Hollow zeolite spheres

Figure 4.33 Procedure of the LBL technique used for preparation of hollow zeolite spheres. Reproduced with permission from [133], Copyright (2001) Elsevier...

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. 

Dong, A., Ren, N., Yang, W., Wang, Y Zhang, Y., Wang, D., Hu, J., Gao, Z., and Tang, Y. (2003) Prqtaration of hollow zeolite spheres and three-dimensionally ordered macroporous zeolite monoliths with functionalized interiors. Adv. Funct. Mater., 13, 943-948. 

First, the as-synthesized nanozeolites were separated from the mother liquid by highspeed centrifugation, and then redispersed in water (2 3 wt%), and the pH value was adjusted to 9.5 by 0.1M aq. NH3 to form zeolite suspensions. Second, hollow nanozeolite spheres were prepared by the LBL technique according to the procedure presented in Figure 4.33. 

Solid polymeric colorants may also be prepared by using solid absorbent materials such as metal oxides, metal salts of aluminosilicate, clays, diatomites, hydro-talcite, silica, zeolite, hollow glass spheres, organic-inorganic mesoporous hybrid... 

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,... 

Wang, D.J., Tang, Y., Dong, A.G., Zhang, Y.H., Wang, Y.J. Hollow cancrinite zeolite spheres in situ transformed from fly ash cenosphere. Chin. Chem. Lett. 14(12), 1299-1302 (2003)... 

As surface area and pore structure are properties of key importance for any catalyst or support material, we will first describe how these properties can be measured. First, it is useful to draw a clear borderline between roughness and porosity. If most features on a surface are deeper than they are wide, then we call the surface porous (Fig. 5.16). Although it is convenient to think about pores in terms of hollow cylinders, one should realize that pores may have all kinds of shapes. The pore system of zeolites consists of microporous channels and cages, whereas the pores of a silica gel support are formed by the interstices between spheres. Alumina and carbon black, on the other hand, have platelet structures, resulting in slit-shaped pores. All support materials may contain micro, meso and macropores (see text box for definitions). 

P-06 - Fabrication of hollow fibers and spheres composed of zeolites by layer-by-layer adsorption method... 

Hollow fibers and spheres of zeolite (labeled as HFZ and HSZ, respectively) were successfully fabricated using carbon fibers and polystyrene (PS) spheres as templates respectively, through layer-by-layer technique, coupled with removal of the templates by calcination. The optimum performance conditions to obtain these kinds of materials were systematically studied. The wall thickness and composition of these novel materials can be readily tailored by varying the number of nanozeolite/PDDA (poly(diallyldimethyl ammonium chloride)) deposition cycles and zeolite type used, respectively. The properties of these novel materials were characterized by means of XRD, IR and SEM. 

P-12 - Preparation of zeolite Beta/polystyrene beads and the corresponding hollow spheres... 

Sonochemistry in synthesis Spaciousness index Sphares, silicalite Spheres, mesoporous silica Spheres, MFI, hollow Spheres, zeolite, hollow Spin echo double resonance Spinel ceramic from zeolites Spiropyrane in zeolite Y Sr exchange Sr removal Sr,K-KFl, synthesis SSZ-33 ( CON)... 

Figure 2 Hydrogen evolution from aqueous NH3BH3 solution in the presence of hollow silica-alumina composite spheres prepared with (a) L(-l-)-arginine and (b) ammonia, (c) H-BEA zeolite, and (d) spherical silica-alumina composite particles.

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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