Adsorption and thermogravimetric characterization of mesoporous materials with uniform organic-inorganic frameworks

Two-dimensional hexagonal HMM-1 and three-dimensional hexagonal HMM-2 order ed mesoporous materials with hybrid ethanesilica frameworks were characteri zed using nitrogen adsorption, argon adsorption, and high-resolution thermo gravimetry (TGA) under nitrogen and air atmosphere. Nitrogen and argon adso rption isotherms for these materials featured rather narrow capillary conde nsation steps. Adsorption-desorption hysteresis in primary mesopores was ob served in the case of argon adsorption at 77 K. The pore diameter of HMM-1 was determined on the basis of the geometrical relation among the pore size , pore volume, and unit-cell size and was found to be in excellent agreemen t with the pore diameter calculated according to the method calibrated usin g MCM-41 silicas. This provided a confirmation of the applicability of the geometrical method for two-dimensional hexagonal materials with arbitrary f ramework composition. Low-pressure adsorption data provided evidence that t he surfaces of HMM-I and HMM-2 interact somewhat more weakly with nitrogen adsorbate than the silica surface, which can be explained as a consequence of the substitution of weakly interacting siloxane bridges by larger and pr esumably even more weakly interacting ethane bridges present in the framewo rks of the hybrid materials. At low pressures, the statistical thickness of nitrogen film in the HMM-I pores was found to be somewhat lower than that in the MCM-41 pores. Some differences in surface interactions with nitrogen and argon were also observed between HMM-1 and HMM-2, and these difference s may be attributable to a different degree of exposure of organic groups o n the pore surface of these two materials. The surfactant content in as-syn thesized materials was found to correlate with the pore Volume after surfac tant removal. The latter was essentially complete after the solvent extract ion, as judged from TGA. Thermogravimetric data also suggest that ethane gr oups of HMM-1 and HMM-2 were stable up to at least 553 K in air and up to a t least 813 K under nitrogen atmosphere.