Preparation of Fe3O4Spherical Nanoporous Particles Facilitated by Polyethylene Glycol 4000
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Much interest has been attracted to the magnetic materials with porous structure because of their unique properties and potential applications. In this report, Fe3O4nanoporous particles assembled from small Fe3O4nanoparticles have been prepared by thermal decomposition of iron acetylacetonate in the presence of polyethylene glycol 4000. The size of the spherical nanoporous particles is 100–200 nm. Surface area measurement shows that these Fe3O4nanoporous particles have a high surface area of 87.5 m2/g. Magnetization measurement and Mössbauer spectrum indicate that these particles are nearly superparamagnetic at room temperature. It is found that the morphology of the products is greatly influenced by polyethylene glycol concentration and the polymerization degree of polyethylene glycol. Polyethylene glycol molecules are believed to facilitate the formation of the spherical assembly.
KeywordsNanoporous Magnetite Polyethylene glycol Transmission electron microscopy Magnetic measurement
In the past decade, a variety of methods have been developed to form highly structure-controlled materials of functionalized metal, semiconductor, and copolymer nanoparticles on the nano- or microscale. As a versatile kind of material, magnetite has attracted much attention in recent years. Magnetite is a common ferrite that has a cubic inverse spinel structure . The compound has exhibited unique electric and magnetic properties based on the transfer of electrons between Fe2+ and Fe3+ in the octahedral sites. Besides having practical applications in industry such as in ferrofluids [2, 3], catalysis , ceramics , and energy storage , properly coated or surface-modified magnetite nanoparticles can be applied in clinical diagnosis and used as a medicine transporter [7, 8, 9, 10].
Magnetite nanoparticles are usually synthesized in aqueous solutions [11, 12] via coprecipitation of Fe2+ and Fe3+ ions by a base. During these reactions, several parameters have to be controlled carefully, including pH value, mixing way of raw materials, temperature, nature, and concentration of anions. Other synthesis methods such as polyol-mediated sol–gel  and sonochemical  are also proposed. To overcome the limitations introduced by aqueous precipitation reactions, several groups have developed nonaqueous approaches for the production of magnetite [15, 16, 17, 18]. Monodispersed magnetite nanoparticles with tunable size can be produced by these nonaqueous approaches.
Mesoporous Fe3O4 nanostructures with strong enough magnetization strength are especially interesting for high capacity drug loading and targeted drug delivery as well as other biomedical and catalytic applications. To our knowledge, several researches reported the successful preparations of mesoporous Fe3O4. Zhu et al.  successfully prepared nanoporous and monodispersed Fe3O4 aggregated spheres by hydrothermal method. Hou et al.  reported a route to assemble magnetic particles into size-controlled 3D spheres with cyclodextrins as surfactants by solvothermal method. Here, we report a new-route preparation of Fe3O4 nanoporous particles assembled from the small Fe3O4 nanoparticles by thermal decomposition of iron acetylacetonate [Fe(acac)3. Polyethylene glycol 4000 (PEG 4000), an easily available chemical, was introduced in the reactions. The effect of PEG on the morphology of products is investigated.
[Fe(acac)3] and octadecyl amine were purchased from Alfa Aesar Company. PEG 4000, oleic acid, and diphenyl ether were purchased from Sinopharm Chemical Reagent Co., Ltd. All chemicals were used without further treatment.
Synthesis of Fe3O4Spherical Nanoporous Particles
The synthesis was carried out using airless procedures. The synthesis of magnetic Fe3O4 spherical nanoporous particles was developed from previous method . In a typical synthesis, Fe(acac)3 (2 mmol), PEG 4000 (6 mmol), oleic acid (6 mmol), and octadecyl amine (6 mmol) were mixed into 40 mL of diphenyl ether in a N2 atmosphere under vigorous stirring. The mixture was stirred at 70 °C until PEG 4000 melted, then heated to 265 °C, and refluxed for 30 min. The product was black. The black powder was collected with a permanent magnet, then redispersed in ethanol by supersonic for 15 min. The washing process was repeated three times. At last, the powder was dried at 40 °C in vacuum.
X-ray diffraction (XRD) patterns of the samples were recorded on a Rigaku D/max 2550V diffractometer equipped with a Cu KR (1.5418 Å) X-ray source. The morphology and chemical composition of the products were examined by transmission electron microscopy (TEM, JEM-2100F). Samples were dispersed in ethanol by supersonic for 15 min and then dropped onto carbon film-coated grids. Magnetization measurements were taken with a vibrating sample magnetometer (VSM) at room temperature. The surface area of the products was measured by nitrogen adsorption–desorption isotherms using the Brunauer–Emmett–Teller (BET) method (Micromeritics Tristar3000). The samples were degassed under vacuum at room temperature before measurements were taken. Mössbauer spectrum of the product at room temperature was recorded on a Wissel spectrometer with the57Co in Pd matrix as the source moving in constant-acceleration regime. Hyperfine interaction parameters were derived from the Mössbauer spectrum using a least-squares method. The spectrometer was calibrated using a standard 25-μm α-Fe foil.
Results and Discussion
Hyperfine parameters of room-temperature Mössbauer spectrum for Fe3O4spherical nanoporous particles
Hyperfine field (KOe)
Isomer shift (mm s−1)
Quadrupole splitting (mm s−1)
Line width (mm s−1)
In summary, the Fe3O4nanoporous particles are synthesized in the presence of polymer PEG 4000 by thermal decomposition of iron acetylacetonate. The morphology of product can be tuned by the amount of PEG 4000. When the concentration of PEG 4000 is decreased, monodispersed Fe3O4nanoparticles around 8 nm are produced. Particles tend to assemble as the PEG 4000 amount increase, and last form spherical nanoporous particles. The size of the spherical nanoporous particles is 100–200 nm. BET measurement shows these Fe3O4nanoporous particles have a high surface area of 87.5 m2/g and a number of porous less than 4 nm. The saturation magnetization of nanoporous particles is 56.4 emu/g. Magnetization measurement and Mössbauer spectrum indicate that these particles are nearly superparamagnetic at room temperature, which confirms that these spherical particles are assembly of small monodispersed Fe3O4nanoparticles. Moreover, polymerization degree of PEG also has great influence on the morphology of the product. We believe that these Fe3O4spherical nanoporous particles will be promising materials for applications in advanced magnetic materials.
This research project was supported by Shanghai Nanotechnology Promotion Center (0852nm03200) and Equipment Sharing Platform of East China Normal University.
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