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Zn-substituted iron oxide nanoparticles from thermal decomposition and their thermally treated derivatives for magnetic solid-phase extraction

: Kubíčková, L.; Koktan, J.; Kořínková, T.; Klementová, M.; Kmječ, T.; Kohout, J.; Weidenkaff, A.; Kaman, O.


Journal of magnetism and magnetic materials 498 (2020), Art. 166083
ISSN: 0304-8853
Fraunhofer IWKS ()

Controlled thermal decomposition of zinc and iron acetylacetonates in the presence of oleic acid and oleylamine provided surfactant-capped magnetic nanoparticles with narrow size distribution and the mean diameter of ≈15 nm. The combined study by XRD, XRF and Mössbauer spectroscopy revealed three important features of the as-prepared nanoparticles. First, the actual ratio of Zn:Fe was considerably lower in the product compared to the initial ratio of metal precursors (0.14 vs. 0.50). Second, a pure stoichiometric Zn-doped magnetite system, specifically of the composition Zn0.37Fe2.63O4, with no signatures of oxidation to maghemite was formed. Third, Zn2+ ions were distributed at both tetrahedral and octahedral sites, and the observed preference for the tetrahedral site was only twice as high as for the octahedral site. Furthermore, carbon-coated nanoparticles were achieved by pyrolysis of the surfactants at 500 °C, providing a potential sorbent of organic pollutants with room-temperature magnetization as high as 79.1 emu g−1 and very low carbon content of 5 wt%. The thermal treatment, albeit intended only for the carbonization of surfactants, did alter also the non-equilibrium cation distribution toward the equilibrium one by the relocation of a considerable fraction of the octahedrally coordinated Zn2+ to the tetrahedral sites. Preliminary experiments with magnetic solid-phase extraction of β-estradiol from aqueous solutions evidenced applicability and reusability of the carbon-coated product in the separation of steroid pollutants.