Yoji Makita

Near-infrared laser-triggered carbon nanohorns for selective elimination of microbes

Carbon nanomaterials, such as carbon nanohorns and carbon nanotubes, have attracted considerable attention for their biomedical applications. We report here the first application of carbon nanohorns (CNHs) as potent laser therapeutic agents for highly selective elimination of microorganisms. This is the first report, supported by direct observations, of the highly selective elimination of yeast and bacteria (Saccharomyces cerevisiae and Escherichia coli) by employing molecular recognition element–CNH complexes and a near-infrared laser.

Fe-Al layered double hydroxides in bromate reduction: Synthesis and reactivity

This study presents a rare use of layered double hydroxides of Fe(II) and Al(III) (Fe-Al LDH), as reported for the first time for bromate removal from aqueous solutions. The Fe-Al LDH samples were prepared with Fe/Al molar ratios of 1-4 using a co-precipitation method at pH 7, with subsequent hydrothermal treatment at 120°C. The Fe-Al LDH (molar ratio of Fe/Al=1, 2) with a layered structure exhibited nearly complete removal of bromate from initial concentration of 100μmol/dm(3) at a wide pH range of 4.0-10.5 over a 2h reaction period; the residual bromate concentration in the solution was lower than the detection limit of 0.07μmol/dm(3) (9μg-BrO(3)(-)/dm(3)). During the reaction period, bromide was released into the solution via a reduction process. Reactivity of Fe-Al LDH with a Fe/Al molar ratio of 2 did not decrease the bromate reduction efficiency during 30days.

Uptake properties of phosphate on a novel Zr–modified MgFe–LDH(CO3)

We prepared a novel Zr-modified MgFe-LDH(CO(3)) composite by adding a mixed solution of MgCl(2), FeCl(3), and ZrOCl(2) and another mixed solution of 1mol/dm(3) NaOH and 1mol/dm(3) Na(2)CO(3) to distilled water at a constant pH of 10. The composite exhibited only a poorly crystalline structure, resembling that of layered double hydroxides (LDH) from X-ray diffraction. The phosphate uptake is dependent on pH, decreasing with an increase in pH. This composite shows a much greater uptake of phosphate ions in P-enriched seawater (0.33mg-P/dm(3)) than amorphous zirconium oxide and MgFe-LDH(CO(3)). The uptake isotherm was fitted with a Freundlich relation. These phosphate-uptake behaviors closely resemble those of the relevant Zr-MgAl-LDH, which is estimated to be a composite of MgAl-LDH with amorphous zirconium hydroxide on the surface from X-ray absorption spectroscopy. Therefore, a similar structure of Zr-modified MgFe-LDH(CO(3)) composite probably causes the marked increase in phosphate uptake from P-enriched seawater.

Photoinduced antiviral carbon nanohorns

Nanocarbons, such as carbon nanohorns (CNH) and carbon nanotubes, are materials of interest in many fields of science and technology because of their remarkable physical properties. We report here a novel approach for using NIR laser-driven CNH as an antiviral agent. NIR laser-driven functional CNH complexes could open the way to a new range of antiviral materials.

Synthesis of a novel layered double hydroxides [MgAl4(OH)12](Cl)2·2.4H2O and its anion-exchange properties

A novel layered double hydroxide of Mg and Al with composition [Mg(0.96)Al(4.00)(OH)(12)]Cl(1.86)(CO(3))(0.03)·2.4H(2)O, designated as MgAl(4)-Cl, was synthesized by mixing crystalline gibbsite (γ-Al(OH)(3)) and solid MgCl(2)·6H(2)O with subsequent hydrothermal treatment at 160 °C for 72h. The MgAl(4)-Cl exhibited a crystalline material of a layered structure, as evidenced from X-ray diffraction. Anion uptake experiments with the MgAl(4)-Cl showed that Cl(-) in the interlayer space can be exchanged with anions such as Br(-), H(2)PO(4)(-), CO(3)(2-) or dodecyl sulfate (DS(-)) from aqueous solutions with preservation of the layered structure. Uptake of NO(3)(-), BrO(3)(-) or SO(4)(2-) on the MgAl(4)-Cl showed different behavior; these anions can be exchanged within 1h maintaining the layered structure, but a release of Mg(2+) cations from the sample was observed with increased reaction time, resulting in collapse of the layered structure and formation of the gibbsite phase, as determined from chemical analyses and X-ray diffraction.

