Image analysis has been applied to the TEM observation of activated carbon fibers, in order to evaluate the pore structure visually. It is suggested that the present method can show the shape of the pores as well as providing a quantitative estimation of the pore structure. The results are consistent with those obtained by common gas adsorption method and with synthesized molecular graphics TEM images of pores. The pore analysis on activated carbon fibers by TEM combined with image processing can provide a powerful tool to characterize the porous structure of activated carbons from a different new viewpoint.
Ordered mesoporous silicas with spherical morphology and average particle size in the range between 100 nm and 2 μm were synthesised according to two novel routes. Both synthesis routes used tetraethoxysilane, water, alcohol and aqueous ammonia for producing spherical silica beads. The porosity was created by adding two different kinds of pore structure directing agents to the starting solution: one was an n-alkyltrialkoxysilane which was covalently bonded to the silica framework, the other was an n-alkylamine which acted as a nonionic template. After calcination and post treatment the resulting particles showed a specific surface area up to 1000 m2 g-1, a specific pore volume of up to 0.8 cm3g-1 and an average pore diameter between 2 and 6 nm.
A new type of optically active organic-inorganic composite was prepared by a sol–gel method in which tetraethoxysilane (TEOS) is hydrolyzed in the presence of an optically active organic compound (d-lactose, d-glucose, d-sorbitol, d-fructose, l-tartaric acid, l-malic acid, or l-mandelic acid). Optical resolution of tris(pentane-2,4-dionato)metal complexes was performed by using the new sol–gel derived composites, composites prepared by conventional techniques (kneading with l-lactose, l-fructose or l-tartaric acid, and impregnation with an l-lactose, l-fructose or l-tartaric acid solution) and the optically active organic compounds themselves. The sol–gel derived composites showed much higher optical resolution abilities than the composites prepared by conventional techniques. In addition, the optically active organic compounds could not resolve the racemate into the enantiomers under similar conditions. X-ray diffraction and NMR results disclosed that an optically active organic compound in the sol–gel derived composite is highly dispersed, most likely, because it bonds to silicon atoms. Thus, it was deduced that optically active molecules dispersed at a molecular level recognize the chirality of the metal chelate compound. The high-resolution ability of the sol–gel derived composites arises from the combined effect of the silica support (adsorbing power) and the highly dispersed molecules (chiral recognition power).
The Si-C-(Ti)-O inorganic fibers prepared by pyrolyzing poly(titano) carbosilane organic polymer precursors are well known to keep a very high tensile strength of about 250 kg mm(-2) at high temperatures above 1000 degrees C in air for several hours. The structural evolution during the organic-to-inorganic conversion was measured by small angle X-ray scattering (SAXS) using a point-collimated Cu K alpha X-ray beam and a two-dimensional imaging plate detector. The SAXS profile for the fibers generally comprises two components; an anisotropic scattering observed in the lower q region (< 0.07 Angstrom(-1)) and an isotropic one in the higher q region (> 0.1 Angstrom(-1)), where q = 4 pi sin theta/lambda is the scattering vector. The isotropic SAXS profiles, which sensitively depend on the pyrolyzing temperature, are contributed from the beta-SiC nanoparticles embedded in the amorphous matrix of the fibers. The very high mechanical strength of the Si-C-(Ti)-O inorganic fibers originates from the formation of a carbon-rich shell-like interface boundary surrounding the beta-SIC nanoparticles which is sharply separated from the amorphous matrix. (C) 1998 Elsevier Science Limited. All rights reserved.
Periodic functions are designed from the Gauss distribution function and from the fundamental theorem of algebra. These functions can be used to describe the outer shape as well as the inner structure of particles. A function has been found that forms a link between the circular functions and the Gauss distribution function.
Function follows conformation in biological macromolecules. In general there are a number of possible conformational states. Which state is favored is determined by physicochemical context. The fusion of the features that comprise this context to form a particular conformational state is at the core of cellular control and biological information processing. We have developed a simulation system to investigate the information processing capabilities of networks of context-sensing macromolecules (to be illustrated by a simple example).
Embedding structures of a metal nanoparticle in an oxide matrix were first achieved by electron beam irradiation. In the system of Al/α-Al2O3. Al nanoparticles derived from θ-Al2O3 migrated and embedded in α-Al2O3 matrix having epitaxy relation, {112̄0}α-Al2O3//{200} Al. The driving force of the embedding is momentum transfer from electrons or ions to Al atoms of nanoparticles in the pole piece of transmission electron microscopy.
