Norihito Sakaguchi

Molybdenum–Vanadium‐Based Molecular Sieves with Microchannels of Seven‐Membered Rings of Corner‐Sharing Metal Oxide Octahedra

Crystalline microporous oxides such as zeolites are indispensable materials in various applications ranging from industrial processes to everyday life, such as catalysts, ion-exchange materials, and molecular sieves. Most of them contain tetrahedrally coordinated metal atoms, but octahedrally coordinated metal centers have recently attracted much attention as building blocks of crystalline microporous metal oxides. Manganese oxides (pyrolusite, hollandite, todorokite, and romanechite) with micropores are the only crystalline porous materials based solely on octahedra (octahedral molecular sieves). These manganese oxides contain microtunnel pores consisting of {MnO6} octahedra that share edges and corners. Here we describe a novel type of octahedral molecular sieve, namely, crystalline orthorhombic Mo3VOx (x = 11.2), in which the microchannel is constructed by seven-membered rings of corner-sharing MO6 (M = Mo or V) octahedra. It is isostructural to orthorhombic MoVNbTeO compounds, which are very active and selective oxidation catalysts for light alkanes. These mixed metal oxides have a layered orthorhombic structure with a slab composed of sixand seven-membered rings of corner-sharing {MO6} octahedra and pentagonal {(M)M5O27} units with a {MO7} pentagonal bipyramid and five edge-sharing {MO6} octahedra, whereM is Mo, V, or Nb. The layered sixand seven-membered rings form channel structures. The Te atom is believed to be located both in the sixand seven-membered rings and block the channel. Recently, we succeeded in preparing an orthorhombic Mo3VOx compound that contains only Mo and V, [6] in which the channel is expected not to be blocked (Figure 1).

Sink effect of grain boundary on radiation-induced segregation in austenitic stainless steel

We have investigated the orientation dependence of grain boundaries in radiation-induced segregation (RIS) in an austenitic stainless steel under irradiation using a high-voltage electron microscope (HVEM) at the Hokkaido University HVEM facility and a new rate equation model for RIS, which incorporates the grain boundary sink strength for point defects. The tilt grain boundaries were chosen for the present study. It was observed that, after electron irradiation at a dose rate of 2.0 x 10 3 dpa s 1 to 10 dpa at temperatures of either 623 or 723 K, RIS was enhanced as the tilt angle increased but was suppressed at coincidence grain boundaries (Σ9 and Σ3). The present result indicates that one needs to explicitly consider the grain boundary sink strength as an important factor affecting radiation-induced grain boundary phenomena (RIGBPH). This work can be thought as a study of the radiation-induced grain boundary phenomena associated with grain boundary engineering related to non-equilibrium phenomena.

Quantitative studies of irradiation-induced segregation and grain boundary migration in FeCrNi alloy

Abstract An irradiation-induced phenomenon was studied on account of solute segregation and concurrent grain boundary migration in a model Fe Cr Ni alloy during electron irradiation with a high voltage electron microscope (1000 kV) and also by computer simulation. The calculation was conducted by solving the coupled rate equations for solute and defect concentrations, which involve the Kirkendall effects at a grain boundary sink, so that the solute redistribution profiles experimentally obtained were quantitatively explained. We also extensively studied the effects of the probe size in the EDS analysis on composition profiles, the Gibbsian segregation in the vicinity of a grain boundary and the discriminant of segregation under irradiation, as well as other important factors that influence the phenomenon.

Tetrahedral Connection of ε-Keggin-type Polyoxometalates To Form an All-Inorganic Octahedral Molecular Sieve with an Intrinsic 3D Pore System

A new type of polyoxometalate-based porous material was successfully synthesized. The new material is the first fully inorganic Keggin-type polyoxometalate-based microporous material with intrinsically ordered open micropores and is the third member of the small family of octahedral molecular sieves (OMSs). Twelve MoO6 or VO6 octahedra surround a central VO4 tetrahedron to form ε-Keggin polyoxometalate building blocks (ε-VMo9.4V2.6O40) that are linked by Bi(III) ions to form crystalline Mo-V-Bi oxide with a diamondoid topology. The presence of a tetrahedral shape of the ε-Keggin polyoxometalate building block results in arrangement of microporosity in a tetrahedral fashion which is new in OMSs. Owing to its microporosity, this Mo-V-Bi oxide shows zeolitic-like properties such as ion-exchange and molecule adsorption.

