Micelle templated silica surface

D. Brunei, N. Bellocq, P. Sutra, A. Cauvel, M. Lasperas, P. Moreau, F. Di Renzo, A. Galarneau, and F. Fajula, Transition-metal ligands bound onto the micelle-templated silica surface. Coord. Chem. Rev. 180, 1085-1108 (1998). 

Since the disclosure by Mobil of Micelle-Templated Silicate structures called MCM-41 (hexagonal symmetry) or MCM-48 (cubic symmetry) [1,2] many other structures have been synthesized using different surfactants and different synthesis conditions. All of these Micelle-Templated Silicas (MTS) have attracted much interest in fields as diverse as catalysis, adsorption, waste treatment and nanotechnology. MTS materials possess a high surface area ( 1000 m2/g), high pore volume ( 1 mL/g), tunable pore size (18-150 A), narrow pore size distribution, adjustable wall thickness (5-20 A). The silica walls can be doped with different metals for catalytic applications, like Al orTi, for acidic or oxydation reactions, respectively. 

Even though there is great interest in such systems based on polymers as supporting materials, this chapter essentially focuses on the use of minerals as support. The use of silica has been historically investigated, mainly for its large surface area. As mentioned later, micelle-templated silica (MTS) has recently been disclosed. 

Sutra, P., Fajula, F., Brunei, D., Lentz, P., Daelen, G. and Nagy, J. B. Si-29 and C-13 MAS-NMR characterization of surface modification of micelle-templated silicas during the grafting of organic moieties and end-capping, Colloids Surf., A, 1999, 158, 21-27. 

Some degree of success in supported enantioselective catalysis was accomplished by using functionalisation of mineral support. Due to their unique textural and surface properties, mesoporous micelle-templated silicas are able to bring new interesting properties for the preparation of optically active solids. Many successfully examples have been reported for enantioselective hydrogenation, epoxidation and alkylation. However, the stability of the immobilised catalysts still deserves efforts to allow industrial development of such attractive materials. 

In conclusion, the study of the influence of grafted chain length on the hydrophobicity of silica gel allowed us to choose a convenient surface treatment, which was successfully transposed to MCM-41 materials. These former materials were demonstrated to be particularly suitable for the considered new field of applications, and to present advantages compared to silica gels. Finally, Micelle-Templated-Silica materials represent a class of useful models for a comprehensive study of the mechanisms of energy dissipation during forced intrusion and more generally of the physical chemistry of surfaces. 

In this respect, the recently discovered family of materials synthetized by silicate condensation around surfactant micelles (Micelle-Templated Silica, MTS) provides unique inorganic support [11,12] due to their regular arrays of uniformly sized channels in the mesopore range of 20-100 A. This solid was recently impregnated with cesium oxides with the aim to obtain superbase catalysts [13]. Nevertheless, the leaching of the basic particles cannot be excluded. In view to avoid such possible phenomena, we have studied the covalent attachment of basic functions such as amino groups on the MTS surface... 

The pretormed siliceous supports were KiescIgel-60 71 and Micelle Templated Silica (MTS) 72 prepared by published methods and showing textural characteristics similar to those of MC M 4I. namely hexagonal unit cell ao = 4.3 nm surface area 958 in g mesoporous volume 0.76 ml g (33]. 

Spherical particles in the micrometric size range of mesoporous MSU-X silica were obtained with nonionic PEO-based surfactant by a new, easy and highly reproducible synthesis pathway leading to Micelle Templated Structures (MTS) with large surface area and narrow pore size distribution. First results on their adsorption properties show that they could be used for HPLC applications. 

The overall performance of a catalyst is known to depend not only on the inherent catalytic activity of the active phase but also on the textural properties of the solid. The ability to control the specific surface area and the pore size distribution during the synthesis of amorphous silica-aluminas has been described for both surfactant micelle templated syntheses (M41-S (1), FSM-16 (2), HMS (3), SBA (4), MSU (5), KIT-1 (6)) and cluster templated sol-gel syntheses (MSA (7), ERS-8 (8)). 

Micelle-templated porous silicas and organosilicas typically exhibit well-accessible porous structures with a high specific surface area and large pore volume. A micelle-templated formation of ordered mesoporous... 

The mesoporous silica materials can be synthesized in presence of assembled cationic surfactant micelle templates, which serve as structure-directing agents for polymerizing sihca component by electrostatic interaction [99]. However, the surface of mesoporous silica materials needs to be modified by co-condensation (one-pot synthesis) [100] /grafting (post-synthesis modification) in order to prepare its well-dispersed composite with enhanced interfacial adhesion [101],... 

Hybrid silica materials were prepared via a sol-gel pathway at pH 9. The influence of anionic surfactant (SDS) was studied by comparing templated materials (TbSn series) with hybrid materials obtained without surfactant (Tbn series). Two mechanisms of mesostructure formation can be considered as represented on Fig. 2. The pka of aminopropyl chain is about 10.6 in the reaction mixture propyl-amines are partially protonated. Electrostatic interactions between dodecylsulfate anion and NH and sodium cation neutralization may then occur, resulting in the condensation of the silica structure around surfactant micelles and aminopropyl groups at the surface of the pores. The other mechanism is SDS chains complex-ation by P-CD cavity, which wonld result in P-CD gronps located at the surface of the pores and aminopropyl less accessible, due to steric hindrance caused by P-CD bulky groups. A complete characterization of the prodncts and adsorption capacities will help nnderstanding the formation mechanism of mesoporons hybrid silica. 

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