Abstract

The design and development of efficient catalysts for electrochemical nitrogen reduction reaction (ENRR) under ambient conditions are critical for the alternative ammonia (NH₃) synthesis from N₂ and H₂O, wherein iron‐based electrocatalysts exhibit outstanding NH₃ formation rate and Faradaic efficiency (FE). Here, the synthesis of porous and positively charged iron oxyhydroxide nanosheets by using layered ferrous hydroxide as a starting precursor, which undergoes topochemical oxidation, partial dehydrogenated reaction, and final delamination, is reported. As the electrocatalyst of ENRR, the obtained nanosheets with a monolayer thickness and 10‐nm mesopores display exceptional NH₃ yield rate (28.5 µg h⁻¹ mg_cat.⁻¹) and FE (13.2%) at a potential of −0.4 V versus RHE in a phosphate buffered saline (PBS) electrolyte. The values are much higher than those of the undelaminated bulk iron oxyhydroxide. The larger specific surface area and positive charge of the nanosheets are beneficial for providing more exposed reactive sites as well as retarding hydrogen evolution reaction. This study highlights the rational control on the electronic structure and morphology of porous iron oxyhydroxide nanosheets, expanding the scope of developing non‐precious iron‐based highly efficient ENRR electrocatalysts.

Abstract

The hybrid composed of anisotropic niobate layers modified with MoC nanoparticles is synthesized by multistep reactions. The stepwise interlayer reactions for layered hexaniobate induce selective surface modification at the alternate interlayers, and the following ultrasonication leads to the formation of double‐layered nanosheets. The further liquid phase MoC deposition with the double‐layered nanosheets leads to the decoration of MoC nanoparticles on the surfaces of the double‐layered nanosheets. The new hybrid can be regarded as a stacking of the two layers with anisotropically modified nanoparticles. The relatively high temperature in the MoC synthesis causes partial leaching of the grafted phosphonate groups. The exposed surface of the niobate nanosheets due to the partial leaching may interact with MoC to succeed in the hybridization. The hybrid after heating exhibits photocatalytic activity, indicating that this hybridization method can be useful for hybrid synthesis of semiconductor nanosheets and co‐catalyst nanoparticles toward photocatalytic application.

Abstract

Background

Engineered living materials (ELMs) combine living cells with non-living scaffolds to obtain life-like characteristics, such as biosensing, growth, and self-repair. Some ELMs can be 3D-printed and are called bioinks, and their scaffolds are mostly hydrogel-based. One such scaffold is polymer Pluronic F127, a liquid at 4 °C but a biocompatible hydrogel at room temperature. In such thermally-reversible hydrogel, the microorganism-hydrogel interactions remain uncharacterized, making truly durable 3D-bioprinted ELMs elusive.

Methods

We demonstrate the methodology to assess cell-scaffold interactions by characterizing intact alive yeast cells in cross-linked F127-based hydrogels, using genetically encoded ratiometric biosensors to measure intracellular ATP and cytosolic pH at a single-cell level through confocal imaging.

Results

When embedded in hydrogel, cells were ATP-rich, in exponential or stationary phase, and assembled into microcolonies, which sometimes merged into larger superstructures. The hydrogels supported (micro)aerobic conditions and induced a nutrient gradient that limited microcolony size. External compounds could diffuse at least 2.7 mm into the hydrogels, although for optimal yeast growth bioprinted structures should be thinner than 0.6 mm. Moreover, the hydrogels could carry whole-cell copper biosensors, shielding them from contaminations and providing them with nutrients.

Conclusions

F127-based hydrogels are promising scaffolds for 3D-bioprinted ELMs, supporting a heterogeneous cell population primarily shaped by nutrient availability.

Graphical Abstract

Here, we report the synthesis of two-dimensional (2D) layered metal-organic framework (MOF) nanoparticle (NP) superstructures via an ice-templating strategy. MOF NP monolayers and bilayers can be obtained by regulating the concentration of colloidal MOF NPs without any external fields during self-assembly. Adjacent polyhedral MOF NPs are packed and aligned through crystalline facets, resulting in the formation of a quasi-ordered array superstructure. The morphology of the MOF layers is well preserved when subjected to pyrolysis, and the obtained carbon NPs have hollow interiors driven by the outward contraction of MOF precursors during pyrolysis. With the advantages of large surface areas, hierarchical porosity, high exposure of active sites, and fast electron transport of the 2D layered structure, the mono- and bilayered carbon NP superstructures show better oxygen reduction activity than isolated carbon particles in alkaline media. Our work demonstrates that ice-templating is a powerful strategy to fabricate superstructures of various MOFs and their derivatives.

Inorganic material-based Janus nanosheets are classified based on their base materials, and their preparation methods and applications are summarized.

Controlling the morphology, composition, and crystalline phase of mesoporous nonnoble metal catalysts is essential for improving their performance. Herein, well-defined P- and B-codoped NiFe alloy mesoporous nanospheres (NiFeB-P MNs) with an adjustable Ni/Fe ratio and large mesopores (11 nm) are synthesized via soft-template-based chemical reduction and a subsequent phosphine-vapor-based phosphidation process. Earth-abundant NiFe-based materials are considered promising electrocatalysts for the oxygen evolution reaction (OER) because of their low cost and high intrinsic catalytic activity. The resulting NiFeB-P MNs exhibit a low OER overpotential of 252 mV at 10 mA cm(-2), which is significantly smaller than that of B-doped NiFe MNs (274 mV) and commercial RuO2 (269 mV) in alkaline electrolytes. Thus, this work highlights the practicality of designing mesoporous nonnoble metal structures and the importance of incorporating P in metallic-B-based alloys to modify their electronic structure for enhancing their intrinsic activity.

Degradation of contaminants of emerging concern in aqueous media using bimetallic oxides is a promising novel strategy that requires engineering new catalytic routes in bimetallic oxides to perform advanced oxidation; however, several challenges to synthesizing and developing such materials with enhanced, sustainable catalytic features are still being investigated. This study presents the effective use of a manganese cobaltite bimetallic spinel compound for sonocatalysis. We prepared three morphologies of manganese cobaltite for using in the sonocatalytic degradation of oxytetracycline (OTC). The morphology of manganese cobaltite was tuned by changing the amounts of the Mn and Co precursors in the early stage of synthesis. Several manganese cobaltite spinels with different structures-porous layered-like cubes (MCO-PLC), layered-like ellipsoids (MCO-LE), and rough spheroids (MCO-RS) were obtained and characterized using various techniques. A promising catalytic degradation capability of MCO-PLC for OTC (10.0 mg L-1) was obtained at a natural pH within 120 min. We also investigated the reusability of MCO-PLC sonocatalyst and metal (Mn and Co) leaching in water media. The sonocatalytic mechanisms and fragments produced from OTC during degradation were determined via electron paramagnetic resonance and gas chromatography-mass spectroscopy analyses.

A CNTs supported amorphous Ni–P alloy NPs catalyst is synthesized by a simple one-pot microwave heating method. The resulting outstanding hydrogenation performance is due to the high-dispersion of Ni–P NPs and the enhanced metal–support interaction.

Water dispersible K₄Nb₆O₁₇·3H₂O-based Janus nanosheets were successfully prepared and exhibited unique behaviour at the water–air interface and at the water–toluene interface.

The unique 3D heterostructure can highly tolerate the volume expansion over repetitive charge/discharge of lithium-ion batteries, which has been demonstrated through in situ transmission electron microscopy.

Inclusion of different nanosheets derived from layered materials as a way to control the gelation of a hydrogel based on F127 tri-block copolymers functionalized with dimethacrylate (127-DMA).

2D heterostructures exhibit a considerable potential in electrolytic water splitting due to their high specific surface areas, tunable electronic properties, and diverse hybrid compositions. However, the fabrication of well-defined 2D mesoporous amorphous-crystalline heterostructures with highly active heterointerfaces remains challenging. Herein, an efficient 2D heterostructure consisting of amorphous nickel boron oxide (Ni-B-i) and crystalline mesoporous iridium (meso-Ir) is designed for water splitting, referred to as Ni-B-i/meso-Ir. Benefiting from well-defined 2D heterostructures and strong interfacial coupling, the resulting mesoporous dual-phase Ni-B-i/meso-Ir possesses abundant catalytically active heterointerfaces and boosts the exposure of active sites, compared to their crystalline and amorphous mono-counterparts. The electronic state of the iridium sites is tuned favorably by hybridizing with Ni-B-i layers. Consequently, the Ni-B-i/meso-Ir heterostructures show superior and stable electrochemical performance toward both oxygen evolution reaction (OER) and hydrogen evolution reaction (HER) in an alkaline electrolyte.

<p>A method to exfoliate pre-crystallized mesoporous TiO₂ thin films in alkaline solutions, preserving the ordered structure.</p>

Lithium-sulfur (Li-S) batteries have attracted particular interest as promising next-generation energy storage devices because of their high theoretical energy density and low cost. The real performance of Li-S batteries is, however, far from achieving the expected values, even when using a porous, highly conductive host of sulfurs to improve their electric conductivity and accommodate their volume changes. The performance restrictions are mainly attributable to the slow reaction kinetics of converting lithium polysulfides species to lithium sulfide and elemental sulfur during the charging and discharging processes, respectively. Recent studies show that single-atom catalysts (SACs) with superior catalytic activity offer an effective strategy for solving this tough issue. The recent advances in utilizing SACs for Li-S batteries, which involve catalyst preparation, battery performance, and mechanistic insights, are summarized here. Modification of the cathodes and separators with SACs helps to absorb polysulfide and promote their conversion kinetics, thus suppressing the notorious "shuttle effect." In addition, the introduction of SACs into Li-S batteries promotes the efficiency of Li stripping/plating and prevents the growth of Li dendrites. Overall, the boost effects of SAC on Li-S batteries performance are noticeable and deserving of more research attention to develop better Li-S batteries.

A unique structural transformation of a lepidocrocite-type layered titanate, K0.8Ti1.73Li0.27O4, into a rutile-type TiO2 has recently been realized via dilute HCl treatment and subsequent drying at room temperature for producing rutile-nanoparticle-decorated protonated layered titanate exhibiting highly efficient photocatalytic activity. Herein, the authors report synthesis of a lepidocrocite-type layered cesium titanate with nominal compositions of <inline-formula>
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Dual-functional Janus nanosheets were prepared by growing poly(N-isopropylacrylamide-co-N-hydroxymethylacrylamide) chains on one face of individual negatively-charged nanosheets derived from K4Nb6O17¢3H2O via surface-initiated atom transfer radical polymerization. They exhibited aggregation behavior in water upon heating based on the thermo-responsiveness of the poly(N-isopropylacrylamide-co-N-hydroxymethylacrylamide) chains and the intrinsic cation exchangeability of the unmodified face.

Inorganic-organic hybrid gels were prepared using TiO2 nanoparticles modified with organophosphonic acid bearing C-ON bonds by a radical exchange reaction. The modification of TiO2 with N-tert-butyl-N-(1-dihydroxyphosphoryl-2,2-dimetylpropyl)aminoxymethyl benzene (DEPN-BA) and isodecyl phosphonic acid (IDP) was confirmed by IR and 31P MAS NMR. ESR spectroscopy indicated the presence of nitroxide radicals with heating of the modified nanoparticles at 120C. Hybrid gels were prepared using TiO2 nanoparticles, which were modified with DEPN-BA and IDP (IDP_DEPN-BA_TiO2), and a poly(4vinylbenzyl chloride) derivative bearing C-ON bonds (PCMS-TEMPO). It was found that the radical exchange reaction with CON bonds was necessary for preparing hybrid gels. It is assumed that a three-dimensional network was formed by crosslinking between the polymers and modified TiO2 nanoparticles.

Metal-organic frameworks (MOFs) can serve as high-surface-area templates to generate hierarchically ordered nanoporous carbon electrodes for high-performance supercapacitor devices. Here we describe a simple chemical approach to synthesize dense three-dimensional (3D) arrays of core-shell ZnO@ZIF-8 and Co(CO3)0.5(OH)·0.11H2O@ZIF-67 nanowires on a conductive carbon cloth. Annealing the core-shell structures at high temperatures converted the MOF shell into a composite of nanoporous carbon (NC) mixed with conductive metal oxides. The conformal nature of the MOF-coating process generates a NC film with continuous conductive paths from the outer surfaces of the nanowires down to the flexible carbon electrode. Carbonization of ZIF-67 transforms the material into conductive sp2 type carbon mixed with Co3O4 nanostructures. Because Co3O4 is a faradic metal oxide with a high theoretical capacitance, these Co3O4/NC hybrid heterostructure arrays are a promising candidate material for use in an electrochemical supercapacitor device. The Co3O4/NC hybrid electrodes had good performance and exhibited a high areal capacitance of 1.22 F·cm-2 at 0.5 mA·cm-2. Conformal deposition of MOFs via the chemical vapor method offers a promising new platform to design conductive, ultrahigh surface area electrodes that preserve the 3D morphology for applications in supercapacitors and electrocatalysis.

A layered sodium silicate, octosilicate (Na2Si8O17·nH2O), was modified with an organosulfonic-acid moiety (sulfonated propyl (SPr) group, sulfonated phenethyl (SPhE) group, or sulfonated p-trifluoromethylphenyl (STFPh) group) for use as a host material to accommodate a cationic guest, tris(2,2′-bipyridine)ruthenium(II) cation ([Ru(bpy)3]2+). The organosulfonic-acid moiety was bound to the silicate layer via a reaction of an alkylammonium-exchanged octosilicate with a silane coupling agent, and subsequent treatment (oxidation or sulfonation) of the bound organosilyl groups
the surface densities of the organosulfonic-acid moiety were varied by controlling the added amount of silane coupling agents. Adsorption of [Ru(bpy)3]2+ onto surface-modified octosilicates was conducted to find that some surface-modified octosilicates successfully adsorbed [Ru(bpy)3]2+ in the interlayer space (intercalation), while other surface-modified octosiliates did not. In addition, the UV-vis absorption and the luminescence indicate that intercalated [Ru(bpy)3]2+ diffused in the interlayer and that the distribution of the time-averaged location varied depending on the kind and amount of the organosulfonic-acid moieties. Thus, the kind and surface density of the organosulfonic-acid moiety, which correlates to the interactions between the group and the guest species, the volume of free nanospace for adsorption and motion of guests, and the swelling properties, are the key factors not only for the intercalation ability but also for the dynamics of the guest in the interlayer space.

The evolution of organic-inorganic hybrids is highly desirable for the further acquisition of functionalities not achievable with conventional polymer materials in terms of mechanical, electronic, optical, and magnetic properties. Element-blocks, which are heterogeneous structures consisting of organic and inorganic components mixed at the element level, and their highly ordered polymeric derivatives, element-block polymers, are highly useful for overcoming a number of difficult problems. Among the various approaches to establishing element-blocks, this review focuses on surface modification of inorganic nanostructures with organic molecules to control interactions at the interfaces between organic and inorganic components in the organic-inorganic hybrids. For the design of surface-modified inorganic-nanostructure-based element-blocks, the dimensional features of inorganic nanostructures and the methods of modifying organic molecules on the surfaces are discussed from the viewpoint of nanomaterials. Finally, various applications using surface-modified inorganic-nanostructure-based element-blocks are introduced in terms of polymer-based hybrids and hierarchal architectures to provide successful examples, which are important to the development of polymeric materials based on element-blocks.

Transparent organic-inorganic hybrids with a whitish colour were prepared from cellulose diacetate (CDA) nanosheets derived from Dion-Jacobson-type ion-exchangeable layered perovskite HLaNb2O7 center dot xH(2)O (HLaNb) to prepare CDA-based hybrids bearing covalent bonds between HLaNb nanosheets and CDA matrices for improved mechanical properties. An n-decoxy derivative of HLaNb (C10_HLaNb) was exfoliated in acetonitrile by ultrasonication. TEM and AFM images revealed that C10_HLaNb was exfoliated into individual nanosheets. In order to explore the local environment around HLaNb nanosheets, a very small amount of CDA was reacted with a C10_HLaNb nanosheet dispersion [molar ratio COH:(NbOH + NbOC10H21) = 4:1] at 80 A degrees C, and solid-state C-13 NMR with cross polarization and magic angle spinning techniques showed that an alcohol-exchange-type reaction was proceeded to graft the CDA chains to the HLaNb nanosheets via new Nb-O-C covalent linkages. The CDA-based hybrids were prepared by dispersing 5 mass% of HLaNb nanosheets in CDA and subsequent heating at 80 A degrees C for 1-7 days to cause a grafting reaction, and the product prepared by a 1-day grafting reaction exhibited improved mechanical properties compared to neat CDA; the Young's modulus, tensile strength and toughness increased by 18, 34 and 78%, respectively. The mechanical properties deteriorated with further extension of the reaction period, however. In addition, a hybrid film prepared by mixing CDA and a C10_HLaNb nanosheet dispersion exhibited only a slight improvement in mechanical properties. These results clearly indicate that formation of an appropriate number of Nb-O-C bonds at the nanosheet/CDA interfaces is effective for improving mechanical properties.

Mesostructured manganese phosphonate (MnP) with a uniform nanorod morphology has been prepared through an easy surfactant-mediated procedure, in which cetyltrimethylammonium bromide acts as a structure-directing agent and 1-hydroxyethane 1,1-diphosphonic acid is used as the phosphonic bridging molecule. Suitable interaction between the micelles and precursors is proved to play an essential role in the formation of a mesophase. By optimizing the reaction conditions (e.g., Mn/P ratio, pH, and aging time), a mesostructure can be realized in manganese phosphonate. Furthermore, our MnP sample shows great potential as a high-performance pseudocapacitive material due to the abundant accessible active sites and rapid ion/electron transportation arising from the unique mesostructural architecture.

