Nature-inspired synthesis of magnetic non-stoichiometric Fe3O4 nanoparticles by oxidative in situ method in a humic medium

Change of color of the solutions during synthesisNature-inspired synthesis of magnetic non-stoichiometric Fe3O4 nanoparticles by oxidative in situ method in a humic medium. Pankratov D.A., Anuchina M.M. //Materials Chemistry and Physics. 2019. V.231. P.216-224.

Magnetic iron oxide nanoparticles in humic substances shell - Fe3-δO4@HS were synthesized by oxidative in situ method in aqueous solutions of humic substances from metallic iron precursor. Humic substances interacting with metallic iron under natural conditions act as a complex reagent that participates in acid-base, redox, complexation reactions and adsorption processes. The Fe3-δO4@HS particles is the final product of corrosion of metallic iron in the presence of HS. Products were characterized by dynamic light scattering, scanning and transmission electron microscopy, X-ray powder diffraction, Mössbauer spectroscopy, magnetometry, infrared spectroscopy, thermogravimetric analysis, differential scanning calorimetry, and evolved gas analysis. It was demonstrated that the samples contained particles with sizes of 40–50 nm comprised of ∼24 nm magnetite-like crystalline cores coated by humic substances. The synthetic approach used in this article can be used as a model of corrosion processes of ferrous metals in nature. In addition, magnetite-like nanoparticulates stabilized with humic substances can be promising as bioavailable iron additives for agricultural applications.

In recent years, a great amount of efforts was devoted to the study of innovative materials based on magnetic iron oxide nanoparticles (MIONP). These materials found application as chemical catalysts, data storage systems, permanent magnets, magnetic refrigeration systems, materials for electrodes, materials for radio and electromagnetic shielding and passivation reagents. It was also reported that they could be used in agricultural compositions [9], water treatment sorbents, as contrast agents for magnetic resonance imaging, radiation therapy, chemotherapy treatment, radionuclide-free Mössbauer brachytherapy, hyperthermia therapy, targeted drug delivery and many other applications. Fe3O4 based materials, mixed iron oxide containing both Fe(II) and Fe(III), are especially interesting because of their unique magnetic properties. These properties make it possible to use Fe3O4 MIONP in almost every field of science and technology mentioned above. Fe3O4 MIONP are also present in some biological materials, such as magnetic bacteria, and even in the cells of higher living organisms, providing magnetoreception for biological objects in the magnetic field of the Earth for orientation and navigation.

Magnetite Fe3O4 nanoparticles can be synthesized by various methods including physical, chemical, and biological. Physical methods include gas-phase deposition and electron beam lithography. Biological methods are based on using various magnetotactic bacteria, which can create biogenic magnetite nanoparticles in nature. Chemical methods include “Massart method” based on the co-precipitation of Fe(II) and Fe(III) salts in alkaline solutions. Numerous other methods of obtaining Fe3O4 nanoparticles can be employed such as sol-gel method; hydrothermal and solvothermal methods; synthesis under supercritical conditions; ultrasound irradiation; microemulsion technique including the use of reverse micelles; gas−liquid interfacial synthesis; electrochemical synthesis; flow injection technique, and high temperature decomposition of iron-organic precursors. Synthesis conditions define the size, morphology, shape and exact chemical composition of the final Fe3O4 MIONP product.

It is necessary to maintain the stability of magnetic iron oxide nanoparticles in the reaction medium and prevent their agglomeration. A number of strategies can be used to achieve it such as grafting; coating with inorganic layers, such as silica, for example; coating with biomolecules, and others organic compounds, surfactants, and polymers [37]. Humic substances (HS) can be used as surfactants as well. Moreover, they provide bioavailability, biocompatibility, and environmental safety of materials based on Fe3O4 MIONP.

HS are complex mixtures of natural macromolecular compounds which originate from the decomposition of plants and animal residues by microorganisms and abiotic environmental factors. HS are natural polyelectrolytes containing hyperbranched aromatic structures with abundant functional moieties such as carboxyl, phenolic, carbonyl, and amino groups. HS have an ability to form ionic, donor-acceptor, and hydrophobic interactions with iron oxide nanoparticles because they possess a large number of functional groups. HS are organic matrixes of soil and aquatic ecosystems and play an important role in the circulation of iron in nature. Iron oxide nanoparticles with HS are responsible for migration of iron and other elements in soils and water streams. These compounds are biologically available forms of iron for plants [44] and therefore hold promise for medical application. The development of new methods for the synthesis of Fe3O4@HS MIONP and investigation of their properties is of great scientific and practical interest.

Recently, it was found that Fe3-δO4@HS can be obtained in the course of corrosion of metallic iron under partially anaerobic conditions in aqueous solutions of HS. In fact, the aforementioned process is the oxidative in situ synthesis of Fe3-δO4@HS MIONP from iron where HS play multiple roles of acid-base, redox, chelation, and surface-active agents. This work is devoted to the description of synthesis method and the study of physical and chemical properties of Fe3-δO4@HS nanoparticles.

We have demonstrated that by reacting aqueous solutions of humic substances with metallic iron in partially anaerobic conditions, non-stoichiometric Fe3-δO4@HS nanoparticles can be prepared by oxidative in situ synthesis. In this study, two types of Fe3-δO4@HS MIONP have been synthesized and isolated. The products contain particles with the sizes in the range of 30 ÷ 50 nm with crystallite cores of ∼24 nm as demonstrated by SEM, TEM, powder XRD and Mössbauer spectroscopy. Using powder XRD, Mössbauer spectroscopy, and magnetometry, it was determined that the prepared compounds mainly contain non-stoichiometric Fe3-δO4 (where δ ≈ 0.15). Magnetite particles are stabilized by HS absorbed onto the surface as was conclusively shown by IR spectroscopy and TGA-DSC-EGA methods. Thus, we conclude that Fe3-δO4@HS MIONP is the final product of corrosion of metallic iron in the presence of HS. The obtained products are thermodynamically stable under these conditions and can be formed in nature by corrosion of metal in contact with soils. Moreover, the stabilization of the nanoparticles by HS may significantly affect iron migration processes in the environment, as well as its bioavailability.

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link to DOI - 10.1016/j.matchemphys.2019.04.022 Ссылка на (С) издателя link to Google Scholar Ссылка в Интеллектуальной системе тематического исследования научно-технической информации МГУ

Nature-inspired synthesis of magnetic non-stoichiometric Fe3O4 nanoparticles by oxidative in situ method in a humic medium. Pankratov D.A., Anuchina M.M. //Materials Chemistry and Physics. 2019. V.231. P.216-224.

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