Tomitsugu Taguchi

Selective cesium removal from radioactive liquid waste by crown ether immobilized new class conjugate adsorbent.

Conjugate materials can provide chemical functionality, enabling an assembly of the ligand complexation ability to metal ions that are important for applications, such as separation and removal devices. In this study, we developed ligand immobilized conjugate adsorbent for selective cesium (Cs) removal from wastewater. The adsorbent was synthesized by direct immobilization of dibenzo-24-crown-8 ether onto inorganic mesoporous silica. The effective parameters such as solution pH, contact time, initial Cs concentration and ionic strength of Na and K ion concentrations were evaluated and optimized systematically. This adsorbent was exhibited the high surface area-to-volume ratios and uniformly shaped pores in case cavities, and its active sites kept open functionality to taking up Cs. The obtained results revealed that adsorbent had higher selectivity toward Cs even in the presence of a high concentration of Na and K and this is probably due to the Cs-π interaction of the benzene ring. The proposed adsorbent was successfully applied for radioactive Cs removal to be used as the potential candidate in Fukushima nuclear wastewater treatment. The adsorbed Cs was eluted with suitable eluent and simultaneously regenerated into the initial form for the next removal operation after rinsing with water. The adsorbent retained functionality despite several cycles during sorption-elution-regeneration operations.

Finite size effects of nanoparticles on the atomic pair distribution functions.

The finite size effects of nanoparticles on the atomic pair distribution functions (PDF) are discussed by calculating the radial distribution functions (RDF) on nanoparticles with various shapes, such as sheet, belt, rod, tube and sphere, assuming continua. Their characteristics are shown depending on the shapes and the sizes of the nanoparticles. The formulas of a PDF analysis which take account of such effects are presented and are found to reproduce the experimental data.

A Reliable Hybrid Adsorbent for Efficient Radioactive Cesium Accumulation from Contaminated Wastewater.

Cesium (Cs) removal from nuclear liquid wastewater has become an emerging issue for safeguarding public health after the accident at the Fukushima Daiichi Nuclear Power Plant. A novel macrocyclic ligand of o-benzo-p-xylyl-22-crown-6-ether (OBPX22C6) was developed and successfully immobilized onto mesoporous silica for the preparation of hybrid adsorbent. The benzene ring π electron is the part of crown ether of OBPX22C6 for easy orientation of the macrocyclic compound for making the π electron donation with Cs complexation. The potential and feasibility of the hybrid adsorbent as being Cs selective was evaluated in terms of sensitivity, selectivity and reusability. The results clarified that the Cs removal process was rapid and reached saturation within a short time. Considering the effect of competitive ions, sodium (Na) did not markedly affect the Cs adsorption whereas potassium (K) was slightly affected due to the similar ionic radii. However, the oxygen in long ethylene glycol chain in OBPX22C6 was expected to show strong coordination, including Cs-π interaction with Cs even in the presence of the high amount of K and Na. Due to its high selectivity and reusability, significant volume reduction is expected as this promising hybrid adsorbent is used for Cs removal in Fukushima wastewater.

In Situ TEM Observation of Growth Process of Zirconium Hydride in Zircaloy-4 during Hydrogen Ion Implantation

In situ observation during hydrogen ion implantation was performed with a transmission electron microscope installed in an ion accelerator to investigate the growth process of Zr hydride in Zircaloy-4. To clarify the effect of radiation damage, some samples were irradiated with 4 MeV Ni3+ ions prior to hydrogen implantation. Growth processes of Zr hydrides accompanying the formation of dislocations were observed. The crystallographic relationship between the Zr matrix and Zr hydrides was identical with that found in previous studies: inter- and intragranular hydrides exhibiting a tendency to grow in the (112-0) direction. This growth can be attributed to a shear mechanism in which there are partial dislocations along basal planes. In specimens preirradiated with Ni ions, the growth rate of hydrides was suppressed, but the growth direction was not affected by radiation defects. It was also confirmed that the black spots induced by Ni3+ ion irradiation grew during hydrogen ion implantation, suggesting the formation of hydrides at the defects.

