Microporosity and connectivity of ordered mesopores of SBA-15 silica were studied using nitrogen adsorption and novel methods based on selective pore blocking via organosilane modification, and on the imaging of inverse platinum replica of ordered mesoporous structure. It was found that SBA-15 exhibits a relation between the pore size, pore volume and specific surface area which is significantly different from that for cylindrical or hexagonal pores, which suggests that the SBA-15 structure is more complex than an array of hexagonally ordered channels, even if they are corrugated. Nitrogen and argon adsorption measurements provided evidence that large mesopores are accompanied by a certain amount of significantly smaller pores (of the size below about 3.4 nm) with a broad distribution primarily in the micropore/small-mesopore range. The modification of SBA-15 via chemical bonding of small trimethylsilyl ligands partially blocked the complementary pores, and the bonding of larger octyldimethylsilyl groups made them essentially fully inaccessible to nitrogen molecules, which manifested itself in dramatic changes in the relation between the pore size, pore volume, and specific surface area. After dissolution of the SBA-15 framework, platinum wires grown inside the porous structure formed bundles, as seen from transmission electron microscopy. These results provided strong and unambiguous evidence that large ordered mesopores of SBA-15 are accompanied by much smaller disordered pores and that an appreciable fraction of the latter is located in the pore walls, providing connectivity between the ordered large-pore channels. The complementary pores are suggested to form as a result of penetration of poly(ethylene oxide) chains of the triblock copolymer template within the silica framework of as-synthesized SBA-15. We also studied thermal stability of SBA-15 structure and its complementary porosity. As inferred from nitrogen adsorption data, the complementary porosity was retained to a significant extent even after calcination at 1173 K, but most likely completely disappeared at 1273 K. The heat treatment was accompanied not only by a significant decrease in the specific surface area and pore volume but also by narrowing the pore size distribution at temperatures up to 1173 K. Thus, we were able to demonstrate for the first time that the SBA-15 sample with nitrogen adsorption properties similar to those of MCM-41 can be obtained via calcination at 1273 K, although the pore volume and specific surface area of such SBA-15 material is relatively low.

CMK-1 ordered mesoporous carbons were synthesized using MCM-48 silica templates with a wide range of unit-cell parameters and pore sizes. Sucrose and furfuryl alcohol were employed as carbon precursors. It was confirmed that the isolation of the CMK-1 carbon via dissolution of the MCM-48 template is accompanied by a structural transformation, which manifests itself in the change of the X-ray diffraction pattern. It is suggested that the transformation is related to the disconnected nature of the two interwoven parts of the CMK-1 framework (which are formed in two enantiomeric MCM-48 channel systems separated by the silica wall) and may involve a mutual displacement of these two parts to create some contact between them and fix their mutual position. It was shown that the application of different MCM-48 templates allowed for tailoring of the CMK-1 unit-cell size. However, the primary mesopore size of CMK-1 was found to be relatively constant. This was explained as a consequence of the formation of primary mesopores of CMK-1 in the space previously occupied by the MCM-48 pore walls, and attributed to the similarity in the pore wall thickness for the MCM-48 templates used. Our study confirmed that the uniform mesopores of CMK-1 are accompanied by micropores and that the carbon prepared using MCM-41 as a template collapses upon the template removal to yield high-surface-area disordered microporous structure. It was also shown that thermogravimetric weight loss behavior under air atmosphere provides important insights to the structural integrity and quality of the CMK-1 samples.