| Abstract
| - Hydrogen adsorption isotherms in single-wall carbon nanohorns (SWNHs) have been measured at 20 K. Thepore volume from hydrogen adsorption is compared with that from nitrogen adsorption at 77 K to determinethe density of confined hydrogen in the internal space of SWNHs; it indicates that the average density ofconfined hydrogen inside SWNHs at 20 K is higher than that of liquid hydrogen in the bulk and nearlyapproaches the density of solid hydrogen at the triple point. The surface area from hydrogen adsorption usingthe BET theory is anomalously large compared with that for nitrogen; however, an alternative method (modifiedBET theory), in which an assumption is made that the energy of a molecule in the second layer is larger thanthat in the liquid, gives a reasonable surface area, especially when the adsorbed hydrogen in the first layer isassumed to be in a solid state. In the modified BET model, a packing constraint of the second layer due tothe cylindrical geometry of SWNH is also taken into account. The solidlike behaviors of adsorbed hydrogenwould be attributed to quantum effects, which give a strongly attractive pore situation for the hydrogen−SWNH system.
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