The microporosity of the heat-treated single-wall carbon nanohorn (SWNH) particles is characterized by nitrogen adsorption at 77 K and the molecular potential calculation using the function, which is based on the Lennard-Jones pair potential. The depth difference of the molecular potential for N 2 between the SWNH intraparticle pore and the interparticle space is close to 1000 K. Although the SWNH without the heattreatment has no open intra-nanohorn space, the intraparticle pores open with the high-temperature treatment in O 2 . The heat-treatment at 693 K opens almost perfectly the intraparticle pores, leading to 0.47 mL g -1 of the micropore volume and 1010 m 2 g -1 of the specific surface area. The subtraction of the N 2 adsorption isotherm of the SWNH from that of the SWNH treated at 693 K gave the N 2 adsorption isotherm only in the intraparticle pore spaces. The adsorption sites derived from the difference adsorption isotherm are assigned to the pores having different interaction potentials.

The adsorption isotherm of N 2 in internal nanopores of the single wall carbon nanohorn (SWNH) particles was compared with that of the external surfaces of the SWNH assembly. The presence of two strong adsorption sites of the internal nanopores and external nanopores of the assembly were evidenced by the analysis of the adsorption isotherm. The calculated interaction potential of the external nanopore was much deeper than that of the internal nanopore.

We propose a new equation of the absolute adsorption isotherm for supercritical gas and examine the effectiveness of this equation using density functional theory (DFT). The new equation can well describe both DFT results and experimental data of a high-pressure adsorption isotherm of a supercritical gas. This equation provides important parameters of the averaged fluid-pore wall and fluid-fluid interaction energies, suggesting that adsorbed layer has two states. One is an attractive state in low-pressure region and another is a repulsive interacting state in high-pressure region. In the case of DFT results of nitrogen adsorption on the regular slit pore of pore width = 2σ (σ:  Lennard-Jones size parameter of an adsorptive molecule), the obtained enthalpy change of this transition from Clausius−Clapeyron equation is 4.4 kJ/mol. It is slightly smaller than that of vaporization of bulk liquid nitrogen at boiling point (5.57 kJ/mol).