Meso/macroporous materials

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). 

The preparations of the meso-macroporous materials are processed by the method described elsewhere [6-8],... 

Many practical applications of hierarchically micro-meso-macroporous materials have recently been emerging, including photocatalysis, catalysis, separation, and... 

Terms such as symmetric and asymmetric, as well as microporous, meso-porous and macroporous materials will be introduced. Symmetric membranes are systems with a homogeneous structure throughout the membrane. Examples can be found in capillary glass membranes or anodized alumina membranes. Asymmetric membranes have a gradual change in structure throughout the membrane. In most cases these are composite membranes... 

Porous materials are elassified into three different categories based on the size of pores rpore, that is, microporous for rpore < 20 A, mesoporous for 20 A< Tpore < 500 A, and macroporous for rpote > 500 A. Here I will discuss micro- and meso-porous materials. Microporous crystals (hereafter called zeolites) with more than 150 different framework-type stmctures have been reported. 

In China, most of the traditional RFCC catalysts (such as Orbit, DVR, and MFC mentioned above) are based on alnmina matrix, and the most widely used materials for alumina matrix preparation are alumina sol and modified active alumina [4]. Alumina matrix combines the virtnes of alumina-sol (better attrition resistance and coke selectivity) and active alnmina (higher cracking activity), thus improving the cracking activity and selectivity of the catalysts. However, the coke selectivity of the alumina matrix is nnsatisfactory when processing resid feed due to the insufficient amount of meso/macropores and higher concentration of acid sites. 

In an experiment carried out with 100 mg/1 methylene blue concentration the behaviour was the same as described before, but, there was a time in which SC-155 reached the saturation and the material stopped the adsorption the AC-ref instead continued the adsorption at longer times due to its higher carbon contents. Then, the great difference in adsorption kinetics observed between SC-155 and AC-ref is justified by the more expanded structure of carbon microdomains of SC-155 than the reference, and by the higher radius of meso-macropores observed for the SC-155 the last point provides an easy access of molecules to be adsorbed into the grains of the material, minimizing diffusional problems. 

The physical and chemical activation processes have been generally employed to prepare the porous carbons.18"35 However, the pore structures are not easily controlled by the activation processes and the size of the pores generated by the activation processes is limited to the micropore range only. Recently, much attention has been paid to the synthesis of meso/macroporous carbons with various pore structures and pore size distributions (PSD) by using various types of such inorganic templates as silica materials and zeolites.17,36 55... 

The meso/macroporous carbons have attracted much attention in their application as electrode materials in EDLCs, since the meso/macropores promote the formation of an effective doublelayer or the transfer of ions into the pores, resulting in the increases in the electrolyte wettability and the rate capability.67,68 In this regard, there has been considerable research targeted towards developing the synthetic methods of novel meso/macroporous carbons.17,36"55,69 72 Various types of such inorganic templates as silica materials and zeolites are widely used for the synthesis of the meso/macroporous carbons, since it was revealed17,36"55 that these inorganic templates contribute to the formation of the meso/macropores with various pore structures and broad PSD. 

The strategy of this method is to utilize the inherent porosity of bulky substrates in the construction of hierarchical stractures by incorporating additional pore systems. Diatoms are unicellular algae whose walls are composed of silica with an internal pore diameter at submicron to micron scales. Zeolitization of diatoms, in which zeolite nanoparticles are dispersed on the surface of diatoms followed by a hydrothermal conversation of a portion of the diatom silicas into zeolites, resulted in the formation of a micro/mesoporous composite material. Similarly, wood has also been used as a substrate to prepare meso/macroporous composites and meso/macroporous zeolites. After the synthesis, wood is removed by calcination. ... 

According to the lUPAC recommendations [238], the term micropores should be apphed to voids smaller than 20 A in diameter, mesopores are those with diameters between 20 and 500 A, and macropores have diameters larger than 500 A. The micropores and thin mesopores mosdy contribute to the value of the inner surface area, whereas the wide mesopores and, in particular, macropores make up most of the total pore volume of porous materials. It should be noted that the overwhelming majority of porous styrene—DVB copolymers are typically meso-porous materials however, the initially introduced name macroporous polymers became generally accepted and we will not deviate from this traditional scientific jargon. 

Kim et al. [64] analyzed porous carbon by using colloidal sUica particles as templates. Carbon with micro, meso and macropores were obtained modifying the initial pH of the carbon precursor solutions. This fabrication method produces materials with narrow pore size distribution in a broad range of pore size. The fuel cell test showed better DMFC performance for carbons with high meso-macropore area with large pore than that with micropores. Again, this effect was attributed to the fact that meso and macropores produce a favorable dispersion of PtRu metal species and allow the access of perfluorosulfonate ionomer for the formation of the triple phase boundary. 

Yuan Z-Y, Su B-L (2006) Insights into hierarchically meso-macroporous structured materials. J Mater Chem 16 663-667... 

Nb-based catalysts are among the investigated systems in total removal of -butanol due to the capacity of niobium to adopt variable oxidation states. Thus, Nb-doped hierarchically micro(meso) macroporous Ti02 (anatase phase) (Figure 17.10) synthesized via a self-formation procedure showed close performances with catalysts in which the same materials served as supports for noble metals [46]. The efficiency of these catalytic systems in the total oxidation of butan-l-ol was enhanced by the improved diffusion through the intrinsic macro-porous network. An effect of the niobium content was evidenced as welL... 

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