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Local structure and water cleaning ability of iron oxide nanoparticles prepared by hydro-thermal reaction
Authors:Koya Shibano  Shiro Kubuki  Kazuhiko Akiyama  Zoltán Homonnay  Ernő Kuzmann  Stjepko Krehula  Mira Ristić  Tetsuaki Nishida
Affiliation:1. Department of Chemistry, Graduate School of Science and Engineering, Tokyo Metropolitan University, Minami-Osawa 1-1, Hachi-Oji, Tokyo, 192-0397, Japan
2. Laboratory of Nuclear Chemistry, Institute of Chemistry, E?tv?s Loránd University, Pázmany P. s., 1/A, Budapest, 1117, Hungary
3. Division of Materials Chemistry, Ru?er Bo?kovi? Institute, P.?O. Box 180, Zagreb, 10002, Croatia
4. Department of Biological and Environmental Chemistry, Faculty of Humanity-Oriented Science and Engineering, Kinki University, Kayanomori 11-6, Iizuka, Fukuoka, 820-8555, Japan
Abstract:
Nanoparticles (NPs) of Fe3O4 and γFe2O3 synthesized by hydrothermal reaction were characterized by X-ray diffractometry (XRD), 57Fe-Mössbauer spectroscopy and field emission scanning electron microscopy (FE-SEM). A decrease in concentration of methylene blue (MB) aqueous solution due to bulk Fe0-NP γFe2O3 mixture with the mass ratio of 3:7 was measured by ultraviolet-visible light absorption spectroscopy (UV-Vis). The Mössbauer spectrum of NP Fe3O4 prepared from hydrothermal reaction was composed of two sextets with absorption area (A), isomer shift (δ) and internal magnetic field (H int) of 56.3 %, 0.34±0.03 mm s???1 and 49.0±0.30 T for tetrahedral (T d) FeIII, and 43.7 %, 0.66±0.11 mm s???1 and 44.0±0.71 T for octahedral (O h) FeII?+?III. The FeII/FeIII ratio was determined to be 0.280 for NP Fe3O4, giving ‘x’ of 0.124 in Fe3???xO4. These results show that NP Fe3O4 prepared by hydrothermal reaction was not regular but nonstoichiometric Fe3O4. Consistent results were observed for XRD patterns of NP Fe3???xO4 indicating sharp intense peaks at 2Θ of 30.2, 35.7 and 43.3° with a large linewidth of 0.44°, yielding the crystallite size of 29–37 nm from the Scherrer’s equation. Iso-thermal annealing of NP Fe3???xO4 at 250 °C for 30 min resulted in the precipitation of NP γFe2O3 with δ of 0.33±0.03 mm s???1 and H intof 46.4±0.27 T due to magnetic tetrahedral FeIII. The Debye temperature of NP Fe3???xO4 was respectively estimated to be 267±5.45 K for Fe $^{mathrm{III}}(T_{mathrm{d}})$ and 282±7.17 K for Fe $^{mathrm{II+III}}(O_{mathrm{h}})$ , both of which were smaller than that obtained for bulk Fe3O4 of 280±4.15 K and 307±5.70 K, indicating that the chemical environment of iron of NPs is less rigid than that of the bulk compounds. A leaching test using methylene blue (MB) and mixture of bulk Fe0-NP γFe2O3 (3:7) showed a remarkable decrease in MB concentration from 1.90 × 10???2 to 9.49 × 10???4 mM for 24 h with the first order rate constant (k MB) of 2.1 × 10???3 min???1. This result verifies that MB decomposing ability is enhanced by using NP γFe2O3 compared with the k MB of 1.1 × 10???4 min???1 previously obtained from the leaching test using MB and bulk mixture of Fe0???γFe2O3 (3:7).
Keywords:
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