Shiro Kubuki

Non-HPLC Rapid Separation of Metallofullerenes and Empty Cages with TiCl4 Lewis Acid

Rapid and efficient separation/purification of pure metallofullerenes M(x)@C(n) (M = metal; x = 1, 2; n > 70) and carbide metallofullerenes of the type M(y)C(2)@C(n-2) (y = 2, 3, 4; n - 2 > 68) has been reported. The present method utilizes rapid and almost perfect preferential formation of TiCl(4) (generally known as a Lewis acid)-metallofullerene complexes, which easily decompose to provide pure metallofullerene powders by a simple water treatment. The present method enables one to separate the metallofullerenes up to >99% purity within 10 min without using any type of high-performance liquid chromatography (HPLC). It is found that the oxidation potentials of the metallofullerenes are crucial factors for efficient purification. The current separation/purification technique may open a brand-new era for inducing further applications and commercialization of endohedral metallofullerenes.

Structural characterization of gel-derived calcium silicate systems

The main aim of this study is to synthesize calcium silicate ceramics that exhibit suitable properties to be used for biomedical applications. In the present work, attention was paid to the understanding of processing-structure relationships. A particular effort was made to clarify the identification of Ca-O-Si bonds by means of spectroscopy. The calcium silicate systems were prepared via a sol-gel route, varying the chemical compositions, the catalyst concentration, and the temperature and time of aging and heat treatment. The processes and the phases evolved during the sol-gel procedure were determined. The bond systems were investigated by Fourier transform infrared (FTIR) and (29)Si magic angle spinning nuclear magnetic resonance (MAS NMR) spectroscopy and the aggregate structures by scanning electron microscopy (SEM), small-angle neutron scattering (SANS), small-angle X-ray scattering (SAXS), wide-angle X-ray scattering (WAXS), and X-ray diffraction (XRD) measurements.

Crystallization mechanism of aluminoferrate glass accompanying a precipitation of nanocrystals of dicalcium ferrite (Ca2Fe2O5) and mayenite (12CaO.7Al2O3)

Heat treatment of 60CaO·27Al 2 O 3 ·13Fe 2 O 3 glass resulted in a precipitation of antiferromagnetic dicalcium ferrite (Ca 2 Fe 2 O 5 ) and mayenite (12CaO·7Al 2 O 3 ). The effective magnetic moment of the sample decreased from 2.0 to 1.7 µ B owing to the precipitation of antiferromagnetic particles. The Mossbauer spectrum of the heat-treated sample consisted of two sextets (magnetic hyperfine structure) which were superimposed on two quadrupole doublets. The sextets were assigned to Fe 3+ occupying octahedral (O h ) and tetrahedral (T d ) sites in the nanocrystals of dicalcium ferrite with a mean diameter >10 nm. The quadrupole doublets were assigned to Fe 3+ (T d ) occupying Al 3+ sites in mayenite particles and the glassy phase. IR transmittance of the sample showed a gradual decrease along with the heat treatment. A Johnson–Mehl–Avrami (JMA) plot from the IR-transmission method yielded activation energies (E a ) of 4.9±0.4 and 4.3±0.4 eV for 60CaO·27Al 2 O 3 ·13Fe 2 O 3 and 60CaO·35Al 2 O 3 ·5Fe 2 O 3 glasses, respectively. These values are equal to E a obtained from a Kissinger plot by the DTA method, i.e., 4.2±0.3 and 4.6±0.3 eV, and also to the Al–O bond energy (4.4 eV). These results reveal that crystallization of calcium aluminoferrate glass is triggered by cleavage of Al–O bonds at an early stage in order to form mayenite particles containing Fe 3+ . After a prolonged heat treatment, the relative absorption area of sextets in the Mossbauer spectra increased at the expense of two doublets. This change suggests a migration of Fe 3+ (T d ) from mayenite particles and the glassy phase into dicalcium ferrite particles. JMA and Kissinger plots for iron-free 60CaO·40Al 2 O 3 glass yielded E a values of 5.6±0.4 and 6.0±0.3 eV, respectively, equal to the sum of the Al–O (4.4 eV) and Ca–O bond energies (1.4 eV), indicating simultaneous cleavage of Al–O and Ca–O bonds.

