A new determination method of an absolute adsorbed amount nab from the surface excess mass nex for high-pressure adsorption isotherms of a supercritical gas was proposed. The effectiveness of new method was examined by using the density-functional theory (DFT). The DFT study showed that this analysis can provide reasonable results; both of the absolute adsorbed amount determined from the proposed method and the DFT agreed within 5% at 90 MPa and only 1% below 5 MPa. Furthermore, we applied this new method to the experimental surface excess isotherm in the literature, which has a maximum. The analyzed absolute adsorption isotherm from the surface excess adsorption isotherm having a maximum were of IUPAC type I or type II. This method gave the thickness of the interfacial layer of the adsorbed phase.

No abstract

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