Porous aluminosilicate crystals

Zeolite Membranes Zeolites are porous aluminosilicate crystals composed of Si04 and AIO4 tetrahedra arranged in various geometric patterns. The tetrahedra arc... 

Nanociystalline zeolites (ciystal sizes of less than 100 nm) are porous aluminosilicate nanomaterials with increased surface areas relative to conventional micron-sized zeolites. Nanocrystalline zeolites are potentially useful for CWA decontamination applications because of their enhanced absorptive and catalytic properties. This chapter describes FTIR and solid state NMR studies of the thermal reactivity of two CWA simulants, 2-CEES (2 chloroethyl sulfide) and DMMP (dimethylmethylphosphonate) on nanocrystalline zeohtes, such as NaZSM-5 (sihcalite, purely siliceous form of ZSM-5) and NaY, with crystal sizes of approximately 25 nm. 

One of the major criticisms of MOFs with respect to their use as heterogeneous catalysts is their lower crystal stability compared with that of zeolites and other porous aluminosilicates [21]. In fact, it is well known that some of the first MOFs reported such as MOF-5 are notoriously instable and the crystal structure tends to collapse on storage under ambient conditions or during the reaction [22]. This lack of stability seems to be relatively common for Zn- and Cu-containing MOFs. For instance, Cu3(BTC)2 (BTC 1,3,5-benzenetricarboxylate) is unstable in the presence of thiols, probably due to the strong... 

Zeolites are crystalline aluminosilicates that are used as catalysts and that have a particular chemical and physical structure (Decroocq, 1984 Goursot et al., 1997). They are highly porous crystals veined with sub-microscopic channels. The channels contain water (hence the bubbling at high temperatures), which can be eliminated by heating (combined with other treatments) without altering the crystal structure (Occelli and Robson, 1989). 

With the growing interest in nanochemistry (Ozin, 1992), many attempts have been made in recent years to prepare porous crystals having larger channel widths than those in the aluminosilicate zeolites (i.e. 0.8 nm). In particular, great excitement was generated by the preparation of the wide-pore aluminophosphate, VPI-5, by Davis and his co-workers in 1988 and again when the first member of a new group of mesoporous molecular sieves , MCM-41, was prepared by Mobil scientists in 1992. 

Qtudies of new perspective fine porous crystal zeolites have shown that their properties depend strongly on cations compensating the negative charge of the aluminosilicate framework. 

The entrapment-type nanocomposites can be prepared from zeolites and they are of two types zeolite-inorganic and zeolite-organic. Zeolite crystals are three-dimensionally linked network structures of aluminosilicate, aluminophosphate (ALPO), and silicoaluminophosphate (SAPO) composition and are porous, the pores being in the range of 2.8 to 10 A. Many of the highly siliceous, ALPO, and SAPO zeolites have been synthesized using organic templates such as tetrapropyl... 

Small amounts of synthetic zeolites (based on metal aluminosilicates) can be added to the system to adsorb unwanted organic odour-producing molecules and/or to remove the moisture that contributes to odours (by trapping them in their highly porous crystal structures). This technique is successfully used in extruded polyolefin pipes, injection and extrusion blow-moulded containers, barrier packaging materials, extrusion coatings, and sealant polymers. 

Molecular sieve zeolites. These zeolites are porous crystalline aluminosilicates that form an open crystal lattice containing precisely uniform pores. Hence, the uniform pore size is different from other types of adsorbents which have a range of pore sizes. Different zeolites have pore sizes from about 3 to 10 A. Zeolites are used for drying, separation of hydrocarbons, mixtures, and many other applications. 

Because of the uniquely ordered structure of template-synthesized porous carbons, they themselves can be used as templates to replicate other materials with an ordered porous structure that is difficult to make using traditional methods [121,338-348], Thus, CMK-3 carbon was first demonstrated as a template to prepare mesoporous silica [121,338]. An OMC prepared from an MCM-48 template was used to prepare nanostructured silica [339]. Nanocasting of CMK-3 using ZSM-5 crystals yielded a mesoporous zeolite with both mesopores and micropores [340]. More recently, the preparation of a novel class of mesoporous aluminosilicate molecular sieves was described [341]. The preparation of mesoporous boron nitride (MBN) and mesoporous carbon nitride (MBCN) with very high surface area and pore volume was recently realized using a well-ordered hexagonal mesoporous carbon as a template and boron trioxide as a boron source [342]. Nonspherical silica nanocases with a hollow core and mesoporous shell were also produced [343]. 

Zeolite molecular sieves are crystalline, porous inorganic solids, typically aluminosilicates, with channel diameters ranging from 0.3 to 1.2 nm and beyond, and crystal sizes typically between 0.5 and 5 /im. If species are selectively adsorbed into the well-defined channel systems of zeolites, the sensor response can be made selective for those species, while larger molecules are only adsorbed on the outer surface of the sensor membrane. Furthermore, many zeolites show ion exchange capability which introduces numerous possibilities for intrapore modifications. 

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