Area-selective surface modification of Si substrates bearing OH-and H-terminated areas by fluorescent 1-pyrenylphosphonic acid (PYPA) was achieved using chlorobenzene at 140 degrees C for 2 h in an autoclave. The OH-terminated area was successfully modified, as shown by X-ray photoemission spectroscopy and contact angle measurement, while no reaction proceeded between PYPA and the H-terminated area. SiO2 nanoparticles were reacted with PYPA under the same conditions to form Si-O-P bonds, suggesting that dehydration coupling proceeded between the OH-terminated area and PYPA.

We report a methodology for creating protonated layered titanate rutile heterojunctions on the outer particle surface of protonated layered titanate by treating layered potassium titanate (K0.8Ti1.73Li0.27O4) with dilute HC1 and then drying it at room temperature under reduced pressure. After Pt co-catalyst loading, this protonated layered titanate/rutile composite with heterojunctions showed higher photocatalytic H-2 evolution activity from water under simulated solar light compared to that of Pt-Poaded P25, the standard photocatalyst for this reaction. The high photo catalytic activity was ascribable to enhanced photocatalytic activity of the protonated layered titanate based on an efficient charge separation at the protonated layered titanate rutile heterojunctions in addition to the sensitization effects of rutile, which absorbs light with longer wavelengths compared to those of protonated layered titanate.

Enantioselectivity by octacalcium phosphate (OCP) is revealed through the incorporation of (S)-(-)-methylsuccinic acid (MeSuc) into its crystal lattice, with hardly any (R)-(+)-MeSuc incorporated. This phenomenon clearly indicates that OCP recognizes the steric structures of guest molecules, extending chiral recognition in inorganic materials to three-dimensional crystal growth.

Template-based electropolymerization of terthienyl-carboxylate-protected TiO2 nanoparticles (1-TiO2 NPs) in a tracketched membrane template produced the corresponding hybrid nanotubes (NTs) of the TiO2 NPs and polythiophene. New multicomponent hybrid NTs consisting of TiO2 NPs, polythiophene, and porphyrin can be synthesized.

Ab initio calculations based on the density functional theory (DFT) were performed with respect to the structure and orbital energy values of a simple [HPO3BH](4) cage, and the results were discussed with structural parameters reported for other borophosphonate cages as well as with the calculated orbital energy values of its silsesquioxane analogue, [HSiO1.5](8). In addition, two novel borophosphonate cages capable of use as elementblock monomers were prepared from two boronic acid-t-butylphosphonic acid reactions.

<p>Element blocks, which are composed of various elements, have been widely studied due to their potential application in electric, optical, magnetic and biological fields. Element blocks can be used as functional materials without any further modifications, but it is also possible to polymerize them to prepare element block polymer materials, which are expected to be a series of new functional materials. Magnetite is one of the well-known magnetic oxides, and magnetite nanoparticles are known to exhibit superparamagnetism. In this review, we focus on surface-modified magnetite nanoparticles which can be considered as element blocks. Surface modification of magnetite nanoparticles has been achieved by using silane coupling agents, phosphorus coupling agents, carboxylic acids or alkyl amines based on according to purpose and application to improve their dispersibility and biocompatibility. And magnetite nanoparticles with grafted polymers are potentially useful to the fabrication of magnetite-based medical and biomedical materials. These element blocks prepared from magnetite nanoparticles via surface modification can be applicable to various applications including drug delivery system, hyperthermia and separation of biological matters or heavy metal ions. Examples are demonstrated for typical applications.</p>

Nanostructured amorphous silica in rice plants (biosilica or plant opal) plays an important role in plant growth related to food production. However, the same silica has a structural supporting role as well that has not been uncovered. The current study focuses on the structural design of the two main types of biosilicas in rice plants for the improvement of their mechanical properties. One structural motif is platelike silicas, which cover most of the surfaces of leaf blades. Another is fan-shaped silicas, which are aligned inside leaf blades, providing a stiff backbone. These biosilica structures consist of 10-100 nm diameter nanoparticles. The mechanical properties, such as hardness and Young's modulus, of the biosilicas are associated with their relative density. Thus, the rice plant mechanics is inferred to be designed by changing the packing of the nanoparticles. Silica plates consisting of loosely packed particles have relatively low density and high flexibility enabling coverage of leaf blade surfaces, while fan-shaped silicas, which consist of tightly packed nanoparticles, are rigid to support the leaf blades as a backbone.

Transparent TiO2/PMMA hybrids with a thickness of 5 mm and improved refractive indices were prepared by in situ polymerization of methyl methacrylate (MMA) in the presence of TiO2 nanoparticles bearing poly(methyl methacrylate) (PMMA) chains grown using surface-initiated atom transfer radical polymerization (SI-ATRP), and the effect of the chain length of modified PMMA on the dispersibility of modified TiO2 nanoparticles in the bulk hybrids was investigated. The surfaces of TiO2 nanoparticles were modified with both m-(chloromethyl)phenylmethanoyloxymethylphosphonic acid bearing a terminal ATRP initiator and isodecyl phosphate with a high affinity for common organic solvents, leading to sufficient dispersibility of the surface-modified particles in toluene. Subsequently, SI-ATRP of MMA was achieved from the modified surfaces of the TiO2 nanoparticles without aggregation of the nanoparticles in toluene. The molecular weights of the PMMA chains cleaved from the modified TiO2 nanoparticles increased with increases in the prolonging of the polymerization period, and these exhibited a narrow distribution, indicating chain growth controlled by SI-ATRP. The nanoparticles bearing PMMA chains were well dispersed in MMA regardless of the polymerization period. Bulk PMMA hybrids containing modified TiO2 nanoparticles with a thickness of 5 mm were prepared by in situ polymerization of the MMA dispersion. The transparency of the hybrids depended significantly on the chain length of the modified PMMA on the nanoparticles, because the modified PMMA of low molecular weight induced aggregation of the TiO2 nanoparticles during the in situ polymerization process. The refractive indices of the bulk hybrids could be controlled by adjusting the TiO2 content and could be increased up to 1.566 for 6.3 vol % TiO2 content (1.492 for pristine PMMA).

Crystallization behavior of cubic boron nitride (c-BN) from amorphous boron nitride (a-BN) by high-pressure, high-temperature (HP-HT) treatment with the intentional addition of a controlled amount of water was studied. The a-BN precursor was prepared by pyrolysis of a boric acid-urea complex with urea/boric acid = 2 at 1000 degrees C for 3 h under an ammonia atmosphere. Hexagonal BN (h-BN) were initially crystallized from a-BN containing 2 mass% of water after HP-HT treatment at 7.7 GPa and 1200 degrees C, and the formation of c-BN was observed after 5 min. The crystallization of c-BN from a-BN containing 8 mass% of water after HP-HT treatment at 7.7 GPa and 1200 degrees C was observed even after 1 min, indicating that the crystallization of c-BN was promoted by increasing the amount of water added. In addition, since neither h-BN nor c-BN was crystallized from a-BN without intentional water addition after the same HP-HT treatment, the addition of water promoted the crystallization of both h-BN and c-BN from a-BN. Since no transformation from h-BN to c-BN was observed during HP-HT treatment at 7.7 GPa and 1200 degrees C, it was concluded that c-BN was directly crystallized from a-BN. After HP-HT treatment at 7.7 GPa and 1650 degrees C for 1 min, both h-BN and c-BN were crystallized from a-BN containing 8 mass% of water. These results clearly indicate that the addition of water has a positive effect on crystallization of c-BN from a-BN. (C) 2016 Elsevier Ltd. All rights reserved.

A sol-gel-derived carboxyl-functionalized lamellar-type silsesquioxane was prepared to investigate its potential for use as a host material for intercalation reactions with n-alkylamines and alkylene diamines. Upon intercalation of n-alkylamines and alkylene diamines, the interlayer distances increased as shown by X-ray powder diffraction patterns, and IR spectra showed the presence of absorption bands attributable to v(COO-) and delta(NH3+) modes. The amounts of intercalated n-alkylamines were determined from n-CnH2n+1NH2/-COOH molar ratios which, based on CHN analysis, exhibited values from 0.76 to 0.88; whereas the values determined for the alkylene diamines were 0.83 (NH2C4H8NH2), 0.45 (NH2C8H16NH2) and 0.33 (NH2C12H24NH2). These results show that intercalation of n-alkylamines and alkylene diamines into lamellar-type silsesquioxane bearing carboxyl groups proceeded successfully via acid-base mechanisms. (C) 2016 The Ceramic Society of Japan. All rights reserved.

Although tremendous effort has been directed to synthesizing advanced TiO2, it remains difficult to obtain TiO2 exhibiting a photocatalytic efficiency higher than that of P25, a benchmark photocatalyst. P25 is composed of anatase, rutile, and amorphous TiO2 particles, and photoexcited electron transfer and subsequent charge separation at the anatase-rutile particle interfaces explain its high photocatalytic efficiency. Herein, we report on a facile and rational hydrothermal treatment of P25 to selectively convert the amorphous component into crystalline TiO2, which is deposited between the original anatase and rutile particles to increase the particle interfaces and thus enhance charge separation. This process produces a new TiO2 exhibiting a considerably enhanced photocatalytic efficiency. This method of synthesizing this TiO2, inspired by a recently burgeoning zeolite design, promises to make TiO2 applications more feasible and effective.

We report a new, environmentally and economically friendly photocatalytic process with unprecedentedly high activity for partial cyclohexane oxidation. Mesoporous silicas containing isolated tetra-hedrally coordinated Ti and Fe oxide nanoparticles immobilized on the pore surface were synthesized by reacting SBA-15 with Ti(IV) acetylacetonate and Fe(III) acetylacetonate successively. A variety of characterizations suggested that the grafted tetrahedrally coordinated Ti species were coupled with Fe oxide nanoparticles via Ti-O-Fe bonds. The SBA-15 photocatalysts showed a high yield (up to sub-mmol) and nearly 100% selectivity for the production of cyclohexanol and cyclohexanone with molecular O-2 under solar light. The unprecedentedly high activity could be explained by the lengthened lifetime of the active Ti species by electron delocalization over Ti-O-Fe bonds and the visible light (lambda &gt; 420 nm)-induced activity endowed by Fe oxide nanoparticles coupled to the Ti species.

The activity of Au nanoparticle-loaded P25 TiO2 (Au/P25) plasmonic photocatalysts, evaluated by the oxidative decomposition of formic acid in water under visible light irradiation, was enhanced up to 3 times by simply mixing Au/P25 with photocatalytically inactive h-BN nanosheets as a result of electron transfer from photoexcited Au/TiO2 to the h-BN nanosheets and retardation of the charge recombination.

We report a simple, low-cost methodology for unprecedentedly enhancing the photocatalytic activity of layered inorganic semiconductors. A layered titanate with a lepidocrocite-type structure scarcely showed photocatalytic activity for a test reaction, the oxidative decomposition of formic acid in water into CO2, under simulated solar light, but it showed highly enhanced photocatalytic activity upon mixing with a much smaller amount (approximately 10 wt%) of commercially available TiO2 nanoparticles (P25) in water. The photocatalytic activity of the mixture was approximately 5 times that of P25, a benchmark photocatalyst. From various analyses, the enhancement resulted from the transfer of photoexcited electrons from the layered titanate to P25 at their particle interfaces and retardation of charge recombination. When applied to a photocatalyst for H-2 production from water containing methanol under simulated solar light, the layered titanate/P25 mixture showed considerably enhanced activity and the apparent quantum yield was 23% (at 320 nm). By replacing P25 with Pt co-catalyst-loaded P25, the apparent quantum yield of the mixture increased from 23 to 73%, although an extremely small amount (below 0.06%) of Pt was used in the system.

? 2015 the Society of Polymer Science, Japan. Design of interfaces is an important factor in control of the structures and properties of inorganic-organic hybrid materials, and surface modification with self-assembly monolayers (SAM) can provide interesting inorganicorganic hybrid materials. Here, we focus on SAM-based surface modification of layered inorganic materials via grafting reactions. Layered perovskites can be modified with alcohols using alcohol-exchange reactions to yield alkoxy-modified products. Methods of surface modification with organophosphonic acids have also been developed for modification of layered perovskites and layered potassium hexaniobate. Modification with organophosphonic acids is more attractive than modification with common silylation reagents, since homocomdensation is unlikely to occur under moderate conditions. Exfoliation of SAM-modified materials provides nanosheets covered with SAM. Since these SAM-modified nanosheets exhibit excellent compatibility with polymers as well as interesting, surface properties, they can be employed for preparation of polymer-based hybrid materials. A similar strategy can be employed for surface modification of titanium oxide nanoparticles.

The growth of Ce:Y3Al5O12(Ce:YAG) single-crystal phosphors (SCPs) by the Czochralski technique is analyzed in terms of segregation coefficient, solubility and absorption cross-section. The emission characteristics of these SCPs are investigated in a wide temperature range, from liquid He temperature up to 500 degrees C. The internal quantum efficiency of SCPs achieves its maximum at about 250 degrees C. Thermal quenching of SCPs at high temperature is attributed to the Mott-Seitz mechanism. In the case of ceramic powder phosphors, a continuous droop is observed with the temperature due to defect-related non-radiative recombination paths. It is shown that (Ce:YAG SCPs + blue LEDs/LDs) can cover a wide range of color temperatures 5500-7000 K, with color rendering indices around 70. In conclusion, it is shown that Ce:YAG SCPs are the most efficient and temperature stable converters to fabricate high-brightness white light sources with high-power blue LEDs and LDs.

Thermoresponsive inorganic-organic hybrid nanosheets were prepared by surface modification of layered perovskite HLaNb2O7 center dot xH(2)O (HLaNb) with poly(N-isopropylacrylamide) (PNIPAAm) through surface-initiated atom transfer radical polymerization (SI-ATRP). The PNIPAAm-modified HLaNb could be exfoliated into nanosheets, which had a plate-like morphology with a thickness of ca. 25 nm. The aqueous suspension of the PNIPAAm-modified nanosheets in water exhibited phase transitions with increases in temperature to above 34 degrees C. The nanosheets did not form precipitates when dispersed in water, even though the modified polymer chains became hydrophobic at high temperatures.

Triethylphosphine oxide [(C2H5)(3)P=O; TEPO] was intercalated into protonated Dion-Jacobson-type ion-exchangeable layered perovskites, HLaNb2O7 center dot xH(2)O (HLaNb) and HCa2Nb3O10 center dot xH(2)O (HCaNb), by hydrolysis of their n-decoxy derivatives (C10O-HLaNb or C10O-HCaNb) in the presence of TEPO. The interlayer distances of the products (TEPO/C10O-HLaNb and TEPO/C10O-HCaNb) were smaller than those of the corresponding n-decoxy derivatives, but still larger than those of anhydrous protonated forms of HLaNb and HCaNb. The solid-state P-31 NMR signals of the products observed at 94 ppm (TEPO/C10O-HLaNb) and 93 ppm (TEPO/C10O-HCaNb) exhibited large downfield shifts from that of the physisorbed TEPO. IR spectroscopy also showed decreases in the nu(P=O) band wavenumbers upon the reactions. These results clearly indicate that TEPO is intercalated and interacted with Bronsted acid sites, the surface hydroxyl groups generated via hydrolysis of n-decoxy groups. The difference in nu(P=O) band wavenumbers as well as that in gallery heights suggests that TEPO exhibited different orientations with respect to the inorganic layers. The chemical shifts of solid-state P-31 NMR signals suggested high Bronsted acidity of HLaNb and HCaNb.

TiO2 nanoparticles (NPs) modified with oleyl phosphate were synthesized through stable Ti-O-P bonds and were utilized to prepare poly(methyl methacrylate)- (PMMA-) based hybrid thin films via the ex situ route for investigation of their optical properties. After surface modification of TiO2 NPs with oleyl phosphate, IR and C-13 CP/MAS NMR spectroscopy showed the presence of oleyl groups. The solid-state P-31 MAS NMR spectrum of the product revealed that the signal due to oleyl phosphate (OP) shifted upon reaction, indicating formation of covalent Ti-O-P bonds. The modified TiO2 NPs could be homogeneously dispersed in toluene, and the median size was 16.1 nm, which is likely to be sufficient to suppress Rayleigh scattering effectively. The TEM images of TiO2/PMMA hybrid thin films also showed a homogeneous dispersion of TiO2 NPs, and they exhibited excellent optical transparency even though the TiO2 content was 20 vol%. The refractive indices of the OP-modified TiO2/PMMA hybrid thin films changed higher with increases in TiO2 volume fraction, and the hybrid thin film with 20 vol% of TiO2 showed the highest refractive index (n = 1.86).

Recent developments in the preparation of inorganic and inorganic-organic hybrid materials from inorganic layered compounds are reviewed. The focus is placed on three topics: preparation of new ion-exchangeable layered perovskites and a tungstic acid from Aurivillius phases via selective leaching of bismuth oxide sheets; grafting reactions for the preparation of two-dimensional inorganic-organic hybrids; and conversion of two-dimensional inorganic-organic hybrids into inorganic compounds. (C) 2014 The Ceramic Society of Japan. All rights reserved.

