Hirokazu Oda

Removal of ionic substances from dilute solution using activated carbon electrodes

Abstract Removal of various electrolytes from aqueous solution and a recycling operation were carried out using a flow-through capacitor. The amount of ions removed corresponds to the surface area and especially the micropore volume of the activated carbon electrode. Introduction of acidic functional groups on the surface of the carbon promoted ion removal (i.e. increase in rate and capacity), but there is a limit to the amount of functional groups that can be introduced with good effect. The adsorption–desorption properties of various alkali, alkaline earth and heavy metal sulfates were investigated. It was found that removal characteristics were different for the different types of ions. Depletion of the electrode also differed depending on the electrolyte that was removed. When copper and zinc ions were removed, the surface area of the cathode was reduced by a small amount.

Adsorption of benzoic acid and phenol from aqueous solution by activated carbons—effect of surface acidity

Abstract Effect of surface acidic groups of activated carbons on their adsorption characteristics for substrates from aqueous solutions were studied. Six kinds of carbons obtained commercially and their heat-treated products were used. Pore-size distribution, BET surface area and surface acidity were measured. Adsorption isotherms for benzoic acid and phenol from aqueous solutions (single or double components) were obtained. Substitution adsorption, i.e. substrate adsorbed preliminarily is substituted by another substrate, was also carried out. It was found that adsorption of benzoic acid is scarcely affected by surface acidity of carbons and the amount adsorbed is almost entirely controlled by the specific surface area of carbons. On the contrary, adsorption of phenol is retarded considerably by the acidity of carbons. In the case of solution of double components, benzoic acid is adsorbed predominatedly. The phenol adsorbed preliminarily is easily substituted by benzoic acid, but the substitution of benzoic acid by phenol scarcely proceeds.

Adsorption of aromatic amines and o-substituted derivatives of phenol from organic solutions by activated carbons-effect of surface acidity

Abstract In order to study the effect of surface acidity of activated carbons on their adsorption characteristics, three kinds of aromatic amines and four kinds of o -substituted phenols were adsorbed from organic solutions by twelve kinds of activated carbons of different acidity and of known pore-structure. It was demonstrated that the surface acidity had a marked effect on the adsorption characteristics and that the effect was linked with the polarity of the solvents.

Effect of air-oxidation on the pore-structure of coals and cokes or chars obtained from oxidized coals

Abstract Seven kinds of coals (C, 77.8–89.8 wt% daf) were oxidized with air at 150 °C for 1, 5 and 10 h. The oxidized coals were heat-treated at various temperatures between 300 and 1500 °C with intervals of 50 or 100°C. The pore-structure of the oxidized coals and the cokes or chars obtained from the oxidized coals was compared with those of parent coals and their cokes or chars. True densities were measured in methanol and straight-chain hexane and pore volumes were determined by the Dubinin-Polanyi procedure. For the coals, the methanol-density increased with extent of oxidation; the hexane-density increased at first, but then decreased and again increased in the course of the oxidation. The air-oxidation of coals has a marked and controlling effect on the development of the pore-structure of cokes and chars in the course of the carbonization.

Preparation of hollow carbon-microbeads from water-in-oil emulsion using amphiphilic carbonaceous material

Abstract Carbon microbeads were prepared from water-in-oil emulsion using amphiphilic carbonaceous material and urea. With urea as a forming agent with a concentration 1–20 wt.%, hollow carbon-microbeads were obtained, and their particle size ranged between 2 and 15 μm. The true density of the hollow carbon-microbeads was changed, by varying the concentration of urea and the heat-treatment temperature. In particular, a pore size of about 50 A was predominantly produced under a certain condition.

Temperature-dependence of propagation velocity of ultrasonic wave in coals

Abstract To study the characteristics of the change of rheological properties of coals on heating, the propagation velocity of an ultrasonic wave of 100 KHz was determined for 27 coals of different rank (C, 71.2–94.5%) in the temperature range 77–523 K. It was difficult to establish a clear relationship between absolute values of the velocity and rank of coals, but the temperature-dependence of the velocity appears to be a function of the carbon content of the coals, similar to the well-known correlation between hardness and rank of coals. The change of propagation velocity in 17 coals was determined continuously while the coals were heated from room temperature up to 673 K at 0.5 Kmin−1. At temperatures below 523 K the velocity decreased almost linearly with increasing temperature; however it was observed that the velocity suddenly decreased at a certain temperature above 523 K, which was specific for each individual coal. This specific temperature was found for both caking coals and non-caking coals and was significantly lower than the initial softening temperature detectable by the conventional plastometer or dilatometer.

