Hironori Orikasa

A study of the CNO reaction by using isotopically labelled C and NO

The role of O- and N-containing surface species in the course of NO reduction over phenol-formaldehyde resin char and amorphous 13C was investigated. The presence of O-containing complexes on the char surface was shown to increase the reactivity towards NO by providing free reactive sites. The presence of O2 also enhanced the NO reduction reaction greatly. A mass balance during temperature-programmed reaction indicated nitrogen accumulation on the char surface. The reaction mechanism was examined by a transient kinetic approach, in which the reactant gas was switched from 14N16O to 15N18O. The surface N-containing species produced and accumulated in the first stage, C(14N), was found to react with 15N18O, yielding 14N15N. This indicated that one N2 formation path is the reaction between nitrogen-containing surface compound and NO.

Brilliant and tunable color of carbon-coated thin anodic aluminum oxide films

When a thin anodic aluminum oxide (AAO) film on an Al substrate is uniformly coated with carbon by chemical vapor deposition, the saturation of interference color is substantially enhanced and, as a result, the coated AAO film exhibits a brilliant color. Such remarkable saturation enhancement is predominantly due to the carbon deposited on the inner walls of nanochannels of the AAO film, which efficiently screens the reflected light from AAO–Al interface. The brilliant carbon-coated AAO film is useful for weather-resistant decorative purposes and holds promise as an effective broadband optical limiter for nanosecond laser pulse.

Fabrication of densely packed multi-walled carbon nanotube ultrathin films using a liquid–liquid interface

We describe the fabrication of a densely packed ultrathin film of multi-walled carbon nanotubes (MWCNTs) at a liquid–liquid interface. The MWCNTs, which were synthesized using an anodic aluminium oxide (AAO) film as a template, were dispersed in water. Then hexane was added to the dispersion to create the liquid–liquid interface. The MWCNTs were smoothly assembled at the interface to form an ultrathin film when ethanol was added to the MWCNT water dispersion/hexane solution. The ultrathin film can be transferred onto a solid substrate using the Langmuir–Blodgett deposition technique. With addition of 10 vol% ethanol to the solution, an ultrathin film of MWCNTs with coverage of about 70% was fabricated. The multilayer film was fabricated by repeated deposition of the ultrathin film.

Reaction of NO with soot over Pt-loaded catalyst in the presence of oxygen

Abstract NO x and particulate matter are the main environmental hazards in the diesel exhaust. In order to explore a suitable method to remove NO X as well as particulate matter, we have examined the catalytic reduction of NO X with soot in the presence of oxygen. Pt catalyst loaded on Al 2 O 3 -coated honeycomb was found to be more active than K, Ca and Cu catalysts. Even in the presence of 8% O 2 , NO can be reduced to N 2 by soot with Pt catalyst. NO was completely converted to N 2 in the isothermal reaction at 500°C, and the high activity of the catalyst retained for a long time period. The effects of Pt catalyst and O 2 on the mechanism of C-NO reaction was examined by using step response experiment.

Controlled filling of Permalloy into one-end-opened carbon nanotubes

Controlled filling of Permalloy into a one-end-opened carbon nanotube (∼40 nm in inner diameter, 900 nm in length) array embedded in an anodic aluminium oxide film was achieved by an electrochemical route. Thanks to the electron-microscopically transparent carbon nanotubes, the time course of the electrochemical deposition process was readily visualized by means of transmission electron microscopy, revealing that Permalloy filling started from the pore bottom of the carbon nanotubes. This novel bottom-up filling opens a route to controllable filling of materials of interest into carbon nanotubes with one open end. The magnetic properties of the controlled filled carbon nanotubes in the array were studied. Interestingly, even in the case of isolated Permalloy nanoparticles inside the carbon nanotubes in the array, prominent magnetic anisotropy with an easy magnetization direction along the carbon nanotube axis was observed. In addition to the Permalloy-filled carbon nanotube array as embedded in the anodic aluminium oxide film, individual carbon nanotubes filled with Permalloy were also obtained.