Ce:(Y1-xLux)(3)Al5O12 single-crystals are investigated in detail as phosphors for high-brightness LEDs and LDs. It is demonstrated that single-crystal phosphor plates (SCPPs) present very advantageous characteristics in comparison with standard powder phosphors. On the one side, the very high quantum efficiency of the SCPPs does not decrease with the temperature increase, and on the other side, the SCPPs possess a high thermal conductivity, so that these can be efficiently cooled to avoid device overheating. The optical properties of these SCPPs are investigated from room temperature to 300 degrees C.Ce:Y3Al5O12 SCPPs are adequate for high-brightness cool white light sources. Instead, Ce:(Y1-xLux)(3) Al5O12 SCPPs, whose emission shifts to the green with the Lu concentration, are very promising for neutral and warm white light sources in conjunction with a red-phosphor. It is shown that these white sources exhibit a color rendering over 90 for a wide range of excitation and SCPP emission wavelengths.

Organically modified niobate nanosheets are promising building blocks for the design of advanced hybrid materials. Nanosheets with controlled thickness and surface composition are important for precise structural design of the nanosheet-based materials. In this work, single-layered and Organic double-layered niobate nanosheets functionalized by phenylphosphonate moieties were selectively prepared by interlayer grafting of A-type and B-type intercalation derivatives of potassium hexaniobate (K4Nb6O17 center dot 3H(2)O) with phenylphosphonic acid (PPA), followed by exfoliation by ultrasonication. in acetonitrile. The interlayer grafting of PPA was monitored using X-ray diffraction (XRD), Fourier transform infrared (FTIR), and solid-state NMR spectroscopy, and the thicknesses of the exfoliated nanosheets were measured by atomic force microscopy (AFM). Transparent hybrid films were obtained by incorporating the single- and double-layered nanosheets into an epoxy matrix.

Nanosheets bearing CF3(CF2)(7)C2H4O groups on their surface were prepared from a CF3(CF2) 7C2H4O derivative of ion-exchangeable layered perovskite HLaNb2O7 center dot xH(2)O (HLaNb) via exfoliation, and were further utilized to prepare epoxy-based hybrids. The CF3(CF2)(7)C2H4O derivative of HLaNb (C10F_HLaNb) was prepared by reacting the n-decoxy derivative of HLaNb with 1H,1H,2H,2H-perfluorodecanol, CF3(CF2)(7)C2H4OH. TEM and AFM observations revealed that the C10F_HLaNb was exfoliated into individual nanosheets bearing surfaces covered with CF3(CF2)(7)C2H4O groups after ultrasonication in acetonitrile. The nanosheet dispersion in acetonitrile was employed to prepare epoxy-based hybrids, and the FE-TEM image of the epoxy-based hybrid with 5 mass% of the nanosheets (C10F_HLaNb/epoxy_5) showed that the nanosheets were dispersed in the epoxy matrix. Thermogravimetry of C10F_HLaNb/epoxy_5 and neat epoxy resin indicated that the initial mass loss due to water decreased and the thermal decomposition retarded by introducing C10F_HLaNb nanosheets. Dynamic mechanical thermal analysis revealed that the glass transition temperature of C10F_HLaNb/epoxy_5 (161 degrees C) was higher than that of neat epoxy resin (110 degrees C). These results clearly exhibit that thermal properties were improved by incorporating nanosheets bearing hydrophobic CF3(CF2) 7C2H4O groups in the epoxy resin most likely due to a decrease in water content. A water uptake test demonstrated that the water uptake rate of C10F_HLaNb/epoxy_5 was lower than that of the neat epoxy.

TiO2 nanoparticles were prepared from titanium tetrachloride (TiCl4) in CH2Cl2 at 80 °C for 30 h, 42 h and 70 h using urea hydrogen peroxide (UHP) as an oxygen donor with a TiCl 4: UHP molar ratio of 1 : 2. The XRD patterns and Raman spectroscopy results showed that the products consisted of anatase TiO2. IR and solid-state 13C NMR with cross polarization and magic angle spinning techniques revealed the presence of urea. TEM observation revealed that the products prepared by the reactions for 30 and 42 h consisted of water-dispersible spheroid nanoparticles with a long axis of ~5 nm, while an aggregation of nanoparticles was evident upon reaction for 70 h. Thermogravimetry, inductively-coupled plasma emission spectrometry and CHN analysis showed that the amount of urea increases in the following order: TiO2-42h, TiO2-70h, TiO2-30h. The photocatalytic activity of the products dispersible in water (TiO 2-30h and TiO2-42h) was estimated based on the degradation behaviour of methylene blue, and TiO2-42h showed higher photocatalytic activity than TiO2-30h. It is proposed that TiCl 4 was directly oxidized by UHP to form anatase TiO2 in the early stage of the process. © 2013 The Royal Society of Chemistry.

TiO2 nanoparticles with an average diameter of less than 10 nm were prepared via a non-hydrolytic sol-gel route in a TiCl4-diisopropyl ether-CH2Cl2 system. After modification with n-octylphosphonic acid (OPA) to increase their organophilic character, the TiO2 nanoparticles were used for preparation of TiO2/epoxy hybrid films. Characterization by FT-IR, solid-state C-13 cross-polarization/magic angle spinning (CP/MAS) and P-31 MAS NMR techniques showed the preservation of the n-octyl groups and the presence of TiOP bonds on the surface of TiO2 nanoparticles. Hybrid films with various TiO2 contents were prepared via a wet process and casting using CH2Cl2 as a solvent. The resulting films were highly transparent. The refractive indices of TiO2/epoxy hybrid films at 633 nm increased monotonously from 1.51 for the pure polymer to 1.66 for the hybrid containing 62.4 mass% of TiO2 nanoparticles. Copyright (c) 2013 John Wiley & Sons, Ltd.

Cubic silicon nitride (c-Si3N4) was prepared at 37-38 GPa and similar to 1773K by shock compression of residues of polysilazane, perhydropolysilazane (PHPS), pyrolyzed at 873, 1073 and 1273 K for 2 h. The residues pyrolyzed at 873 and 1073 K were amorphous materials, while the residue pyrolyzed at 1273 K consisted mainly of crystalline alpha-Si3N4. The relative amount of c-Si3N4 was the smallest in the shock-compressed product of the residue pyrolyzed at 1273 K, indicating that use of amorphous residues is advantageous for formation of c-Si3N4. (C)2013 The Ceramic Society of Japan. All rights reserved.

Microstructural behavior of gamma-Fe2O3 formation in reactions between FeOCl and n-C5H11ONa was thoroughly investigated. Reactions were conducted at 50-150 degrees C for 3 days in an autoclave using n-C5H11OH as a solvent. X-ray diffraction (XRD) patterns and infrared (IR) spectra of the products suggested the crystallization of gamma-Fe2O3 besides the formation of n-pentoxy derivatives of FeOCl. Scanning electron microscopic observation revealed that the FeOCl particles were divided into thin sheets upon reaction. The selected area electron diffractions (SAED) of the sheets revealed the crystallization of gamma-Fe2O3 at even 80 degrees C, apparently due to the fact that the gamma-Fe2O3 crystallization process involved a collapse from n-pentoxide derivatives with large separations between two adjacent layers. In the reaction at 150 degrees C, a part of the sheets was converted into highly oriented polycrystalline gamma-Fe2O3 in improved crystallinity, and the SAED clearly showed that an oriented transformation with a crystallographic relationship of FeOCl (010)//gamma-Fe2O3 (110) occurred. The reaction at 120 degrees C, on the contrary, led to the formation of randomly oriented gamma-Fe2O3 crystallites within a sheet. (C) 2013 Published by Elsevier Masson SAS.

Terbium is the key element for highly efficient green phosphors and visible-near IR Faraday isolators. We have recently shown the potential of LiTbF4 and Tb0.81Ca0.19F2.81 as visible Faraday rotators. In this work, we present a detail spectroscopic analysis of Tb3+ (4f(8)) in these two compounds with different crystal structures. By means of the Judd-Ofelt theory, the emission branching ratios and lifetimes of the Tb3+ excited states have been estimated. These results are compared with experimental values obtained for the emitting D-5(4) level, as well as with the absolute light yield measurements. Tb3+ in LiTbF4 exhibits a high quantum efficiency, and its radiative lifetime is confirmed to be 7 ms. Instead, the ionic conductor Tb0.81Ca0.19F2.81, which presents a high concentration of vacant sites, shows a lower quantum efficiency and a radiative lifetime about three times larger than estimated. Absorption and emission spectra of Tb0.81Ca0.19F2.81 are broad, so that any fine structure of energy levels can be resolved. In contrast, a detailed study of the splitting of Tb3+ multiplets in Stark energy levels is carried out for LiTbF4. (C) 2013 AIP Publishing LLC.

Hybrids possessing both oligomeric ethylene oxide chains and Ti-O-P networks were prepared from TiCl4 and organodiphosphonic acid [(HO)(2)OP(C2H4O)(3)C2H4PO(OH)(2)] via a nonhydrolytic sol gel process and subsequently treated with a LiClO4 solution. The P/Ti ratio was fixed at 2 and the ethylene oxide unit/Li+ ratio was changed from 5 to 20. Li+ ions are likely to be solvated by ether oxygen atoms. Li+ ion transport in the hybrids with ionic conductivity values in the 10(-5) S cm(-1) range was observed at ambient temperatures.

Czochralski grown Ce and Gd-doped Y3Al5O12 (Ce, Gd:YAG) single crystal demonstrated superior performance features in a new concept of white LED where it is used as thin single crystal phosphor plates (SCPPs). New SCPP-based white LED realizes epoxy resin free package, which allows to eliminate the photodegradation issue of the organic material. Optical, thermal and electrical properties of SCPPs and SCPP-based white LEDs are discussed with the powder phosphor and commercial LED reference. SCPPs showed significantly higher values and better stability under the high temperatures, irradiation and current. Quantum efficiency was found to be as high as 93%. (C) 2012 Elsevier B. V. All rights reserved.

Gas barrier silica coatings were prepared from perhydropolysilazane (PHPS) by vacuum ultraviolet (VUV) irradiation under several irradiation conditions to investigate the relationship between their water vapor transmission rate (WVTR) and the irradiation conditions. PET substrates were coated with PHPS using its xylene solution, and the coatings were irradiated with VUV light (172nm). The oxygen concentrations and irradiation distances were varied. The sample irradiated under conditions of lower oxygen concentration (less than 5%) and shorter irradiation distance (2.6 mm) showed the lowest WVTR (0.721 g m(2) d(-1)). The sample irradiated under conditions of higher oxygen concentration (19%) and longer irradiation distance (13.4 mm), on the other hand, showed the highest WVTR (2.738 g m(2) d(-1)). These results suggest that VUV irradiation improves the gas barrier properties by Si-N bond cleavage rather than by oxidative reactions caused by O(D-1) and O-3. (C)2013 The Ceramic Society of Japan. All rights reserved.

Periodic mesoporous silicon-aluminum-carbon-nitrogen (Si/Al/C/N) frameworks with P6mm hexagonal symmetry were synthesized by a solvent nanocasting route using mesoporous carbon (CMK-3) as hard template and preceramic polymers containing both -[R1R2Si-N(R3)]n- and -[R4Al-N(R5)]n- backbones (with R 1 = R2 = R3 = R4 = H and R 5 = CH2CH3) as ceramic precursors. The preceramic polymers are prepared through a simple and cost-effective procedure by blending poly(perhydropolysilazane) and poly(ethyliminoalane) as precursors of silicon nitride/silicon (Si3N4/Si) and carbon-containing aluminum nitride (Al/C/N), respectively. The blended polymers with various and controlled Al:Si ratios were infiltrated into the porous structure of CMK-3, followed by a pyrolysis-template removal cycle performed under nitrogen at 1000 C (2 h, ceramic conversion), then in an ammonia atmosphere at 1000 C (5 h, template removal). This procedure resulted in the formation of periodic mesoporous Si/Al/C/N frameworks with surface areas of 182-326 m2 g-1, a pore size distribution of 4.1-5.9 nm, and pore volumes in the range of 0.51-0.65 cm3 g-1. The uniformity of the mesopores and periodicity of the obtained amorphous micrometer-size powders, studied by transmission electron microscopy (TEM), small-angle X-ray diffraction (SA-XRD), and N2 sorption, are affected by the Al:Si ratio. Amorphous materials did not exhibit weight change up to 1400-1470 C in flowing nitrogen, and their behavior in air, up to 1000 C (with dwelling time of 5 h), is dependent on the proportion of AlN and Si 3N4 phases. The as-obtained powders then were decorated with Pt (nano)particles by impregnation to form supported catalysts. The as-formed catalysts showed attractive reactivity and robustness in our probe reaction, namely, the hydrolysis of an alkaline solution of sodium borohydride at 80 C. Our main results are reported therein. © 2013 American Chemical Society.

Transparent TiO2/epoxy hybrid films with high refractive indices have been prepared from a 9-mass% aqueous TiO2 (rutile form) dispersion by a combination of dispersion medium exchange and surface modification with n-octylphosphonic acid (OPA). The dispersion medium was exchanged from H2O to N-methylformamide (NMF) by distilling off H2O after the addition of NMF. The TiO2 surface was then modified with OPA by heating at 80 degrees C for 24h. IR and NMR spectra of the OPA-modified TiO2 nanoparticles (NPs) revealed that the OPA moiety was grafted onto the surface of the TiO2 NPs through TiOP bonds. The resulting OPA-modified TiO2 NPs were employed to prepare epoxy-based hybrid films possessing excellent transparency. The transmittance in the entire visible range (400800nm) of the hybrid film containing 66.3mass% TiO2 was above 94%. This hybrid film also exhibited the highest refractive index (n=1.74), which represented a remarkable increase from that of the pure epoxy resin film (n=1.51).

Bridged polysilsesquioxane possessing dimanganese complex moiety, a model complex for catalase, exhibited catalytic activity for the hydrogen peroxide decomposition reaction without any deactivation. The catalytic activity was mostly retained, even after 24-h acid treatment at 80 degrees C, improving thermal stability after immobilization.

High optical quality LiREF4 (RE = Tb3+, Dy3+, Ho3+, Er3+ and Yb3+), PrF3 and CeF3 single crystals have been grown by the Czochralski technique. Their magneto-optical properties have been measured and analyzed in detail in the ultraviolet-visible wavelength region, and their figures of merit as Faraday rotators have been determined. CeF3 presents superior properties above 300 nm, showing a figure of merit higher than that of the reference material, terbium-gallium-garnet, which is nowadays used in the visible-near infrared. PrF3 is the best rotator for the 220-300 nm range. Towards shorter wavelength and in the vacuum ultraviolet, it is shown that the LiREF4 crystals are unique rotators. Overall, the rare-earth fluoride single crystals studied here exhibit better properties than other materials considered so far, and therefore they have potential to cover the increasing demand for new and improved Faraday rotators in the ultraviolet-visible wavelength region. (C)2012 Optical Society of America

alpha-Zirconium phosphate (alpha-ZrP) was prepared by liquid-phase deposition. Boric acid was added to a solution containing [ZrF6](2-) anions, and phosphoric acid dropwise to cause slow decomposition of [ZrF6](2-) and the subsequent reaction with H3PO4 to form alpha-ZrP. X-ray diffraction, scanning electron microscopy, solid-state P-31 nuclear magnetic resonance spectroscopy, infrared spectroscopy, thermogravimetry, and elemental analyses indicate the formation of single-phase alpha-ZrP.

Spherical aggregates of leaf-like YPO4 particles have been prepared by the reactions of tri-n-butylphosphate [PO(OC4H9)(3), TBP] with the acidic Y(NO3)(3) aqueous solution in an autoclave at 180 degrees C. The products of the reactions for 1,3 and 6 h consisted of an intermediate exhibiting an intense X-ray diffraction line at d approximate to 1.28 nm, while those of reactions for 12-48 h were pure YPO4. The products of the reactions for 8 and 8.5 h were mixtures of the intermediate and YPO4. YPO4 formation thus seems to proceed via the formation of the intermediate. Since the intermediate seems to be Y[PO2(OC4H9)(2)](3), it is likely that TBP was hydrolyzed to form PO2(OC4H9)(2)(-) ions, which then reacted with Y3+ ions to form the solid intermediate, Y[PO(OC4H9)(2)](3). Scanning electron microscopy (SEM) revealed the corresponding morphological change from the belt-like products to spherical aggregates of leaflike particles, indicating that the solid intermediate Y[PO2(OC4H9)(2)](3) was hydrolyzed to form leaf-like YPO4 particles. (C) 2012 The Ceramic Society of Japan. All rights reserved.

