Colloidal-crystal-templated macroporous

Theoretically, colloidal-crystal-templated macroporous structures should have a relatively low surface area because of the dominant presence of large pores. However, macroporous carbons prepared by this mechanism can possess a high surface area because a considerable number of micropores may be present as... 

Sadakane, M., Asanuma, T., Kubo, J. et al. (2005) Facile procedure to prepare three-dimensionally ordered macroporous (3DOM) perovskite-type mixed metal oxides by colloidal crystal templating method, Chem. Mater. 17, 3546. 

Several approaches towards the synthesis of hierarchical meso- and macro-porous materials have been described. For instance, a mixture that comprised a block co-polymer and polymer latex spheres was utilized to obtain large pore silicas with a bimodal pore size distribution [84]. Rather than pre-organizing latex spheres into an ordered structure they were instead mixed with block-copolymer precursor sols and the resulting structures were disordered. A similar approach that utilized a latex colloidal crystal template was used to assemble a macroporous crystal with amesoporous silica framework [67]. 

A general three-step procedure for the formation of macroporous materials by colloidal crystal templating is illustrated in Figure 6. In the first step, monodispersed colloidal spheres assemble into ordered 3D or sometimes 2D arrays to serve as templates. Secondly, the voids of colloidal crystals are filled by precursors that subsequently solidify to form composites. Finally, the original spheres are removed, creating a solid framework with interconnected voids, which faithfully replicate the template arrays. 

Figure 6 A schematic of the general procedure for preparing ordered macroporous materials by colloidal crystal templating. (1) Assembly of colloidal particles to form colloidal crystal template (2) Filling the interstices/voids with precursors to form composites and (3) Removal of templates. (Reprinted from Ref. 175, 2000, with permission from Elsevier)...

Complex templates combine soft and hard template techniques. This methodology is used for synthesizing hierarchically bimodal and trimodal meso-macroporous materials with interconnected pore channels combining a surfactant template with a colloidal crystal template (Yuan and Su, 2004). 

Three-dimensionally ordered macroporous ceramic with high LR ion conductivity was prepared by colloidal crystal templating method using monodispersed polystyrene beads [12]. Monodispersed polystyrene beads with 3 pm diameter were dispersed in water and then filtrated by using a membrane filter under a small pressure difference. After this treatment, polystyrene beads were accumulated on the membrane filter with closed pack structure, as shown in Fig. 4.2. Then, the membrane consisting of accumulated polystyrene beads was removed from the membrane filter and put on a glass substrate. After drying at room temperature, the... 

Further extension of the sol-gel and colloidal crystal templates include control of the outer shape of the colloidal crystal by assembling the PS particles in an aqueous droplet at the air/oil interface [23]. The assemblies then have regular shape (on the length scale of a few millimeters) spheres, ellipsoids, and concave disks. This was controlled by the addition of surfactant and an applied electric field. The cubic close-packed, ordered macroporous titania or silica obtained had similar outer shape as the template. 

Recently, inqjortant efforts have been made to fabricate photonic crystals by colloidal crystal templating [1-5], Colloidal crystals are self-organized arrays of silica or latex spheres, having the periodicity required for photonic band gaps. The basic idea is to use a colloidal crystal as a template, infiltrate the interstitial spaces between the spheres with another material and, then, remove the spheres by chemical etching or combustion. Since the resulting macroporous structures have a complete photonic bandgap [6,7], these materials have many applications in photonics. 

Fig.1 Scheme of preparation routes to macroporous networks by colloidal crystal templating... 

Stein A, Schroden RC (2001) Colloidal crystal templating of three-dimensionally ordered macroporous solids materials for photonics and beyond. Cnrr Opin Solid State Mater Sci 5 553... 

Figure 3.7 Colloidal crystal templating method to produce three-dimensionally ordered macroporous materials...

If mixed-metal alkoxide precursors can be prepared and their reactivity can be controlled, ordered macroporous mixed metal oxides can be produced by a sol-gel method using a colloidal crystal template. Alkoxides of Ti and Zr with other metals are easily prepared by mixing titanium alkoxide and zirconium alkoxide with alkoxides of other metals or metal salts, and the formed mixed metal alkoxides can infiltrate the voids of templates. Therefore, production of mixed metal oxides with Ti and Zr is straightforward. 

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,... 

The colloidal-crystal-templating approach offers yet another new approach to preparing 3-D macroporous solid materials [6,17]. Spherical colloidal particles of submicrometer size can self-organize themselves into a colloidal crystal, the so-called opal [64], which can be utilized as an endotemplate to fabricate ordered macroporous carbons of two types volume-templated carbon, which is an exact inverse replica of the opal template, and surface-templated carbon, which is formed by coating the colloidal spheres. Zakhidov et al. [64] were the first to use colloidal crystals as templates to prepare highly ordered 3-D macroporous carbon of both types. As schematically illustrated in Figure 2.39, for the volume-templat-ing approach, a carbon precursor is infiltrated into interstitial spaces between colloidal spheres. Carbonization and removal of the opal template leave behind a 3-D periodic carbon structure (i.e., an inverse carbon). With this approach, macroporous carbon structures with a wide range of pore sizes have been produced. 

Hoshina, K., and Kanamura, K. (2005) Preparation of three dimensionally ordered macroporous Lio.ssLao.ssTiOs by colloidal crystal templating process. Solid State Ionics, 176, 2345-2348. 

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