Preparation and Capacitive Properties of a Carbonaceous Material Containing Nitrogen

Carbonaceous materials containing nitrogen (C/N materials) were prepared by pyrolysis of diaminomaleonitrile (AMN). A C/N material prepared by the pyrolysis of AMN at 1020 K (AMN1020K) had a C/N atomic ratio of 2.0 and a noncrystalline carbonaceous structure with a Brunauer, Emmett, and Teller (BET) surface area of 230 m 2 g ―1 . A possible formation mechanism of a C/N material has been proposed on the basis of the products, X-ray diffraction, and electron spectroscopy for chemical analysis (ESCA). The material AMN1020K showed large capacitances of 200 F g ―1 and 130 F cm ―3 when a current density of 10 mA cm ―2 (2 A g ―1 ) is applied in a three-electrode cell in 1 M H 2 SO 4 aqueous solution, in comparison to those of activated carbon (180 F g ―1 and 61 F cm ―3 ) having a BET surface area of 2300 m 2 g ―1 . The ESCA study indicated that pyridinic and quarternary nitrogen atoms existed in the C/N materials, which results in producing a pseudocapacitance in addition to the electric double-layer capacitance. The introduction of nitrogen into the carbonaceous material improves the wettability of the material, which should also improve the capacitance.

Characterization of carbonaceous gel beads prepared in presence of polymer using water-in-oil emulsion

Abstract Carbonaceous gel beads were prepared by addition of polymers using ammonia water of amphiphilic carbonaceous material through water-in-oil emulsion. By addition of poly(vinylalcohol), carbonaceous gel beads having dimples were obtained, where the number and size of dimples were dependent on the additive amount and molecular weight of poly(vinylalcohol). However, only beads with smooth surfaces were obtained by addition of poly(vinylpyrrolidone) and poly(ethyleneglycol). The morphology of beads is significantly influenced by interfacial tension at the water-oil interface. The surface area of beads prepared by addition of polymers remarkably increased by heat treatment from 5 m 2 g −1 to 289 m 2 g −1 and a pore size of about 20 A was predominantly produced in the case of PVA. In addition, the carbonaceous gel prepared by addition of PVA exhibited a high graphitizability, similar to that of green cokes. Thus, it was found that physicochemical properties of gel beads prepared by addition of PVA are significantly altered.

Effect of surface acidity of activated carbons on their characteristics of adsorption from the vapour phase-comparison of retention time for carbons used as adsorbents for gas chromatography

Abstract Seventeen kinds of activated carbons of different surface acidity and of known pore-structure were used as adsorbents for gas chromatography. The retention time of various kinds of substrates was determined for each carbon at different temperatures. It was found that surface acidity of carbons has a marked effect on increasing the retention time for polar substances while showing no effect for non-polar substances. Retention times varied with temperature which suggested, when the effect of surface acidity is taken into account, that the pores which were effective for the Chromatographic adsorption have been determined by the temperature. The heat of adsorption calculated on the basis of the retention times observed at different temperatures showed an inverse correlation with dielectric constant of the adsorbates.

Development of Direct Methanol Fuel Cell Catalyst Using Marimo Nano Carbon

In this study, a fibrous carbon material, Marimo nano carbon (MNC), was investigated as a catalyst support material for a direct methanol fuel cell. MNC comprises diamond particles in its core and carbon nanofilaments that radiate outward from the diamond core. The MNC-supported Pt catalyst (Pt/MNC) exhibited better performance than the conventional catalyst support material (i.e., carbon black). Higher Pt dispersion was observed on MNC compared to carbon black, with decreased Pt loading. Pt/MNC exhibited high electrochemical activity.Graphical AbstractThe images of Marimo nano carbon, a is model of primary particle of MNC, b is SEM image of secondary particle of MNC, c is the high-magnification SEM image of b