The effect of heat treatment on the surface morphology of fused silica glass substrates was investigated. It was found that the water vapor pressure during heat treatment had a strong influence on the flattening of the silica glass surface. The surface of the frosted glass changed into a transparent and lustrous surface after heat treatment with water vapor at 1200 degrees C for 48 h, whereas surface irregularities remained for heat treatment under a dry atmosphere. It was suggested that the difference in surface flattening was caused by changes in surface viscosity that depended on the concentration of OH groups on the surface. In order to quantitatively understand the effect of the heat treatment atmosphere, power spectral density (PSD) analysis and a novel peak and valley method were applied to the experimental results. From the PSD analysis, it was found that the Mullins&apos; model could not explain the smoothing behavior by heat treatment. The peak and valley method, which could separate the surface morphology into the surface irregularities and the background undulation, revealed that the Mullins&apos; model limitation was mainly for the surface and the background undulation could be understood within the model. These results indicate that there are different mechanisms between for the surface smoothing and for the relaxation of the background undulation. (C) 2011 American Institute of Physics. [doi:10.1063/1.3587229]

The hydrolysis behavior of 1,4-bis(triethoxysilyl)benzene (BTB), a precursor of bridged polysilsesquioxane, was investigated with high-resolution Si-29 nuclear magnetic resonance (Si-29 NMR) spectroscopy at ambient temperature in a system with BTB:ethanol:water:HCl = 1:10:x:0.8 x 10(-4) (x = 3, 6 or 9). Signals due to hydrolyzed triethoxysilyl groups as well as unhydrolyzed triethoxysilyl groups [-Si(OEt)(3), -Si(OEt)(2)(OH), -Si(OEt)(OH)(2) and -Si(OH)(3) (OEt = OCH2CH3)] formed four sub-regions based on the number of hydroxyl groups bound to a silicon atom. In addition, one silicon environment influenced the other silicon environment by an intra-molecular interaction between two silicon atoms, and each sub-region for monomeric species thus contained four signals. Based on the development of signal intensity, it is revealed that one of the two triethoxysilyl groups in BTB is hydrolyzed preferentially. Thus, when a triethoxysilyl group is hydrolyzed, the -Si(OH) (x) (OEt)(3-x) (x = 1, 2) groups formed undergo further hydrolysis, which is opposite to the tendency expected from the hydrolysis behavior of organotrialkoxysilanes under acidic conditions.

Silsesquiazanes bearing different groups [RSi(NH)(1.5)](n) (R = C(12)H(25), Ph, H) were hydrolyzed and the resulting products were characterized. (C(12)H(25)Si(NH)(1.5))(n) was hydrolyzed by heating in an autoclave with water at 120 degrees C for 16 h. [PhSi(NH)(1.5)](n) was hydrolyzed by heating with water at 50 degrees C for 16 h. [HSi(NH)(1.5)](n) was dispersed in water at room temperature to induce hydrolysis. In the cases of [C(12)H(25)Si(NH)(1.5)](n) and [PhSi(NH)(1.5)](n), IR analysis showed that Si-NH-Si bonds remained and that terminal Si-NH(2) bonds in silsesquiazane were preferentially hydrolyzed to form Si-OH bonds or Si-O-Si bonds. Solid-state (29)Si CP/MAS NMR analysis revealed the formation of a Si-O-N network containing various Si environments. All the Si-H and Si-N bonds in [HSi(NH)(1.5)](n), on the other hand, were converted into Si-O bonds. These results reveal that Si-O-N networks can be formed from silsesquiazanes bearing dodecyl and phenyl groups under relatively moderate conditions. Copyright (C) 2010 John Wiley & Sons, Ltd.

Phenylsilsesquiazane (PhSSz) prepared by ammonolysis of phenyltrichlorosilane was spin-coated on Si(100) substrates. The resulting PhSSz films were subsequently converted into phenylsilsesquioxane films via hydrolysis in an autoclave under various hydrothermal conditions. IR spectroscopy revealed that the relative intensities of Si-N-Si and N-H stretching bands decreased, while a Si-O-Si stretching band appeared. Upon heating at 160 degrees C for 72 h with 0.5 mL of water, PhSSz was completely converted into phenylsilsesquioxane. Another poysiloxane film was obtained from a polysilazane prepared by ammonolysis of a mixture of phenyltrichlorosilane and trichlorosilane (PhHSSz). FE-SEM and AFM observations revealed that the phenylsilsesquioxane film and the poysiloxane film had dense structures and smooth surfaces.

A new layered inorganic-organic hybrid possessing a Ti-O network has been prepared by a reaction between titanium oxychloride (TiOCl) and lithium ethoxide (LiOEt) at 120 degrees C for 7 days. The XRD analysis indicates that the interlayer distance of TiOCl increases from 0.80 to 1.19 nm, and the solid-state C-13 NMR spectroscopy and elemental analysis show partial substitution of ethoxy groups for chlorine atoms.

Precursors for nitride-based ceramic composites have been prepared from two types of building blocks, cage-type poly(iminoalane) with Al-N backbones and cyclic poly(silazane) with Si-N backbones. Two combinations of poly(iminoalane) and cyclic poly(silazane) were utilized to prepare precursors. For the combination of poly(isopropyliminoalane) and [MeSi(H)NH](n), two building blocks were connected via dehydrocoupling, while Pt-catalyzed hydrosilylation was utilized for the combination of poly(allyliminoalane-co-ethyliminoalane) and [Me(H)SiNH](n). The ceramic yields of poly(iminoalane)s increased upon reactions with [MeSi(H)NH](n).

Two-dimensional monoclinic WO3 nanoplates with high specific surface areas are synthesized through a novel conversion process using tungstate-based inorganic-organic hybrid micro/nanobelts as precursors. The process developed involves a topochemical transformation of tungstate-based inorganic-organic hybrid belts into WO,3 nanoplates via an intermediate product of H2WO4 nanoplates, utilizing the similarity of the W-O octahedral layers in both H2WO4 and WO3. The as-obtained WO3 nanoplates show a single-crystalline nanostructure with the smallest side along the [001] direction. The WO3 nanoplates are 200-500 nm x 200-500 nm x 10-30 nm in size, and their specific surface areas are up to 180 m(2) g(-1). Photocatalytic measurements of visible-light-driven oxidation of water for O-2 generation in the presence of Ag+ ions indicate that the activity of the as-obtained WO3 nanoplates is one order of magnitude higher than that Of commercially available WO3 powders.

In this work an intercalation-chemistry-based method to synthesize tungstate and tungsten oxide nanosheets was described. A layered bismuth tungstate (Bi2W2O9) was used as the W-containing starting material. After the bismuth oxide layers were leached by a chloride acid, a protonated form, H2W2O7 center dot xH(2)O with sizes of 5-15 mu m, was achieved. The intercalation reaction of n-octylamine with H2W2O7 center dot xH(2)O in heptane and the subsequent dissolution-recrystallization process led to the formation of tungstate-based inorganic organic hybrid nanobelts. Orthorhombic WO3 center dot H2O nanosheets were obtained by removing the organic species of the as WO3 center dot H2O nanosheets at 250-450 degrees C, monoclinic WO3 nanosheets were achieved. The results of XRD, TEM and SEM indicate that the obtained WO3 center dot H2O and WO, were single-crystalline nanosheets with areas of (200-500) nm x (200-500) nor and thicknesses of 10-30 nm. The SAED patterns suggest that the WO3 center dot H2O and WO3 nanosheets possessed a reduced directions of [010] and [001], respectively. N-2 adsorption measurement results indicate that the specific surface areas of the as-obtained WO3 center dot H2O and WO3 nanosheets were up to 250 and 180 m(2)/g, respectively. The formation mechanisms for hybrid nanobelts, WO3 center dot H2O and WO3 nanosheets were discussed. The proposed novel route was efficient in producing two-dimensional WO3 nanosheets on a large scale.

Reactions between a layered aluminophosphate [AlPO4(OH)](C 6H5C2H4NH3) and an nalkylammonium ion [n-propylammonium (C3), n-butylammonium (C4) or n-hexylammonium ion (C6)] were examined. Upon reactions, the X-ray diffraction (XRD) patterns of the products showed changes in the interlayer distance from 1.97 nm to 1.66 nm (AlPO-C3), 1.86 nm (AlPO-C4), and 2.26 nm (AlPO-C6), and the interlayer distance thus increased linearly with increases in the length of the n-alkyl chains. Solid-state 13C nuclear magnetic resonance spectroscopy with cross polarization and magic angle spinning techniques ( 13C CP/MAS NMR) and infrared adsorption (IR) spectroscopy showed that C6H5C2H4NH3+ ions were eliminated and n-CnH2n+1NH3 + ions were introduced. Scanning electron microscopy (SEM) images showed, moreover, that the platy morphology of [AlPO4(OH)](C 6H5C2H4NH3) was maintained upon reactions. These results demonstrate that [AlPO 4(OH)](C6H5C2H4NH 3) underwent ion-exchange reactions with n-alkylammonium ions. © 2009 Materials Research Society.

Perhydropolysilazane (PHPS) was modified with trimethylamine-alane adduct, AIH(3)center dot NMe(3), with two nominal Si/Al molar ratios (I and 5), and the resulting poly (aluminasilazane)s were pyrolyzed under an N(2) atmosphere. Poly(aluminasilazane) with a nominal Si/Al molar ratio of 5 (PAS5) was insoluble because of the formation of cross-link points via dehydrocoupling. In the system with a nominal Si/Al molar ratio of I (PAS 1), on the contrary, AIH(3-)N center dot Me(3) cleaved the Si-N bonds in addition to forming Al-N bonds, drastically modifying the Si-N backbone of PHPS. In addition, a large portion of aluminium was lost in the PAS1 preparation. Thermogravimetric analysis revealed that PAS5 exhibited a ceramic yield of 78% up to 900 degrees C, while the ceramic yield for PAS1 was 61%. The XRD patterns of the pyrolyzed residues from PAS1 and PAS5 suggest the formation of a 2H wurtzite-type compound and silicon nitride. (c) 2007 Elsevier Ltd. All rights reserved.

To prepare stable polymer-titania hybrids, titania particles were modified using urushiol (extracted from Japanese lacquer) via surface complexation. The urushiol moieties underwent hydrosilylation and radical graft-polymerization to yield polymer-titania hybrids in which the titania particles were dispersed in polymer matrices.

A protonated form of the Ruddlesden-Popper-type ion-exchangeable layered perovskite H2La2Ti3O10 (H2LaTi) has been modified with n-alkylamine and n-alcohols to yield intercalation compounds and alkoxy derivatives, respectively. As concerns the intercalation of n-alkylamines into H2LaTi, no reaction of H2LaTi with n-butylamine occurred in anhydrous solvent, and the addition of water was required for the successful intercalation of n-butylamine into H2LaTi. The successful uptake of n-butylammonium ions from an n-butylammonium hydroxide aqueous solution suggests that the intercalation mechanism is of the ion-exchange type rather than the acid-base type. For interlayer surface modification with n-alcohol, no direct reaction of H2LaTi with n-alcohol occurred, but the n-propoxy derivative of H2LaTi formed by using the intercalation compound of H2LaTi with n-butylamine as an intermediate. In addition, reactions between the n-propoxy derivative of H2LaTi and n-alcohols (n-butanol, n-octanol, n-decanol, and n-dodecanol) led to the formation of various n-alkoxy derivatives via an alcohol-exchange-type reaction. As the model for n-alkoxy derivatives of H2LaTi, a bilayer arrangement of the n-alkyl chain possessing an all-trans ordered state with a 75 degrees tilting angle is proposed. The reaction mechanisms of these reactions are also discussed.

The formation process of novel tungstate-based inorganic-organic hybrid nanobelts/nanotubes with lamellar mesostructures has been investigated, with an emphasis on monitoring the morphological and microstructural changes of the products during the reactions of H(2)W(2)O(7)center dot xH(2)O (x = 3.49) with n-alkylamines (C(m)H(2m+1)NH(2), 4 &lt;= m &lt;= 14) in a system of heptane/n-alkylamine/H(2)W(2)O(7)center dot xH(2)O (n-alkylamine:H(2)W(2)O(7)center dot xH(2)O molar ratio of about 30) under ambient conditions. The results indicate that normal intercalation occurrs in the early stage to form intercalation compounds with double-octahedral W-O layers, which are then dissolved in the highly alkaline aqueous solutions confined in the reverse-micelle-like media, where the dissolved species recrystallize to form hybrid nanobelts/nanotubes with single-octahedral W-O layers. Both the intercalation compounds obtained after a short reaction time (e.g., 30 min) and the hybrid nanobelts/nanotubers formed after a long reaction time (e.g., 5 days) possess a bilayered arrangement of n-alkyl chains, but their tilt angle in the intercalation compounds (42 degrees) is much smaller than that in the hybrid nanobelts/nanotubes (71 degrees). The interlayer water released from H(2)W(2)O(7)center dot xH(2)O upon intercalation of n-alkylamine reacts with excess n-alkylamine molecules to form highly alkaline aqueous solutions, which have vital effects on the subsequent dissolution of the double-octahedral W-O layers to be single-octahedral layers. In addition, the high molar n-alkylamine:H(2)W(2)O(7)center dot xH(2)O ratios (e.g., 30) are necessary to form tungstate-based inorganic-organic nanobelts/nanotubes, and the nonpolar solvents not only facilitate the reactions between n-alkylamines and H(2)W(2)O(7)center dot xH(2)O but also favor the formation of belt/tubelike morphology.

The local environments and dynamics of hydrogen atoms in five samples of protonated forms of ion-exchangeable layered perovskites, Dion-Jacobson-type H[LaNb2O7] and H[LaTa2O7], Ruddlesden-Popper-type H-2[SrTa2O7] and H-2[La2Ti3O10], and H-1.8[(Sr0.8Bi0.2)Ta2O7] derived from an Aurivillius phase, Bi2Sr2Ta2O9, have been investigated by solid-state H-1 nuclear magnetic resonance spectroscopy (NMR). Solid-state H-1 NMR with a magic-angle spinning technique conducted at room temperature reveals that the mean electron densities around the H-1 nuclei in these protonated forms are relatively low, and that they decrease in the following order: H-1.8[(Sr0.8Bi0.2)Ta2O7]&gt; H-2[LaNb2O7]&gt; H-2[SrTa2O7]&gt; H[LaTa2O7]&gt; H-2[La2Ti3O10]. The temperature-dependent solid-state H-1 broad-line NMR spectra measured at 140-400 K reveal a decrease in the signal width for all of these five samples upon heating due to motional narrowing. The NMR spectra of H[LaNb2O7] and H[LaTa2O7] are different from the other three protonated forms due to the weaker dipole-dipole interactions at low temperatures and lower mobility of the hydrogen atoms at high temperatures. (c) 2006 Elsevier Inc. All rights reserved.

alpha,omega-Diaminoalkanes (NH2(CH2) NH2; n = 2, 4, 8, and 12) are intercalated in the interlayer space of the protonated form of a layered perovskite, H1.8Bi0.2Sr0.8Ta2O7 (HSrTa). The amounts of a,co-diaminoalkanes, which possess a monolayer arrangement in the interlayer space, are calculated as ca. 0.5 per [Bi0.2Sr0.8Ta2O7]. A model for alpha,omega-diaminoalkane-HSrTa intercalation compounds is proposed, and the model is consistent with that proposed for n-alkylamine-HSrTa intercalation compounds.

Soluble precursors possessing both Al-N and B-N backbones have been prepared from LiAlH4, LiBH4, and RNH2 center dot HCl (R = Me and Et) in one pot. The infrared (IR) and nuclear magnetic resonance (NMR) spectra of the precursors indicate that the precursors possess Al-H and B-H groups as well as Al-N, B-N, Al-(mu-H)(2)-Al, and Al(mu-H)(2)-B bonds. TG analysis reveals that the ceramic yield of the precursor [AB11_Me (LiAlH4/LiBH4/MeNH2 center dot HCl = 1/1/2)] up to 1000 degrees C under an argon atmosphere is 74.4 mass %. The transmission electron microscopic (TEM) images and the X-ray diffraction (XRD) pattern of AB11_Me that was pyrolyzed at 1600 degrees C indicate that the average size of crystalline aluminum nitride (AlN) is about 14nm and that crystalline AlN particles are distributed homogeneously in an amorphous matrix.

Poly(allyl iminoalane-co-ethyl iminoalane)s {[HAlN(allyl)](m)[HAlNEt](n); Allyl/Et-alanes}, have been prepared by reactions of lithium hydridoaluminate (LiAlH4) with a mixture of allylamine hydrochloride (CH2=CHCH2NH2 center dot HCl; allylNH(2) center dot HCl) and ethylamine hydrochloride (CH3CH2NH2 center dot HCl; EtNH2 center dot HCl) with various allyl/Et ratios. Spectroscopic analyses indicate that Allyl/Et-alane(1/3) (allyl/Et = 1/3) contains octamers possessing Al-H and C-H groups as well as C=C, Al-N, and C-N bonds. The loss of aluminum during pyrolysis of Allyl/Et-alane(1/3) at 1600 degrees C under an Ar atmosphere is 15%, which is less than the value reported for the pyrolysis of poly(ethyliminoalane) (36%). The suppression can be ascribed to cross-linking reactions involving allyl groups (hydroalumination and polymerization of the allyl groups), judging from infrared (IR) and solid-state nuclear magnetic resonance (NMR) spectroscopy. (c) 2006 Elsevier B.V. All rights reserved.

An iminoalane-silazane polymer (ISP), an Al-Si-N-C precursor, has been synthesized via Pt-catalyzed hydrosilylation between poly(allyl iminoalane-co-ethyl iminoalane) ([HAlN(allyl)](m)[HAlN (ethyl](n) AE-alane) and 1,3,5,7-tetrahydro-1,3,5,7-tetramethylcyclotetrasilazane {[Me(H)SiNH](4), TCS}. The IR and H-1 NMR spectra of ISP indicate that the relative amounts of the allyl groups decrease slightly in comparison with those of AE-alane, suggesting that hydrosilylation occurs partially. TG analysis up to 900 degrees C reveals that the ceramic yield of ISP is 83.1 mass%. It is suggested that the high ceramic yield can be ascribed to cross-linking reactions occurring during pyrolysis. Possible reactions during pyrolysis are hydrosilylation, polymerization of the C=C bonds in the allyl groups and dehydrocoupling among the SiH groups, NH groups and AlH groups in ISP. The pyrolyzed residue at 1700 degrees C contains crystalline AlN, 2H-SiC, beta-SiC and beta-Si3N4 and amorphous carbon, as revealed by solid-state nuclear magnetic resonance (NMR) spectroscopy, Raman spectroscopy and X-ray diffraction (XRD) analysis. Copyright (c) 2006 John Wiley & Sons, Ltd.

