Tadahiro Ishii

Dispersion and Purification of Single-Wall Carbon Nanotubes Using Carboxymethylcellulose

We have developed a novel method for the purification of single-wall carbon nanotubes (SWNTs) that involves annealing in air and dispersing the SWNTs in an aqueous solution of carboxymethylcellulose (CMC). The purity of the resulting SWNTs was evaluated by analytical techniques such as electron microscopy, Raman spectroscopy, and thermogravimetric analysis (TGA). As a result, it was revealed that CMC functioned as an effective dispersion reagent in the exfoliation of the SWNT bundles and thereby, SWNTs with appreciably high quality were prepared.

Detection and average content levels of carcinogenic and mutagenic compounds from the particulates on diesel and gasoline engine mufflers

Abstract Carcinogenic and mutagenic compounds, which were extracted from the particulates that adhered to inner surfaces of diesel and gasoline engine mufflers, were quantified by the series method of Soxhlet extraction, liquid-liquid partition, thin-layer chromatography, and spectrofluorometry. Mutagenic activity of their neutral and acidic fractions was tested in the improved Ames assay by the preincubation method with Salmonella typhimurium TA98 in the presence and absence of metabolic activation system (S-9 mix). The average content levels (μg/g tar) of polycyclic aromatic hydrocarbons from gasoline engine cars were greater than those from diesel engine vehicles. However, the levels of nitro derivatives of PAHs and polycyclic quinones from the diesel engines were greater than from the gasoline engines. Mutagenic activity of the diesel acidic fraction was the highest among the diesel and gasoline fractions, and was significantly higher in the absence of the S-9 mix. Furthermore, the relative value ( R c = 0 ) of infrared absorption of carbonyl stretching vibration to that of methylene asymmetric stretching vibration of the diesel acidic fraction was the highest among the diesel and gasoline fractions. These results strongly suggest that highly direct-acting mutagens in the acidic fraction are at higher levels in diesel emission particulates than those from gasoline, and that these mutagens are carboxylic acid, aldehyde, and alcohol derivatives of PAHs and NPAHs.

Correlation between the concentrations of polynuclear aromatic hydrocarbons and those of particulates in an urban atmosphere.

The new technique for preparation of gases of a known concentration presented here makes it possible to prepare gases for environmental measurements and studies. The apparatus and operations of this technique are simple. The stability of the concentration of gas generated from the generator is excellent and the generation sustains for several hours a t least. The concentration varies to a smaller extent with changes in temperature and air flow rate than with the permeation tube technique. The prepared gas contains some water vapor which is preferred for experiments meant to simulate the real atmosphere. In this paper, SOz, NO, NOz, HCN, HzS, and NH3 gas generation was described, but other gases such as hydrogen fluoride and carbon dioxide can also be prepared by the same technique.

Concentration distribution of conducting species with time resolution in electrochemical undoping process at the polypyrrole-film-coated electrode in the light of electric percolation

Concentration distribution of conducting species of polypyrrole films in the electrochemical undoping process was determined by a spectroscopic method using a photodiode array in the simulated film experiment. A polypyrrole film in the doped state was set on an insulating glass plate and connected to an electrode at the end of the film. The length of the film corresponds to the film thickness in the ordinary experiment of film-coated electrodes. The film was reduced or undoped by the potential step. Absorbance responding to the potential step was monitored at 14 segments of the film by the photodiode array with effective spatial resolution of 0.36 mm. Then the concentration distribution of the oxidized conducting species was determined every 50 ms. The conversion occurred not only near the electrode but also at the top of the film. It stopped at the conversion ratio 0.87. 13% of the conducting species was left behind from the reduction in the uniform distribution. The incomplete conversion was attributed to electrical disconnection of conducting clusters from the electrode on the basis of the percolation theory.

Characterization of water contribution to excimer laser ablation of collagen

Abstract In order to gain an obvious insight into the role of water in the mechanism of the excimer laser ablation of the cornea, we have macroscopically investigated the ablation behavior of collagen gel in the swelled state by direct photoetching using an ArF excimer laser with time-resolved photography, and furthermore, the thermal effects on the microscopic structures of the collagen molecules by FTIR–ATR spectroscopy. The hydrated collagen film (HF) has a smaller threshold fluence than the dried collagen film (DF). From the time-resolved photographs, the ejected materials were detected only for HF. It was predicted that the effect of bubble formation for HF contributes to the etching. The FTIR–ATR spectroscopic results revealed that the existence of the water suppressed the denaturation of the collagen to gelatin on the surface in the irradiated region. Overall, it was inferred that during the ablation process for HF, the laser energy would be mostly consumed as the latent heat of evaporation of water, that is, the water in the gel matrix would contribute to the suppression of the increment in the temperature in the irradiated region.