A Novel Method for the Preparation of Green Photoluminescent Undoped Zinc Oxide Film Involving Excimer Laser Irradiation of a Sol-Gel-Derived Precursor

A green photoluminescent (PL) undoped zinc oxide film was successfully prepared by a novel method involving KrF excimer laser irradiation of a sol-gel-derived precursor. This method requires the appropriate energy fluence (Ef) of 100 mJ/cm2 of the laser, and has the advantage of practical production at a low substrate temperature of 473 K in air. Transmission electron microscopy (TEM) and X-ray diffraction (XRD) observations showed that the green PL film has close-packed columnar crystals in an upper layer, where the green PL centers involving oxygen vacancies are presumed to be present.

Synthesis of lithium-rich LixMn2O4 spinels by lithiation and heat-treatment of defective spinels

Single-phase lithium manganese oxide spinels were synthesized in two steps: (1) the preparation of defective spinel precursors with different Li ∶ Mn ratios through lithium insertion into Li-birnessite manganese oxide in a LiNO3 flux at 400 °C, followed by (2) heat-treatment of the precursors at 750 °C in air. Depending upon the Li ∶ Mn ratio, the precursors yielded three types of single-phase spinels: a lithium-deficient type with lithium and oxygen deficiencies, stoichiometric LiMn2O4, and a lithium-rich type with lithium in the 16d-site of space group Fdm but with oxygen deficiency. The electrochemical measurements showed that good rechargeability on cycling between 3–4.3 V could be obtained in all the lithium-rich spinels Li[LixMn2 − x]O4 − δ, where 0 < x < 0.33 and δ < 0.2.

Boron Isotope Ratio Measurements by Negative Thermal Ionization Mass Spectrometry Method Using Boron-free Seawater

We used boron-free seawater as an ionization promoter for negative thermal ionization mass spectrometry to obtain correct and precise boron isotope ratios. The time profiles were recorded for a whole exhaustion process with 1–10ng boron samples. From a maximum in the initial stable stage, the boron isotope ratios were obtained with 0.05% reproducibility from 1–10ng and 50–400ng boron samples. The observed boron isotope ratio (42/43) is 0.24841±0.0013 for NIST SRM 951, which was a little smaller than that obtained with Ca(NO3)2 as an ionization promoter (42/43=0.24900±0.00013). The negative mode results were normally larger than the positive mode results. The observed value (42/43) was corrected to an absolute value (10/11=0.2455, 02461) using the Rayleigh fractionation factor (1.011835). The standard 0.2473 for Na2BO+ 2 (86/87) was also corrected to an absolute value (10/11=0.2459) using the Rayleigh fractionation factor (1.005666). The positive and negative mode results agreed well within experimental error.

Morphology, Structure and Photoluminescence Properties of Zinc Oxide Films Prepared by Excimer Laser Irradiation of Sol–Gel-Derived Precursors

Morphology, structure and photoluminescence (PL) properties of zinc oxide (ZnO) films prepared by KrF-excimer-laser irradiation of sol–gel-derived precursors were studied. The precursors with a film thickness of 100 or 180 nm were irradiated by the laser at various energy fluences (Ef). Atomic force microscopy and transmission electron microscopy observations revealed that the laser irradiation at an Ef≥100 mJ/cm2 produced crystal growth of close-packed ZnO crystals in an upper layer. Laser irradiation at a high Ef (150 mJ/cm2) of the thinner precursor produced a remarkable crystallization throughout the film, resulting in larger grain size and smooth film surface. Our observation results suggest that the crystallization proceeds by sintering or solidification via melting. The films obtained at Ef≥100 mJ/cm2 showed green PL. The PL spectra were not significantly influenced by the excitation wavelength except for the thinner film irradiated at a high Ef (150 mJ/cm2); it showed a striking increase in the green PL intensity when excited at 275 nm instead of 325 nm. The unique excitation-wavelength dependence may be related to its characteristic threshold of electron excitation.

Boron Isotope Fractionation in Column Chromatography with Glucamine Type Resins

Glucamine type polymers have specific affinity toward boric acid and borate ion. Among them, Chelest Fiber GRY-L showed larger fractionation for boron isotopes than other polymers in our previous study. For this study, we used Chelest Fibers with different fiber lengths (1.0 mm, 0.5 mm, and 0.3 mm) as column packing materials to perform chromatographic separation of boron isotopes. The shorter fiber has larger packing density when packed into the column using a dry method. The 0.3-mm-long fiber has a larger backpressure than fibers of other lengths. Boron adsorption capacities were measured using the breakthrough operation. At this time, the 0.5-mm-long fiber showed the highest capacity. When we measured the isotope ratio profile for fibers of different length using column chromatography, 0.5-mm-long fibers displayed the highest boron isotope fractionation. The 0.5-mm-long fiber is promising as a packing material of column chromatography for boron isotope separation. We also changed operation methods. The lower eluent concentration and the slower flow rate are suitable for boron isotope separation.