Zeolites hollow crystals

As mentioned in the previous section, hollow zeolite spheres of LTA, FAU, BEA, MFI can be prepared in the presence of polystyrene beads as templates by using an LBL self-assembly technique. Recently, several research groups have tried to adopt similar methods to synthesize zeolite-template composites on the surfaces of templates with various shapes and sizes, properties, and structures through self-assembly or in situ-crystallization approaches. Subsequent removal of the templates forms zeolite materials with analogical skeletons of the templates. Up to now, the reported templates include microspheres, carbon fibers, polyurethane foams, and microbe structures,[144,145] as well... 

Zeolite shells on polystyrene beads were prepared by a combination of layer-by-layer (LbL) and hydrothermal synthesis techniques. The negatively charged polystyrene beads were surface modified in order to adsorb zeolite Beta nanocrystals. Such particles were then adsorbed on the surface of the beads and induced to grow into a continuous film of intergrown crystals of zeolite Beta. The effect of the preliminary treatment on the formation of the zeolite film was studied. Finally the polystyrene beads used as macro-templates were removed by calcination in air, yielding hollow spheres of zeolite Beta. The zeolite Beta/polystyrene composites and the corresponding hollow zeolite spheres were characterized by XRD, SEM, TG/DTA and BET surface area measurements. 

An improved polymerization-induced colloid aggregation (im-PlCA) method was developed to prepare zeolite microspheres with hierarchical porous stractures and a uniform size, which could easily be carried out by adding urea and formaldehyde to an acidic pH precontrolled colloidal solution, as obtained from a hydrothermal crystallization process. After removing the polymeric component, solid and hollow zeolite microspheres can be obtained under different preparation conditions [172]. 

Figure 11.9 (a) SEM and (b) TEM images of hollow zeolite beta crystals. (Reproduced with permission from Ref. [56].)... 

Pdrez-Ramirez, J. (2005) Creation of hollow zeolite architectures by controlled desilication of Al-zoned ZSM-5 crystals. 

In this chapter, we provide an overview of the recent research and development in the preparation, characterization, and application of novel porous carbons using both the endotemplate and the exotemplate methods. A discussion of zeolite templates for microporous carbons is followed by that of ordered mesoporous silica templates for OMCs, nanoparticle templates for mesoporous carbons, sol-gel processed porous carbons, self-assembled colloidal crystal templates for ordered macroporous carbons, and colloidal sphere templates for hollow carbon spheres, as well as other templating approaches to preparing carbon nanostructures. Then,... 

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]. 

Fodor, D., Pacosovd, L., Krumeich, F., and van Bokhoven, J-A. (2014) Facile synthesis of nano-sized hollow single crystal zeolites under mild conditions. Chem. Commun., 50, 76-78. 

The size and shape of crystals of minerals can be ascertained by interpreting the SEM micrographs of the raw materials (viz., fly ash) and the end products obtained from the zeolitization process [8]. The SEM micrographs of fly ash reveal flie presence of spherical particles of size 50-80 pm along with broken hollow spheres. 

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