Spectroscopic characterization of Fe-doped synthetic chrysotile by EPR, DRS and magnetic susceptibility measurements

Our plain-English summary of Spectroscopic characterization of Fe-doped synthetic chrysotile by EPR, DRS and magnetic susceptibility measurements, by E. Borghi, M. Occhiuzzi, E. Foresti, et al (Physical Chemistry Chemical Physics, 2010).

The study

• Authors: E. Borghi, M. Occhiuzzi, E. Foresti, I.G. Lesci, N. Roveri
• Journal: Physical Chemistry Chemical Physics
• Published: 2010;12(1):227-38
• Cited by: 10 articles, as counted by NIH iCite
• Read it: PubMed · Publisher

Abstract

Fe-doped synthetic geomimetic chrysotile nanocrystals represent a reference standard to investigate the health hazard associated with asbestos fibers and constitute interesting inorganic nanotubes for specific technological applications in light harvesting systems, optoelectronics and photonics. As the fiber toxicity is catalyzed by iron ions in specific crystallographic sites and the mechanical behaviour of synthetic chrysotile nanotubes is strongly affected by the iron doping extent, the characterization of Fe substitution to Mg and/or Si sites in the chrysotile structure appears highly important. By EPR, DRS spectroscopic analyses and magnetic investigations, Mg and/or Si ion replacement by Fe(3+) in a synthetic geomimetic chrysotile structure has been investigated. The results highlight that, as a function of the Fe doping extent and of the Fe doping process, iron can replace both Mg and Si sites. The contemporary iron substitution into the octahedral and tetrahedral sheets is associated with the presence of both of isolated Fe(3+) centres in high-spin 3d(5) configuration (S = 5/2, (6)A(1)((6)S)) in O(h) and T(d) symmetry and of intra-lattice clustered species. Increasing the Fe doping extent increases the concentration of aggregated species, while magnetic susceptibility confirms a paramagnetic anisotropy. The results allow to define the opportunity of using or not metallic Fe during the synthesis to obtain doped chrysotile nanocrystals with tailored morphological and structural properties suitable as a reference to study asbestos toxicity and apt to prepare new inorganic nanotubes and quantum wires for innovative technological applications.

In plain English

This laboratory chemistry study examined synthetic chrysotile nanofibers into which iron had been deliberately added ("doped"). The authors made two series of samples. One series (0.29 to 0.94 percent iron by weight) was made in a steel reactor that left metallic iron present during synthesis. The other (0.67 to 1.78 percent iron by weight) was made in a low-iron alloy reactor, without metallic iron. Both series were analysed by EPR. The second series was also analysed by UV-visible diffuse reflectance spectroscopy, and two of its samples by magnetic susceptibility. The series made without metallic iron was more crystalline. The authors reported that iron replaced both silicon and magnesium in the fiber structure, as isolated ions and as clusters, with more in the silicon (tetrahedral) sites. As iron content rose, the amount of clustered iron increased. The magnetic measurements indicated interacting iron ions. The authors concluded that iron-doped synthetic chrysotile intended as a reference material for asbestos health research should be made without metallic iron and with low iron content. It was a materials study, and no people, animals or cells were tested.

We wrote this plain-English summary from the full article with the help of AI, and a second AI model checked each sentence against the article. It is not the authors' wording; the abstract and the article are their own account.

What the study did and found

• Design: Laboratory physical-chemistry characterization of synthetic iron-doped chrysotile fibers by spectroscopy and magnetic measurements
• Who was studied: Two series of synthetic Fe-doped chrysotile fiber samples. Series (X): 0.29, 0.67, 0.71 and 0.94 %wt Fe. Series (*): 0.67, 0.81, 1.67 and 1.78 %wt Fe. EPR was recorded on both series. DRS was recorded on series (*). Magnetic susceptibility was measured only on the series (*) samples with 0.67 and 1.78 %wt Fe.
• Exposure: Iron doping of synthetic chrysotile at different levels. Series (X) was made in a stainless steel reactor (65 %wt Fe) with metallic iron present during synthesis. Series (*) was made in a C-276 alloy reactor (6.5 %wt Fe) without metallic iron.
• Main results:
  • Series (*), made without metallic iron, was more crystalline. Its EPR spectra were better resolved than those of series (X) at similar iron content.
  • EPR and UV-Vis spectroscopy identified two isolated Fe3+ sites, one in tetrahedral coordination and one in octahedral coordination.
  • In series (*), the concentration of Fe3+ detected by EPR (shown as a percentage in Fig. 3) was 39.1 at liquid-nitrogen temperature and 19.4 at room temperature, each with a stated uncertainty (6.5 and 2.7), irrespective of iron content.
  • In all samples, the ratio of EPR signal area at liquid-nitrogen temperature to that at room temperature was about 2. The authors concluded that antiferromagnetic interactions operate in the clustered (oligomeric) iron species.
  • In the UV-Vis spectra of series (*), tetrahedral (silicon-site) isolated iron was always more abundant than octahedral (magnesium-site) isolated iron. Iron clusters increased with increasing iron loading.
  • The authors interpreted the UV-Vis spectra as indicating no iron outside the crystal framework.
  • Effective magnetic moments at room temperature were 6.91 Bohr magnetons for the 0.67 %wt Fe sample and 6.85 Bohr magnetons for the 1.78 %wt Fe sample. The authors reported crossover points and ferromagnetic behaviour in both samples.
• The authors' conclusion: The authors concluded that, to obtain Fe-doped synthetic chrysotile suitable as a reference model for asbestos health hazard research, metallic iron must be excluded during synthesis and the extent of iron doping must be low.
• Limitations the authors state:
  • A broad underlying EPR band made it impossible to estimate accurately the relative amounts of the different Fe3+ species.
  • The UV-Vis estimates of the iron species depend on mathematical deconvolution and are somewhat inaccurate.
  • How iron was distributed between silicon and magnesium sites could not be determined quantitatively.

Topics

Medical terms in this study, explained in our Lexicon: Chrysotile, Crystallographic Site.

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