N. Setoyama

Characterization of porous carbons with high resolution αs-analysis and low temperature magnetic susceptibility

Abstract The effectiveness of integrated characterization of porous carbons with different approaches such as the high resolution α s -method for N 2 adsorption, X-ray diffraction, and magnetic susceptibility measurement is shown. The theoretical basis for the high resolution α s -analysis for N 2 adsorption using GCMC simulation and the background of magnetic susceptibility of carbon are given. The applicability of the integrated characterization to changes of ACF with heating at 1473–3173 K in Ar is shown. The activated mesocarbon microbead (a-MCMB) and activated carbon aerogel (a-CA) were examined by the integrated characterization method. a-MCMB showed an unusual magnetic relaxation below 10 K due to random magnetism. The random magnetism was associated with the mutually isolated network structure of nanographitic units. a-CA also showed random magnetism at low temperature, which was associated with the spin isolated nanographitic structure similar to a-MCMB.

Grand canonical Monte Carlo simulation for nitrogen adsorption in graphitic slit micropores: effect of interlayer distance

Adsorption isotherms of N2 by slit-shaped graphitic micropores at 77 K were simulated using grand canonical Monte Carlo (GCMC) simulation and compared the simulated isotherms with experimental adsorption isotherms of N2 on pitch-based activated carbon fibers. The pore was modeled as the slit space between parallel smooth graphite surfaces. The concept of the effective pore width which can be determined experimentally was used for the simulation. The effect of the layer distance (d002) of the graphitic structure on the simulated N2 adsorption isotherm was examined. The observed d002 of activated carbon fiber (ACF) well simulated the experimental result.

Density of He adsorbed in micropores at 4.2K

The density of He adsorbed in the cylindrical micropores of zeolites NaY and KL has been determined by He adsorption at 4.2K. He adsorption isotherms were then compared with N2 adsorption isotherms at 77K. Crystallographic considerations of the micropore volumes gave the density of the He adsorbed layer, which is necessary for assessment of ultramicroporosity of less-crystalline microporous solids, such as activated carbons. The determined density of He adsorbed in the cylindrical micropores of the zeolite was in the range 0.22 to 0.26 gml−1, greater than that of He adsorbed on a flat surface (0.202 gml−1). A value for the density of He between 0.20 to 0.22 gml−1 is recommended for evaluation of ultramicroporosity of a slit-shaped microporous system such as activated carbon.

Nitrogen adsorption on fluorinated activated carbon fiber

Nitrogen adsorption isotherms for fluorinated activated carbon fiber (F-ACF) and fluorinated carbon black (F-CB) were measured at 77 K. Surface structures of F-ACF and F-CB were examined by αs-plot analysis using the adsorption data on the nonporous carbon black (CB) and F-CB. The surface energy of F-ACF was lower than that of ACF. The micropore structure of ACF was preserved even after fluorination, although the limiting adsorption amount and the micropore width decreased with fluorination.

Ultramicropore Characterization by He Adsorption

Abstract He adsorption isotherms of several kinds of activated carbon fibers were gravimetrically measured at 4.2 K. The He adsorption isotherms were compared with the N 2 adsorption isotherms. The density of He adsorbed in cylindrical micropores of zeolites was determined, which coincided with the theoretical density of He adsorbed on the flat surface of graphite. The observed density was used for evaluation of the microporosity from the He adsorption. The micropore size distributions by He and N 2 were calculated; the distribution from He is broader and shifts to smaller value compared to that from N 2 . It was shown that He adsorption at 4.2 K can assess more correctly microporosity, in particular ultramicroporosity.

Ultramicroporosimetry of Porous Solids by He Adsorption

Abstract The adsorption isotherms of He on different kinds of microporous carbon fibers(activated carbon fibers:ACFs) at 4.2 K have been determined gravimetrically. The He adsorption isotherms were of more typical type I than the N 2 adsorption isotherms, suggesting that He molecules can have access even to ultramicropores without slow diffusion problem. Both He and N 2 adsorption isotherms were analyzed by the two-term Dubinin-Radushkevich equation. Only polyacrylonitrile-based ACF had the same micropore volume by He adsorption and that N 2 adsorption. On the other hand, the micropore volumes by He adsorption of other ACF samples were greater than those by N 2 adsorption, indicating the presence of ultramicropores. The structural causes for the ultramicropores were suggested.

Recrystallization-induced defect porous nature of C60 crystals

Defective state of C60 crystals was controlled by the recrystallization and annealing. The defective structure was examined by the X-ray diffraction and N2 adsorption at 77 K. Recrystallized C60 crystals without annealing showed broad diffraction peaks and the N2 adsorption isotherm had marked low pressure uptake and a hysteresis in the high pressure region, indicating presence of both micropores and mesopores. The average micropore width was 8 Å which is closed to the C60 molecular size, while the average mesopore one was 50 Å. The mesopores disappeared by annealing up to 393 K. On the other hand micropores of 8 Å remained even by heating up to 673 K.