The passage of adsorbed molecules, through pores of nanometre dimensions, under a concentration gradient, is important in several processes. The basic equations for single-component flow in pores identify a diffusive and cooperative (viscous) component to the flux. Three simulation techniques, including non-equilibrium molecular dynamics (NEMD), have been used to investigate (spherical) methane and ethane adsorbates in model graphite pores at ambient temperatures. The NEMD method measures flux directly and shows an interesting behaviour in the total diffusion coefficients, including transitions and values substantially in excess of the Darken diffusion coefficient, calculated from self-diffusion. A simple Stokes–Einstein type of model can account for some results. The instances where this model fails can be rationalised in terms of confinement effects, and the relative contribution of kinetic energy to the Hamiltonian.
A thin film made of an ion-exchangeable layered compound, K4Nb6O17, was prepared by a novel method. Fine particles of K4Nb6O17 obtained by wet-grinding of the powder were coated on a substrate and calcined. Recrystallization of the fine particles at 1073K was confirmed by XRD and SEM, and very flat and large crystals with the b-axis perpendicular to the substrate surface were obtained. The obtained thin film had a layered structure and an ion-exchange property similar to that of K4Nb6O17 powder. The adsorption of CO was investigated for the thin film calcined at 1073K by IR spectroscopy. The initially IR-inactive H+ species were suggested to be transformed into OH groups as a result of CO adsorption at the interlayer space.
Surface pressures of Langmuir (L) films of fullerene C60 were measured as a function of surface area. The occupied area of L film prepared from a solution of 0.1mgcm-3 was too small in comparison with the expected molecular area. On atomic force microscopic photographs of Langmuir-Blodgett (LB) films of fullerene C60 transferred on a mica substrate, particles with ∼1300Å diameter and ∼150Å height were observed. Particles aggregated to form flocs. This aspect corresponds to the fractal aggregation of C60 crystalline islands and explains smaller occupied area. The formation process of L films was discussed. Strong attractive interaction between fullerenes and steric repulsive interaction between islands were suggested.
X-ray reflectivity (XR) measurements were carried out for amphiphilic diblock copolymer monolayers on water surface. From XR data, the layer thickness, and surface and interface roughnesses could be determined as a function of surface pressure. The XR experiments were performed using an 'Air-Water Interface X-ray Reflectometer' with conventional X-ray source (Cu target) in our laboratory. LB trough was equipped to the reflectometer: so the in situ measurements could be carried out for spread monolayers on water surface at different surface pressures. Kiessig fringes were observed for specular measurement for amphiphilic diblock copolymer, poly(alpha-methylstyrene)-poly(decyl 4-vinylpyridine) (P(alpha MSt)-b-P(4VP-C10H21I)) monolayers on water surface. It was observed that the thickness of the monolayer became thicker with increasing surface pressure. By curve fitting for the data obtained for the monolayer at surface pressure of 37 mN m(-1), the thicknesses of P(alpha MSt)(50) and P(4VP-C10H21I)(50) layers was determined to be 21 and 22 Angstrom, respectively. Because the chain length of P(alpha MSt)(50) is calculated to be 126 Angstrom in all-trans conformation, it was indicated that the molecules did not get aligned even when they were pressed to become such a dense state. (C) 1998 Elsevier Science Limited. All rights reserved.
Towards the morphology control of oriented porphyrin aggregates by added saccharides, three amphiphilic porphyrins bearing boronic acid groups were synthesised. Among them, an amphiphilic tetraphenylporphyrin (4) bearing two octadecyl groups at 5,10-positions and two boronic acid groups (acting as saccharide-binding sites) at 15,20-positions has been found to act as a membrane-forming amphiphile in an aqueous system. Spectroscopic (UV–Vis and CD), light-scattering, DSC and electron micrographic studies have established that in aqueous media 4 forms stable fibrous aggregates only in the presence of saccharides, which are chirally twisted by the absolute configuration of the added saccharides. This is a novel method to control the aggregate morphology by saccharides and well imitates the morphological functions of certain cell membranes, the surfaces of which are covered by saccharides.
Our recent studies on the simple synthetic route to the thin films of the periodic silica-surfactant mesostructured materials are summarized. By depositing the mixtures of the prehydrolyzed tetramethoxysilane and alkyltrimethylammonium salts under anacidic condition on solid supports, transparent thin films of the periodic silica-surfactant mesostructured materials formed. The resulting transparent films have been used as a precursor of the porous silica films and a support for organic photoactive species. Compared with other reported reactions for the silica-surfactant mesostructured materials, this method possesses advantages such as the ease of operation and the possibility to control microstructure and macroscopic morphology.
Unusually sensitive wavelength dependence of hole-burning efficiency in oriented J-aggregates is explained by the hierarchical structure of one-dimensional J-aggregates proposed by us from the experimental results of the concentration dependence of the dichroic spectra.