Highly conductive barium iron vanadate glass containing different metal oxides

Abstract 20BaO·5ZnO·5Fe2O3·70V2O5 glass annealed at 450°C for 30 min showed a marked decrease in the electric resistivity (ρ) from 4.0×105 to 4.8 Ωcm, while 20BaO·5Cu2O·5Fe2O3·70V2O5 glass from 2.0×105 to 5.0 Ωcm. As for the conduction mechanism, it proved that n-type semiconductor model in conjugation with the small polaron hopping theory was most probable. Since ZnII and CuI have a 3d10-electron configuration in the outer-most orbital, Ga2O3- and GeO2-containing vanadate glasses were explored in this study. 20BaO·5Ga2O3·5Fe2O3·70V2O5 glass showed a less remarkable decrease of ρ from 4.5×105 to 100 Ωcm, and 20BaO·5GeO2·5Fe2O3·70V2O5 glass from 3.3×106 to 400 Ωcm. Activation energies for the conduction (Ea) of GeO2- and Ga2O3-contaning glasses before the annealing were respectively estimated to be 0.42 and 0.41 eV. It proved that barium iron vanadate glass with a smaller Ea value could attain the higher conductivity after the annealing at temperaures higher than the crystalization temperature.

Various Three-Dimensional Structures Connected by Al–O/OH/Acetate–Al Bonds

In the present work, significantly various structures connected by Al-O/OH/acetate-Al bonds were synthesized in a versatile sol-gel route. The various bond systems result in several three-dimensional (e.g., fibrous, highly porous, and compact) macrostructures. The shared acetate and OH ions provide the fibrous character; the shared OH ions and oxygen-bridges between octahedral Al(III) ions assist in the formation of a porous network; and the oxygen-bridges between differently (octa-, tetra-, and pentahedrally) coordinated Al(III) ions characterize the compact structures. The newly developed synthesis route is a fast and low-energy consumption sol-gel technique. This method applies only two starting materials and does not adopt any basic agent or catalyst. The synthesis is fast because it does not require any time-consuming peptization; a 3-D network forms directly from the initial solution. The low energy consumption arises from the low temperature of reactions (80 °C) and heat treatment (400-600 °C).

57Fe Mössbauer study of iron-containing soda-lime silicate glass with COD reducing ability

Water cleaning effect was investigated for iron-containing silicate glass. A leaching test for 10 days using 500 mL of simulated waste water and 2.0 g of 0.5x(Na2O⋅CaO)⋅5Fe2O3⋅(95−x)SiO2 glass (20 ≤ x ≤ 50), abbreviated as xNCFS glass, resulted in a remarkable decrease in chemical oxygen demand (COD) from 290 to 26.7 mgL−1. Mossbauer spectra of xNCFS glasses with x of 20, 30, 40, and 50 showed a marked decrease in the absorption area for tetrahedral FeII, suggesting that organic compounds responsible for high COD were decomposed as a result of the oxidation of FeII to FeIII in the NCFS glass. It was concluded that NCFS glass was effective for the cleaning of environmental water polluted by organic compounds.

Effect of phosphorus precursors on the structure of bioactive calcium phosphate silicate systems

The main aim of this work was to synthesize calcium phosphate silicate bioceramics by a low energy-consuming sol-gel method applying various phosphorous precursors (triethyl phosphate, phosphoric acid, and ammonium hydrogen phosphate). The investigations concentrated on the influence of phosphorous initial compounds on the bond and crystalline structures and the material quality. The application of the alkoxide and inorganic P-precursors results in considerably different textures. The inorganic PO4-containing precursors lead to sol formations. The sol systems can be characterized by a randomly bonded aggregate structure. Monolith gel systems can only be prepared by using TEP. The alkoxide P-precursor more effectively furthers the connection between the phosphorous and silicon tetrahedra than the inorganic phosphate compounds. Over the P-precursors, the catalyst also affects the structure and properties. In the present work, a special attention was paid to identify the POSi bonds in the FTIR and 31P NMR spectra. The bond systems were investigated by FTIR, 31P and 29Si MAS NMR spectroscopies, the morphology by SEM, WAXS, and XRD measurements, and the water solubility of the ceramic systems also was tested.