A nanocomposite possessing perovskite-related nanosheets dispersed in a siloxane network was prepared by cohydrolysis of the n-decoxy derivative of an ion-exchangeable layered perovskite, HCa2Nb3O10.xH(2)O (HCaNb), and tetramethoxysilane (TMOS) via a sol-gel process involving exfoliation. In the X-ray diffraction (XRD) pattern of the product after drying for 1d, the (00l) reflections disappeared. The transmission electron microscopy (TEM) image of the product after drying for 1d showed dark lines with a thickness of 1.5 nm, which was consistent with the thickness of an individual nanosheet, indicating exfoliation of HCaNb. In the XRD patterns of the reaction products of the n-decoxy derivative of HCaNb and TMOS before drying and after drying for 60 min, (00l) reflections were detected. After drying for 80 min, the intensity of the (00l) reflections decreased. The intensity decreased with an increase in the drying time, indicating that the exfoliation of HCaNb occurred during the drying process. (c) 2006 NIMS and Elsevier Ltd. All rights reserved.

The organic-to-inorganic conversion process of cage-type poly (ethyliminoalane), (HAINEt)(n) (n is mainly 8), was investigated by analyzing the gases evolved during pyrolysis. The conversion process can be divided into three temperature ranges: up to 300 degrees C, 300-600 degrees C, and above 600 degrees C. Below 300 degrees C, ethylene and ethylamine were formed probably via Al-N bond cleavage to form nitrogen terminal ( N:), and polymerization of cages could occur via two possible reactions involving nitrogen terminals. The conversion process between 300 and 600 degrees C involved the evolution of ethylene, ethane and methane, whose formation can be attributed to radical reactions. Ethylamine was also formed in this temperature range. Methane formation was also observed in the temperature range above 600 degrees C, and appears to be ascribable to the rearrangement of the mineralized network.

Si-Al-N-C precursors have been prepared from perhydropolysilazane (PHPS) and cage-type poly (ethyliminoalane) [(HAINEt)(n); PEIA, n is mainly 8] with different Si/Al molar ratios (Si/Al = 3, 1, 1/3). Spectroscopic analysis indicates that essentially no Si-N-Al linkages form, indicating that the precursors are blended polymers. TG analysis reveals that the ceramic yields of the blended precursors up to 900 degrees C are higher than those of PHPS and (HAINEt)n, suggesting that cross-linking reactions occur during pyrolysis. Possible reactions are dehydrocoupling and radical reactions, as suggested by the results of solid-state nuclear magnetic resonance (NMR) spectroscopy. The results of solid-state NMR spectroscopy and X-ray diffraction (XRD) analysis indicate that the residue pyrolyzed at 1600 degrees C contains mainly crystalline AIN, 2H-SiC and beta-SiC.

Trifluoroacetate (TFA, CF3COO) groups have been successfully bound to the interlayer surface of a protonated form of Dion-Jacobson-type layered perovskite, HLaNb(2)O(7)(.)nH(2)O (HLaNb), via a reaction between its n-propoxy derivative and trifluoroacetic acid (TFAH, CF3COOH). The interlayer distance increases approximately to 1.8 nm upon treatment with TFAH, and varies in the range from similar to 1.7 to similar to 2.0 nm depending on the amount of water adsorbed in the interlayer space. The high stability of the guest species upon dispersal in organic solvents and the change in the infrared (IR) spectrum profile with respect to that of TFAH indicate that the guest species are TFA groups bound to the surface of perovskite-like slabs of HLaNb. The interlayer distance indicates that the TFA groups possess a bilayer arrangement, and a unidentate type of coordination is proposed based on consideration on the coordination geometry. (c) 2005 Elsevier Ltd. All rights reserved.

The organic-to-inorganic conversion process of cage-type poly(ethyliminoalane), (HAlNEt)n (n is mainly 8), was investigated by analyzing the gases evolved during pyrolysis. The conversion process can be divided into three temperature ranges: up to 300°C, 300-600°C, and above 600°C. Below 300°C, ethylene and ethylamine were formed probably via Al-N bond cleavage to form nitrogen terminal (≡ N:), and polymerization of cages could occur via two possible reactions involving nitrogen terminals. The conversion process between 300 and 600°C involved the evolution of ethylene, ethane and methane, whose formation can be attributed to radical reactions. Ethylamine was also formed in this temperature range. Methane formation was also observed in the temperature range above 600°C, and appears to be ascribable to the rearrangement of the mineralized network.

Si-Al-N-C precursors have been prepared from perhydropolysilazane (PHPS) and cage-type poly (ethyliminoalane) [(HAlNEt)n
PEIA, n is mainly 8] with different Si/Al molar ratios (Si/Al-3, 1, 1/3). Spectroscopic analysis indicates that essentially no Si-N-Al linkages form, indicating that the precursors are blended polymers. TG analysis reveals that the ceramic yields of the blended precursors up to 900°C are higher than those of PHPS and (HAlNEt)n, suggesting that cross-linking reactions occur during pyrolysis. Possible reactions are dehydro-coupling and radical reactions, as suggested by the results of solid-state nuclear magnetic resonance (NMR) spectroscopy. The results of solid-state NMR spectroscopy and X-ray diffraction (XRD) analysis indicate that the residue pyrolyzed at 1600°C contains mainly crystalline AlN, 2H-SiC and β-SiC.

The structures of sol-gel derived hybrid gels prepared by co-hydrolysis of tetraethoxysilane (TEOS)-organotrialkoxysilane (RTES, RSi(OC2H5)(3), R = CH3, C5H11, C8H17 and C6H5) mixtures (TEOS: RTES: CH3CH2OH: HO: HNO3 = 0.5:0.5:10:x:0.3; x = 2, 5, 10 and 20) were characterized based on signal intensities of Si-29 CP/MAS NMR as a function of the contact time. The contact time dependencies of the signals for Q(4) (Si(OSi)(4)) units were successfully simulated by assuming distributed cross relaxation times (T-SiH) and an intrinsic H-1 spin-lattice relaxation time in the rotating frame (T-1p(H)); the latter was different from the apparent T-1p(H) value estimated by assuming single T-SiH. The distribution ranges of T-SiH for the TEOS-RTES gels broadened as the water content increased, suggesting that the Q(4) units tended to be separated from the T units and that the local concentration of H-1 spins around the Q(4) unit tended to decrease. (C) 2004 Published by Elsevier B.V.

The photocatalytic activities of triple-layered Aurivillius phases, Bi(2)A'NaNb3O12 (A'= Sr, Ca) and Bi2CaNaTa3O12, and of protonated forms prepared from these Aurivillius phases through selective leaching of bismuth oxide sheets were investigated. UV-Vis diffuse reflectance spectra showed blue shifts of the adsorption edges upon selective leaching. Although none of the triple-layered Aurivillius phases were active for photocatalytic H-2 evolution from a 20 vol% ethanol solution, all the corresponding protonated forms showed photocatalytic activities for H-2 evolution. The effects of the changes in electronic structures and interlayer surface creation on photocatalytic activities are discussed. (C) 2004 Elsevier B.V. All rights reserved.

The hydrolysis and condensation processes of titanium iso-propoxide modified with catechol (C6H4(OH)(2); H(2)cat) have been investigated by H-1, C-13 and O-17 nuclear magnetic resonance spectroscopy. The hydrolysis reactions of the modified titanium iso-propoxide in the system with Ti:tetrahydrofuran (THF): H2O = 1:20: x (x = 1, 2 and 5 in a molar ratio) are essentially completed in the initial stage (&lt;1 h), and the condensation reactions also proceed significantly during this stage. Upon hydrolysis with H2O/Ti = 1, the iso-propoxy groups are selectively hydrolyzed and the catecholate groups remain bound to titanium. With H2O/Ti = 2 and 5, both the iso-propoxy and catecholate groups are hydrolyzed, and the hydrolysis of the iso-propoxy groups is relatively preferential. Approximately half the catecholate groups are stably bound to titanium, even after hydrolysis with H2O/Ti = 5.

The C-C bonds immobilized in the interlayer space of layered perovskite, HLaNb2O7.xH(2)O, have undergone hydrosilylation reactions with chlorohydrosilanes. The C=C bonds are immobilized by the reaction between an n-propoxyl derivative of HLaNb2O7-xH(2)O and 4-penten-l-ol to form a CH2=CH(CH2)(3)O- derivative of HLaNb2O7.xH(2)O, and a corresponding increase in the interlayer distance from 1.54 to 1.85 nm is observed. The CH2=CH(CH2)(3)O- derivative is further treated with dichloromethylsilane or trichlorosilane, and the interlayer distance increases to 2.41 (dichloromethylsilane) or 2.07 (trichlorosilane) nm. Solid-state C-13-CP/MAS-NMR spectroscopy and infra-red (IR) spectroscopy reveal that the C=C groups disappear after the treatment with dichloromethylsilane or trichlorosilane, and C-13-NMR signals assignable to the hydrosilylated products are clearly observed. Besides hydrosilylation reactions, siloxane formation involving hydrolysis of the Si-Cl groups also proceeds. The structure of the perovskite-like slabs in HLaNb(2)O(7)(.)xH(2)O is preserved throughout the process, indicating the successful modification of immobilized C-C groups via hydrosilylation with no structural change in the inorganic host layers. (C) 2003 Elsevier B.V. All rights reserved.

Organic derivatives of the protonated triple-layered perovskite HCa2Nb3O10.xH(2)O with n-alkoxyl groups on the interlayer surface have been prepared by grafting n-alcohols. Interlayer surface modification of HCa2Nb3O10.xH(2)O is achieved by a direct reaction of HCa2Nb3O10.xH(2)O with methanol or ethanol, and single-phase n-alkoxyl derivatives of HCa2Nb3O10.xH(2)O (n greater than or equal to 3 in n-CnH2n+1O-\groups) can be formed by reacting n-alkoxyl derivatives (methoxyl and n-propoxyl derivatives) with n-alcohols in an autoclave at 150 C. X-ray diffraction analysis shows the changes in interlayer distances upon treatment of HCa2Nb3O10.xH(2)O or intermediate n-alkoxyl derivatives with n-alcohols. Solid-state C-13 CP/MAS (cross polarization and magic-angle spinning) NMR spectroscopy demonstrates the presence of signals due to n-alkoxyl groups originating from the reactant n-alcohol molecules. Differential thermal analysis curves of the products exhibit exothermic peaks at temperatures higher than 200 C. These results indicate successful preparation of HCa2Nb3O10.xH(2)O derivatives possessing various n-alkoxyl groups (n-CnH2n+1O-, n = 1-4, 6, 8, 10, 12, 14, 16, and 18) on the interlayer surface. Although a reaction between an n-propoxyl derivative and n-decanol does not proceed at 80 degreesC, a single-phase n-decoxyl derivative can be obtained at 80 C by adding a small amount of water (1 mass %), which strongly suggests a hydrolysis-esterification mechanism. IR and solid-state C-13 CP/MAS NMR spectroscopies indicate that the n-alkyl chains in n-alkoxyl derivatives (n greater than or equal to 10 in n-CnH2n+1O-groups) possess an all-trans conformation. A linear relationship with a slope of 0.166 nm/carbon atom is observed between the interlayer distance and the number of carbon atoms in the n-alkyl chains, suggesting that the n-alkyl chains of n-alkoxyl groups are present as bilayers with a tilt angle of 41 in the interlayer space.

The conversion process of an Aurivillius phase, Bi2W2O9, into a layered tungstic acid by hydrochloric acid treatment has been investigated, and resultant H2W2O7.nH(2)O has been fully characterized. The c parameter of Bi2W2O9 (2.37063(5) nm] decreases to 2.21(1) nm in an acid-treated product dried at ambient temperature. The a and b parameters of Bi2W2O9 [a = 0.54377(1) nm and b = 0.54166(1) nm] also decrease slightly to a = 0.524(1) nm and b = 0.513(1) nm in the acid-treated product dried at ambient temperature, indicating structural changes in the ReO3-like slabs in Bi2W2O9 upon acid treatment. Drying at 120 degreesC leads to a further decrease in the c parameter (1.86(1) nm] with no notable change in the a and b parameters [a = 0.5249(2) nm and b = 0.513(2) nm]. The formation of an expandable layered structure is demonstrated by the successful intercalation of n-octylamine [interlayer distance 2.597(9) nm] and n-dodecylamine (interlayer distance 3.56(2) nm]. The compositions of the acid-treated products are determined to be H2W2O7-nH(2)O typically with n = 0.58 for the air-dried product and n = 0 for the product dried at 120 degreesC. As a consequence, the composition of the layer is H2W2O7, and the decrease in the c parameter upon drying is ascribable to the loss of interlayer water. Scanning electron microscopy reveals no morphological change during acid treatment, which strongly suggests a selective leaching of the bismuth oxide sheets as a reaction mechanism. High-resolution transmission electron microscopy (HREM) observation of the acid-treated product shows consistency with a structural model for H2W2O7, derived from Bi2W2O9 through removal of the bismuth oxide sheets and contraction along the c axis. HREM observation also reveals that the WO6 octahedra arrangement changes slightly with acid treatment. A one-dimensional electron density map projected on the c axis for the product dried at 120 degreesC, H2W2O7, shows good consistency with that calculated for the structural model.

Organic derivatives of a layered perovskite compound, HLaNb2O7.xH(2)O (HLN), with interlayer surfaces possessing n-alkoxyl groups (n-decoxyl and n-propoxyl) have been allowed to react with various alcohols and a diol (ethylene glycol) to form new organic derivatives via substitution reactions. The reaction of an n-propoxyl derivative of HLN with n-decanol leads to the formation of n-decoxyl groups bound to the interlayer surface of the perovskite-like [LaNb2O7] slab. In a similar fashion, the reaction of an n-decoxyl derivative of HLN with 2-propanol results in the formation of an isopropoxyl derivative. The reaction of the n-decoxyl derivative of HLN with tert-butyl alcohol also proceeds, though the reaction is not completed even after 14 days. After the reaction of the n-decoxyl derivative of HLN with ethylene glycol, only one of the two hydroxyl groups in ethylene glycol is reacted, and -OCH2-CH2OH groups are present on the interlayer surface. Water is required for proceeding the substitution reaction between the n-propoxyl derivative of HLN and n-decanol, and the reaction mechanism involving hydrolysis of the alkoxyl groups on the interlayer surface and subsequent esterification is proposed.

Intercalation behavior of n-alkylamines into a protonated form of a layered perovskite, H-1.8[Sr0.8Bi0.2Ta2O7] derived from an Aurivillius phase, Bi2SrTa2O9, has been investigated. H-1.8[Sr0.8Bi0.2Ta2O7] can accommodate n-alkylamines (CmHm+1NH2; m = 4, 8, 12, 18) to form intercalation compounds via an acid-base mechanism. The interlayer distance increases to 2.071(2) (m = 4) 2.840(9) (m = 8), 3.83(1) (m = 12), and 5.17(2) (m = 18) nm. In contrast, H-1.8[Sr0.8Bi0.2Ta2O7] does not form any intercalation compound with pyridine, which is a weaker base, indicating that the protons in H-1.8[Sr0.8Bi0.2Ta2O7] are weakly acidic. The IR spectra of the intercalation compounds with n-alkylamines (m = 12 and 18) clearly show that n-alkyl chains possess an all-trans conformation. A linear relationship is observed between the interlayer distance and the number of carbon atoms in n-alkyl chains, and this corresponds to a bilayer arrangement of the n-alkyl chains with a tilt angle of 60degrees. Despite the relatively high proton content (1.8 H+ per [Sr0.8Bi0.2Ta2O7]), only 0.9-1.0 mol of n-alkylamines per [Sr0.8Bi0.2Ta2O7] is intercalated. This observation can be reasonably interpreted based on the surface geometry of the perovskite-like slab and the size of n-alkylamines.

Chemical modification of niobium pentaethoxide (Nb(OCH2CH3)(5); Nb(OEt)(5)) with catechol (C6H4(OH)(2); H(2)cat) was investigated using infrared spectroscopy, H-1 and C-13 nuclear magnetic resonance spectroscopy, compositional analysis and mass spectrometry. Niobium pentaethoxide was chemically modified with catechol by the formation of catecholate groups (cat(2-)) bound to niobium, and a corresponding release of ethanol Was observed. The obtained product was [(cat)Nb(OEt)(3)](n), which included the dimmer [(cat)Nb(OEt)(3)](2).

The conversion of a Sr-Ti bimetallic methoxyethoxide precursor into SrTiO3 via hydrolysis and/or calcination was investigated. Hydrolysis with various water/metal molar ratios (r(H); r(H) = 0.5, 2, 4, 6, 8, 10) in tetrahydrofuran at reflux resulted in a decrease in the amount of the methoxyethoxyl groups, and the hydrolyzed products were soluble with r(H) less than or equal to 2. At r(H) greater than or equal to 8, SrTiO3 was crystallized without calcination. Both the hydrolyzed and unhydrolyzed precursors (r(H) = 0, 0.5, 2) were calcined in dry air at 550degrees-800degreesC. SrTiO3 was crystallized on calcination at greater than or equal to550degreesC from amorphous materials with a considerable loss of carbon, which was present as both chars and carbonate ions.