Tip artifact in atomic force microscopy observations of InAs quantum dots grown in Stranski–Krastanow mode

The tip artifact in atomic force microscopy (AFM) observations of InAs islands was evaluated quantitatively. The islands were grown in the Stranski–Krastanow mode of molecular beam epitaxy. The width and height of the islands were determined using transmission electron microscopy (TEM) and AFM. The average [1¯10] in-plane width and height determined using TEM excluding native oxide were 22 and 7nm, respectively; those determined using AFM including the oxide were 35 and 8nm, respectively. The difference in width was due to the oxide and the tip artifact. The sizes including the oxide were deduced from TEM observations to be a width of 27nm and a height of 6nm with correction for the thickness of the oxide. The residual difference of 8nm between the width determined using AFM and that determined using TEM including the oxide was ascribed to the tip artifact. The results enable us to determine the actual size of the islands from their AFM images.

Ultrathin inorganic molecular nanowire based on polyoxometalates

The development of metal oxide-based molecular wires is important for fundamental research and potential practical applications. However, examples of these materials are rare. Here we report an all-inorganic transition metal oxide molecular wire prepared by disassembly of larger crystals. The wires are comprised of molybdenum(VI) with either tellurium(IV) or selenium(IV): {(NH4)2[XMo6O21]}n (X=tellurium(IV) or selenium(IV)). The ultrathin molecular nanowires with widths of 1.2 nm grow to micrometre-scale crystals and are characterized by single-crystal X-ray analysis, Rietveld analysis, scanning electron microscopy, X-ray photoelectron spectroscopy, ultraviolet–visible spectroscopy, thermal analysis and elemental analysis. The crystals can be disassembled into individual molecular wires through cation exchange and subsequent ultrasound treatment, as visualized by atomic force microscopy and transmission electron microscopy. The ultrathin molecular wire-based material exhibits high activity as an acid catalyst, and the band gap of the molecular wire-based crystal is tunable by heat treatment.

Preparation, Structural Characterization, and Ion-Exchange Properties of Two New Zeolite-like 3D Frameworks Constructed by ε-Keggin-Type Polyoxometalates with Binding Metal Ions, H11.4[ZnMo12O40Zn2]1.5– and H7.5[Mn0.2Mo12O40Mn2]2.1–

Two new ε-Keggin-type polyoxometalate-based 3D frameworks, Na1.5H11.4[ε-Zn(II)Mo(V)10.9Mo(VI)1.1O40{Zn(II)}2] and (NH4)2.1H7.5[ε-Mn(II)0.2Mo(V)6Mo(VI)6O40{Mn(II)}2], are prepared, and their structures are determined by powder X-ray diffraction, Fourier transform infrared, Raman spectroscopy, and elemental analysis. ε-Keggin-type polyoxomolybdate units, [ε-ZnMo12O40] and [ε-Mn0.2Mo12O40], are linked with Zn(2+) and Mn(2+), respectively, in a tetrahedral fashion to form 3D frameworks. They show zeolite-like ion-exchange properties and redox properties. The ε-Keggin-based 3D framework shows high chemical composition diversity and can incorporate different elements in the framework.

DNA/Ag Nanoparticles as Antibacterial Agents against Gram-Negative Bacteria

Silver (Ag) nanoparticles were produced using DNA extracted from salmon milt as templates. Particles spherical in shape with an average diameter smaller than 10 nm were obtained. The nanoparticles consisted of Ag as the core with an outermost thin layer of DNA. The DNA/Ag hybrid nanoparticles were immobilized over the surface of cotton based fabrics and their antibacterial efficiency was evaluated using E. coli as the typical Gram-negative bacteria. The antibacterial experiments were performed according to the Antibacterial Standard of Japanese Association for the Functional Evaluation of Textiles. The fabrics modified with DNA/Ag nanoparticles showed a high enough inhibitory and killing efficiency against E. coli at a concentration of Ag ≥ 10 ppm.

Effect of additional minor element on radiation-induced grain boundary segregation in austenitic stainless steel under electron irradiation

Abstract Radiation-induced segregation (RIS) influences the chemical and mechanical properties of structural materials of fission and fusion reactors. In the present study, we investigated the effect of minor alloying elements on RIS in austenitic stainless steel on the basis of the rate theory at or near grain boundaries. It was assumed that the additional minor elements interacted with vacancies and formed additive–vacancy complexes. The effects of additional element concentration and the binding energy between additives and vacancies on solute segregation at the grain boundary were clarified by the present calculations, and the results were compared with recent electron irradiation experiments using a high-voltage electron microscope (HVEM).

Heterogeneous dislocation formation and solute redistribution near grain boundaries in austenitic stainless steel under electron irradiation

We investigated the radiation-induced segregation (RIS) near grain boundaries in austenitic stainless steel under electron irradiation, taking into account the simultaneous evolution of faulted dislocation loops and network dislocations. The formation of a dislocation-free zone (DLFZ) in the vicinity of the grain boundary due to in situ irradiation was observed using a high-voltage electron microscope (HVEM). Predicted temperature and dose dependencies of DLFZ formation agreed with the experimental results. The relationship between RIS and DLFZ formation near a grain boundary has been substantially clarified.