Mesoporous structure

Sol-gel processing forms the basis for various routes employed for the fabrication of a wide diversity of functional materials. To impart a structural organization at various length scales, the syntheses are performed using templates. Most consist of a self-organized ensemble of surfactants and co-polymers [1-10]. They have been successfully applied to control the geometry and dimensions of pores that are periodically arranged as in the initial structures. Mesoporous silica materials of the MCM family, which were first synthesized by a team from the Mobil oil company [11,12], are a well-known example. 

To avoid the limitations of the small apertures and cavities provided by zeolites, mesopores have been created inside zeolites X, Y and DAY.[140] By dealumination of the zeolite structure, mesoporous regions that are completely surrounded by micropores were obtained, and these intrazeolitic cavities were then used as the space in which to assemble metal complexes. The preparation of a cobalt-salen-5 complex provided a catalytic material that shows improvements in the conversion,... 

Highly structured mesoporous silicas using a surfactant template provide a well characterized, ultra-high surface area material.5 In this volume Jaroniec provides an excellent summary of various novel materials based on this chemistry for Hg2+ adsorption. In this report we discuss results from a recent study utilizing two types of silica gels and a nanoparticulate fumed silica, all surface modified with complexing functional groups, for the adsorption of Cu2+ and Pb2+. 

Incorporation of titanium oxide species within the framework of mesoporous silicas has been shown to produce highly efficient photocatalytic materials. Extremely careful preparation conditions [84] leads to highly structured materials comprising anatase nanoparticles of dimension between 5 and 10 run. The channeled structure, together with the hydrophobic/hydrophilic character, are also key features controUing their enhanced photoreactivity. The photocatalytic activity of such mesoporous catalysts has been studied for the degradation of phenol in aqueous solutions [85]. It was observed that for structured mesoporous materials with low Ti content, the turnover frequency was four times greater than that for standard P25. 

On the basis of the results of various characterization techniques, it was found that MCM-41 consists of 4 levels of structure mesopores, crystaUites, grains and particles. AU these levels have been successfuUy characterized. Estimates of surface area by SAXS and SANS are higher, while those from mercury porosimetry are much lower, than those estimates by BET methods the estimates obtained from geometrical consideration using variable waU thickness are close to the BET results. It was confirmed that mesopores in MCM-41 are curved rather than straight channels and, even though they do not have an ideal mesopore structure, they can be considered as model mesoporous materials for gas adsorption studies. 

This paper describes a new synthesis strategy of preparing thermally stable mesostructured transition metal oxides, namely, two-step synthesis (TSS). Basically, the synthesis course involves two steps (1) formation of a mesostructured transition metal oxide solid mediated by surfactant in a basic aqueous solution and (2) treatment of the solid product in an acidic organic solvent containing the respective precursor from which the solid product was produced. The final material synthesized according to such a method is thermally stable and structurally mesoporous with high surface area and uniform pores arranged disorderedly. 

Ultrasounds in synthesis 06-P-14 Wall structure, mesoporous silica 06-P-05... 

Borini, S., Boarino, L. and Amato G. Coulomb blockade sensors based on nano-structured mesoporous silicon , (2007) Physica E. 38,197-9. 

Recently, synthesis of ordered mesoporous crystalline P-Mn02 using KIT-6 as a hard template has been reported. " Because of the large surface area and accessibility to the crystalline wall with the ordered mesoporous structure, mesoporous P-Mn02 facilitates fast transport of... 

OMC carbons obtained from replication of structured mesoporous silicas show a narrow pore size distribution, but with mesopores smaller (< 15 nm) than those obtained from colloidal replication. PtRu nanoparticles supported on ordered mesoporous carbon CMK-3 were analyzed by Din et al. [63] Although a good nanoparticle dispersion was obtained, the catalyst synthesized showed a worse performance than nanoparticles supported on Vulcan XC-72 for methanol oxidation. 

The goal of this chapter is to gather the methods most commonly used for the preparation of gold catalysts supported on common oxide powders. For the sake of brevity, deposition on more specific supports, such as structured mesoporous supports, zeolites, and carbon is barely reported in this chapter, and we refer to Chapter 4 of the book on gold catalysis [7]. The methods described are mainly those performed in the liquid phase. The preparations of model catalysts, that is, on films or single crystals and those of bimetallics are excluded. 

The fabrication process for metal silicate nanotubes is depicted in Fig. 32A. HRTEM image of the as-prepared SNT template (Fig. 32B) showed its hollow structure and hierarchical pore structure mesopores at the wall with about a 30 nm thickness and macropores at the center. This hierarchical pore structure is veiy suitable to prepare silicate materials. Under hydrothermal conditions, metal ions and other ions in water solution could easily diffuse into the pores of the SNT template and react with silica species to form metal silicates in situ (Fig. 32C). The original silica mesopores, where the reaction occurs, are uniformly dispersed in the walls, and the metal ions in water solution could easily diffuse into the pores of the SNT template. The whole silica wall with about 30 nm thickness can be readily converted to metal silicates under the reaction conditions. 

Supramolecular templating M41S-structures Mesoporous (2-30 nm) uni-modal and bimodal... 

Wang Y, Song S, Shen PK, Guo C, Li CM (2009) Nanochain-structured mesoporous tungsten carbide and its superior electrocatalysis. J Mater Chem 19 6149-6153... 

Initial solution Wet gel r- structuring agent Inorganic precursor Hybrid inorganic/ organic structured Mesoporous inorganic network... 

Fig. 36 Core—shell-structured mesoporous silica-supported Rh catalyst...

Plyuto Y., Berquier J.-M., Jacquiod C., RicoUeau C. Ag nanoparticles synthesised in template-structured mesoporous silica films on a glass substrate. Chem. Commun. 1999 1653-1654 Roser S., Patel H.M., Lovell M.R., Muir J.E., Mann S. X-ray reflection studies on the monolayer-mediated growth of mesostructured MCM-41 silica at the air/water interface. J. Chem. Soc., Chem. Commun. 1998 829-830... 

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