Porous Structure of Ordered Silica with Cagelike Pores Examined by Successive Adsorption of Water and Nitrogen

To examine the porous structure of ordered silica with cagelike pores, we measured successive adsorption of water at 283 K and nitrogen at 77 K on four kinds of SBA-16 and four kinds of KIT-5. For materials with smaller necks, we found the amount of nitrogen condensed inside the large cavities decreased rapidly with ail increase in water filling and reached a small value at water filling, just before the Onset of pore condensation of water inside the spherical cavities. This clearly indicates that most of the cavities are isolated front bulk nitrogen gas with water frozen ill the necks. A comparison with the accessibility Curve of voids expected For a random distribution of neck, sizes throughout all ordered Structure indicates the presence of correlation in the spatial distribution of neck sizes in the material, In addition, the relative pressure range of water, in which the amount of nitrogen condensed in the large cavities considerably drops, gave information about pore size distribution of the necks. However, for materials with larger necks, the amount of nitrogen condensed inside the large cavities decreased gradually with ail increase in water filling because pore condensation of water occurs simultaneously in the necks and cavities.