CTAB-Templated Mesoporous Silica

The influence of relative himiidity (RH) dining film drying was investigated by GISAXS [79], illustrating the importance of processing conditions that are often considered secondary to chemical conditions. The authors demonstrated the importance of the modulable steady state (MSS), that is, the state that follows 

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Mesoporous silica spheres were synthesized under the catalyst of ammonia in the mixed water-DMF solvent. In typical synthesis, 0.8 g (2.2 mmol) CTAB was heated slightly to allow it dissolved in the mixed solvent of 19.0 g (1.06 mol) water and 19.0 g (0.26 mol) DMF. After cooling to room temperature, 1.0 g (15 mmol) ammonia and 2.08 g (10 mmol) TEOS were added to the mixture with an electromagnetic stirrer and the stirring rate was kept about 480 rpm. After stirring for 16 to 25 h, the white solid product was Filtered on a Buchner funnel and allowed to dry in air at room temperature. The dried precipitate was immersed into highly diluted aqueous ammonia (pH 10) and kept at 100 °C for 2 days, the product was washed with distilled water and dried at room temperature in air. Then the product was calcined at 550 °C for 4h to remove the templates. 

In summary, nanometer-sized mesoporous silica and alumina spheres with tunable diameters (80 - 900 nm) can be synthesized in organic solvent. Mesoporous silica spheres templated by cationic surfactant (CTAB) have hexagonal array with monodispersed pore size (-2.4 nm), high surface areas (-1020 m2/g), and pore volume (1.02 cm3/g). Mesoporous alumina spheres templated by amphiphilic triblock copolymer show a large disordered mesopore (10.0 nm) and high BET surface area (360 m2/g). 

Using an elegant approach, Che et al. prepared chiral mesoporous silica using bio-inspired surfactants [63]. The trimethylammonium group of the quaternary amine used as a surfactant in the synthesis of MCM-41 (CTAB) was replaced by L-alanine. The chirality of the amino acid in the polar head of the surfactant induces chirality in the micelle used as template (see Figure 3.15). This simple modification in the surfactant allowed the preparation of the first chiral mesoporous silica with tunable pore size and ordered porosity. A key step in this synthesis is the transfer of the chirality from the surfactant to the solid, which was accomplished by electrostatic interaction between the terminal amino acid and the... 

Use of mixture of surfactant (e.g., C18-3-1 and CTAB for MCM-41, Gemini surfactant mixture for MCM-48) as template and post-synthesis hydrothermal treatment.[1] This method can give high-quality and large-pore mesoporous silica materials. 

One-step direct synthesis of the highly stable mesoporous silica-based material is also possible. MMS-H[209] has a structure analogous to that of MCM-48 but which contains zeolite building units. A mixture of CTAB and Brij30 was used as template for the mesopores. The use of TPAOH without the assistance of NaOH helps to introduce zeolite secondary building units, as well as the direct formation of acidity after removal of the template. This material was also found to possess superior thermal, hydrothermal, steam, and mechanical stabilities. 

Fig. 6 Schematic representation of the synthetic route to obtain constitutional silica mesoporous membranes is (a) filled with mesostructured silica-CTAB, (b) then calcinated, (c) reacted with hydrophobic ODS and finally filled with the hydrophobic carriers. Generation of directional ion-conduction pathways which can be morphologically tuned by alkali salts templating within dynamic hybrid materials by the hydrophobic confinement of ureido-macrocyclic receptors within silica mesopores [130]...

To better control the ordering of mesopores in the silica shell, along with particle size and shape, the hard template method in combination with surfactant templating has been studied intensively. Typically, hollow particles with hexagonally ordered mesoporous shells can be obtained by using PS beads and CTAB in an aqueous ammonia solution. After the growth of a silica-surfactant meso-structured composite shell on the surfeice, the PS template is finally removed by calcination to form hollow spheres. Several reports have succeeded in... 

On this basis, a rapid and nondestructive method, ellipsometric porosimetry (EP), has been developed in which adsorption-desorption isotherms are determined from the variations of film refractive index efr induced by the change of partial pressme of a solvent above a film. The setup combines a pressure-controlled chamber (conventional gas volumetric characterization devices) and a classical eUipsometer thus, HeS is determined for each vapor pressure and is a direct measme of the adsorption isotherm. A typical example is shown in Figure 33.3a for a Si02 templated with CTAB thin film (Martinez Ricci, M.L., Fuertes, M.C., Violi, I.L., Grosso, D., and Soler lUia, G.J.AA., Rational design of mesoporous films for synthesis of responsive Bragg reflectors (unpublished).). The refractive index increases from eff (630 nm) = 1.21, for a large fraction of air inside micropores and/or mesopores within the silica nanostructure, to (630 nm) = 1.37 when pores are saturated with water. The steep increase at intermediate vapor pressures is associated with the capillary condensation inside pores. The hysteresis in the desorption branch is due to the presence of water in the necks that join pores, whose effective radii are smaller than the pore radius. 

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