Takeo Ebina

Highly transparent flexible clay films modified with organic polymer: structural characterization and intercalation properties

We are developing transparent flexible clay films with high thermal resistance and gas barrier properties. The clay films were fabricated by casting aqueous dispersions of synthetic Na+-saponite mixed with various loadings of water-soluble organic polymer. In this paper, the structural, optical, and physical properties of the films are reported. The structure of these films has been found to have an alignment of densely packed clay platelets interspersed with polymer chains between clay platelet edges. The parallel stacking of clay platelets is enhanced by adsorption of anionic polymer on the positively charged edges of the clay platelets so that excellent optical transparency is maintained even for high clay loading (up to 90 wt%). Also, polymer chains bounded on particle edges are tightly confined by upper and lower layers of clay platelets, rendering these films more thermally stable. The degradation temperature of the films is more than 350 °C. Differential scanning calorimetry analysis reveals that the melting point of the polymer in the clay layers is shifted towards the higher temperature range, up to 440 °C. However, the segregation of polymers towards the film surface occurs with the polymer loading, which reduces the thermal resistance of the film due to weaker interaction of adsorbed polymer on the films surface. Consequently, films with higher clay loading (>80 wt%) provide excellent optical and physical properties, these films will be promising for a wide variety of applications such as displays or other electronic devices.

Density functional study for estimating Brønsted acid site strength in isomorphously substituted ZSM-5

We use local density functional theory to study the Bransted acid strength of a series of clusters that model a catalytic acid site within zeolite ZSM-5. We consider models of the formula (A)3Si-OH-T(A)3 where A = OH and OSi(OH)3; T = Si, Al, B, Ga or Fe. We have studied the effect of replacing Si with trivalent metal cations on the structure and acid strength of the zeolite ZSM-5. Our results also show the effect of cluster size on the calculated properties. It is suggested that a more accurate descriptor of the decreased electron density around the hydroxyl hydrogen would be the electrostatic potential calculated on the total electron density surface. We studied the molecular electrostatic potential maps for the cluster models to test this fact. It is observed that the calculation results predict that acid strength increases in the order B-ZSM-5<Fe-ZSM-5<Ga-ZSM-5<Al-ZSM-5, which shows a good agreement with experimental results. The results show a prospective trend to predict properties of metal substituted zeolites which a special emphasis on Bronsted acid strength of zeolites.

Synthesis of new microporous layered organic–inorganic hybrid nanocomposites by alkoxysilylation of a crystalline layered silicate, ilerite

We have developed microporous organic–inorganic hybrid nanocomposites by alkoxysilylation of 4,4′-biphenyl-bridged alkoxysilane compounds, which contain triethoxysilyl, methyldiethoxysilyl, and dimethylethoxysilyl groups at each end of the 4,4′-biphenylene unit ((CH3)n(C2H5O)3−n-Si-C12H8-Si-(OC2H5)3−n(CH3)n, n = 0, 1, or 2, abbreviated as BESB(0), BESB(2), or BESB(4), respectively, where the number in parentheses indicates the number of methyl groups in these molecules), in the interlayer of a crystalline layered silicate, ilerite. XRD, 29Si solid-state NMR and fluorescence spectroscopy revealed the immobilization and bridging formation of the BESB molecules between the silicate layers by condensation, not only with H-ilerite, but also with the BESB molecules. The interlayer structures exhibited different molecular arrangements. BESB(0) and BESB(4) molecules are present as a monolayer arrangement in which BESB(0) molecules form the oligomeric species caused by close stacking like a dimer. BESB(2) molecules form mainly bilayer-like aggregates in the interlayer. The structural differences are caused by the different reactivities of the BESB molecules, which control their polymerization in the interlayer. The resultant BESB(0)- and BESB(2)-ilerite had high microporosity with BET surface areas (508 and 578 m2 g−1 for BESB(0)- and BESB(2)-ilerite, respectively). The micropores showed higher toluene adsorptivity than several other porous silica materials due to the successful surface modification. Consequently, this approach provides a new method for constructing novel microporous nanocomposites, the key to improved selectivity and activity in separation and catalytic applications.

Effect of exchangeable cation on the swelling property of 2:1 dioctahedral smectite—A periodic first principle study

We used both localized and periodic calculations on a series of monovalent (Li+, Na+, K+, Rb+, Cs+) and divalent (Mg2+, Ca2+, Sr2+, Ba2+) cations to monitor their effect on the swelling of clays. The activity order obtained for the exchangeable cations among all the monovalent and divalent series studied: Ca2+ > Sr2+ > Mg2+ > Rb+ > Ba2+ > Na+ > Li+ > Cs+ > K+. We have shown that, in case of dioctahedral smectite, the hydroxyl groups play a major role in their interaction with water and other polar molecules in the presence of an interlayer cation. We studied both type of clays, with a different surface structure and with/without water using a periodic calculation. Interlayer cations and charged 2:1 clay surfaces interact strongly with polar solvents; when it is in an aqueous medium, clay expands and the phenomenon is known as crystalline swelling. The extent of swelling is controlled by a balance between relatively strong swelling forces and electrostatic forces of attraction between the negatively charged phyllosilicate layer and the positively charged interlayer cation. We have calculated the solvation energy at the first hydration shell of an exchangeable cation, but the results do not correspond directly to the experimental d-spacing values. A novel quantitative scale is proposed with the numbers generated by the relative nucleophilicity of the active cation sites in their hydrated state through Fukui functions within the helm of the hard soft acid base principle. The solvation effect thus measured show a perfect match with experiment, which proposes that the reactivity index calculation with a first hydration shell could rationalize the swelling mechanism for exchangeable cations. The conformers after electron donation or acceptance propose the swelling mechanism for monovalent and divalent cations.

