Zn-substituted iron oxide nanoparticles from thermal decomposition and their thermally treated derivatives for magnetic solid-phase extraction
Abstract
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 approximate to 15 nm. The combined study by XRD, XRF and Mossbauer 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 degrees 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 co-ordinated Zn2+ to the tetrahedral sites. Preliminary experiments with magnetic solid-phase extraction of beta-estradiol from aqueous solutions evidenced applicability and reusability of the carbon-coated product in the separation of steroid pollutants.