Silica mesostructures

This paper will present a comparative assessement between the preparation of functionalized silica mesostructures by grafting and direct incorporation methods. The use of both electrostatic and non-electrostatic surfactant assembly routes in relation to these functionalization modes will also be discussed. 

Pure silica mesostructures were prepared using both electrostatic surfactant (cetyltrimethylammonium bromide, CTAB) assembly and neutral alkylamine (octylamine and dodecylamine) assembly. Thus, tetraethoxysilane (TEOS) was added to solutions of framework-forming surfactants and stirred for 24 hours. The exact conditions for the synthesis procedures are described in a previous publication.20 Although Soxhlet extraction over ethanol was used to remove the framework-bound surfactant molecules from the amine-assembled mesostructures, 650°C calcination was necessary to remove the CTAB from the... 

Figure 18.6 Fabrication of polymer-silica mesostructured materials through a self-assembly process by (a) addition of reactive monomers to the precursor solution, followed by postdeposition polymerization (b) addition of a polymerizable surfactant and (c) direct addition of a soluble polymer to the synthesis solution.

The present paper provides an overview of the physical properties of silica mesostructures with representative wormhole and lamellar framework structures assembled through S°P pathways. The wormhole framework silica, denoted HMS silica, was assembled using an alkylamine surfactant as the structure director and a silicon alkoxide as the inorganic precursor. The lamellar framework silica with a vesicular hierarchical structure, denoted MSU-G silica, was obtained from tetraethylorthosilicate (TEOS) as the silica precursor and a bi-functional gemini amine surfactant of the type RNH(CH2)2NH2. We then provide examples of the catalytic activity of these disordered mesostructures in comparison to more ordered framework mesostructures such as hexagonal MCM-41. 

The formation of surfactant-silica mesostructure can be considered as a result of the assembly of surfactant and silica species. This assembly involves many physical and chemical processes, such as the assembly of surfactant molecules, and hydrolysis and polymerization of inorganic species. The balance of all processes and all interactions between surfactant and inorganic species determines the final mesostructure. 

The first example of this method was reported in 1995, where silica mesostructures were produced as a near-exact negative copy of the LLC (Hi phase) template [33]. As an indication of the versatility of this method,... 

The deposition-precipitation method is applied to pure anatase titanias with high surface areas and silica mesostructures doped with Ti/Ti02. The effect of the type and density of surface functionalities both on the deposition of gold and on the catalytic properties of the resulting materials in the oxidation of CO in the presence of H2 are discussed. 

Here, the DP method has been applied in order to investigate fundamental issues regarding the use of SBA-15 as a catalyst support, specifically the stability of the silica mesostructure, the dimensions of the incorporated metallic particles and the location of introduced metallic active sites. 

Electrodeposition or pulsed-laser deposition techniques are additional possibilities for forming thin mesostructured films. These techniques have mainly been applied to non-silica mesostructured films such as niobia or platinum, but also hexagonally oriented mesoporous silica films were prepared by pulsed-laser deposition. ... 

Investigation of the Degree of Incorporation Phenyltrimethoxysilane into the Silica Mesostructures... 

Now, we obviously have a vicious circle. At 25 °C, the phenylsiloxy residues become effectively incorporated into the silica mesostructure however, this mesostructure is not well-ordered, is not stable against extraction, but partially collapses and exhibits only low porosity. On the other hand, after synthesis at 110 °C, the sample is well-ordered, stable against extraction, and has high porosity, but the amount of phenylsiloxy residues that have become attached to the silica structure is only very small. This result is astonishing, especially in view of the strong influence that the substitution by PTMOS (even at an only 10% level) has on the appearance at the SFD aquired at 110 °C (see Section 36.2). 

Figure 11.S TEM images of an ultrathin section of the hierarchically ordered silica mesostructure ZSU-4 obtained with a mixture of silicone surfactant and PEO-PPO-PEO block copolymer as the template (left) X-ray...

Tablets. Pore sizes of ordered silica mesostructures obtained by various methods.

Innocenzi P, Martucd A, GugUelmi M, Bearzotti A, Traversa E (2001) Electrical and structural characterisation of mesoporous sUica thin films as humidity sensors. Sens Actuators B Chem 76 299-303 Innocenzi P, Falcaro P, Bertolo JM, Bearzotti A, Amenitsch H (2005) Electrical responses of silica mesostructured films to changes in environmental humidity and processing conditions. J Non-Cryst Solids 351 1980-1986 Jacobs PA (1977) Carboniogenic activity of zeolites. Elsevier Scientific, New York... 

The compositional modification of silica frameworks by other elements (often metals) is achieved via a number of methods. The most frequently used method is the direct addition of the guest elements precursors to the synthesis solution (gel). Hence, the modifying elements are incorporated into the solid structure along with silica during mesophase formation. This method enables a uniform distribution of the guest element in the resulting framework. A second modification route is to introduce the guest element after formation of the silica mesostructure. This can... 

Lebeau B., Fowler C.E., Hall S.R., Mann S. Transparent thin films and monoliths prepared from dye-functionalised ordered silica mesostructures. J. Mater. Chem. 1999 9 2279-2281... 

Chatterjee, P., Hazra, S., and Amenitsch, H. (2012) Substrate and drying effect in shape and ordering of micelles inside CTAB-silica mesostructured films. Soft Mater., 8, 2956-2964. 

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