Influence of electronic state and dispersion of platinum particles on the conversion and selectivity of hydrogenation of an α,β-unsaturated aldehyde in supercritical carbon dioxide

Abstract The selective hydrogenation of cinnamaldehyde (CAL) was investigated using silica supported platinum catalysts in supercritical carbon dioxide. Selectivity to cinnamyl alcohol (COL) is enhanced as Pt0/Pt2+ ratio increases; namely, zero-valent metallic surface is beneficial to the formation of COL compared with less reduced surface. The influence of Pt0/Pt2+ ratio is more significant on the selectivity than on the total conversion. For the catalyst with small Pt0/Pt2+ value, the selectivity also depends on the degree of platinum dispersion. The selectivity to COL is higher for higher degree of platinum dispersion. The CO2 pressure did not affect the conversion and selectivity so much.

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.

Manipulation of pore size distributions in silica and ormosil gels dried under ambient pressure conditions

Abstract Sol–gel derived silica and organically modified silica gels were solvent-exchanged and dried from various solvent mixtures in order to control the magnitude of capillary stress imposed on the gel, and to limit shrinkage during the drying process. A collection of trends was identified in the evolution of porosity, pore size distributions, and surface area of gels dried from various alcohols and acetone/alkane mixtures. By selecting n-alcohols of increasing length from 2 to 5 carbon units, the average pore size of silica gels was adjusted systematically from 4.1 to 3.1 nm with a relatively narrow pore size distribution. The use of acetone/alkane mixtures to modify the capillary stresses that are experienced by drying gels was demonstrated to be effective in controlling pore size and pore volume at high fractions of alkane. Ambient pressure drying thus provides an efficient method of porosity control in materials derived from the sol–gel process.

A DFT study on clay–cation–water interaction in montmorillonite and beidellite

Abstract This study is the first attempt to generate a realistic model for the clay–cation–water system. We use a molecular description of the solvent and clay sheet. We have chosen two clay materials from 2:1 dioctahedral smectites (1) montmorillonite and (2) beidellite to monitor the effect of negative charge on the location of interlayer cation (Na + ), as the negative charge gets introduced in the clay system from octahedral Al substitution and tetrahedral Si substitution as the case may be (1) and (2), respectively. We use Grand Canonical Monte Carlo (GCMC) simulation to locate the interlayer cation and to calculate the number of interlayer water molecules surrounding the cation (Na + ) for both the clay materials. The results show that each Na + cation is surrounded by five water molecules. The minimum energy conformer obtained from GCMC calculations has been used to generate the cluster model for Local Density Functional (LDF) calculations. The results show the Na + cation moves towards the negative center of the clay cluster. It is also observed that Na + cation gets more stabilized in montmorillonite in comparison to beidellite.

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.

Bactericidal allophanic materials prepared from allophane soil. I. Preparation and characterization of silver/phosphorus-silver loaded allophanic specimens

Abstract We prepared two kinds of silver-loaded sterilizing allophanic specimens for the development of natural allophane usage. One of them was synthesized by ion exchange of silver onto allophane soil carrier (silver loaded allophanic specimen (SLA)) and the other one by co-loading phosphorus and silver onto the same carrier using both ligand- and ion-exchange methodologies (phosphorus–silver loaded allophanic specimen (PSLA)). Chemical and mineralogical compositions of these specimens were estimated by X-Ray Powder Diffraction (XRD), X-Ray Fluorescence analysis (XRF), and chemical analysis. Also, chemical forms of loaded silver in these specimens were determined by Transmission/High-Resolution Electron Microscopy (TEM/HREM) and X-Ray Photoelectron Spectroscopy (XPS). The amount of silver loading (ca. 0.18%) in SLA was about 1/5 of silver loading in zeolite specimens when prepared under similar conditions. On the other hand, the amount of silver loading in PSLA enhanced to 6–7 times than that of SLA. Silver elution speed from SLA to water was rapid and the elution rates of silver (percentage of the amount of silver eluting to the amount of silver loading) after 2 h of stirring were about 30%. In contrast to this, the elution rates of PSLA fell off to about 1/10 from that of SLA. While increasing the amount of silver loading, phosphorus co-loading influenced elution speed of silver loading remarkably. In both the allophanic specimens, the loaded silver contains Ag+ ion, metallic silver and silver oxide as chemical species. Metallic silver was confirmed to exist as ultra-fine particles of several ∼40 nm size. For PSLA specimens, the existence of silver diphosphate (Ag4P2O7) was emphasized along with the other three kinds of chemical species.