Ordered mesoporous silica

Template Synthesis and Catalysis of Metal Nanoclusters in Ordered Mesoporous Silicas... 

Nanostructured silica and ordered mesoporous silicas have been envisaged as small enzyme immobilization supports [196]. The encapsulation approach is required either to further immobilize enzymes adsorbed in the channels by reducing the pore opening by further silylation or by encapsulating the enzyme directly [197]. 

Pore shape affects the determination of the pore size of ordered mesoporous silicas by mercury intrusion... 

Ordered mesoporous silicas present mesopores of appropriate size to be evaluated and compared in their field of superposition (3-50 nm) of the methods of pore size evaluation by N2 volumetry and Hg intrusion. The usual models to evaluate pore sizes by Hg intrusion refer to cylindrical pores [1,2]. Here we evaluate the influence of some non ideal characteristics of the SBA-15 system, namely uneven pore walls, mesopore interconnection or presence of micropores [3, 4], on the mercury intrusion. 

SBA-15 samples with diameters from 5 to 10 nm have been prepared by tuning the temperature of the first step of the synthesis [5], MCM-41 has been prepared in the presence of hexadecyl trimethyl ammonium by using methylamine as pH-controlling agent [6], The pore size from N2 adsorption at 77 K has been evaluated by the Broekhoff and de Boer method, shown to correctly evaluate the pore size of ordered mesoporous silicas [7]. 

Ordered mesoporous silica have already been studied as carriers for drug delivery [1,2] recently, their use has also been proposed in bone tissue engineering [3,4], in combination with bioactive glass-ceramic scaffolds [5,6]. The kinetics of ibuprofen release in SBF [7] from MCM-41 silica with similar pore diameter has shown puzzling discontinuities [3,6,8] aim of the present work is to assess whether these anomalies may be related to structural changes in the MCM-41 mesoporous spheres under the adopted conditions. 

We also include in this class of quasi-2D nanostructured materials Titania deposited inside ordered mesoporous silica (because an inner coating of mesoporous silica may be realized), or nano-dot type Titania particles well dispersed in the ordered porous matrix. We do not consider here solids which contain linear or zig-zag type TiOTiO-nanowires in a microcrystalline porous framework, such as ETS-4 and ETS-10, notwithstanding the interest of these materials also as photocatalysts,146-151 because these nanowires are located inside the host matrix, and not fully accessible from the gas reactants (the reactivity is essentially at pore mouth). 

For example, MSU-1 prepared using Tergitol is a disordered hexagonal mesoporous (25-48 A) silica. More recently, triblock copolymers based on ethylene oxide (EO) and propylene oxide (PO) have been used to make well-ordered mesoporous silicas having ID channels with pore sizes in the range of 50-300A... 

Surface Modifications of Ordered Mesoporous Silica Materials. .122... 

The key effect of oxide supports on the catalytic activities of metal particles is exerted through the interface between oxides and metal particles. The key objective of this study is to develop synthesis methodologies for tailoring this interface. Here, an SSG approach was introduced to modify the surface of mesoporous silica materials with ultrathin films of titanium oxide so that the uniform deposition of gold precursors on ordered mesoporous silica materials by DP could be achieved without the constraint of the low lEP of silica. The surface sol-gel process was originally developed by Kunitake and coworkers.This novel technology enables molecular-scale control of film thickness over a large 2-D substrate area and can be viewed as a solution-based... 

Recently, new ordered mesoporous silicas have also been synthesized by using self-organization of amphiphilic molecules, surfactants and polymers either in acidic or basic condition. A schematic phase diagram of water-surfactant is shown in the figure. 

Figure 1. Scheme for the liquid crystalline templating mechanism proposed by Kresge et al 1 for synthesis of mesoporous silica MCM-41. Formation of a hexagonal array of cylindrical micelles possibly mediated by silicate anions followed by condensation of the silicate anions from the silicate source (tetraethylorthosilicate) leads to templated framework structure. Calcination or extraction of the template produces hexagonally ordered mesoporous silica. 

Matos JR, Mercuri LP, Jaroniec M, Kruk M, Sakamoto Y, Terasaki O (2001) Synthesis and characterization of europium-doped ordered mesoporous silicas. J Mater Chem 11 2580-2586... 

A two-step procedure based on the attachment of an organogold precursor within the channels of thiol-functionalized ordered mesoporous silica HMS-C16 and SBA-15 has been carried out. In a second step, the chemical reduction yields Au NPs exclusively located within the pore channels [177]. 

Since the discovery of ordered mesoporous silica materials such as MCM-41 [1] and FSM-16 [2], many attempts have been made to apply them for various type of catalysis [3]. Especially, much attention has been paid to the catalytic functions generated through the incorporation of heteroelements into mesoporous silica matrix, but not so much to those of mesoporous silica without heteroelements. This may be because silica itself is known to be inactive for many catalytic reactions. 

Among the inorganic templates, zeolite produces more regulated pores as compared to the silica template. If nano-channels in zeolite are completely filled with carbonaceous precursor and then the carbon materials are extracted from the zeolite framework, one can obtain the porous carbon of which structure reflects the porosity of the original zeolite template. The ordered mesoporous silica templates, e.g., MCM-4 838,39,47 and SBA-1547 have been employed to prepare the ordered porous carbons by the procedures involving the pore filling of the silica template with carbonaceous precursor followed by carbonization and silica dissolution. The resulting pore sizes of the ordered mesoporous carbons are smaller than about 10 nm. 

Ford DM Simanek EE Shantz DF, Engineering nanospaces Ordered mesoporous silicas as model substrates for building complex hybrid materials, Nanotechnology, 2005,16, S458-S475. 

George, J., Shylesh, S. and Singh, A. P. Vanadium-containing ordered mesoporous silicas Synthesis, characterization and catalytic activity in the hydroxylation of biphenyl, Appl. Catal., A, 2005, 290, 148-158. 

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