Daiju Matsumura

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.

Direct observation of magnetic depth profiles of thin Fe films on Cu(100) and Ni/Cu(100) with the depth-resolved x-ray magnetic circular dichroism

A depth-resolved technique in the x-ray magnetic circular dichroism (XMCD) has been developed and applied to Fe/Cu(100) and Fe/Ni/Cu(100) in order to observe the magnetic depth profile directly. It was confirmed that the surface two layers of the 7 ML Fe/Cu(100) are ferromagnetically coupled, while the inner layers are in the spin density wave (SDW) state at 130 K. The technique enables one to extract the XMCD spectra from the surface ferromagnetic (FM) and inner SDW regions separately, indicating that the FM/SDW interface has an antiparallel magnetic coupling, and that the SDW region has the bulk-like feature. For Fe/Ni/Cu(100), we have observed magnetically live surface layers and some thickness dependent magnetic coupling between the Fe surface and Ni film.

Development of a depth-resolved x-ray magnetic circular dichroism: application to Fe/Cu(100) ultrathin films

A depth-resolved technique is applied in the x-ray magnetic circular dichroism (XMCD) method by controlling the probing depth of the electron yield XMCD spectra. The usefulness of this technique is demonstrated for the study of magnetic structures of 4 and 8 ML Fe films grown on Cu(100), which are known to exhibit peculiar magnetic depth profiles. It was directly shown that the 4 ML film is uniformly magnetized, while the magnetic moment is localized at the surface in the case of the 8 ML film. The XMCD spectrum for each layer of the 4 ML film was separately extracted. All the extracted spectra were almost identical to each other, confirming the ferromagnetic coupling over the whole film. As for the 8 ML film, it was suggested that the surface two layers are ferromagnetically coupled, while the inner layers are in a spin density wave state with a wavenumber q = 2π/2.4d.

Local structure anomaly around Ge dopants in Mn3Cu0.7Ge0.3N with negative thermal expansion

Local structure analysis of Cu and Ge atoms in the negative thermal expansion material Mn3Cu0.7Ge0.3N was conducted using x-ray absorption fine structure measurements. The temperature dependence of the interatomic distance was found to reflect the macroscopic negative thermal expansion both for Cu–Mn and Ge–Mn shells, although the magnitude of the relative change was much larger for Ge–Mn than Cu–Mn. An enhanced anomaly of the Debye–Waller factor was observed for the Ge–Mn shell in the temperature region of the negative expansion, indicating the presence of static local disorder around Ge impurities. These local structure anomalies strongly suggest that the local and inhomogeneous strain around Ge is essential in broadening the discontinuous volume contraction.

Anomalous metallic state in the vicinity of metal to valence-bond solid insulator transition in LiVS2.

We investigate LiVS2 and LiVSe2 with a triangular lattice as itinerant analogues of LiVO2 known for the formation of a valence-bond solid (VBS) state out of an S=1 frustrated magnet. LiVS2, which is located at the border between a metal and a correlated insulator, shows a first order transition from a paramagnetic metal to a VBS insulator at Tc approximately 305 K upon cooling. The presence of a VBS state in the close vicinity of insulator-metal transition may suggest the importance of itinerancy in the formation of a VBS state. We argue that the high temperature metallic phase of LiVS2 has a pseudogap, likely originating from the VBS fluctuation. LiVSe2 was found to be a paramagnetic metal down to 2 K.

Dynamic structural change in Pd-perovskite automotive catalyst studied by time-resolved dispersive x-ray absorption fine structure

Dynamic structural change in Pd-perovskite automotive catalyst, LaFe0.9Pd0.1O3, which has a high catalytic activity during aging, was studied by in situ time-resolved dispersive x-ray absorption fine structure spectroscopy at 200–500 °C. An Al2O3-based conventional catalyst was also studied. In a reductive atmosphere, both catalysts showed similar temperature dependences of structural transformation from an oxide to a metal. However, different temperature dependence was observed in an oxidative atmosphere. A faster response in the structural change was observed in the Pd-perovskite catalyst than in the Pd/Al2O3 catalyst. It was revealed that Pd-perovskite shows a considerably fast structural change to the oxidized state via the movement of Pd atoms into the perovskite crystal, in comparison with Pd/Al2O3 showing two-step structural change for making PdO.

