Nanoporous solids

X.B. Pinpointing the Location of Nanoparticles Supported on Nanoporous Solids... 

In 1992, Mobil reported a novel family of molecular sieves known as the M41S materials that established an entirely new area in nanoporous solids (168,169). The M41S materials expanded the range of pore sizes into the mesoporous domain (20-300 A). The impact of this discovery on molecular sieve research has been profound. In 1998, an international conference solely devoted to mesoporous molecular sieves was founded (170). The journal Microporous Materials even re-... 

Generally speaking new nanoporous solids have well-defined pore structures. 

We need to use electromagnetic waves which can penetrate solids to elucidate the nanopores. At the same time, characterization of nanoporous solids must be examined from different angles and levels using optimum methods. The necessary levels are electronic, atomic, and morphological structures. 

Recently, N2 adsorption isotherm of nanoporous solids is measured at 77 K over the wide relative pressure range of 10" to 1. Such a wide pressure range adsorption isotherm leads to high resolution as-plot which provides accurate surface area and pore volume even for... 

These categories of nanomaterials are useful due to the rather different physical behavior, growth and structure of each type. For example, nanoclusters are closely akin to molecules in terms of transport and reactive processes. Nanoparticles are somewhat like classical colloids, but in a smaller size regime. Nanoporous solids have unique abilities to encapsulate, bind and react with other nanoparticles and nanoclusters, as well as molecules. Nanocrystals can have relaxed or contracted lattices, and unusual reactivity relative to their larger counterparts. 

Nanoporous solids pore diam. 0.5-10 nm Zeolites, phosphates etc. 

The book starts with a brief introduction to nanomaterials followed by chapters dealing with the synthesis, structure and properties of various types of nanostructures. There are chapters devoted to oxomolybdates, porous silicon, polymers, electrochemistry, photochemistry, nanoporous solids and nanocatalysis. Nanomanipulation and lithography are covered in a separate chapter. In our attempt to make each contribution complete in itself, there is some unavoidable overlap amongst the chapters. Some chapters cover entire areas, while others expound on a single material or a technique. Our gratitude goes to S. Roy for his valuable support in preparing the index manuscript. 

This scheme can be extended to nonconducting or semiconducting nanoporous solids incorporating redox-active centers via chemical doping prompted by sol-gel methodologies (Domenech and Alarcon, 2002b, 2003 Domenech et al. 2004b-d). Eventually, the materials can be electrochemically modified (Rolison and Bessel, 2000). 

Fig. 17 Bronsted acid-induced LLC phase formation of a chiral imidazolinone monomer as means of generating nanoporous, solid-state, chiral Diels-Alder catalysts. Partially reproduced with permission from [120]. 2005 by the American Chemical Society...

Two-dimensional arrangements might be monolayers of clusters on a suitable substrate or two or more coupled ID arrays. While layers are accessible via self-assembly, LB, or electrodeposition, coupled arrays could be obtained by filling clusters into the parallel channels of a crystalline nanoporous solid. 2D networks of clusters might be precursors for simple neural networks, utilizing the Coulombic interaction between ballistic electrons in a 2D electron gas. This concept has been discussed by Naruse and in general introduces new possibilities for the interconnection approach in various fields, e.g. parallel processing and quantum functional devices. 

Surface and structural properties of nanoporous solids can be studied directly by employing modem techniques such as atomic force microscopy, electron microscopy, X-ray analysis and various spectroscopic methods suitable for materials characterization and surface imping [4]. In addition, these properties can be investigated by indirect methods such as adsorption [1, 11-13], chromatography [14, 15] and thermal analysis [16]. The quantities evaluated from adsorption, chromatographic and thermodesorption data provide information about the whole adsorbent-adsorbate system. These data can by used mainly to extract... 

Framework and Surfaces Since compositions and structures are very diverse, surface and framework properties are also extremely varied. In terms of compositions, coordination, and chemical environments, several methods are particularly informative for the characterization of nanoporous solids, such as nuclear magnetic resonance methods (NMR), UV-visible spectroscopy, Fourier-transform infrared spectroscopy (FTIR), Raman spectroscopy, x-ray absorption spectroscopies, x-ray photoelectron emission spectroscopy (XPS), and electron paramagnetic resonance (EPR) (4, 6). Among them, sohd state NMR techniques arc largely employed and will be briefly described in the following. 

Materials made of finely divided particles exhibit much higher surface area than bulk materials. Clearly, smaller particles result in an increased dispersion, that is, a higher surface to volume ratio. For pores, the situation is similar, except for the opposite curvature, which is usually negative (concave) for pores, whereas the surface curvature may be seen as mainly positive in the case of nanoparticles. A nanoporous solid is also finely divided but in terms of numbers of cavities or voids. The resulting areas of the exposed surfaces are greatly increased. 

NMR imaging of gas adsorption/desorption in nanoporous solids, such as Y-AI2O3 and ZnO powders and partially sintered ceramics of these materials, as well as Vycor porous glass was analysed using Brunauer-Emmett-Teller (BET) theory. Visualization of gaseous xenon and methane in the void spaces of aerogels offered unique information and insights into the pore structure and molecular diffusivities of occluded sorbates. ... 

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