Protonated forms of layered perovskites were derived from Aurivillius phases, Bi(2)ANaNb(3)O(12) (A = Sr or Ca), by the substitution of bismuth oxide sheets with protons via acid treatment. The conversion into the protonated forms was achieved easily using 6 M HCl at room temperature. Preservation of the structure of the perovskite-like slabs and contraction in the e axis were confirmed by X-ray and electron diffraction analysis as well as by transmission electron microscopy. The compositions of the resulting products were determined to be H-1.8[A(0.8)Bi(0.2)NaNb(3)O(10)] (A = Sr or Ca) by inductively coupled plasma emission spectroscopy and thermogravimetry. The acid-treated product H-1.8[Sr0.8Bi0.2NaNb3O10] was capable of accommodating n-alkylamines in the interlayer space, which is in good agreement with the proposed layered structure.

A precursor derived from (HAIN(i)Pr)(m) and [MeSi(H)NH](n), which mainly consisted of cage-type compounds and cyclic compounds, respectively, was converted into Al-Si-N-C ceramic composites via pyrolysis. A dehydrocoupling reaction between AlH groups and NH groups occurred at low temperatures (less than or equal tosimilar to250degreesC), which mainly accounts for its high ceramic yield (69% up to 900degreesC). At high temperatures (greater than or equal tosimilar to250degreesC), the organic groups were decomposed. The product pyrolyzed at 1350degrees and 1500degreesC under Ar contained a 2H wurtzite-type compound and a beta-Si3N4-type compound, while beta-SiC was clearly detected in addition to these compounds in the product pyrolyzed at 1600degreesC under Ar. On the other hand, the product pyrolyzed at 800degreesC under NH3 and subsequently at 1350degreesC under N-2 consisted of AIN and beta-Sialon.

An Aurivillius phase, Bi2SrTa2O9, which consists of perovskite-like stabs and bismuth oxide sheets, was treated with 3 M hydrochloric acid for 72 h, and the resultant product was characterized. Scanning electron microscopy investigation indicated that no morphological change occurred during the acid treatment. X-ray diffraction (XRD) analysis revealed that the product exhibited tetragonal symmetry with a = 0.391 +/- 0.004 run and c = 0.98 +/- 0.01 run, and the a parameter is consistent with a typical value for cubic perovskite oxides. High-resolution electron microscopy (HREM) observations along both [001] and [010] showed that the structure of the perovskite-like slabs in Bi2SrTa2O9 was retained after the acid treatment. The compositional analyses revealed the loss of a large portion of bismuth and a part of strontium (present in the bismuth oxide sheets due to B &lt;----&gt; Sr disorder) and the introduction of protons. These observations indicate that the bismuth oxide sheets in Bi2SrTa2O9 were selectively leached and that protons were introduced into the interlayer space to form a protonated layered perovskite, H-1.8[Sr0.8Bi0.2Ta2O7]. Though diffraction techniques (XRD and electron diffraction) demonstrated that an average structure of H-1.8[Sr0.8Bi0.2Ta2O7] consisted of perovskite-like slabs stacked without displacement, HREM observation along [010] demonstrated that both a simple stacking sequence without displacement (P-type) and a stacking sequence with a relative displacement by (a + b)/2 (I-type) were present in H-1.8[Sr0.8Bi0.2Ta2O7].

Magadiite, a layered sodium polysilicate, was organically modified by esterification of interlayer silanol groups with various aliphatic alcohols. Methanol was directly reacted with H-magadiite (acid-treated magadiite) by refluxing. The methanol-treated product showed an increase in the basal spacing and the C-13 NMR signals due to methyl groups. The H-2 NMR spectrum of CD3OD-treated H-magadiite showed Pake doublet patterns of quadrupole coupling constants of 43 and 48 kHz and asymmetry factors of 0, indicating the fixation of the C-O axis. When aliphatic alcohols with the carbon chain length longer than 4 were used, an H-magadiite/N-methylformamide (NMF) intercalation compound was used as an intermediate for esterification. The basal spacing of butanol-treated H-magadiite was 1.40 nm, the value of which was smaller than that of H-magadiite/NMF (1.63 nm) and larger than that of H-magadiite (1.15 nm). C-13 spin-lattice relaxation times (T-1) of butyl groups showed a low mobility of the alpha carbon. Other alcohols (CnH2n+1OH (n = 2-16) and (CH3)(3)COH) were also reacted with the silanol groups. The differential thermal analysis (DTA) curves of the products showed exothermic peaks. The alkyl chains are apparently lying parallel to the inner surface because almost constant basal spacings were observed despite the variation in the alkyl chain length. The butanol-treated H-magadiite was dispersed in toluene and cast, resulting in the formation of a transparent nanocomposite film.

Titanium tert-butoxide (Ti(OC(CH3)(3))(4); Ti((OBu)-Bu-t)(4)) was chemically modified with catechol (C6H4(OH)(2)) and hydrolysis and condensation behavior of a resultant modified alkoxide was studied. Spectroscopic results revealed that the reaction between titanium tert-butoxide and catechol resulted in the formation of catecholate groups (C6H4O22-) bound to titanium and corresponding release of tert-butanol. The mass spectrometry and cryoscopy indicated that main species was a dimer [(C6H4O2)(2)Ti-2((OBu)-Bu-t)(4)]. The hydrolysis of the modified alkoxide in the system with Ti:tetrahydrofuran (THF):H2O = 1:10:x (x = 0.5-10) resulted in the partial hydrolysis, and all the hydrolyzed products after the drying under reduced pressure were soluble in THF and chloroform.

The preparation and pyrolysis of a blended precursor possessing Ti-N and Al-N bonds were investigated. The precursor was prepared by mixing (HAIN(i)Pr)(n), whose main component was a cage-type compound, and an aminolysis product of Ti(NMe2)(4) with MeHNCH2CH2NHMe with a molar ratio of Ti:Al = 2:1. IR analysis of the products pyrolyzed under NH3-N-2 indicated that a large proportion of the organic groups in the precursor were removed by an amine-exchange reaction during the pyrolysis under NH3; thus, the products contained only a small amount of carbon. On the contrary, a considerable amount of carbon was present in the product pyrolyzed under Ar. Composites consisting of AIN and an NaCl-type compound were obtained after pyrolysis of the precursor under both NH3-N-2 and Ar. The composition of the NaCl-type compound depended significantly on the pyrolysis atmosphere. Copyright (C) 2001 John Wiley & Sons, Ltd.

A kaolinite-nylon 6 intercalation compound was prepared by the polymerization of 6-aminohexanoic acid (AHA) in the interlayer space of kaolinite. The intercalation of AHA was achieved by a guest displacement reaction using a kaolinite-methanol intercalation compound as an intermediate. After AHA dissolved in a mixed solvent of methanol and water (1:3) was added to a kaolinite-methanol intercalation compound, the mixture was stirred for 3 h. The basal spacing of the product increased to 1.23 nm, indicating the intercalation of AHA molecules with a monolayer arrangement between the layers of kaolinite. AHA was polymerized by a heat treatment at 250 degreesC for 1 h under a nitrogen flow. Although the basal spacing of the heat-treated product slightly decreased to 1.16 nm, the spacing was larger than those of kaolinite and the kaolinite-methanol intermediate. The formation of a kaolinite-nylon 6 intercalation compound was confirmed by the appearance of IR bands due to amide I (1637 cm(-)1) and amide II (1550 cm(-1)).

Silanol groups in protonated magadiite (H-magadiite) were characterized by H-1 and H-2 solid-state nuclear magnetic resonance (NMR). H-magadiite and deuterated (D) magadiite were synthesized by the treatment of Na-rich magadiite with 0.2 N HCl and 0.2 N DCl, respectively. In the H-1 NMR spectrum measured at room temperature, silanol groups of H-magadiite showed two signals at 3.75 and 5.70 ppm, indicating that two types of silanol groups were present. The ratio of silanol groups associated with strong hydrogen bonding (5.70 ppm) to those with weaker hydrogen bending (3.75 ppm) was 2 to 1. The H-2 NMR spectra of deuterated magadiite were measured in the temperature range from 150 to 440 K. In the spectra measured at temperatures below 294 K, silanol groups showed Pake doublet patterns. These patterns were composed of two components corresponding to the two types of silanol groups shown in the H-1 NMR analysis. Both silanol groups produced wobbling motions with increasing temperature. Above 294 K, the profile of the Pake doublet pattern was transformed gradually to a near triangular pattern, indicating that the silanol groups underwent other motions also, such as a two-site jump.

Highly transparent silica-surfactant nanocomposite films containing photosynthetic pigments have been successfully formed through the solubilization of chlorophyll a (Chl a) into surfactant micelles. The UV-vis absorption spectra indicated that a large amount of Chl a were transformed into pheophytin a in the films. These photosynthetic pigments were well dispersed in the surfactant assemblies and their chlorin rings were exposed to the surface of silica layers. Even under an air atmosphere, the photostability of immobilized pigments was largely improved in comparison with that in a homogeneous Chl a solution. Because both Chl a and pheophytin a molecules are effective for the photosensitive charge separation, the present film system is very suitable for heterogeneous immobilizing media for photosynthetic pigments from the viewpoint of in vitro biomimetic devices for solar energy conversion.

The conversion of tetrakis(diethylamino)titanium (Ti(NEt2)(4)) into titania via either a combination of hydrolysis (Ti(NEt2)(4) : THF : H2O = 1 : 10 : x, x = 2, 4, 10) at ambient conditions and calcination (method A) or hydrolysis in a water-tetrahydrofuran (THF) mixture (Ti(NEt2)(4) : THF : H2O = 1 : 10 : 100) at reflux (method B) was investigated. Titanium tertiary butoxide (Ti((OBu)-Bu-t)(4)) was also used as a substitute for Ti(NEt2)(4). The hydrolysis via method A resulted in the formation of amorphous solids containing organics. Thermal analyses showed that the hydrolysis products showed mass losses up to 500 degreesC probably due to the presence of diethylamine (Et2NH) formed via the hydrolysis of Ti(NEt2)(4) in the hydrolysis products, while a mass loss of the hydrolysis product from Ti((OBu)-Bu-t)(4) was completed up to about 200 degreesC. After calcination at greater than or equal to 600 degreesC, anatase or a mixture of anatase and rutile was obtained. The crystallization behavior of the hydrolysis products from Ti(NEt2)(4) was different from that of the hydrolysis product from Ti((OBu)-Bu-t)(4). The hydrolysis via method B gave only an amorphous material from Ti(NEt2)(4), while a crystalline titania (anatase and brookite) formed from Ti((OBu)-Bu-t)(4).

The pyrolysis processes of poly(isopropyliminoalane) ((HAIN(i)Pr)(n)) were investigated, using mass spectrometry to analyze the gases and infrared spectroscopy to analyze the residual solids. The major mass loss (in the temperature range of 240 degrees-540 degrees C) consisted of two different pyrolysis stages. At the first stage (240 degrees-320 degrees C), (HAIN(i)Pr)(6) was detected continuously as a gas, and the precursor was converted to a cross-linked structure. A polymerization mechanism without a release of organic compounds has been proposed, and the formation of (HAIN(i)Pr)(6) during polymerization (besides its evaporation) has been suggested. The second stage (320 degrees-560 degrees C) involved the formation of various organic compounds, and radical processes for their formation were proposed.

Lamellar organoammonium silicates with variable silicon environments have been synthesized by the reaction of a layered polysilicate kanemite with aqueous solutions of hexadecyltrimethylammonium (C(16)TMA) chloride. While the structure of kanemite is composed of only Q(3) silicate species ((SiO)(3)SiO), SiO4 units with both Q(3) and Q(4) ((SiO)(4)Si) environments were present in the silicate frameworks of the lamellar C(16)TMA silicates. The Q(4) species mainly formed by intralayer condensation of the Q(3) species in the individual silicate sheets in kanemite rather than by interlayer condensation between the adjacent sheets. The intralayer condensation can be suppressed by lowering the reaction temperature and/or shortening the reaction time, which results in the relative retention of the silicate framework of kanemite in the lamellar C(16)TMA silicates.

Surface silanol groups of FSM-type mesoporous silica were modified with 1,4-butanediol, and the esterified material was successfully used as the adsorbent to accommodate chlorophyll alpha molecules. Pheophytinization was effectively suppressed by the presence of the surface organic groups grafted onto the mesoporous silica, whereas pheophytinization occurred in unmodified mesoporous silica.

Synthesis and pyrolysis of a soluble precursor possessing an Nb-N backbone structure were investigated. The precursor was prepared by aminolysis reaction of tetrakis(diethylamido)niobium with isopropylamine. The precursor was soluble in benzene, and had a polymeric structure possessing Nb-N-Nb imido-bridges. The precursor was pyrolyzed under NH3-N-2 (at 600 degrees C for 2 h under NH3 and subsequently at 1350 degrees C for 8 h under N-2) and Ar (at 1500 degrees C for 2 h) atmospheres. delta-NbN was obtained as a main crystalline phase after the pyrolysis of the precursor under NH3-N-2 whereas pyrolysis of the precursor under Ar led to the formation of NbC as the only crystalline phase. More than 90% of niobium which was present in the precursor remained in both of the pyrolyzed products.

A novel soluble precursor with a Zr-N-Zr backbone structure was prepared by an aminolysis reaction of Zr(NEt2)(4) with Pr(i)N(H)2. Pyrolysis of the precursor under NH3-N-2 atmospheres led to the formation of ZrN as a main crystalline phase with a ceramic yield of 45.2%. Aggregated particles consisting of very minute particles with diameters of 50-300 nrl were obtained.

Carriers were successfully doped into RbCa2NaNb4O13 by the substitution of Sr2+ for Na+, yielding electroconducting niobates with a layered structure consisting of four perovskite-like layers. Single-phase products of polycrystalline RbCa2Na1-xSrxNb4O13 (x = 0.2 and 0.4) were synthesized by the solid-state reaction of RbCa2Nb3O10, Sr5Nb4O15, Nb2O5 and Nb metal. The solid solutions were indexed based on a tetragonal structure, corresponding to the end-member RbCa2NaNb4O13. With the increase in the amount of strontium substitution, an expansion of the c-axis was observed while the a-axis was essentially constant. The products showed semiconducting properties. (C) 1999 Academic Press.

Alkykamines and water were intercalated between the layers of kaolinite by utilizing a kaolinite/methanol intercalation compound as an intermediate. A kaolinite/methanol intercalation compound was synthesized by guest displacement reaction of a kaolinite/N-methylformamide intercalation compound with methanol. The basal spacing increased up to 5.75 nm when octadecylamine was used. It increased linearly with the length of alkyl chains by 0.255 nm per carbon atom, suggesting that the alkylamine molecules in the interlayer space of kaolinite take a bilayer arrangement with their alkyl chains almost perpendicular to the layers of kaolinite. Water molecules were also intercalated into kaolinite by displacement of methanol. The basal spacing of the product was 1.00 nm under wet conditions and 0.85 nm after drying. By using hydrated kaolinite as an intermediate, pyridine molecules were intercalated into kaolinite, thus, the hydrated kaolinite also shows the ability as an intermediate for displacement reactions. These results demonstrate that kaolinite has higher intercalation ability for a wider variety of guest species than previously accepted if appropriate intermediates are used. (C) 1999 Elsevier Science B.V. All rights reserved.

Polycrystalline samples with nominal compositions K_<1+x>Nb_4O_6(0&le;x&le;1.0)were prepared by the solid-state reaction of KNbO_3, Nb_2O_5 and Nb. Powder X-ray diffraction analysis revealed that the KNb_4O_6-type compound was obtained as the major phase when x&ge;0.4. Transmission electron microscopy observations showed that when x=0.4, the KNb_4O_6-type compound contained intergrowth defects. In contrast, when x=1.0, practically no intergrowth defects were observed, although this sample contained KNbO_3 as an impurity phase. The relation between the nominal composition and the formation of the intergrowth defects is discussed.

Taxol, an anticancer substance, was adsorbed into FSM-type mesoporous silicas with the pore sizes larger than 1.8 nm, while it was not adsorbed into the channels with the pore size less than 1.6 nm, indicating that mesoporous silicas have a molecular sieving property for relatively large molecules. The adsorption behavior of Taxol depended on the solvents; Taxol was not adsorbed into mesoporous silicas when methanol or acetone was used but was adsorbed when dichloromethane or toluene was used. The adsorption behavior of Taxol is discussed on the basis of the solubility parameters of the solvents. The proton-acceptor solubility parameter (delta a) is a predominant factor in this liquid-solid partition system. The adsorption-desorption of an extract from yew needles was performed using the mesoporous silica and several elution solvents. In the adsorption, many components including Taxol were adsorbed into mesoporous silica. When the desorption of the extract components adsorbed into the mesoporous silica was performed with a mixture of methanol and water with varied ratios, the targeted molecule, Taxol, with a few addition of components was separated from the adsorbed components. This adsorption-desorption behavior was elucidated by the solubility parameter (delta) as well as delta a.

Polycrystalline samples with nominal compositions K1+xNb4O6 (0 less than or equal to x less than or equal to 1.0) were prepared by the solid-state reaction of KNbO3, Nb2O5 and Nb. Powder X-ray diffraction analysis revealed that the KNb4O6-type compound was obtained as the major phase when x greater than or equal to 0.4. Transmission electron microscopy observations showed that when x=0.4, the KNb4O6-type compound contained intergrowth defects. In contrast, when x=1.0, practically no intergrowth defects were observed, although this sample contained KNbO3 as an impurity phase. The relation between the nominal composition and the formation of the intergrowth defects is discussed.

