Hiromichi Hayashi

Effect of layer charge on fixation of cesium ions in smectites

In order to rationalize the influence of layer charge on cesium fixation in smectite, remaining Cs+ or Na+ in cesium- or sodium-saturated smectite specimen (Cs- or Na-specimen), respectively, were examined after Ba2+ exchange using a tracer method. The location of sorbed Cs+ in smectite was also studied by X-ray photoelectron spectroscopy (XPS). A linear multiple regressive model has been used to formulate a relation between the amount of cesium left after Ba-exchange of Cs- specimen and the layer charge characteristics. A good correlation between the amount of remaining Cs and octahedral charge was observed for the Cs-specimen whereas for Na-specimen there was no viable change. From the analysis of the chemical states of sorbed-Cs by XPS, two sorption sites were proposed for the Cs-specimen.

Preparation of Copper Nitride (Cu3N) Nanoparticles in Long-Chain Alcohols at 130–200 °C and Nitridation Mechanism

In our laboratory, we are studying copper nitride (Cu3N) nanoparticles as a novel conductive ink that is stable to oxidation and can be metallized at low temperature. In this study, Cu3N nanoparticles prepared via the reaction of copper(II) acetate monohydrate with ammonia gas in long-chain alcohol solvents were characterized by X-ray diffraction analysis, transmission electron microscopy, Fourier transform infrared spectroscopy, and elemental analysis. In addition, we used thermogravimetry-differential thermal analysis to compare the thermal decomposition properties of the prepared Cu3N particles and commercially available Cu3N particles. The decomposition temperature of the prepared particles was more than 170 °C lower than that of the commercial particles. We also examined the influences of the reaction temperature and the alkyl chain length of the alcohol solvent on the product distribution of the reaction and the morphology of the particles. Our results indicated that increasing the solvent hydrophobicity and eliminating water from the reaction system by increasing the temperature affected the product distribution. On the basis of an observation of chromatic change of the reaction solvent and an analysis of the byproducts in the alcohol solvent after the reaction, we propose a mechanism for the formation of Cu3N.

Hydrothermal synthesis and characterization of indium containing beta zeolite

Abstract The hydrothermal synthesis of indium containing beta zeolite has been reported. The efficiency of the synthesis depends mainly on the concentration of indium, synthesis temperature, and pH of the gel. Beta indium has been synthesized in a range of different SiO2/In2O3 ratios using tetraethylammonium ion as a template. For SiO2/In2O3 ratio around 40, beta indium was obtained as a pure phase with a good yield. The product was contaminated with ZSM-5 in case of low In2O3 content. If the synthesis is carried out at higher temperatures the possibility of the formation of ZSM-5 increases, whereas lowering the temperature takes longer, about 10–14 days. Upon calcination to remove the organic template, some demetallation occurs which lowers the crystallinity. Indium species present in the beta zeolite framework were characterized by IR NMR. The extra framework indium species probably exist in a cationic state. The catalytic activity of the sample was tested by the benzoylation reaction of naphthalene.

Quantum chemical calculation on clay-water interface

Abstract We use a molecular description of the solvent and clay sheet to model the clay-water interactions. Quantum chemical calculations both semiempirical (MNDO — modified neglect of differential overlap) and first principle (DFT — density functional theory) were performed on localized cluster models of montmorillonite to study the interaction of one water molecule near the vicinity of the clay surface. The minimized orientation of water molecules with respect to the clay surface is determined. It is observed that lower energy is obtained when the two hydrogens of the water molecule point towards the clay surface i.e. the oxygen of water molecules is going away from the clay surface. The effect of tetrahedral substitution in the clay matrix on the water interaction has also been studied to show that tetrahedral substitution in clays has a distinct effect on the clay-water interaction with respect to stabilization energy.

Use of silicate crystallite mesoporous material as catalyst support for Fischer-Tropsch reaction

Abstract Novel uniform mesoporous materials (silicate crystallite mesoporous material, SCMM) were synthesized by hydrothermal treatment of Si, Mg and/or Al containing hydroxide precipitates, along with quaternary ammonium salt, and were applied as catalyst support for Fischer–Tropsch reaction. SCMM is composed of aggregates of homogeneous layer silicate crystallites, as identified by X-ray diffraction (XRD) patterns and transmission electron microscopy (TEM) photographs which are structurally analogous to smectite clay. The mesopore of SCMM corresponds to interparticle space of disk-shaped crystallites (6–25 nm in diameter) aggregated by edge-to-face bonding. Two kinds of SCMM with variable negative charge locations were used as support materials of Co-catalysts for hydrogenation of CO. Conversion of CO was high on SCMM compared with that of silica gel. Furthermore, the main products obtained were hydrocarbons. In case of SCMM type with negative charge near the surface, olefins and branched hydrocarbons were efficiently produced in CO conversion reaction; where as another SCMM type having negative charge at the middle of crystallite platelets produced mainly normal hydrocarbons for the same reaction. This may be due to the role of the negative charge of SCMM which affects the chemical state of Co-catalyst supported on SCMM. The function of SCMM as compared to other mesoporous materials is better in terms of homogeneous and site-specific distribution of negative charge, which is further helpful in controlling the surface phenomenon as confirmed by the existence of linear CO species adsorbed on Co.

