Ordered Macroporous-Mesoporous Materials

The following lists some macrotemplates used in conjunction with mesoporous 

Zeolites with Hierarchical Porous Structure Combining Microporous with Meso-/Macro porous 

The presence of a bimodal inicro-/mesoporous structure provides improved accessibility to the active sites of hierarchical zeolites, which, in many cases, impacts positively on their catalytic activity compared to conventional zeoHtes with micrometer crystal sizes. Hierarchical zeolites possess a collection of singular properties  

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The synthesis of ordered macroporous crystalline materials has been attracting much attention. Walls of macroporous materials are larger than those of mesoporous materials, and this macroporosity can be introduced into a wide variety of transition metal oxides. Potential applications of these materials include photonic materials, catalysts and electrode materials. The ordering scale is close to the wavelength of light, and interest has therefore been shown in photonic materials. In some cases, introduction of macroporosity increases the surface area, and these materials show better catalytic performance than that of nonporous materials. Similar to mesoporous materials, macropores are favoured for diffusion of reactants compared with nonporous materials and many applications, such as in a Li battery electrode, have been reported. 

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

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. 

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. ... 

A novel approach is reported for the accurate evaluation of pore size distributions for mesoporous and microporous silicas from nitrogen adsorption data. The model used is a hybrid combination of statistical mechanical calculations and experimental observations for macroporous silicas and for MCM-41 ordered mesoporous silicas, which are regarded as the best model mesoporous solids currently available. Thus, an accurate reference isotherm has been developed from extensive experimental observations and surface heterogeneity analysis by density functional theory the critical pore filling pressures have been determined as a function of the pore size from adsorption isotherms on MCM-41 materials well characterized by independent X-ray techniques and finally, the important variation of the pore fluid density with pressure and pore size has been accounted for by density functional theory calculations. The pore size distribution for an unknown sample is extracted from its experimental nitrogen isotherm by inversion of the integral equation of adsorption using the hybrid models as the kernel matrix. The approach reported in the current study opens new opportunities in characterization of mesoporous and microporous-mesoporous materials. 

Si CP/MAS-NMR was used to characterise mesoporous materials derived from sodium silicate and organotrialkoxysilanes.493 Multinuclear NMR studies have been reported on periodic mesoporous organosilicas.494,495 13C and 29Si MAS-NMR spectra were used to characterise ordered macroporous organo-silica materials.496 A similar study has been made of mesoporous organosilica/ clay heterostructures.497... 

As mentioned earlier in this chapter, it is the social demands and wide applications of porous materials that keep them under continuous exploration. From natural zeolites to synthesized ones, from low-silica zeolites to high-silica ones, from aluminosilicate molecular sieves to aluminophosphate-based ones, from extra-large microporous materials to mesoporous materials, and from inorganic porous frameworks to MOFs, together with newly emerging macroporous materials, all these porous materials have ordered and uniform porous systems. 

Zeolite monlith with macropores can be considered as a micro-macroporous material. Mechanically stable zeolite monoliths[177] containing 3-D, ordered, closed macropores have been fabricated by hydrothermal treatment of nano-zeolite seeded mesoporous silica spheres. The easy speed of sedimentation and digestion renders the whole process suitable for large-scale production of macroporous zeolite materials. 

Zeolites, as previously described, are crystalline microporous solids with well-defined structures made up of interlocking microporous Si04 and A104. Microporous means that the pores have dimensions of less than 20 A, on the order of the size of many petroleum-related molecules, and their crystalline nature means that they have a narrow pore distribution (mesoporous materials have pore sizes between 20 A and 500 A, macroporous materials have pores larger than 500 A). This combination of features not only restricts the size of molecules that can enter the pores, but also the dimensions of the transition state and of the molecules that can successfully leave. For these reasons, zeolites have been termed shape selective. ... 

Zeolites are widely used as acid catalysts, especially in the petrochemical industry. Zeolites have several attractive properties such as high surface area, adjustable pore size, hydrophilicity, acidity, and high thermal and chemical stability. In order to fully benefit from the unique sorption and shape-selectivity effects in zeolite micropores in absence of diffusion limitation, the diffusion path length inside the zeolite particle should be very short, such as, e.g., in zeolite nanocrystals. An advantageous pore architecture for catalytic conversion consists of short micropores connected by meso- or macropore network [1]. Reported mesoporous materials obtained from zeolite precursor units as building blocks present a better thermal and hydrothermal stability but also a higher acidity when compared with amorphous mesoporous analogues [2-6]. Alternative approaches to introduce microporosity in walls of mesoporous materials are zeolitization of the walls under hydrothermal conditions and zeolite synthesis in the presence of carbon nanoparticles as templates to create mesopores inside the zeolite bodies [7,8]. 

Sen T, Tiddy GJT, Casci JL, Anderson MW (2004) Synthesis and characterization of hierarchically ordered porous silica materials. Chem Mater 16 2044 Deng Y, Liu C, Yu T, Liu F, Zhang F, Wan Y, Zhang L, Wang C, Tu B, Webley PA, Wang H, Zhao D (2007) Facile synthesis of hierarchically porous carbons from dual colloidal crystal/block copolymer template approach. Chem Mater 19 3271 Luo Q, Li L, Yang B, Zhao D (2000) Three-dimensional ordered macroporous structures with mesoporous silica walls. Chem Lett 29 378... 

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... 

Indeed, the past ten years have witnessed rapid advances in using template carbonisation to produce ordered porous carbon materials, ranging from microporous to mesoporous and macroporous carbons. The template carbonisation method has thus been regarded as one of the most effective approaches to prepare porous carbon materials with desirable physical and chemical properties. It has, therefore, opened up new opportunities in making novel porous materials for a wide range of applications. 

Porous materials are classified into several kinds depending on the pore size. According to the International Union of Pure and Applied Chemistry (lUPAC) notation, microporous materials have pore diameters of less than 2 mn and mesoporous materials have pore diameters between 2 and 50 nm. Macroporous materials have pore diameters of greater than 50 nm. Hydrothermal synthesis has been the technique of choice to prepare microporous phases. Ordered porous materials, including ordered mesoporous materials and the metal organic frameworks (MOFs), have also been synthesized generally under hydrothermal conditions [1-5]. In this section, we briefly present the synthesis of mesoporous silica materials and MOFs. 

The HPGC material is a composite of ordered micropores, mesopores, and macropores as illustrated in Figure 4.11. The composite structure can create short diffusion pathways for the electrolyte to enter the microporous walls and generate a high energy density of 22.9 Wh.kg in an organic electrolyte. Furthermore, the accessibility of the pores allowed the energy density... 

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