Lamellar and hexagonal mesostructured aluminophosphates (AlPOs) were prepared and characterized. The lamellar mesostructured AlPO (APW-1) formed hydrothermally and the condensed framework was composed of alternating AlO4 and PO4 units. The hexagonal mesostructured. AlPO (APW-2) is formed by transformation of a layered precipitate composed of both aluminophosphate oligomers and alkyltrimethylammonium (ATMA) cations. Calcined APW-2 had a mesoporosity with the BET surface area of 980 m(2) gl and a pore diameter of 1.8 nm after substantial shrinkage of the framework. Lamellar APW-1 formed under most of the conditions surveyed, while hexagonal APW-2 was obtained under very restricted conditions. In this system, the charge matching in the products is the most important factor, although the assemblies of ATMA cations are essential as the structure-directing agents.

Direct intercalation of poly(vinylpyrroridone) (PVP) into the interlayer space of kaolinite at room temperature is achieved by a refined guest displacement method by utilizing both a kaolinite-methanol intercalation compound and PVP dissolved in methanol.

Polycrystalline samples of Na(1-x)Ln(x)NbO(3) (Ln=La, Nd, Sm, Gd) were synthesized by solid-state reactions. Reduced niobates were obtained as single-phase perovskites for x=0.05 and 0.1 when Ln=La and Nd and x=0.05 when Ln=Sm. The Gd-substituted samples could not be prepared under the synthetic conditions studied. Compositional analysis of the products revealed a slight amount of sodium loss during synthesis. The structural parameters obtained from Rietveld analysis revealed an increase in unit-cell volume. All of the obtained samples showed semiconducting behavior. Similar semiconducting behavior was observed for the same x value, suggesting the weak influence of the different Ln species to the electrical properties.

Polycrystalline samples of KTi1-xNb1+xO5 (x = 0.1, 0.2, 0.3) were synthesized by solid-state reactions. The synthesized compounds were blue-colored, suggesting reduced oxidation states. Single phase KTi1-xNb1+xO5 was obtained for 0 ≤ x &lt
0.2, suggesting that the solubility limit is between x = 0.2 and 0.3. The reduced oxides exhibited semiconducting behavior.

p-Nitroaniline molecules were intercalated between the layers of kaolinite, and an acentric arrangement of p-nitroaniline induced by the asymmteric environment of the interlayer region was accomplished.

p-Nitroaniline molecules were intercalated between the layers of kaolinite, and an acentric arrangement of p-nitroaniline induced by the asymmteric environment of the interlayer region was accomplished.

The thermal transformation of a kaolinite-poly(acrylamide) (PAAm) intercalation compound has been investigated. Acrylamide molecules were intercalated between the layers of kaolinite and were subsequently polymerized by heat treatment at 300 degrees C for 1 h. The kaolinite-PAAm intercalation compound was heated in the range 460-620 degrees C under a nitrogen atmosphere. XRD analysis revealed that carbonaceous materials remained between the layers in this temperature range. The Si-29 and Al-27 NMR spectra of the kaolinite-PAAm compounds heated above 500 degrees C showed that the structural change of aluminosilicate layers was relatively suppressed compared with that of kaolinite itself, indicating that the carbonaceous materials hindered the transformation of aluminosilicate layers. This new finding provides a method for controlling the skeletal transformation of inorganic layered materials upon thermal treatment.

Precursors possessing Ti-N bonds were prepared by the reactions between Ti(NMe2)(4) and each of three diamines H2NCH2CH2NH2, Me(H)NCH2CH2N(H)Me, HN(CH2CH2)(2)NH (Ti(NMe2)(4):diamine = 1:2), and were converted into ceramics by pyrolysis, The reactions with H2NCH2CH2NH2 and HN(CH2CH2)(2)NH led to the formation of insoluble solids, whereas a soluble oil was obtained by the reaction with Me(H)NCH2CH2N(H)Me. The pyrolyses under argon gave carbon-rich Ti(N,C,O) phases, but those under NH3- N-2 resulted in the formation of Ti(N,C,O) phases with higher nitrogen contents. Despite the difference in precursor structures the pyrolysis behavior of three precursors under argon was rather similar, suggesting that the precursor obtained from Me(H)NCH2CH2N(H)Me was effectively crosslinked during pyrolysis. (C) 1998 John Wiley & Sons, Ltd.

Hexagonal mesostructured alkyltrimethylammonium-aluminophosphate materials were prepared by using hexadecyltrimethylammonium and dococyltrimethylammonium chlorides as surfactants and by utilizing 1,3,5-triisopropylbenzene as an auxiliary organic additive. Calcination of these materials at 600 degrees C yielded thermally stable mesoporous aluminophosphate materials with large surface areas above 700 m(2) g(-1) and with pore diameters in the range from 1.8 to 3.9 nm. The hexagonal mesostructured materials before calcination had less condensed frameworks as determined by P-31 MAS NMR, which caused certain shrinkages during calcination for the formation of the porous structures. Water and benzene adsorption data indicated that the mesoporous aluminophosphate materials had comparatively hydrophilic mesopores. (C) 1998 Elsevier Science B.V. All rights reserved.

Carrier doping in Srn+1TinO3n+1 (n = 1, 2) was conducted by the substitution of La for Sr and the simultaneous introduction of oxygen vacancies. Single-phase products of (Sr0.95La0.05)(n+1)TinO3n+1-delta(n = 1, delta = 0.05; n = 2, delta = 0.125) were synthesized by the solid-state reaction of Sr2TiO4 (or Sr3Ti2O7), La2O3 and Ti. When TiO2 was used as one of the starting compounds to maintain oxygen stoichiometry, compounds with higher n were observed besides the object phases. Structural refinement by Rietveld analysis revealed that the a-axis expands while the c-axis contracts with La doping. The contraction of the c-axis is attributed to a shortened (Sr,La)-O distance, since the TiO6 octahedra elongated in both a and c directions with doping. The change in the structure is discussed on the basis of the size of the substituting ion. The resistivity of the single-phase products was semiconducting with a very weak temperature dependence down to 80 K. (C) 1998 Elsevier Science B.V. All rights reserved.

A kaolinite-organic intercalation compound containing methanol was proved to be a versatile host for further displacement reaction with aIkylamines, Kaolinite-organic intercalation compounds with polar molecules, such as N-methylformamide (NMF) and formamide, were used as the starting materials. After stirring the kaolinite-NMF intercalation compound with methanol, the basal spacing increased to 1.11 nm. The C-13 MBS NMR result of the product indicated that methanol was intercalated into kaolinite by partial displacement with NMF. By use of the methanol-treated kaolinite intercalation compound as the intermediate, alkylamines were intercalated into the interlayer space of kaolinite by displacing with methanol.

Polycrystalline samples of MgV2-xTixO4 (0 less than or equal to x less than or equal to 1.8) were prepared by solid-state reactions under an argon atmosphere and their electrical properties were studied. X-ray powder diffraction analysis indicated the formation of the spinel phase as the major compound. Solid solutions were formed throughout the system, as indicated by the monotonic variation of the unit-cell parameter. All the samples were semiconducting below room temperature. A minimum in the activation energy required for semiconduction was observed at x = 1.0. A change in resistivity behavior was observed when the titanium content was increased. For 0 less than or equal to x less than or equal to 1.2, the conduction behavior was interpreted as the hopping conduction of thermally activated electrons, whereas the resistivity behavior for 1.4 less than or equal to x less than or equal to 1.8 was characterized by a weak temperature dependence at low temperatures. (C) 1997 Elsevier Science Ltd. All rights reserved.

The reaction between (HAINPr(i))(m) (Pr-i=CH(CH3)(2)) and [MeSi(H)NH](n) (Me=CH3) led to hydrogen elimination to form a hybrid precursor. Thermogravimetry revealed that the ceramic yield of the hybrid precursor was much higher than those of (HAINPr(i))(m) and [MeSi(H)NH](n), which was ascribed to the hydrogen elimination condensation between the AIH groups in (HAINPr(i))(m) and the NH groups in [MeSi(H)NH](n) during precursor synthesis and pyrolysis. The pyrolyzed product under Ar was a mixture of beta-SiC, beta-Si3N4 and 2H wurtzite-type compound, and the particle sizes were in the range of 20-30 nm.

Triethoxy(alkyl)silanes containing 12-18 carbon atoms in the alkyl groups were hydrolyzed and polycondensed to form ordered structured materials. The XRD pattern of each condensed product showed sharp diffraction peaks with higher orders. The basal spacings approximately corresponded to twice the extended molecular length of the alkyl groups, and increased linearly as a function of the alkyl chain length. The SEM images of the products exhibited a platy morphology, and the (SiCP)-Si-29/MAS NMR spectra revealed the formation of siloxane bonds with various silicon sites from T-1 to T-3 environments. All of these results indicated the formation of highly-organized inorganic-organic layered materials.

The solid solution KCa_<2-x>R_xNb_3O_<10>(R=Nd, Sm, Gd, and Ce) was prepared by solid-state reaction using KCa_2Nb_3O_<10> KNbO_3, Nb_2O_5, Nb and rare-earth oxides. The solubility limit of the solid solutions was extended with an increase in the ionic radii of the rare earths. All the solid solutions exhibited similar semiconductive behavior with a linear log ρ-T relationship over a wide temperature range. These results suggest that the conduction mechanism is independent of the type of rare earths and also the unit-cell parameters, which agrees well with the tunneling conduction model with a vibrating barrier.

The solid solution KCa2-xRxNb3O10 (R = Nd, Sm, Gd and Ce) was prepared by solid-state reaction using KCa2Nb3O10, KNbO3, Nb2O5, Nb and rare-earth oxides, The solubility limit of the solid solutions was extended with an increase in the ionic radii of the rare earths. All the solid solutions exhibited similar semiconductive behavior with a linear log p-T relationship over a wide temperature range. These results suggest that the conduction mechanism is independent of the type of rare earths and also the unit-cell parameters, which. agrees well with the tunneling conduction model with a vibrating barrier.

Polycrystalline samples of stoichiometric spinels, Mg1+xTi2-xO4 (0 less than or equal to x less than or equal to 1.0), and spinels with cation diversity, Mg((1+x)y)Ti2-xO4 and Mg(1+x)Ti((2-x)y)O-4 (x=0.4215, y=0.95-1.05), and oxygen deficiency Mg1+xTi2-xO4-delta (x=0.4215, delta=0.05-0.30) were prepared by solid-state reaction of MgO, TiO2 and Ti to examine the effects of the composition and holding time on the structure of the spinel phase, the impurity phase formation behavior and the electrical properties, In addition to Mg2TiO4 (x=1) prepared at 1300 degrees C under an ambient atmosphere, samples were prepared at 1250 degrees C under an argon atmosphere, Compositional analyses revealed that volatilization of compounds and oxidation during firing were negligible, The variation in the unit cell parameter a of the spinel phase indicated solid-solution formation for all stoichiometric samples in spite of the presence of impurities, The impurity-phase formation behavior was strongly dependent upon synthetic conditions, x-value, and induced nonstoichiometry, Other than the insulating Mg2TiO4, resistivity measurements indicated that all samples were semiconducting below room temperature. No distinct variation in resistivity behavior was observed for samples with different holding time or with induced nonstoichiometry.

A hexagonal mesostructured aluminophosphate was successfully synthesized from the mixture of Al((OPr)-Pr-1)3, 85% H3PO4, tetramethylammonium hydroxide, hexadccyltrimethylammonium chloride, and water.

Hydrolysis and initial polycondensation processes in the Si(OEt)(4)(TEOS)-RSi(OEt)(3)-EtOH-water-HC; systems (R=Me, Ph) [TEOS: RSi(OEt)(3):EtOH:water:HCl=1:1:24:x:y (x=12,2/3; y=2x10(-3), 4x10(-3), 8x10(-2))] have been investigated by using Si-29 NMR spectroscopy. For comparison, the alkoxysilanes [TEOS, MeSi(OEt)(3)(MTES), PhSi(OEt)(3)(PTES)] were hydrolysed separately in a similar manner. In a water-rich TEOS-MTES system (water:Si=12:1), a silanol-terminated codimer [Me(HO)(2)SiOSi(OH)(3)] was detected as well as (HO)(3)SiOSi(OH)(3) and Me(HO)(2)SiOSi(OH)(2)Me, suggesting that the hydrolysed monomers were condensed rather randomly. In contrast, ina water-rich TEOS-PTES system, hydrolysed monomers derived from TEOS and those from PTES were condensed independently; a silanol-terminated codimer [Ph(HO)(2)SiOSi(OH)(3)] did not form, and only (HO)(3)SiOSi(OH)(3) and Ph(HO)(2)SiOSi(OH)(2)Ph were detected. These observations in the TEOS-PTES system suggest the presence of the association of the phenyl groups. In water-restricted systems (water:Si=1:3), monomers were only partially hydrolysed, and ethoxy-terminated codimers [R(EtO)(2)SiOSi(OEt)(3) (R=Me, Ph)] formed in both the TEOS-MTES and the TEOS-PTES systems.

Reactions in an Al(OBu(s))(3)-(COOH)(2) (OA)-tetrahydrofuran (THF)/(CD3)(2)SO (DMSO-d(6)) system (Al(OBu(s))(3):THF:DMSO-d(6):OA = 1:5:5:x, x = 0.01-3) were studied, without the addition of water and the process was monitored by NMR. When x less than or equal to 10.3, homogeneous solutions were obtained, whereas white precipitates formed with x greater than or equal to 0.7. The formation of sec-butyl alcohol was evident with x greater than or equal to 0.6, indicating that oxalate groups coordinate to aluminum to release sec-butyl alcohol. C-13 NMR spectra of the solutions after 1 day suggest the presence of polymeric species if 0.03 less than or equal to x less than or equal to 0.6. The addition of a small amount of water resulted in the formation of a white precipitate (Al(OBu(s))(3):THF:DMSO-d(6):OA:H2O = 1:5:5:0.3:y, y = 0.03-0.3), indicating that water, possibly formed by esterification in the Al(OBu(s))(3)-OA-THF/DMSO-d(6) system, does not take a major role in the present system.

Gallium nitride (GaN) was prepared by the pyrolytic conversion of both [Ga(NEt2)(3)](2) and its ammonolysis product at 600 degrees C for 4 h under Ar. The pyrolyzed residues were analyzed by Xray powder diffraction and scanning electron microscopy, and the pyrolysis processes of the precursors under He were investigated by thermogravimetry-mass spectrometry. The XRD pattern of the pyrolyzed residue of [Ga(NEt2)(3)](2) showed well-resolved peaks due to a mixture of cubic and hexagonal close-packed layers of GaN. The broad XRD pattern of the pyrolyzed residue of the ammonolysis product was also attributed to the mixture of cubic and hexagonal close-packed layers of GaN. For the pyrolysis of [Ga(NEt2)(3)](2), the evolution of hydrocarbons was extensively observed at relatively high temperature, but a large amount of carbon (11 mass%) was still detected in the pyrolyzed residue. On the other hand, the amount of carbon was only 1.1 mass% in the pyrolyzed residue of the ammonolysis product. The pyrolysis results of the ammonolysis product under Ar were very similar to those of [Ga(NEt2)(3)](2) under NH3.

Polycrystalline samples of A(1-x)A'xNbO3 (A=Na+, K+; A'=La3+, Sr2+) were prepared by solid-state reactions and the relationship between the structure and electrical properties was examined. Single-phase products were obtained for Na1-xLaxNbO3 (x less than or equal to 0.1), K1-xLaxNbO3 (x less than or equal to 0.15), Na1-xSrxNbO3 (x less than or equal to 0.3), and K1-xSrxNbO3 (x less than or equal to 0.5). The structures of the sodium-containing compounds and potassium-containing compounds were indexed according to a pseudocubic and cubic symmetry, respectively. The resistivity measurements showed semiconductive behavior for the lanthanum-containing samples. The strontium-containing samples showed semiconducting properties for x less than or equal to 0.2, while a transition to metallic conduction at low temperature was observed for x &gt;0.2.

Aluminium nitride (AIN) powder has been prepared by pyrolysing poly(ethyliminoalane) under Ar (at 1600 degrees C for 2 h) and NH3-N-2 (at 600 degrees C for 2 h under NH3 and at 1350 degrees C for 8 h under N-2) atmospheres, and the products have been characterized by X-ray powder diffraction, solid-state (27)A1 NMR spectroscopy, elemental analysis, scanning electron microscopy, and nitrogen adsorption measurement. The only crystalline product was AIN, in which carbon and oxygen were hardly present by solid-solution formation. A considerable amount (17.1 mass%) of carbon remained in the product pyrolysed under Ar, whereas most of carbon was removed during the pyrolysis under NH3-N-2(0.1 mass%). The AIN particles obtained by pyrolysis under NH3-N-2 were finer than those obtained by pyrolysis under Ar. The ceramic yields were 50% (Ar) and 57% (NH3-N-2); the latter value is close to the theoretical yield (58%).

Aluminum nitride (AlN) was prepared by pyrolysis of poly(isopropyliminoalane) under Ar and NH3/N-2 atmospheres. X-ray powder diffraction analysis revealed that the only crystalline phase was AlN, whose lattice constants showed that possible amounts of carbon and oxygen in the lattice should be very small. Chemical analyses showed the presence of carbon only in the product pyrolyzed in Ar; almost all carbon was removed by pyrolysis in NH3/N-2. The ceramic yield for two-step pyrolysis in Ar (1000 degrees C for 2h, 1600 degrees C for 2h) was 32%, while that for pyrolysis in NH3/N-2 (600 degrees C for 2h in NH3, 1350 degrees C for 8h in N-2) was 47%.