Electronic and structural properties of montmorillonite—a quantum chemical study

The importance of geometry and its relation with property in montmorillonite have been studied in terms of octahedral aluminum and tetrahedral silicon present in the framework. Quantum chemical (QC) calculations were performed using MNDO (modified neglect of differential overlap) and DFT (density functional theory) is reported. Cluster calculations were performed on two octahedral aluminum sites present in the unit cell of montmorillonite to show the distinguishability between the two octahedral aluminums. The energy difference between two aluminum octahedral cluster was 1.12 eV. This was further justified by the calculation of magnesium substitution energy for two different positions of aluminum. This difference in two octahedral aluminum sites was mainly due to the typical orientation of the bridging hydroxyl groups attached with the octahedral aluminums. Calculations were also performed on tetrahedral silica hexagons with and without aluminum substitution to predict the Bronsted acid strength of the surface both by MNDO and DMOL QC methods; which shows that aluminum substitution is an unfavorable process in this type of clay. The above structure property relationship in case of montmorillonite will further help in explaining the catalytic activity of the material.

A New Granular Composite with High Selectivity for Cesium Ion Prepared from Phosphomolybdic Acid Hydrate and Inorganic Porous Material

Ammonium molybdophosphate (AMP) was incorporated in the porous alumina matrix (JA) by successive impregnation with H3Mo12O40P and NH4NO3. The loading percentage of AMP crystals on JA increased with the repetition times of impregnation. The distribution coefficients of Cs+ on AMP-loaded granular composite (JAAMP) was above 104 cm3/g in the presence of 1 mol/dm3 while those of other nuclides were less than 10, indicating high selectivity of JAAMP to Cs+. The separation factor of 137Cs to other nuclides 85Sr,60Co, 152Eu,241Am,22Na) (αCs/Sr;Co;Eu;Am;Na =K d,Cs/K d,Sr;Co;Eu;Am;Na) was estimated to be above 103. The breakthrough curve for Cs+ through the column packed with JAAMP exhibited a symmetrical S-shaped profile, and this exchanger proved to be effective for the selective isolation of radiocesium from a simulated high-level liquid waste.

Hydrothermal treatment and strontium ion sorption properties of fibrous cerium( IV ) hydrogenphosphate

Fibrous cerium hydrogenphosphate, CeP, has been treated hydrothermally in 1 mol dm -3 phosphoric acid solution. CEP and its hydrothermally treated product, CeP(HT), have been characterized by X-ray powder diffractometry, scanning electron microscopy, solid-state 31 P MAS NMR spectroscopy, FTIR spectroscopy, chemical and thermal analyses. A poorly crystalline fibrous CeP with a d-spacing of 1.1 nm converted into a highly crystalline CeP(HT) with platelet morphology by hydrothermal treatment. Solid-state 31 P MAS NMR and FTIR measurements confirmed that one kind of phosphate (H 2 PO 4 ) is present in CeP and two kinds of phosphate (HPO 4 , PO 4 ) are present in CeP(HT), in which the integrated intensity ratio of HPO 4 to PO 4 is 2:1. From chemical and thermal analyses, structural formulae for CeP and CeP(HT) are assumed to be CeO(H 2 PO 4 ) 2 2H 2 O and Ce(HPO 4 ) (PO 4 ) 0.5 (OH) 0.5 , respectively. The Na + exchange capacity of CeP amounted to 4.5 mmol g -1 at pH 11 while that of CeP(HT) was less than 1.0 mmol g -1 in the pH range 2–12. The pH dependence of the metal ion distribution coefficients exhibited ideal ion-exchange behaviour on CeP while metal ion distribution coefficients on CeP(HT) scarcely depended on pH. The metal ion selectivities of CeP and CeP(HT) increased in the order: Na + <Ca 2+ <Sr 2+ <K + , and Na + <K + <Ca 2+ <Sr 2+ , respectively. The distribution coefficient for the Sr 2+ ion of CeP(HT) was higher than that of CeP under hydrothermal conditions.

Room-temperature formation of thermally stable aluminium-rich mesoporous MCM-41

The room-temperature (RT) synthesis of MCM-41 mesoporous compounds with high substitution levels of aluminium (Si / Al = 1.5) is achieved in a minimum time of synthesis. The compound shows similar characteristics to hydrothermally synthesized materials. 27Al NMR study confirms the presence of tetrahedral aluminium in as-synthesized material as well as in the calcined material without observing the presence of octahedral aluminium after calcination.

Ab initio study on the topological Li insertion in titanium oxide

Abstract Lithium insertion into anatase was studied by XRD, XPS and ab initio calculations. Lithium insertion in anatase was carried out by n-butyllithium and the product was analyzed by XRD and XPS. A distortion of anatase cell by the lithium insertion and removal was estimated by the ab initio periodic pseudo-potential calculations. As a result, a crystallographic transition from tetragonal to orthorhombic along with a considerable hysteretic change of the cell volume were estimated, which is well consistent with the previously reported XRD cell dimensions. In the lithium-removal process, the wide plateau in calculated cell volume was observed for Li x TiO 2 where lithium uptake x ranges from 0.25 to 1.