Block-Copolymer-Templated Ordered Mesoporous Silica:  Array of Uniform Mesopores or Mesopore−Micropore Network?

Abstract

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.

Effect of disorder on condensation in the lattice gas model on a random graph

“…The strengths of these interactions (parameters of the model) are proportional to the contact surface area between the cells. As known from experiment [54][55][56], the vertical pore diameter is of ≃ 5 -10 nm, the micropore size 3 nm which is of the same order as the thickness of the pore walls. In our model, the horizontal size of the cell coincides with the vertical pore diameter and the vertical size is chosen to be of the same order as the micropore size.…”

Synthesis and characterization of catalytic metal semiconductor-doped siliceous materials with ordered structure for chemical sensoring

“…It has a hexagonal array of uniform tubular channels with pore diameters in the range of 5 -30 nm, much larger than those of MCM-41, involving much lower internal diffusion resistance. Moreover, the thick pore wall (3.1-6.4 nm) provides high thermal stability and hydrothermal stability [23][24][25]. This mesoporous material with uniform pore size and periodic porous structural properties is a suitable candidate for the confined immobilization and growth of semiconductive oxides nanostructures [26,27].…”

Cerasomes: A New Family of Artificial Cell Membranes with Ceramic Surface

“…In particular, the preparation of novel materials with organized nanostructures is a fascinating research subject in the field of hybrid materials (Ulman, 1996;Ozin, 2000;Dabbs & Aksay, 2000;Scott et al, 2001;van Bommel et al, 2003;Cölfen & Mann, 2003). These approaches are generally based on sol-gel techniques that utilize the presence of molecular assemblies as templates, such as rod-like micelles (Yanagisawa et al, 1990;Kresge et al, 1992;Inagaki et al, 1999), block-copolymers (Krämer et al, 1998;Melosh et al, 1999;Ryoo et al, 2000), microemulsions (Sims et al, 1998;Feng et al, 2000), organogels (Ono et al, 1998), cast films of bilayer membranes (Sakata & Kunitake, 1990) and bilayer vesicles (Hubert et al, 2000). Thus, the properties of nanohybrids depend on their nanostructures, especially the structure at the interface between the inorganic and organic components.…”