Materials with Cage Structures Zeolites

In small pore zeolites with cage structure, e. g., faujasites, dye molecules encapsulated by in situ synthesis or crystallization inclusion are stable against extraction.1 2 However, these methods fail for MCM-41 due to the channel structure and the wider pore diameter (3 nm) of the host material. Covalent bonding of guests is necessary to obtain diffusion stability. Therefore, anchoring of organic molecules with catalytic functions into MCM-41 by covalent bonding was recently reported by Brunei et al.3... 

In Zeolite A. The location and distribution of methane within the a-cages of zeolite A were found to be very similar to those found in zeolite Y, consistent with the structural similarities of these two materials. Cohen de Lara et al. (50) complemented their extensive experimental work with MD calculations of a single methane molecule adsorbed in zeolite A. At... 

The following review is concerned with the synthetic and structural chemistry of molecular alumo-siloxanes, which combine in a molecular entity the elements aluminum and silicon connected by oxygen. They may be regarded as molecular counterparts of alumo-silicates, which have attracted considerable attention owing to their solid-state cage structures (see for example zeolites).1 3 Numerous applications have been found for these solid-state materials for instance the holes and pores can be used in different separation techniques.4,5 Recently the channel and pore structures of zeolites and other porous materials have been used as templates for nano-structured materials and for catalytical purposes.6 9... 

In recent years, molecular sieves have found new uses as hosts for the preparation of small metal- and semiconductor clusters that can be grown in confined zeolite spaces and are envisioned for uses in photo-catalysis, non-linear optics, sensors, flat panel displays, etc..[31] The framework-type structures of zeolites can be described with the presence of the n- rings, e.g., 4-, 6-, 8-, 12-rings or double 5-, 6-, 8- rings, or secondary building units, e.g. the sodalite cavity, super cages, and others. These confined spaces can be used for the preparation of optical and electronic materials with desired properties. 

Zeolites, or molecular sieves, are a group of materials with ordered crystalline lattice structures. Within the framework, regular-shaped pores (or cages) are formed. These pores are interconnected to each other through openings (or windows) of the framework. So far, more than 200 unique types of zeolite structures have been identified. Each of the structures is designated with a three-letter code. Details about the zeolite structures and the related materials can be found at the International Zeolite Association s website [24]. 

As in the case of zeolite, the mechanism of action looks similar. No direct comparison can be made because MMT is a layered silicate compared to the cage structure of zeolite, and also because the carbonization agent is no longer a polyol but a char-forming polymer (PA6). Nevertheless, the main conclusion we can draw is that the action of the synergist (nanoclay or zeolite) is to stabilize in a first step the carbonaceous structure forming aluminophosphates and silicophosphates. With the nanoclay, this effect is only effective up to 310°C, whereas it is still efficient at 560°C with zeolite. To keep its protection efficient at high temperatures, the nanoclay permits the formation of protective ceramiclike material after collapse of the phosphocarbonaceous structure. Note that we did not detect any specific influence of the surfactant of the nanoclays, probably because of its low amount in the formulation. 

One difficulty with many synthetic preparations of semiconductor NCs that complicates any interpretation of NMR results is the inevitable distribution of sizes (and exact shapes or surface morphologies). Therefore attempts to make semiconductors as a sort of molecular cluster having a well-defined stoichiometry are of interest to learn potentially about size-dependent NMR parameters and other properties. One approach is to confine the semiconductor inside a template, for instance the cuboctahedral cages of the sodalite framework or other zeolite structures, which have been characterized by multinuclear NMR methods [345-347], including the mesoporous channel material MCM-41 [341, 348]. 

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