Electrochemical behavior of carbon nanorod arrays having different graphene orientations and crystallinity

Carbon and carbon/nickel composite nanorod array electrodes possessing different graphene orientations and crystallinities were synthesized using an anodic aluminium oxide film as a template, and their electrochemical behavior was examined by cyclic voltammetry for the redox reactions of ferri/ferro hexacyanide ions. An attempt was made to examine how the structural differences influence the electrochemical behavior of the arrays and thereby to understand key structural factors affecting their behavior. It was found that the carbon nanorods with the edge planes of graphene sheets exposed to the outer surface were more active than the nanorods covered with the basal planes. Moreover, by using the carbon/nickel nanorod array where each nickel nanorod is covered with a very thin carbon layer, it became possible to evaluate the true electrocatalytic activity of the thin carbon layer. This technique revealed that even a poorly crystallized carbon was intrinsically active, but its high activity was usually concealed from ordinary observation, because of the low electric conductivity.

Crystal formation and growth during the hydrothermal synthesis of β-Ni(OH)2 in one-dimensional nano space

Hydrothermal synthesis of beta-Ni(OH)(2) was performed inside uniform carbon-coated nanochannels of an anodic aluminium oxide film. The time course of crystal formation and growth of Ni(OH)(2) in such one-dimensional nano space was observed using transmission electron microscopy (TEM), and the changes in the number and size of crystals with the hydrothermal reaction period were quantitatively analyzed using the TEM images. Moreover, the effect of the channel size (25, 100 and 300 nm in diameter) on the crystal growth was examined. In the early stage of the reaction, the crystal formation and growth of beta-Ni(OH)(2) in the one-dimensional channels took place in the same manner as in conventional hydrothermal synthesis. However, except for the 300 nm-channels, further crystal growth was hampered by the spatial restriction, and it allowed only the growth toward the channel axis. In the case of the 25 nm-channels, many Ni(OH)(2) crystals of less than 40 nm formed initially, but slowly disappeared except for a few that grew larger at the expense of the small crystals. This finding clearly indicates that the crystal growth of Ni(OH)(2) during the whole hydrothermal process was governed by the Ostwald ripening. With this mechanism and the spatial restriction, single crystals of beta-Ni(OH)(2) nanorods with a length of over 150 nm were finally formed.

Multi-Walled Carbon Nanotube Ultrathin Film Using a Liquid-Liquid Interface: Effect of Alcohol Type to the Film Property

Ultrathin film of multi-walled carbon nanotubes (MWCNTs) was fabricated using a liquid–liquid interface. Water dispersible MWCNTs, which were synthesized using an anodic aluminum oxide film as a template were used as a water phase. Hexane solution was added to the water dispersion as an oil phase. The MWCNTs were assembled at the liquid–liquid interface by adding 10 vol% of alcohol (methanol, ethanol, and 2-propanol) to the MWCNTs water dispersion/hexane solution. The assembled film was transferred to a solid substrate and the effect of alcohol type to the film properties was discussed.

HCN and N2 formation mechanism during NO/char reaction

The reaction of phenol/formaldehyde, resin char with NO was carried out in the temperature raoge from 850 to 1100°C. Nitrogen-containing species formed during the reaction were carefully examinedby ahigh-speed gas chromatograph and a mass spectrometer. Large amounts of N 2 and CO and small amounts of CO 2 and N 2 O were formed by the NO/char reaction. In addition to these, products, a significant amount of HCN was observed in the high-temperature region. The mechanism of HCN formation behavior was examined by step response experiments. It was found that HCN was formed through nitrogen-containing surface species on char, C(N), and its formation rate was greatly affected by the amount of available hydrogen. The N 2 formation was also affected by the amount of available hydrogen in the following manner. N 2 was formed mainly by the reaction of C(N) with gaseous NO. However, a part of C(N), was consumed through the conversion to HCN if sufficient hydrogen was present in the vicinity of C(N). When the HCN formation took place, the amount of C(N) decreased, leading to less N 2 formation. Thus, it is suggested that even in the char-related reaction, hydrogen content is an important factor for the fate of nitrogen.

Template Synthesis of Nanostructured Carbons

Uniform multiwalled carbon nanotubes can be synthesized using one-dimensional nanochannels of an aluminum anodic oxide film as a template. This technique allows one to prepare various types of unique carbon nanotubes. It is possible to prepare carbon nanotubes with a double coaxial structure of heteroatom-doped multiwalls. Test tube like carbon prepared by this technique was found to be dispersible in water without any post treatment. Moreover, a large carbon film with millions of carbon nanopillars on its one side was synthesized and it was demonstrated that such carbon film could be used as a corrosion-resistant but electrochemically active film electrode. In addition to these morphological control, complete filling of ferromagnetic metal into the whole cavity of carbon nanotubes was achieved by the template technique.