Mesoporous oxide architectures

Long JW, I-ogan MS, Rhodes CP, Carpenter EE, Stroud RM, Rolison DR (2004) Nanocrystalline iron oxide aerogels as mesoporous magnetic architectures. J Amer Chem Soc 126 16879 16889. 

Mesoporous oxides have been fabricated using a variety of methods spanning templated self-assembly of nanoparticles, nanocasting and using surfactants to act as a molecular scaffold to help build the mesoporous architecture. Template-free self-assembly of nanoparticles via ice crystallisation has also been achieved, where the phase change from water to ice sculpts the nanoparticles into... 

Fattakhova-Rohfing, D. Brezesinski, T. Rathousky, J. Feldhoff, A. Oekermann, T. Wark, M. Smarsly, B. 2006. Transparent conducting films of indium tin oxide with 3D mesopore architecture. Adv. Mater. 18 2980-2983. 

The inherent limitations of the use of zeolites as catalysts, i.e. their small pore sizes and long diffusion paths, have been addressed extensively. Corma reviewed the area of mesopore-containing microporous oxides,[67] with emphasis on extra-large pore zeolites and pillared-layered clay-type structures. Here we present a brief overview of different approaches to overcoming the limitations regarding the accessibility of catalytic sites in microporous oxide catalysts. In the first part, structures with hierarchical pore architectures, i.e. containing both microporous and mesoporous domains, are discussed. This is followed by a section on the modification of mesoporous host materials with nanometre-sized catalytically active metal oxide particles. 

Amorphous Sn-, Si-, and Al-containing mixed oxides with homogeneous elemental distribution, elemental domains, and well-characterized pore architecture, including micropores and mesopores, can be prepared under controlled conditions by use of two different sol-gel processes. Sn-Si mixed oxides with low Sn content are very active and selective mild acid catalysts which are useful for esterification and etherification reactions [121]. These materials have large surface areas, and their catalytic activity and selectivity are excellent. In the esterification reaction of pentaerythritol and stearic acid catalytic activity can be correlated with surface area and decreasing tin content. The trend of decreasing tin content points to the potential importance of isolated Sn centers as active sites. 

Using the natural polymer, hydrated cellulose, alumina nanocrystalline materials were successfully fabricated. The structure simulates the complex architecture of the origin biological matrix. They were composed of oxide nanograins, mesopores, and the branched system of capillars. These nanostructured alumina fibrous material possess the high absorption ability and may be used as drainage of purulent wound in medicine. 

It seems in Fig. 2g that all the experimental points are lying on a master surface, which is a first indication that there might be a physical law describing the correlation between the pore size and the molecular architecture of the amphiphile. However, because neither the one-phase nor the two-phase model was appropriate to describe the data (as shown elsewhere)," a new model was needed. It seems that in addition to the hydrophobic core (bright yellow), a certain fraction of the hydrophilic poly(ethylene oxide) (PEO) chain contributes to the size of the mesopore Dc (areas I and H in Fig. 3c). Only the remaining fraction of PEO is imbedded in the pore wall. By considering the total volume given by the number of units in the amphiphile chain and the stabilization of the interface I + II/III, it was finally possible to derive an equation that relates the mesopore size to the molecular composition of the amphiphile expressed as Vvb (see Eq. 1) ... 

Another area which was initiated during last year is development of chiral metal oxide based nanomaterials such as chiral Ti02 nanofibres and chiral ZrOj nanotubes. It is anticipated that these chiral metal oxide nanostructures will find very important applications as asymmetric catalysts. In addition the progress in the fabrication of mesoporous silica based chiral nanostructures e.g. helical architectures) should open new opportunities in chiral separation of enantiomeric compounds. 

The conceptual theme of hierarchically stractured materials that are specifically designed to maximize anode or cathode performance can be separately considered in the following components (1) the bulk electrode materials, (2) pores in the bulk material that accommodate fluid flow, (3) mesoporous or structural material to transition from the bulk material to the nanometric dimensions, (4) the nanostmctured transducer, (5) the bio-nano interface, and (6) the biocatalyst (Figure 10.1) [23]. All of the elements must be coupled to achieve electron flow from the electron donor through the architecture to the final electron acceptor. In the anodic half-cell, fuel is oxidized and the liberated electrons are transferred to the electrode and through an external load. The cathode provides the BFC with electromotive force by catalyzing the reduction of oxygen at relatively positive potentials. 

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