The author clarified the characteristic of activated carbon prepared from biomass (rind of sugar cane bagasse (rind), pith of sugar cane bagasse (pith), rice straw (rice), bamboo (barn)) with different ratios of NaOH. In addition, the characteristic of electric double-layer capacitance of each activated carbon was clarified.
Raw materials carbonized for 1 h at 973 K were used as a sample, and the sample was activated for 1 h at 1073 K with the different ratios of NaOH. High BET specific surface area (S_BET) of our activated carbon was obtained (more than 2400 m²/g). The N₂ absorption isotherm at 77 K indicated type I of IUPAC. As analysis of α_s-plot, activated carbon prepared from rind, pith and rice (AC-rind, AC-pith, AC-rice) were microporous with average pore diameter (W_ave) in the range of 0.7-1.4 nm. On the other hand, activated carbon prepared from bam (AC-barn) was microporous with W_ave below 0.7 nm.
Comparison of SEM images between raw carbonized materials and the activated carbon indicated that AC-rind, AC-rice and AC-barn remained proper biomass structure as capillaries after activation.
The electric double-layer capacitance (C_dl) of each raw material increased with an increase of S_total. When the W_ave was focused, C_dl of AC-barn was nearly constant above 0.8 nm and C_dl of AC-rice was nearly constant above 1.1 nm. On the other hand, C_dl of AC-rind and AC-pith increased with an increase of W_ave. From the above results, the high C_dl of AC-pith and AC-rind was considered to be due to wide W_ave.

View full abstract

Cypress charcoals, which were prepared with different temperatures and transferring rates under a flow of super-heated steam, were used for the electrode of electric double layer capacitor (EDLC) with 1 M H₂SO₄ electrolyte. EDLC capacitance of cypress charcoals prepared was about 250 F/g with a current density of 20 mA/g, about 160 F/g with 50 mA/g and about 120 F/g with 1000 mA/g. Capacitance observed was shown to be governed by pore structure of cypress charcoal and was tried to explain by the contributions from microporous and external surface areas. Rate performance evaluated from the ratio of the capacitance measured with 1000 mA/g to that with 50 mA/g was relatively high, about 0.7, for cypress charcoals prepared.

View full abstract

Mesoporous carbon material enables material transfer more easily than that of microporous carbon material such as activated carbon and has a high porosity and effective surface area. The application for the separation material, the absorbent, the catalyst support and the electrode medium of electric double layer capacitor are expected for the mesoporous material. This study attempted to prepare the mesoporous carbon material. Resorcinol (R) as a raw material and acetaldehyde (A) as a cross-linking agent were used to synthesize the RA hydrogels via the sol-gel polycondensation in a slightly basic aqueous solution. The RA hydrogels were freeze-dried and subsequently pyrolyzed at 1073 K for 30 min (at a hearting rate of 10 K/min) to obtain the RA carbon cryogels. This study attempted to control the surface properties of RA carbon cryogels by varying the constituent ratio of precursor solution and pH of RA aqueous solution at the acid treatment to promote the formation of secondary particle of RA hydro gels. The pore structure of RA carbon cryogels depended on the constituent ratio of precursors and pH of RA solution, probably due to the variation of the subsequent gel particle size. The carbon gels prepared in this study were mesoporous materials with a modal diameter of 20 nm.

View full abstract

Influence of pore structure and particle size on rate determining step of lead (II) ions and nitrobenzene adsorption onto activated carbons (ACs) having no surface oxygen had been studied. The adsorption kinetics were examined using the Langumuir type rate equation. Nitrobenzene adsorption rate was found to be always controlled by collision between adsorbate and adsorption sites. Though the rate determining step of lead adsorption might include exterior and inter-particle diffusion, it could be shifted from exterior and inter-particle diffusion to collision between adsorbate and adsorption sites with either increasing mesopore content or reducing particle size by pulverization of ACs.

View full abstract

We previously investigated the pore structure in carbon fibers prepared from polymer blends consisting of carbon precursor resin and pore forming resin by measurements of small-angle X-ray scattering (SAXS), and reported the heat treatment temperature (HTT) dependence of the pore structures elsewhere.
In this paper, a least-square-fitting analysis of theoretical scattering intensities for experimental intensities was introduced in order to get the results with higher reliability. We also measured SAXS intensity of the polymer blend fiber without heat treatment and carbonization to investigate the structure of the pore forming resin in the fiber. We considered the structural change of the pore forming resin and the formed pores with heat treatment and carbonization.

View full abstract

The purpose of the round robin test is to establish the standard procedure for the X-ray diffraction (XRD) measurements of lattice parameters and crystallite sizes of carbon materials (revised Gakushin-method). 5 kinds of carbon samples, glassy carbon heat-treated at 2200°C, a raw coke, high modulus type of pitch based carbon fiber, isotropic graphite block and natural graphite powder, were prepared for the XRD round robin test as the first step in 2002. Two decades of participants (Japanese universities, institutes and companies) carried out the round robin test. The measurement of lattice parameters showed a high accuracy, being the measurement error within 0.0002 nm in the case of graphitized samples. However, the crystallite size measurements showed large scattered results. The coefficient of variation for the crystallite size measurements is more than 10 percent. To improve the accuracy of the crystallite size measurements, it is necessary to use a reliable silicon powder as the standard and to establish a judgment for suitable profile for the diffraction peaks of the standard silicon. In 2004, three samples using different kinds of silicon powder were prepared for the second step of the round robin test. As the consequence of the second step test, the sample with the commercial silicon powder for XRD measurement showed a relatively small scattered result. Moreover, permissible conditions for the profile of silicon diffraction peak were described on the procedure specification.

View full abstract