Capillary condensation in the void space between carbon nanorods

To elucidate the geometrical factor that controls the capillary condensation phenomenon in the void space between the hexagonally arranged cylindrical nanorods of ordered mesoporous carbon material designated as CMK-3 and also to examine the mechanisms of the capillary condensation and evaporation in such pores, we measured the adsorption properties of two kinds of CMK-3 carbons for nitrogen and derived theoretical formulation describing the capillary condensation in the void space between the nanorods by taking into account the influence of adsorption forces on the shape of the liquid-vapor meniscus. Calculations of the equilibrium condensation pressure due to the derived equations gave the relationship between the surface-to-surface distance between the neighboring nanorods and the condensation pressure of nitrogen at 77 K. Using this relationship, we were able to determine the accurate pore structures of the two carbons only from the X-ray diffraction pattern of CMK-3 carbon and the adsorption isotherm of nitrogen at 77 K. The thermal behavior of the adsorption hysteresis of nitrogen in the void space between the carbon nanorods was similar to that in the more restricted space of the ordered mesoporous silicas, suggesting that the mechanisms of adsorption and desorption in such open pores are identical to those in the ordered mesoporous silicas.