Mössbauer study of metallic iron and iron oxide nanoparticles having environmental purifying ability

A relationship between local structure and methylene blue (MB) decomposing ability of nanoparticles (NPs) of metallic iron (Fe0) and maghemite (γ‐Fe2O3) was investigated by 57Fe Mossbauer spectroscopy, X-ray diffractometry and UV-visible light absorption spectroscopy. γ‐Fe2O3 NPs were successfully prepared by mixing (NH4)2Fe(SO4)2⋅6H2O (Mohrs salt) and (NH4)3Fe(C2O4)3⋅3H2O aqueous solution at 30 °C for 1 h, while those of Fe0 were obtained by the reduction of Mohrs salt with NaBH4. From the Scherrers equation, the smallest crystallite sizes of γ‐Fe2O3 NPs and Fe0 NPs were determined to be 9.7 and 1.5 nm, respectively. 57Fe Mossbauer spectrum of γ‐Fe2O3 NPs consists of a relaxed sextet with isomer shift (δ) of 0.33±0.01 mm s−1, internal magnetic field (Hint) of 25.8±0.5 T, and linewidth (Γ) of 0.62±0.04 mm s−1. 57Fe Mossbauer spectrum of Fe0 NP is mainly composed of a sextet having δ, Δ, and Hint of 0.00±0.01 mm s−1 0.45±0.01 mm s−1, and 22.8±0.1 T, respectively. A bleaching test of the mixture of Fe0 a...

Visible-light activated photocatalytic effect of glass and glass ceramic prepared by recycling waste slag with hematite

Abstract A relationship between the local structure and the visible-light activated photocatalytic effect was investigated in the glass and glass ceramics prepared by recycling waste slag, which was discharged from a Tokyo Household Garbage Combustion Plant. For the preparation of a homogeneous sample of waste slag recycled glass, (WSRG), 10 wt% of Na2CO3 and 10–50 wt% of Fe2O3 were added. 57Fe-Mössbauer spectra of WSRG recorded at liquid nitrogen temperature showed three types of magnetic hfs; one due to FeII(Oh) with δ of 1.21 mm s−1 and Hint of 46.7 T, one due to FeIII(Oh) with δ of 0.46 mm s−1 and Hint of 44.1 T, and the other due to FeIII(Td) with δ of 0.38 mm s−1 and Hint of 47.8 T. They were superimposed on a relaxation spectrum due to superparamagnetic hematite. Methylene blue (MB) degradation test with 40 mg of the heat treated WSRG (50 wt% Fe2O3), under the visible-light irradiation for 6 h showed a marked decrease in the concentration of MB from 20 to 7.7 μmol L−1 with a rate constant (k) of 2.7×10−3 min−1 which was close to the k, 9.26×10−3 min− 1, recently obtained in 15Na2O⋅15CaO⋅40Fe2O3⋅ 11Al2O3⋅19SiO2 glass.

Magnetic interaction in oxygenated alpha Fe-phthalocyanines

Alpha iron phthalocyanines (α-FePc) oxygenated at low temperatures were investigated with the help of 57Fe Mossbauer spectroscopy, magnetization measurements (SQUID) and X-ray diffractometry (XRD). Mossbauer spectroscopy revealed that upon oxygenation of α-FePc, new species were formed which could be associated with FeIIIPc oxygen adducts. Unexpectedly, magnetically split spectrum of oxygenated α-FePc was observed below 20 K. In-field Mossbauer spectra in a 5 T external magnetic field at 5K and magnetization measurements indicate antiferromagnetic coupling in oxygenated α-FePc.