anisotropy of Fe3o4-Γ-Fe2o3hollow Nanoparticles for Magnetic Hyperthermia"," ACS Applied Nano Materials, vol. 5, no. 10, pp. 14031 - 14037, American Chemical Society, Oct 2022.

The definitive version is available at https://doi.org/10.1021/acsanm.2c03571

Department(s)

Chemistry

Keywords and Phrases

magnetic shape anisotropy; magnetite and maghemite solid solutions; Mössbauer spectroscopy; X-ray diffraction

International Standard Serial Number (ISSN)

2574-0970

Document Type

Article - Journal

Document Version

Final Version

File Type

text

Language(s)

English

Rights

© 2023 American Chemical Society, All rights reserved.

Publication Date

28 Oct 2022