Mesoporous silica structure

The mechanical incorporation of active nanoparticles into the silica pore structure is very promising for the general synthesis of supported catalysts, although particles larger than the support s pore diameter cannot be incorporated into the mesopore structure. To overcome this limitation, pre-defined Pt particles were mixed with silica precursors, and the mesoporous silica structures were grown by a hydrothermal method. This process is referred to as nanoparticle encapsulation (NE) (Scheme 2) [16] because the resulting silica encapsulates metal nanoparticles inside the pore structure. 

One of the most promising applications of enzyme-immobilized mesoporous materials is as microscopic reactors. Galameau et al. investigated the effect of mesoporous silica structures and their surface natures on the activity of immobilized lipases [199]. Too hydrophilic (pure silica) or too hydrophobic (butyl-grafted silica) supports are not appropriate for the development of high activity for lipases. An adequate hydrophobic/hydrophilic balance of the support, such as a supported-micelle, provides the best route to enhance lipase activity. They also encapsulated the lipases in sponge mesoporous silicates, a new procedure based on the addition of a mixture of lecithin and amines to a sol-gel synthesis to provide pore-size control. 

D. Y. Zhao, Q. S. Huo, J. L. Feng, B. F. Chmelka, and G. D. Smcky, Nonionic triblock and star diblock copolymer and oligomeric surfactant syntheses of highly ordered, hydrothermally stable, mesoporous silica structures, J. Am. Chem. Soc. 120(24), 6024-6036 (1998). 

Similar to higher organisms combining muscles with skeletons to attain mobility, the addition of flexible organic functionalities to the rigid mesoporous silica structures enables the formation of gated systems. Organic species can be covalently attached to silica with relative ease. The main sources for the functionalization of silica are... 

Davidson (2002) Mesoporous silica Structure evolution, role of templates crystallization variables + + n.a. Synthesis of mesoporous silica with defined properties... 

Functionalized Mesoporous Silica Structures Towards Novel Drug Delivery Systems... 

Fig. 27.5. Mesoporous silica nanoparticles as novel drug delivery systems, (a) Cocondensation method to form functionalized mesoporous silica structures in a surfactant template synthesis, (b) TEM image of mesoporous silica nanoparticles and sketch of a novel drug delivery particle which contains functionalized pores, closed by a gate, and is decorated with ligands for cell targeting, (c) Cell targeting by ligand-receptor interaction at the cell membrane, endosomal uptake and controlled release after pH change from early to late endosome...

Zeolites were already employed as templates in the synthesis of microporous carbon with ordered structures.[247] The discovery of ordered mesoporous silica materials opened new opportunities in the synthesis of periodic carbon structures using the templating approach. By employing mesoporous silica structures as hard templates, ordered mesoporous carbon replicas have been synthesized from a nanocasting strategy. The synthesis is quite tedious and involves two main steps (i) Preparation and calcination of the silica mesophase, and (ii) filling the silica pore system by a carbon precursor, followed by the carbonization and selective removal of the silica framework. 

C.Z. Yu, Y.H. Yu, L. Miao, and D.Y. Zhao, Highly Ordered Mesoporous Silica Structures Templated by Poly(butylene oxide) Segment Di- and Tri-block Copolymers. Microporous Mesoporous Mater., 2001, 44, 65-72. 

Yu, C. Yu, Y. Zhao, D. Highly ordered large caged cubic mesoporous silica structures tern-plated by triblock PEO-PBO-PEO copolymer. Chem. Commun. 2000, (7), 575-576. 

P-07 - A Study on the mesoporous silica structures templated by triblock copolymers... 

In this paper, we have demonstrated a simple secondary hydrolysis process to synthesize a highly ordered hexagonal mesoporous silica structure by using nonionic oligomeric surfactant with long hydrophilic chain. This process involves an adsorption step of extra silica source and secondary hydrolysis process and can result in large improvement on the ordering and hydrothermal stability for the mesoporous silica materials. 

The incorporation of metal atoms in mesoporous silica structure is of high interest in catalysis. Ravikovitch et al. 

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