Electron-doped layered perovskite KCa2-xLaxNb3O10 was prepared from KNbO3, Nb2O5, Nb, La2O3 and KCa2Nb3O10 at 1200 degrees C for 10 h under Ar. Essentially single-phase KCa2-xLaxNb3O10 with plate-like morphology was obtained with 0 less than or equal to x less than or equal to 0.3, and lattice parameters increased with increasing x. All the La-doped products showed semiconducting behaviour. Linear (log rho)-T relationships were clearly observed, but the resistivity behaviour deviates from the linear relationship at lower temperatures. A possible conduction mechanism is discussed.

Aluminum nitride (AlN) was prepared by pyrolysis of poly(isopropyliminoalane) under Ar and NH3/N2atmospheres. X-ray powder diffraction analysis revealed that the only crystalline phase was AlN, whose lattice constants showed that possible amounts of carbon and oxygen in the lattice should be very small. Chemical analyses showed the presence of carbon only in the product pyrolyzed in Ar; almost all carbon was removed by pyrolysis in NH3/N2. The ceramic yield for two-step pyrolysis in Ar (1000°C for 2h, 1600°C for 2h) was 32%, while that for pyrolysis in NH3/N2(600°C for 2h in NH3, 1350°C for 8h in N2) was 47%.

Polysiloxane formation in dimethyldiethoxysilane (DMDES)-ethyl alcohol (EtOH(D))-oxalic acid (OA) (DMDES: EtOH(D): OA = 1:2:0.5) and DMDES-dimethylsulfoxide (DMSO)-OA (DMDES: DMSO: OA = 1: 2: 0.5) systems was investigated by gas chromatography-mass spectrometry and Si-29-nuclear magnetic resonance. While the DMDES-EtOH(D)-OA system was homogeneous, the DMDES-DMSO-OA system consisted of two immiscible phases. In both systems, ethoxy-terminated linear oligomers ((EtO)Me2SiO(Me2SiO)(n)SiMe2(OEt); n = 0-4, Et = C2H5, Me = CH3) and cyclic tetramer ((Me2SiO)(4)) were identified. The reaction mechanism for polysiloxane formation is discussed.

The hydrolysis and initial polycondensation processes of methyltriethoxysilane (MTES) have been investigated by high-resolution Si-29-nuclear magnetic resonance spectroscopy (Si-29-NMR). MTES was hydrolyzed in the system with MTES:ethyl alcohol:water:HCl = 1:4:x:y; x = 1, 2, 3, 6; y = 1 X 10(-4), 1 X 10(-2). Signals due to end and middle groups of polysiloxanes formed sub-regions on the basis of the number of hydroxyl groups attached to silicon, and the sub-region for silicon possessing more hydroxyl groups was observed at a lower field. Based on signal intensities, the signals due to the dimers (Me(HO)2SiOSi(OH)2Me and Me(HO)2SiOSi(OH)(OEt)Me) and the trimer (Me(HO)2SiOSiMe(HO)OSi(OH)2Me) (Me = CH3, Et = C2H5) were identified.

The hydrolysis and initial polycondensation processes of methyltriethoxysilane (MTES) have been investigated by high-resolution Si-29-nuclear magnetic resonance spectroscopy (Si-29-NMR). MTES was hydrolyzed in the system with MTES:ethyl alcohol:water:HCl = 1:4:x:y; x = 1, 2, 3, 6; y = 1 X 10(-4), 1 X 10(-2). Signals due to end and middle groups of polysiloxanes formed sub-regions on the basis of the number of hydroxyl groups attached to silicon, and the sub-region for silicon possessing more hydroxyl groups was observed at a lower field. Based on signal intensities, the signals due to the dimers (Me(HO)2SiOSi(OH)2Me and Me(HO)2SiOSi(OH)(OEt)Me) and the trimer (Me(HO)2SiOSiMe(HO)OSi(OH)2Me) (Me = CH3, Et = C2H5) were identified.

The formation of the solid solution Bi-2(Sr2-xCax)CuOy with the 2201 structure has been demonstrated by comparing its lattice parameters with those in Bi2+xSr2-xCuOy and Bi-2(Sr2-xMgx)CuOy systems. The solid-solution range of Bi-2(Sr2-xCax)CuOy has been found to be 0 less than or equal to x less than or equal to 0.15 under the present experimental conditions.

Polycrystalline materials of La1-xMxTiO3(M = Na, K;0≤x≤0.4) were prepared by solid-state reactions under an Ar atmosphere and their electrical properties were investigated as possible candidates for superconducting oxides. XRD analysis showed that the formation of orthorhombic perovskite-type compounds were obtained when × = 0 (LaTiO3) and that pseudo-cubic or cubic phases were obtained when ϗ ≥ 0.1. The lattice constants of the products decreased when × increased, suggesting the formation of solid solutions. There were small deficiencies of the alkali metals. The products in both systems showed semiconductor to metal transitions as temperature decreased when x≥0.1, and striking decreases of resistivity around 25 K were observed in both systems. © 1993, Taylor &amp; Francis Group, LLC. All rights reserved.

A kaolinite-poly(vinylpyrrolidone) intercalation compound has been prepared by the intercalation of an N-vinyl-2-pyrrolidone monomer (VP) and subsequent heat treatment. The intercalation of VP was achieved by treating a kaolinite-ammonium acetate intercalation compound with a VP aqueous solution. The basal spacing decreased from 14.2 to 12.6 , and infra-red spectroscopy (IR) and solid-state 13C nuclear magnetic resonance with cross polarization and magic angle spinning techniques (13C CP/MAS NMR) showed the displacement of ammonium acetate by VP. When the kaolinite-VP intercalation compound was heated at 200°C for 1 h, the basal spacing did not vary. The IR and 13C CP/MAS NMR spectra showed the disappearance of vinyl groups and became similar to those of poly(vinylpyrrolidone) (PVP). These results clearly indicate the polymerization of VP between the layers of kaolinite.

Polysiloxane formation in a tetraethoxysilane (TEOS)-ethyl alcohol (EtOD(H))-oxalic acid (OA) system without the addition of water was investigated by 29Si nuclear magnetic resonance spectroscopy (29Si-NMR). In the system with TEOS:EtOD(H):OA = 1:6:1, considerable amounts of linear oligosiloxanes possessing only ethoxy groups formed, and (EtO)3SiOSi(OEt)3, (EtO)3SiOSi(OEt)2OSi(OEt)3, and (EtO)3Si(OSi(OEt)2)2OSi(OEt)3 were identified. When the amount of OA increased to TEOS:EtOD(H):OA = 1:6:2, the polymerization rate increased considerably. The observed Si-species scarcely possessed hydroxyls, suggesting unique siloxane formation in this system. © 1992 Elsevier Science Publishers B.V. All rights reserved.

The hydrolysis and initial polycondensation processes of dimethyldiethoxysilane (DMDES) have been investigated by high-resolution Si-29 nuclear magnetic resonance spectroscopy (NMR) in a variety of acidic systems (DMDES:ethyl alcohol:water:HCl = 1:4:x:y; x = 2 or 4, 1 x 10(-5) less-than-or-equal-to y less-than-or-equal-to 1 x 10(-2)). On the basis of the behavior of signal intensities, those due to the following monomers and oligomers have been identified: Me2Si(OEt)(OH), Me2Si(OH)2, Me2(HO)SiOSi(OH)Me2, Me2(EtO)SiOSi(OH)Me2, Me2(EtO)SiOSiMe2OSi(OH)Me2, Me2(HO)SiOSiMe2OSi(OH)Me2, (Me2SiO)3, Me2(HO)SiO(SiMe2O)2Si(OH)Me2, and (Me2SiO)4 (where Me = CH3, Et = C2H5). It was shown that the substitution of the hydroxyl group for the ethoxy group resulted in an upfield shift of a signal, which was not consistent with the previous observations in tetra-functional alkoxysilane systems. In the course of the polycondensation process, cyclization reactions became predominant to form a considerable amount of the cyclic tetramer directly from the completely hydrolyzed dimer (Me2(HO)SiOSi(OH)Me2).

Aluminum nitride (AIN) was formed by two-step pyrolysis of poly (isopropyliminoalane) in Ar. The product pyrolyzed at 1000-degrees-C was an amorphous material. Solid-state Al-27-nuclear magnetic resonance spectroscopy (NMR) showed that an AlN-like structure was present in the product. Heat treatment of the pyrolyzed product at 1600-degrees-C yielded crystalline AlN from the amorphous material.

The intercalation of tris-bipyridyl metal complexes (M(bpy)3 2+, M=Ru, Ni, and Co) into the interlayer region of vanadium pentoxide gel (V2O5·nH2O) was confirmed for the first time. The intercalation of the guest species was conducted by the reaction of the complexes with undried V2O5 gel. The saturated amount of adsorbed M(bpy)3 2+ was less than the ion exchange capacity of the V2O5 gel because of bulkiness of M(bpy)3 2+. The transition temperature to orthorhombic V2O5 was higher than that of original V2O5 gel, indicating the stabilization of the layered structure by the intercalation. © 1991.

The structure and distribution of chemical species of hydrolysis and polycondensation products of methyltriethoxysilane in aqueous solutions containing sodium ions have been studied with the trimethylsilylation technique and by <29>^Si n. m. r. spectroscopy. 11 trimethylsilylated derivatives of the products were obtained from the solutions. The recovery of methyltrisilanol (CH_3Si(OH)_3) was much higher than that of the monosilicic acid in an aqueous sodium silicate solution; at the same Si concentration and the same sodium ion-to-silicon molar ratio, suggesting that the polymerization of silicate anions is easier than that of hydrolysis products of methyltriethoxysilane in aqueous solutions. On the basis of the distribution, assignment of <29>^Si n. m. r. peaks corresponding to low-molecular weight species formed from methyltriethoxysilane has been discussed.

In order to investigate the possibility of the use of 1:1 type clay minerals as raw materials for nitride production, kaolinite and antigorite were converted into nitrides by carbothermal reduction. Kaolinite or antigorite was mixed with carbon in two separate experiments. The resulting mixture was heated in N2. Kaolinite was converted into β'-sialon and AIN. Kaolinite was initially transformed into cristobalite and mullite, which were then reduced. In addition to the nitrides, SiC and α-Al2O3 also formed as the reactions proceeded. Essentially, both the SiO2 and Al2O3 components were converted into nitrides and oxynitrides by carbothermal reduction. From the antigorite-carbon mixture, α- and β-Si3N4 were obtained. Forsterite initially crystallized and was reduced. Additionally, MgSiN2 and MgO formed during the conversion. α-Fe and FexSi were also detected. MgSiN2 seemed to act as an intermediate for Si3N4 formation. Therefore, all the Mg-containing phases can not be present as nitrides finally
magnesium was lost as the reactions proceeded. © 1989.

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To develop a carbothermal reduction process for the conversion of oxides to nitrides, a montmorillonite-polyacrylonitrile (PAN) intercalation compound was applied as a precursor. Montmorillonite-carbon mixtures were heated as well as the intercalation compound in N2 at 1100 to 1500° C for comparison. From the intercalation compound, β-sialon, AIN and SiC were mainly formed. Oxides were reduced without their crystallization. On the other hand, in the reactions of the mixtures, some oxides and other kinds of nitride were obtained as principal products in addition to these phases. Furthermore, the intercalation compound was more favourable than the mixtures having a larger amount of carbon in terms of the reduction of oxides and the formation of nitrides. These observations suggest that the layered structure of the intercalation compound led to an effective and specific carbothermal reduction process. © 1988 Chapman and Hall Ltd.

An inclusion compound between zeolite and polyacrylonitrile has been applied as a precursor for the carbothermal reduction process. By heat treatment at 1400 to 1600° C in N2, β-sialon was mainly obtained. The X phase, α-Si3N4, the 15R-AlN phase, AIN, and mullite also formed under certain firing conditions. On the other hand, α-Si2N4 was detected as the principal crystalline phases as well as β-sialon in the products from zeolite-carbon mixtures. Hence, the use of the inclusion compound was advantageous for β-sialon production in the conversion of zeolite to nitrides. © 1988 Chapman and Hall Ltd.

Methyl viologen has been intercalated into the interlayer space of layered tetratitanic acid by a method involving the displacement of guest molecules using an n-propylammonium tetratitanate intercalation compound. The viologen tetratitanate intercalation compound changed colour to blue when irradiated by a mercury lamp under vacuum conditions or a nitrogen atmosphere. The formation of radical cations was confirmed by visible and e.s.r. spectroscopy. The electron donor for the photoreduction is thought to originate from the tetratitanate layers. The colour was stable as long as the vacuum conditions were maintained, and fading did not occur rapidly even after the introduction of air, requiring &gt
1 h for the colour to fade completely. These results indicate remarkable stability of the viologen radical cations in this intercalation compound.

A precursor prepared from a methyltriethoxysilane ((CH3)Si(OC2H5)3, MTES)-B(OC2H5)3-polyacrylonitrile (PAN) composition was used for the synthesis of boron-doped SiC by carbothermal reduction. Initially, MTES was hydrolyzed with HCl (MTES: H2O: HCl = 1 : 1 : 0.01) for 1 h in a sealed vessel. The number-average molecular weight measurement and a NMR spectrum revealed that the species in the solution were mainly oligometric. With the addition of B(OC2H5)3, no significant changes in the distribution of the Si containing species were detected. The mixing of the hydrolyzed solution with a PAN-dimethylsulfoxide solution led to a homogeneous solution. After the evaporation of the solvents and the subsequent heat treatment at 220° C, brown precursor powder was obtained. By the heat treatment at 1600° C in Ar, it was converted to boron-doped SiC powder. © 1988.

As a precursor for AlN production by carbothermal reduction, a hydrotalcite (layered magnesium-aluminum double hydroxide)-polyacrylonitrile (PAN) intercalation compound has been prepared for the first time. After the layers were expanded by the replacement of the interlayer anions with the CH3(CH2)11OSO3- ions, the acrylonitrile monomer was intercalated and subsequently polymerized. By the heat treatments at 1100°C-1600°C in N2, AlN, MgO and MgS formed. MgO was detected in the products heated up to 1300°C. MgS formation was observed in the reactions below 1500°C. On heating at 1600°C, single phase submicron AlN grains were obtained. © 1988.

Only β-sialon was obtained from n-alkylammonium-montmorillonite-polyacrylonitrile (PAN) intercalation compounds in the carbothermal reduction process at 1100°C in N2. Very little oxide crystallized during the conversion. However, an amorphous phase was still present after treatment for 6 h. The main constituent metals in montmorillonite (Si, Al, Mg, and Fe) were mostly retained during the treatment. Since similar XRD patterns were obrained from two kinds of intercalation compounds, having different carbon contents, the suppression of the formation of other phases was not subject to the amount of carbon. When a montmorillonite-carbon mixture having a larger amount of carbon was heated at 1150°C for 6 h, oxides were mainly formed. Therefore, the intimate mixing in the 2D structure of the intercalation compounds resulted in a lower threshold temperature for β-sialon formation, at which other phases did not form. © 1988.

A magadiite (layered polysilicate)-polyacrylonitrile (PAN) intercalation compound was first prepared to investigate its potential as a precursor for the synthesis of non-oxide ceramics by carbothermal reduction. Acrylonitrile monomer was intercalated and polymerized in the interlayer space of a C₁₂H₂₅N(CH₃)₃-magadiite complex. After the cyclization of PAN by the heat treatment in air, the compound was heated in Ar flow for 2h. Above 1300°C, β-SiC was formed without the formation of any crystalline SiO₂ phases. Since the reactions of a magadiite-carbon mixture involved the formation of cristobalite, it was shown that SiO₂ from magadiite was reduced to form β-SiC without crystallization, which was caused by the presence of PAN in the interlayer space.

Silicon nitride was formed from a magadiite (layered polysilicate)-polyacrylonitrile (PAN) intercalation compound through a novel process of carbothermal reduction. SiO₂ from magadiite was reduced above 1400°C without the formation of any crystalline oxides. On heating above 1400°C, both α-and β-Si₃N₄ were detected, and the additional formation of α-and β-SiC was observed by heating at 1600°C. On the other hand, the reactions for the synthesis from a magadiite-carbon mixture involved the formation of cristobalite as well as α-and β-Si₃N₄, and β-SiC. In addition, it was also indicated that the mixture was less reactive for the formation of Si₃N₄. These observations suggest that the reaction process of the magadiite-PAN complex was different from that of the magadiite-carbon mixture, and that the use of the intercalation compound was favorable for Si₃N₄ production.

To establish a new method for the carbothermal reduction process, the conversion of the montmorillonite-polyacrylonitrile (PAN) intercalation compound to nitride and carbide ceramics was studied. In the case of Ar atmosphere, the formation of SiC was observed above 1200 degree C. alpha -SiC was detected above 1300 degree C, while beta -SiC was formed above 1200 degree C. As oxides, Mg-Al-O compound was detected above 1300 degree C. On the other hand, the formation of beta -sialon and SiC was observed by the treatment in N//2 atmosphere above 1200 degree C. AlN was also detected above 1300 degree C. In these processes, the reaction route became unique because of preventing the crystallization of oxides. This fact was ascribed to the presence of PAN in the interlayer space.