Nanostructured metal clusters are often stabilized by surrounding with synthetic polymers. The most popular application of metal clusters is as catalysts for various chemical reactions. The catalysis of metal clusters can be compared to the action of enzyme. Thus, the surrounding polymer of metal clusters can be assigned as a polymeric field and has the functions similar to the protein surrounding the active site of enzyme. Interaction between surrounding polymers and reactive substrates can affect the activity and selectivity of the metal cluster catalysts. Polymers play an important role not only in the catalytic process but also in the formation process of metal clusters. Polymers not only stabilize the metal clusters at a nonequilibrium state, but also control the nanostructure of metal clusters, especially the core/shell structure of bimetallic clusters by coordination interaction.
The planar oxomolybdenum(IV) and Fe(II) tetraphenylporphyrins (tpp) and fullerene C60 are encapsulated by monolayer dispersion technique in the mesoporous ordered channels(2.7, 4.7nm diameter) of FSM-16. They exhibit a stoichiometric adsorption of O2 at 300K and 50–250Torr forming a 1:1 dioxygen complexes(ν(O–O)=928 and 1025cm-1) with MoIVO(tpp) and FeII(tpp) entrapped in FSM-16, although the Mo(=O) and Fe porphyrins are inactive for O2 uptake in crystal and solution. The mesoporous cylindrical channels of FSM-16 act as the confined hydrophobic circumstances to accommodate isolated Mo and Fe porphyrins and prevent the irreversible formation of a paramagnetic μ-oxo dimer, similar to the picket-fenced porphyrin complexes such as MoIVO(tmp)=5,10,15,20-tetramesitylporphyrin). The reversible removal of O2 bound with the Mo and Fe porphyrins proceeds at 300K by high-pressure Hg photoirradiation. The isotopic labeling tracer studies reveal that they are catalytically active for oxygen transfer via fullerene C60 in the selective photo-oxidation of propene towards acetone at 303–393K.
The self-assembly between hexakis(4-carboxyphenoxy)cyclotriphosphazene (1) and hexakis(4-pyridylcarbinoxy)cyclotriphosphazene (2) was investigated. FT-IR spectra and elemental analysis of crystals (3) obtained from a solution containing 1 and 2 in equimolar ratio in DMF suggested that all the carboxyl groups in 1 interact with pyridyl groups in 2 to form a 1:1 complex. The X-ray analysis of 3 showed that the crystals, defined by R=0.054 based on 4212 data, I>3.0σ(I), are monoclinic, space group P21/n with a=13.636(6), b=24.71(1), c=23.56(1)Å, β=102.36(3)°, V=7754(6)Å3, and Z=4. The hydrogen bonded NHO distance ranges from 2.61 to 2.82Å with an average distance 2.69Å and the phenoxy group in the crystals stacked with pyridyl group in the neighboring molecules, leading to the construction of 1:1 1–2 cylindrical structure 3. The characterizations of self-assembly 3 based on cyclophosphazene derivatives are described.
Polymeric receptors for cholesterol were synthesized by crosslinking β-cyclodextrin (β-CyD) with hexamethylene diisocyanate or toluene 2,4-diisocyanate in dimethyl sulfoxide (DMSO) in the presence of cholesterol as the template. Non-imprinted β-CyD polymers were much poorer in the cholesterol adsorption. When β-CyD was cross-linked by epichlorohydrin in aqueous alkaline solutions (even in the presence of cholesterol), the cholesterol adsorbing activity was nil. Use of DMSO as the cross-linking solvent is necessary for the imprinting, since β-CyD molecules form inclusion complexes with cholesterol in this solvent and thus their mutual conformation in the polymer is regulated appropriately for cholesterol binding. The adsorbed cholesterol was completely removed from the polymers by treating the adducts with ethanol, indicating a strong potential for practical applications.
This work describes a new strategy in which a crystalline bacterial cell surface layer (S-layer) composed of a monolayer of a single protein species was used as periodic nanometric template in the nucleation of ordered arrays of gold nanoparticles. A square superlattice of uniform 4 to 5nm sized gold particles with 12.8nm repeat distance was fabricated by exposing the S-layer lattice of Bacillus sphaericus CCM2177, in which thiol groups had been introduced before, to a tetrachloroauric(III) acid solution. Transmission electron microscopical studies showed that the gold nanoparticles were formed in the pore region during electron irradiation of an initially grainy gold coating covering the whole S-layer lattice. The shape of the gold particles resembled the morphology of the pore region of the square S-layer lattice. By electron diffraction and energy dispersive X-ray analysis the crystallites were identified as gold (Au(0)). Electron diffraction patterns revealed that the gold nanoparticles were crystalline but in the long range order not crystallographically aligned. It is postulated that S-layers will allow the fabrication of a wide range of inorganic nanocrystal superlattice arrays.
The dynamic range improvement and realization of the acousto-optic spectrum analyzer are reported. When two RF signals of equal strengths and frequencies f1 and f2 are applied simultaneously to the signal Bragg cell, the analyzer demonstrates a dynamic range of 50dB and frequency resolution 10kHz.