Control of Tc by isomerization of counter anion in Fe(II) spin crossover complexes, [Fe(4-NH2trz)3](R-SO3)2

We have investigated the spin-crossover behavior of the triazole-bridged one-dimensional Fe(II) complexes, [Fe(4-NH 2 trz) 3 ](o-, m-, p-NH 2 C 6 H 4 SO 3 ) 2 .2H 2 O by means of Fe K-edge EXAFS and magnetic susceptibility measurements. In this system, the transition temperature and the hysteresis width are drastically varied by the isomerism of counter anion o-, m-, p-NH 2 C 6 H 4 SO 3 - . Moreover, we have synthesized [Fe(4-NH 2 trz) 3 ](SP150) 2 in which SP150 is known for photo-isomerization, and have investigated its spin-crossover behavior.

Dynamic structural change of Pd particles on LaFeO3 under redox atmosphere and CO/NO catalytic reaction studied by dispersive XAFS

The local structure of Pd metal fine particles on LaFeO3 which has a high catalytic activity was observed by dispersive XAFS optics from the viewpoint of dynamical structure change of Pd during oxide-metal change and CO/NO catalytic reaction. The oxide-metal change of Pd nanoparticles on LaFeO3 and Al2O3 was investigated by 20–50 Hz rate. It was recognized that, under the reductive atmosphere, Pd atoms show similar speed of movement from oxide to metal state both on the two supports. However, under the oxidative atmosphere, Pd atoms on LaFeO3 show faster movement from metal to oxide state than those on Al2O3. CO/NO catalytic reaction on Pd metal nanoparticles was also observed by 0.2 Hz rate. Slow observation mode made the four EXAFS parameters: coordination number, interatomic distance, Debye-Waller factor and edge shift, precisely determined during catalytic reaction. There are two particular differences between Pd particles on LaFeO3 and Al2O3. Large enhancement of interatomic distance of Pd particle was only observed on Al2O3. Stable surface oxide layer of Pd particle is created on LaFeO3.

Spin transition and its photo-induced effect in spin crossover complex film based on [Fe(II)(trz)3]

We have synthesized the [Fe(II)(Htrz) 3 ] complex film by using ion-exchange film (Nafion) as counter anion. From the analysis of Fe Kedge EXAFS spectra, we could prove the existence of one-dimensional Fe chain structure, [Fe(II)(Htrz) 3 ] n on Nafion film. [Fe(II)(Htrz) 3 ]-Nafion showed a spin crossover phenomenon around room temperature. Moreover, the LIESST(Light Induced Spin State Trapping) effect was observed at 4.2 K.

Origin of the enhancement of electrocatalytic activity and durability of PtRu alloy prepared from a hetero bi-nuclear Pt–Ru complex for methanol oxidation reactions

PtRu alloy, prepared by pyrolysis of hetero bi-nuclear Pt–Ru complexes, showed a higher electrocatalytic activity and durability in the methanol oxidation reaction (MOR) than PtRu alloy prepared by pyrolysis of a mixture of K2PtCl4 and RuCl3. The origin of this activity enhancement was investigated by XPS and Ru K edge XAFS measurements. Although both alloys were composed of metallic Pt and RuO2, the RuO2 in the PtRu alloy prepared from the Pt–Ru complex had greater oxygen deficiency than that in the PtRu alloy prepared from the mixture of K2PtCl4 and RuCl3. XAFS measurements showed that the Ru–O distance of the former was longer than that of the latter, suggesting the presence of the weakly coordinated oxygen species, i.e., H2O, in the PtRu alloy prepared from the Pt–Ru complex. The H2O coordinated to Ru can become an active oxidant, i.e., surface Ru–OH, under electrochemical conditions and enhance MOR activity and durability.