MCM-41 siliceous molecular sieves were used to test the applicability of the Kelvin equation for nitrogen adsorption in cylindrical pores of the size from 2 to 6.5 nm. It was shown that the Kelvin equation for the hemispherical meniscus, corrected for the statistical film thickness, is in quite good agreement with an experimental relation between the pore size and the capillary condensation pressure. The agreement can be made quantitative in the pore size range from ca. 2 to 6.5 nm, if a simple correction to the Kelvin equation is introduced. The required statistical film thickness curve (t-curve) was calculated using nitrogen adsorption data for large pore MCM-41 samples and the obtained results were extrapolated using an adsorption isotherm for a macroporous silica gel. Moreover, an accurate analytical representation of the t-curve was found. Since both the corrected Kelvin equation for cylindrical pores and the t-curve have simple analytical forms, they can conveniently be used in a variety of methods to evaluate porosity. It was shown that the BJH method with the corrected Kelvin equation accurately reproduces pore sizes of MCM-41 materials. A comparison was made between the specific surface areas for the MCM-41 samples calculated on the basis of the BET equation and those obtained using other independent methods. The results strongly suggest that when nitrogen adsorption data are used, the BET method overestimates the specific surface area of siliceous materials. The latter conclusion was supported by the examination of the obtained statistical film thickness curve.

CO(2) adsorption-desorption cycles and the corresponding mechanisms over amine supported CO(2) adsorbent (TRI-PE-MCM-41) under dry conditions and in the presence of moisture (20 degrees C as dew point).

The area of periodic mesoporous materials prepared by cooperative assembly in the presence of amphiphile molecules underwent dramatic growth. Among the silica-based materials, many types may be regarded as ordered organic−inorganic nanocomposites. These were divided into five categories:  (i) noncalcined amphiphile/silica mesophases, (ii) mesoporous silicas with organically modified surfaces, (iii) expanded mesoporous silicas, (iv) mesoporous organosilicates, and (v) mesoporous silica with occluded organic materials such as polymers. The diversity of such nanocomposites created new potential opportunities in materials sciences, catalysis, separation, and environmental remediation. These applications involved the development of new chemistry not only within the confined pores and channels but also on functionalized surfaces as well as within the channels walls. The current review deals with recent progress in the synthesis, characterization, and applications of each of these types of periodic mesoporous silica-based hybrid materials.

No abstract

Application of pore-expanded MCM-41 (PE-MCM-41) mesoporous silica coated with 3-[2-(2-aminoethylamino)ethylamino]propyltrimethoxysilane (TRI) has been extensively examined for the adsorption of CO 2 from N 2 . A systematic study of the amine loading as a function of the relative amounts of TRI and water used during the grafting procedure and the temperature of the grafting reaction was carried out. Extremely high levels of active amine content were achieved using prehydrated silica surfaces at grafting temperatures below reflux in order to facilitate thermally controlled water-aided surface polymerization of the aminosilanes. The CO 2 adsorption capacities and rates were determined for all materials as a function of the amount of TRI and water per gram of support added to the grafting mixture. The optimal TRI grafted PE-MCM-41 adsorbent exhibited a 2.65 mmol/g adsorption capacity at 25 °C and 1.0 atm for a dry 5% CO 2 in N 2 feed mixture, which exceeded all literature reported values, for both meso-and microporous materials under the conditions used in this study. Further, the apparent adsorption and desorption rates with the amine functionalized materials were exceedingly high. When considering the grafted amine quantity, the adsorption capacity and rate were found to be mutually dependent on each other, exhibiting an apparent optimal combination. In comparison to zeolite 13X, the optimally loaded TRI-PE-MCM-41 was far superior in terms of dynamic adsorption and desorption performance. These results were further enhanced when the adsorbents were challenged with a humid stream of 5% CO 2 /N 2 . The TRI-PE-MCM-41 exhibited a 10% increase in CO 2 adsorption capacity, whereas the 13X zeolite did not retain any significant CO 2 adsorption capacity.