Concentration profiles of conducting species in polypyrrole films in cyclic voltammetry by means of a diode array detector

The first scan effect, which makes the voltammetric anodic peak of conducting polymers sharp and shifted in the positive direction only on the first scan, was investigated by determining the time-dependent concentration distribution of conducting species of polypyrrole films by means of the UV-visible diode array system with spatial resolution of 0.36 mm. The film in the insulating state was set on a glass plate and connected to an electrode at the end of the film. This experimental set-up corresponds to magnifying the film thickness by three or four orders of magnitude. On the first positive scan, a steep part of the concentration profiles was propagated from the electrode towards the top of the film, exhibiting a clear phase boundary. The anodic peak of the voltammogram appeared at the time when the conducting front reached the top of the film. In contrast, the conversion during the negative scan proceeded uniformly over the film and stopped at a conversion ratio of 0.9, which was regarded as a threshold value of the electric percolation. The second positive scan made the profile smooth. The dependence of the profile on the scanning direction agreed with the voltammetric features. The faradaic component of the voltammogram was constructed from the profile, and compared with the ordinary voltammogram.

Alternation of conducting zone from propagation-control to diffusion-control at polythiophene films by solvent substitution

The conducting zone of polythiophene films grew under the propagation-control in acetonitrile solution at application of the positive potential to the reduced film whereas it grew under the diAusion-control when it was transferred into the propylene carbonate solution. The electrochemically polymerized film was peeled oA from the electrode, and a current feeder was connected to an end of the film. The distribution of the conducting species was detected with a diode array detector through the 850 nm beam irradiated to the film. When the fully reduced film was oxidized potentiostatically in the 0.1 M LiClO4+acetonitrile solution, the conducting zone developed linearly with the electrolysis time at almost a constant speed. This is in accord with the theory of the propagation of the conducting zone. When the reduced film was transferred into the 0.1 M LiClO4+propylene carbonate solution, the conducting zone grew exhibiting a vague boundary. Quantitative analysis said that the growth obeyed at first the propagation theory and then obeyed the square root of the time, represented by diAusion of dopant ions. The diAusion coeAcient was 310 ˇ10 cm 2 s ˇ1 . A new growth model was proposed, in which the filmvsolution interface was oxidized at first by the propagation mechanism and then the conducting zone was dispersed into the film center by diAusion. # 1999 Elsevier Science Ltd. All rights reserved.

Preparation of Iron Ultrafine Particles by the Dielectric Breakdown of Fe(CO)5 Using a Transversely Excited Atmospheric CO2 Laser and Their Characteristics

Iron ultrafine particles containing the γ-phase in a relatively high yield of approx. 50% were prepared by the dielectric breakdown of Fe(CO)5 upon irradiation with a tightly focused laser beam of a transversely excited atmospheric (TEA) CO2 laser. CO is also obtained as a volatile product. The iron particles are fine and isotropic in shape. The particle size is in the range of 9–16 nm with a mean particle size of 13 nm. In X-ray diffractometry, the iron ultrafine particles are found to be a mixture of fcc γ-iron which is normally stable only in the range of 1183–1662 K, bcc α-iron, and iron oxides with a weight ratio of γ-iron:α-iron:iron oxides=42:46:12. The γ-phase thus obtained is paramagnetic at least at 1.8–295 K, and transforms into ferromagnetic bcc α-iron above 473 K, with almost complete conversion into α-iron at 653–693 K Formation of γ-iron ultrafine particles by the dielectric breakdown of Fe(CO)5 is discussed and compared with that by the SF6-sensitized photodecomposition of Fe(CO)5.

Carbon-13 Separation by IRMPD of mixtures of C2F6 and Br2

Abstract The infrared multiple-photon decomposition of mixtures of C 2 F 6 and Br 2 has been examined as functions of various experimental parameters. Carbon-13 was found to be enriched in the main product CF 3 Br; the maximum enrichment factor was 35. The combination of this process with the IRMPD of CF 3 Br provides a closed chemical cycle for efficient carbon isotope separation

Photo-crosslinking polymers by fullerene

Abstract Photochemical addition of furan derivatives to fullerene C60 was applied to the photo-crosslinking of polymers with C60. A polymer having furan units in the side chains was synthesized by the reaction of poly(2-hydroxyethylmethacrylate) with 2-furoic chloride. A 1,1,2,2-tetrachloroethane solution of the polymer was exposed to visible light in the presence of C60. The solution turned to a gel after 10 h and then solidified completely. The photo-crosslinking process was monitored in situ by dynamic viscoelasticity measurement.