Mesoporous nanoparticles

As an intermediate between solid supported layers and the inherent dynamic and nanostructured properties of phospholipid vesicle supports, silica and especially mesoporous silica nanoparticles may provide interesting platforms for dynamic bilayers. Previous studies have shown that stable bilayers can form on both amorphous [102] or functional silica [103, 104] and mesoporous nanoparticles [105] or membranes [106]. This type of biomimetic carrier has great potential as a type of trackable stabilized membrane capable of displaying cellular targeting elements in a close to natural configuration. 

Furthermore, mesoporous nanoparticles with a diameter of about 100 nm can be produced as shown in the upper part of Fig. 27.5b. We intend to use them as the basis for a novel drug delivery system which is sketched in the lower part of Fig. 27.5b. This system has several functions for controlled release and targeting of specific cells. These functions are (1) functionalized pore walls to create a depot effect and controlled release of the drug ... 

Several synthetic strategies to control the sizes of mesoporous nanoparticles have been reported. Lu[272] reported a rapid, aerosol-based process for synthesizing solid, well ordered spherical particles with stable pore mesostructures of hexagonal and cubic topology, as well as layered (vesicular) structures. This method relies on evaporation-induced interfacial self-assembly confined to spherical aerosol droplets. This simple, generalizable process can be modified for the formation of ordered mesostructured thin films. 

Figure 13.10. Representative TEM images of (a) Brij 56-tempiated TSUA-modified mesoporous films, (b) electron diffraction pattern of the cross-sectional TEM image (a), (c) 2-D GISAXS data of a Brij 56-templated photoresponsive nanocomposite thin film, (d) CTAB-templated TSUA-modified mesoporous nanoparticles, (e) CTAB-templated BSUA-modified mesoporous films, and (f) Brij 56-templated BSUA-modified mesoporous films.

Morphology Control In Mesoporous Materials Mesoporous Nanoparticles... 

The number of available surface sites for isopropanol adsorption of bulk tungsten trioxide and monolayer supported tungsten oxide catalysts, even mesoporous nanoparticles, is orders of magnitude (0.9-6 pmol/m ) lower than the heteropolyacids (8-55 pmol/m ). This observation cannot be attributed to the surface structure because all these materials possess polymerized WOg species with octahedral coordination (see Table 5.1). Moreover, no correlation is observed with the specific surface area and the pore diameter because high surface area, mesoporous monolayer supported catalysts possess lower Ns than HPAs. In fact. Table 5.1 shows that those materials do not possess microporosity the specific surface area is only external surface area. This observation shows that the adsorption of alcohol occurs exclusively at the outermost surface layer of WO3 and monolayer supported tungsten oxide catalysts. 

Figure 43.9 TEM of a mesoporous nanoparticle of a bioactive glass composition.

Bray KL (2001) High Pressure Probes of Electronic Structure and Luminescence Properties of Transition Metal and Lanthanide Systems. 213 1-94 Bronstein LM (2003) Nanoparticles Made in Mesoporous Solids. 226 55-89 Bronstrup M (2003) High Throughput Mass Spectrometry for Compound Characterization in Drug Discovery. 225 275-294... 

Abstract A review of the thermolytic molecular precursor (TMP) method for the generation of multi-component oxide materials is presented. Various adaptations of the TMP method that allow for the preparation of a wide range of materials are described. Further, the generation of isolated catalytic centers (via grafting techniques) and mesoporous materials (via use of organic templates) is simimarized. The implications for syntheses of new catalysts, catalyst supports, nanoparticles, mesoporous oxides, and other novel materials are discussed. 

Figure 7.5 Two topologically distinct types of mesoporous gold sponge, each with 50 volume % gold, (a) Swiss-cheese morphology produced by de-alloying, (b) aggregated particle morphology produced by sintering of nanoparticles.

Without sonication, Pt particles adsorb primarily on the external surface of SBA-15 and at the mesopore openings. Sonication promotes homogeneous inclusion and deposition of Pt nanoparticles on the inner surface of the support mesopores, because ca. 90% of the total surface area is from the inner pore walls. Heat treatment... 

Scheme 1. Inclusion of size-controlled PVP-protected Pt nanoparticles in calcined mesoporous SBA-15 silica matrices. Mechanical agitation by low-power sonication affords a high dispersion of nanoparticles ranging in size from 1 to 7nm in the mesopore channels. The method is referred to as capillary inclusion (Cl). The technique is limited by the size of nanoparticles that can fit into the 6-9 nm diameter mesopores [13]. (Reprinted from Ref [13], 2005, with permission from American Chemical Society.)...

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. 

Zeolites have ordered micropores smaller than 2nm in diameter and are widely used as catalysts and supports in many practical reactions. Some zeolites have solid acidity and show shape-selectivity, which gives crucial effects in the processes of oil refining and petrochemistry. Metal nanoclusters and complexes can be synthesized in zeolites by the ship-in-a-bottle technique (Figure 1) [1,2], and the composite materials have also been applied to catalytic reactions. However, the decline of catalytic activity was often observed due to the diffusion-limitation of substrates or products in the micropores of zeolites. To overcome this drawback, newly developed mesoporous silicas such as FSM-16 [3,4], MCM-41 [5], and SBA-15 [6] have been used as catalyst supports, because they have large pores (2-10 nm) and high surface area (500-1000 m g ) [7,8]. The internal surface of the channels accounts for more than 90% of the surface area of mesoporous silicas. With the help of the new incredible materials, template synthesis of metal nanoclusters inside mesoporous channels is achieved and the nanoclusters give stupendous performances in various applications [9]. In this chapter, nanoclusters include nanoparticles and nanowires, and we focus on the synthesis and catalytic application of noble-metal nanoclusters in mesoporous silicas. 

Recently, Somorjai reported the hydrothermal synthesis of SBA-15 in the presence of PVP-stabilized Pt nanoparticles [22]. This is a one-step synthesis of composites of metal nanoparticles and mesoporous silica. 

---