An efficient and simple procedure to prepare chemically stable and partially carbon-cleaned magnetite from solid-state synthesis for clinical practices in medical oncology. (December 2020) - Andrade, Ângela L.
Graphical abstract: Highlights: Chemically stable nanoparticles of magnetite were obtained through a solid-state reaction. The molecular, crystallographic and hyperfine structures confirm that magnetite was indeed formed. A residual carbon coats the magnetite particles, which acts as a protective layer. The carbon layer was to a satisfactory extent removed by immersing the sample in a H2 O2 solution. With this partial carbon removal, the sample released more efficiently magnetocaloric heat. Abstract: As far as medical applications for clinical diagnosis and therapy in oncology are concerned, the use of stables magnetic nanoparticles relies on the magnetocaloric response of their ferrofluid suspensions to an applied alternating current magnetic field. To assure their effectiveness as an advanced material for such a medical technology, some critical properties, as any tendency of the nanoparticles to self-agglomerate and of the magnetic core component to somehow change their chemical nature, must be rigorously inhibited. A sample of chemically stable nanoparticles of magnetite ( F e 2 3 + F e 2 + O 4 2 - ) was synthesized through the method consisting of burning a synthetic commercial maghemite ( γ F e 2 3 + O 3 2 - ) with admixed sucrose, to partially reduce F e 3 + → F e 2 + . The residual carbon, formed on burning the sucrose, tends to coat the nanoparticles and acts as a protective layer hindering the freshly synthesized hot magnetite from being promptly re-oxidized, on cooling the sample in the open-air atmosphere. As a drawback, this carbon layer tends to be a thermal insulator and must be removed, in order to make the magnetite nanoparticles able to be used as a magnetocaloric material and dissipate heat. A chemically gentle removal of the residual carbon was assayed by treating the sample with H2 O2 under stirring or sonication either for 30 min or 60 min. The intrinsic atomic and crystalline structures and other essential properties of this core-shell system were assessed by gas adsorption analysis (BET), powder X-ray diffraction, Fourier-transform infrared spectrometry, Mössbauer spectroscopy and transmission electron microscopy. Theoretical analyses based on the density functional theory (DFT) were used to interpret the harmonic infrared spectra for the produced magnetite. The efficiency in removing the residual carbon layer formed on the magnetite grain surface was checked by saturation magnetization measurements and CHN elemental analysis. The heat releasing ability of the prepared magnetic sample was evaluated under an AC-induced magnetic field. These results evidenced that the treatment with H2 O2 was efficient enough to remove, even though not completely, most of the residual carbon layer, which made the saturation magnetization and the heat released by the treated samples significantly greater than that of the untreated carbon-coated grains. The resulting nano-magnetite was found to be a sufficiently clean material for being used for hyperthermia-based procedures, particularly for medical diagnosis and therapy, in oncology.