Ordered macroporous materials

Macroporous materials with highly ordered and three-dimensional (3D) porous structures are technologically important for many appHcations such as catalysis. 

Other methods to create inorganic macroporous materials with uniform pores include the use of natural biological templates that are subsequently removed 

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Imhof, A. and Pine D.J. (1997) Ordered macroporous materials by emulsion templating. Nature, 389, 948-951. 

Characterization of the XMo,-Si02 materials indicated that the synthesis produced three-dimensional ordered macroporous materials with highly dispersed polyoxometalates covalently incorporated within the wall structures. IR, UV/DRS, solid-state MAS NMR spectra confirmed that the polyoxometalates remained intact in the hybrid macroporous silica materials. At first, three solid XMOu-SiOj materials all exhibited two absorptions with maxima at ca. 200 and 260 nm, respectively (Figure 1). The former is stronger and... 

Subramanian G., Manoharan V. N., Thome J. D., Pine D. J., Ordered macroporous materials by colloidal assembly a possible route to photonic bandgap materials, Adv. Mater. T1 (15)(1999)pp. 1261-1265. 

This article focnses on ordered mesoporous materials that have undergone a rapid growth in the past decade. For completeness, the concurrent progresses in the areas of crystalline microporous and ordered macroporous materials are briefly described. 

Ordered macroporous materials can be templated by colloidal crystals or emulsions. In comparison to microporous and mesoporous materials, the synthesis strategy of macroporous materials is relatively simple. 

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)...

A summary of ordered macroporous materials with different compositions is given elsewhere.Many compositions have been made, ranging from oxides, polymers, " and carbons, to semiconductors and metals. The wall structures of macroporous materials can be amorphous, crystalline, with mesopores or micropores, organically modified, or with surface catalysts. ... 

ORDERED MACROPOROUS MATERIALS STRUCTURALLY TEMPLATED BY COLLOIDAL MICROSPHERES... 

Ordered macroporous materials (OMMs) are a new family of porous materials that can be synthesized by using colloidal microspheies as the template. - The most unique characteristics of OMMs are their uniformly sized macropores arranged at micrometer length scale in three dimensions. Colloidal microspheres (latex polymer or silica) can self assemble into ordered arrays (synthetic opals) with a three-dimensional crystalline structure. The interstices in the colloidal crystals are infiltrated with a precursor material such as metal alkoxide. Upon removal of the template, a skeleton of the infiltrated material with a three-dimensionally ordered macroporous structure (inverse opals) is obtained. Because of the 30 periodicity of the materials, these structures have been extensively studied for photonic applications. In this paper, the synthesis and characterization of highly ordered macroporous materials with various compositions and functionalities (silica, organosilica, titana, titanosilicate, alumina) are presented. The application potential of OMMS in adsorption/separation is analyzed and discussed. 

Ordered macroporous materials have special optical features due to their pore diameters. Since the synthesis of macroporous materials has just started, there are no general synthetic strategies for this type of materials at present, and hence only a few examples will be mentioned here. 

A. Imhof and D.J. Pine, Ordered Macroporous Materials by Emulsion Templating. Nature (London), 1997, 389, 948-951. 

Ordered macroporous materials with pore sizes in the sub-micrometer range have applications in low-dielectric-constant materials and lightweight structural materials. Macroporous oxides such as silica, titania, and zirconia as well as polymers with well defined pore sizes in the sub-micrometer regime have been successfully synthesized.[166,167]... 

The membrane shown in Fig. 4.10 was prepared using this three-dimensionally ordered macroporous polyimide obtained according to the above process with AMPS polymer. The proton conductivity and methanol permeability of the composite membrane are summarized in Table 4.2. The proton conductivity of the composite membrane was higher than that of Nafion and the methanol permeability of the composite membrane was slightly lower than that of Nafion . Both tendencies are good for membrane for direct methanol fuel cell. In this way, three-dimensionally ordered macroporous materials are suitable for matrix of soft proton conductive polymer with higher proton conductivity. 

Such a structure provides highly uniform porous nature. This is the most important point. For example, the uniform reaction may occur in all the pores. A higher mechanical strength may be realized from ordered stmcture. Especially, two-dimensional electrochemical reactions are strongly enhanced by using three-dimensionally ordered porous materials, as mentioned above. In other words, two-dimensional electrochemical reactions are converted to pseudo three-dimensional ones. This procedure is useful for practical applications. Presently, preparation of three-dimensionally ordered macroporous materials is not so easy due to low mechanical strength and the presence of minor defects. More extensive research will be carried out in the near future. 

Following the discovery of ordered mesoporous materials, the templated approach was also employed for the synthesis of ordered macroporous materials. Macroporous materials with uniform pore sizes are predicted to have useful optical properties and may have applications as photonic crystals with optical band gaps. ... 

Ordered macroporous materials with pore sizes of more than 50 nm appeared in the late 1990s with the development of a method using colloidal crystals of monodisperse spheres as a new template.The walls of macroporous materials are larger than those of mesoporous materials, and a number of well-ordered macroporous crystalline transition metal oxides have been prepared.The preparation method... 

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

Well-ordered macroporous Fc203 can be prepared by using iron oxa-late. " Iron oxalate is soluble in ethanol-water mixed solvents, which can infiltrate the voids of templates. Iron oxalate can be converted to Fc203 without melting to form well-ordered macroporous material. If the oxalate salts are not soluble in alcoholic solution, oxalate or oxalate derivatives can be produced in the voids by a two-step method or an in situ method. In the two-step method, nitrate or acetate salts of Mn, Co or Ni infiltrate the voids and then react with oxalic acid to form oxalate salts in the voids. These oxalate salts can be converted to oxide by calcina-In the in situ method, nitrate of Mn or Fe is dissolved in EG-methanol solution, and the solution infiltrates the voids of templates. By heating the solution, EG is oxidised by nitrate to form metal oxalate derivatives. The metal oxalate derivatives can be converted to metal oxides. 

R.C. Schroden and A. Stein, in Colloids and Colloid Assemblies in 3D Ordered Macroporous Material, F. Caruso (Ed.), Wiley-VCH Verlag GmbH and Co., KGaA, Weinheim, 2004, p. 465. 

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