Nanoporous crystalline structures

Morphology and crystalline structure of nanoporous Ti02 layer... 

Preparation, Structure, Properties, and Applications of Co-Crystals and Nanoporous Crystalline Phases of Syndiotactic Polystyrene... 

Structure, preparation, properties, and applications of the nanoporous crystalline phases of syndiotactic polystyrene are described in section 3 of this chapter. 

Figure 10.8 Top and lateral views of the crystalline structures of the two nanoporous crystalline phases of SPS. For the 6-(upper figures) and e-(lower figures) phases, the porosity is distributed as cavities and channels, respectively. (See color insert.)...

Shape and volume of empty space of the 8 nanoporous phase of SPS have been evaluated by considering the space available to probe spheres of given radii into crystalline structures of different polymorphic forms of this polymer. This kind of analysis, for probe sphere radii higher than 0.13 nm, shows that the empty space into the nanoporous form corresponds to cavities (two per unit cell) centered on the center of symmetry of the crystal structure. For instance, the volume of these cavities, evaluated for probe spheres with a radius of 0.18nm, is close to 0.115nm [51]. 

In the section on structure and fundamental properties of SPS, Chapter 9 summarizes the polymorphic behavior of this polymer, the structure of the different forms, and the crystallization and melting behavior. Chapter 10 describes co-crystals and nanoporous crystalline phases of SPS regarding preparation, structure, properties, and new interesting applications, for example, molecular sensors. The section concludes with Chapter 11 on selected topics of crystallization thermodynamics and kinetics of SPS. 

Gies FI, Marler B and Werthmann U 1998 Synthesis of porosils crystalline nanoporous silicas with cage- and channel-like void structures Moiecuiar Sieves Science and Technoiogy vo 1, ed FI G Karge and J Weitkamp (Berlin Springer) pp 35-64... 

U. (1998) Synthesis of porosils Crystalline nanoporous silicas with cage-and channel-like void structures in Molecular Sieves Science and Technology, vol. 1 (eds H.G.Karge and ). Weitkamp), Springer, Heidelberg, pp. 35-64. 

For hard biomass made from crystalline cellulose, an inversed structure was found, with the carbon being the continuous phase, penetrated by a sponge-like continuous system of nanopores (representing the majority volume). These products are also... 

The presence of sulfate ions markedly affects the nanopore structure of titania-sulfate aerogels. In Ti02-S042 materials, unlike in zirconia-sulfate aerogels, the larger sulfate load stimulates formation of a more consolidated structure. The XRD analysis shows that even a crystalline phase (anatase) may be present in fresh, dry aerogels, which, perhaps, is the first observation of this phase in sol-gel titania obtained from the low temperature drying process. 

In the search for a new class of nanomaterials, i.e. crystalline nanoporous semiconductors, a lot of efforts are made to synthesize new compounds with a zeolite-like open framework structure consisting of typical semiconductor elements like As, Sb, Se, etc.11-41 In 1995 Wang and Liebau reported the preparation and structure of oxoselenoantimonates (III) with a zeolite-like channel structure15 61, which are related to the natural mineral cetineite.171 This mineral with composition (K Na)3+x(Sb203)3(SbS3)(0H) (2.8-x)H20 with x = 0.5, first described in 1987 by Sabelli and Vezzalini181, was found in Le Cetine mine in Tuscany, Italy. 

Gas, or vapor molecules, after the degasitication process, can go through the pore structure of crystalline and ordered nanoporous materials through a series of channels and/or cavities. Each layer of these channels and cavities is separated by a dense, gas-impermeable division, and within this adsorption space the molecules are subjected to force fields. The interaction with this adsorption field within the adsorption space is the base for the use of these materials in adsorption processes. Sorption operations used for separation processes imply molecular transfer from a gas or a liquid to the adsorbent pore network [2],... 

From the experimental results it appears that electron transport in nanoporous films is strongly affected by grain boundaries. If the porous structure has a depth of 5 //m and the typical grain size is 10 nm, a minimum of 500 grain boundaries have to be crossed in the transport vertical to the film plane. It may therefore be worthwhile to consider alternative surface-enhanced substrates, which feature fewer grain boundaries, or those where these are completely avoided. There are essentially two possibilities for such films porous structures etched in multicrystalline films, or grown columnar films with single-crystalline columns. 

Note that here the formation of nanoporous structure in crystalline matrix of the anodized semiconductor is considered as a primary event, which results from the specific physical processes caused by current flow localization. However, the contribution of chemical processes cannot be excluded either. In particular, coexistence of two competing mechanisms (porous structure formation and SiC dissolution) resulting in formation of non-SPSC, was proposed above. 

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