Local Crystal Structures of Ge2Sb2Te5 Revealed by the Atomic Pair Distribution Function Analysis

Two types of optical recording crystalline material Ge2Sb2Te5 have been studied by neutron and X-ray powder diffraction measurements. One is the crystalline cubic-phase Ge2Sb2Te5. The other is nanocrystalline-phase Ge2Sb2Te5. In the former, a large atomic displacement of germanium atoms was found by the atomic pair distribution function (PDF) analysis of neutron powder diffraction data. According to the electronic band structure calculation of isoelectronic GeTe, the electrical conductivity at the valence band with holes is not severely affected by the randomness at the cation site, whereas the thermal conductivity is significantly reduced by the randomness. For the nanocrystalline phase, the local crystal structure and the particle size distribution were obtained simultaneously by PDF analysis using a spherical-particle form factor. The lattice parameter is longer than that of the crystalline phase, suggesting an antimony-richer composition than the matrix. This compositional deviation would form the nanoparticle, resulting in nucleation-dominated crystal growth.

Bulk Copper-Nanodiamond Nanocomposites; Processing and Properties

Copper has widespread use as engineering material, because of its structural and functional properties, notably high thermal and electrical conductivity. A major drawback of this base metal and its alloys is a relatively low hardness. This precludes its utilization in applications in which both high conductivity and high strength/hardness are needed, e.g. in injection moulds for plastics. Nanostructured metals and nanocomposites are ways to address the low hardness problem, provided the nanostructured material is thermally stable during processing and service. In the present research, composite powders, with 5 to 30 at % nanodiamond, were consolidated into bulk samples. The copper-nanodiamond composite powders were vacuum encapsulated and extruded at 600°C. A significant proportion of the initial hardness in the powders is retained after extrusion. Transmission electron microscopy (TEM) of the extruded material indicates good bonding between the nanodiamond particles and the copper matrix. Raman spectroscopy on the consolidated samples evidences the presence of graphite, possibly due to partial disintegration of ultradisperse nanodiamond agglomerates.

Deposition of hydroxyapatite on SiC nanotubes in simulated body fluid

SiC nanotubes can become candidate reinforcement materials for dental and orthopedic implants due to their light weight and excellent mechanical properties. However, the development of bioactive SiC materials has not been reported. In this study, hydroxyapatites were found on SiC nanotubes treated with NaOH and subsequently HCl solution after soaking in simulated body fluid. On the other hand, hydroxyapatites did not deposit on as-received SiC nanotubes, the SiC nanotubes with NH4OH solution treatment and SiC bulk materials with NaOH and subsequently HCl solution treatment. Therefore, we succeeded in the development of bioactive SiC nanotubes by downsizing SiC materials to nanometer size and treating with NaOH and subsequently HCl solutions for the first time.

Experimental evidence of crystalline hillocks created by irradiation of CeO₂ with swift heavy ions: TEM study.

In this study, CeO2 was irradiated with 200 MeV Au ions at oblique incidence. Observation of as-irradiated samples by transmission electron microscopy (TEM) shows that hillocks are created not only at the wide surfaces, but also at the crack faces of the thin samples. Since the hillocks created at the crack faces can be imaged by TEM, their shape and crystallographic features can be revealed. From the images of hillocks created at the crack faces, many of the hillocks are found to be spherical. We present the first experimental evidence that hillocks created for CeO2 irradiated with swift heavy ions have a crystal structure whose lattice spacing and orientation coincide with those of the matrix. The mechanism of spherical crystalline hillock formation is discussed based on the present results.

Analyses and the effect of impurities contained in charge stripper foils for the 3-GeV RCS of J-PARC

In J-PARC, the 3xa0GeV rapid cycling synchrotron (RCS) applied hybrid type thick boron-doped carbon (HBC) foils as charge stripper in the multi-turn injection. Although HBC foils have successfully operated to provide a high-power beam for experimental users since the operation of the accelerator started, the deformation and radio-activation of the foils occurred as serious problems. We investigated the cause of the problems, as result we found that impurities in the foil led to these phenomena. In this report, we describe why impurities were mixed in the foil, and which kinds of impurities were found by various methods of analysis. The effect of impurities is also discussed.

Morphology change of multi-walled carbon nanotubes with SiC coating by electron irradiation

The different behaviour between morphology changes of multi-walled carbon nanotube (MWNT) and MWNT with SiC coating was investigated by electron irradiation. High resolution TEM images revealed that deformation of graphitic shells occurred in both MWNT and MWNT with SiC coating by electron irradiation. Electron irradiation began changing the outer and inner diameters of MWNT within 3 minutes exposure, whereas it began changing the diameters of MWNT with SiC coating after 10 minutes exposure. The outer diameter of MWNT increased up to irradiation time of 9 min and then decreased rapidly. On the other hand, the outer diameter of MWNT with SiC coating increased up to irradiation time of 50 min and then was almost saturated. These results lead that the morphology stability of MWNT against electron irradiation can be improved by coating with the SiC layer on MWNT.