Improving the Hydro-stability of MCM-41 by Post-Synthesis Treatment and Hexamethyldisilazane Coating

Surfactant Templated Sulfonic Acid Functionalized Silica Microspheres as New Efficient Ion Exchangers and Electrode Modifiers

“…This could be due to a relatively low degree of cross-linking of the silica network, as revealed by 29 Si NMR ( Q 4 / Q 3 ∼ 0.5) from the distinct resonances observed for the siloxane ( Q n = Si−(OSi) n −(OH) 4 -n , n = 2−4; Q 4 at −110 ppm, Q 3 at −101 ppm), which was often observed when using a cationic quaternary ammonium template that favors the presence of unlinked SiO - groups that are needed for charge compensation . These groups can then contribute to the hydrolysis-driven degradation of the material, in agreement with the rather low chemical stability of mesoporous silica in aqueous medium, even if the presence of organic functions covalently attached to the silica walls is known to contribute to enhance its stability. , Steric hindrance and repulsion between the organic groups could also contribute to decrease the degree of order, as otherwise suggested elsewhere . Anyway, the MPS- n %-SO 3 H materials remained ordered up to a [MPTMS]/([TEOS] + [MPTMS]) molar percentage of 30% (Table ).…”

Postsynthesis Vapor-Phase Functionalization of MCM-48 with Hexamethyldisilazane and 3-Aminopropyldimethylethoxylsilane for Bioseparation Applications

“…This structural degradation is a serious problem in the application of mesoporous molecular sieves as adsorbents for bioseparations because the medium for such separations is aqueous and it is important that structural integrity is retained throughout repeated adsorption and regeneration cycles, generally performed around room temperature. Recent work has shown that the M41S materials are modified by prolonged exposure to water and water vapor, showing decreased structural regularity and a loss of uniformity in pore shape, size and volume. ,− The hydrolysis of siloxane bridges (Si−O−Si bonds) has been identified as the main cause of this structural damage. This mechanism has been confirmed by the increase of the Q 3 (silanol group) signal by 29 Si NMR following contact with water vapor overnight .…”

“…Two potentially important functional groups for bioseparations are hydrophobic and amino groups. Hydrophobic surface modifiers are of interest because they increase the selectivity of the adsorbents for molecules with hydrophobic regions, which include many biological molecules, and have also been shown to increase the stability of mesoporous silica materials in aqueous solutions. ,,,,,, Amino functionalization is of interest because the charge on these surface groups is pH-dependent, so there is the potential to tune them to selectively target oppositely charged species. More importantly, the highly reactive amino group can be utilized as, essentially, a chemical anchor to which other species can be chemically attached …”