Ordered Mesoporous Carbons

In an attempt to further optimize the fuel cell performance of OMC, the materials can also be functionalized and oxygen-containing groups introduced into the surface [80] (see also Section 7.3.2), as well as doped with heteroatoms, such as 

Carbon aerogels were first synthesized by Pekala in 1989 through pyrolysis of organic aerogels [28,29]. They display three-dimensional random close-packed monolithic structure [30,31] of slightly overlapping carbon spheres (3 to 30 nm) 

CARBON MATERIALS AS SUPPORTS FOR FUEL CELL ELECTROCATALYSTS 

3 PHYSICOCHEMICAL PROPERTIES OE CARBON MATERIALS RELEVANT TO EUEL CELL OPERATION 

2007 Zhao et at., 1998). It is interesting to note that different choices of the inorganic precursors, organic templates, reaction conditions, etc. have resulted in a variety of meso-structured materials. The physico-chemical properties of some of these silicates are tabulated in Table 5.1. 

Porous carbon materials with high surface areas and pore volumes prepared from porous inorganic templates are of current interest for energy storage, gas separation, heterogeneous catalysis, and many other applications including water purification, catalyst support as well as electrode material 

Carbonization at800 CinN2 Etching with 46%HFfor24/j 

Carbonization at900°CinN2 Etching with 5-20%HFfor6-12/  

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Zhu S, Zhou H, Hibino M, Honma I, Ichihara M (2005) Synthesis of Mn02 nanoparticles confined in ordered mesoporous carbon using a sonochemical method. Adv Funct Mater 15 381-386... 

Ryoo R., Joo S.H., Kruk M., Jaroniec M. Ordered mesoporous carbons Adv Mater 2001 ... 

Incorporation of nitrogen into the carbons prepared via chemical vapour deposition (CVD) or into the carbon nanotubes yields highly graphitised materials with excellent structure ordering. For example, ordered mesoporous carbons containing 7.0-8.8 wt,% N have been obtained by the CVD method, using the SBA-12, SBA-15, MCM-41, MCM-48, and HMS materials as matrices and acetonitrile as carbon precursor [1],... 

Jo, Y., et ah, Highly interconnected ordered mesoporous carbon-carbon nanotube nanocomposites Pt-free, highly efficient, and durable counter electrodes for dye-sensitized solar cells. Chemical Communications, 2012. 48(65) p. 8057-8059. 

Ill-defined carbon materials that provide a distinct nanostructure, such as spherical particles in the case of soot and carbon black, or hexagonally ordered cylindrical pores in the case of ordered mesoporous carbons, are not discussed here. Surface chemical, thus catalytic properties of these material are closer to carbon black or activated carbon [13], which is frequently reviewed [2-4]. Here, the higher degree of sp3 hybridization often results in a higher reactivity, however, at lower selectivity, as compared to nanocarbons exposing large basal plane fractions of the overall surface. 

Besides ODH processes, a few reports about non-oxidative dehydrogenation (DH) over carbon catalysts also exist. At the reaction temperature of 823-873 K, propane is reported to react to propylene and hydrogen in high yield (30-40 %) over ordered mesoporous carbon, which was shown to be much more active than graphitic and/or nanostructured carbon (CNTs) [66], On the other hand, a hybrid catalyst system for... 

Liu etal. [32] reported the characteristics and reactivity of highly ordered mesoporous carbon-titania hybrid materials synthesized via organic-inorganic-amphiphilic coassembly followed by in situ crystallization. In the degradation of Rhodamine B these materials also show enhanced properties due to the dispersion/stabilization of small titania nanocrystals and the adsorptive capacity of the nanocarbon. 

Park, I.-S. Choi, S. Y. Ha, J., High-performance titanium dioxide photocataiyst on ordered mesoporous carbon support. Chem.Phys. Lett. 2008,456 198-201. 

Gu, Z., Deng, B. and Yang, J. (2007) Synthesis and evaluation of iron-containing ordered mesoporous carbon (FeOMC) for arsenic adsorption. Microporous and Mesoporous Materials, 102(1-3), 265-73. 

Among the inorganic templates, zeolite produces more regulated pores as compared to the silica template. If nano-channels in zeolite are completely filled with carbonaceous precursor and then the carbon materials are extracted from the zeolite framework, one can obtain the porous carbon of which structure reflects the porosity of the original zeolite template. The ordered mesoporous silica templates, e.g., MCM-4 838,39,47 and SBA-1547 have been employed to prepare the ordered porous carbons by the procedures involving the pore filling of the silica template with carbonaceous precursor followed by carbonization and silica dissolution. The resulting pore sizes of the ordered mesoporous carbons are smaller than about 10 nm. 

Zhou, H., Zhu, S., Hibino, M., and Honma, I. Electrochemical capacitance of self-ordered mesoporous carbon. J. Power Sources 122, 2003 219-223. 

Tanaka, S., Nishiyama, N., Egashira, Y., and Ueyama, K. Synthesis of ordered mesoporous carbons with channel structure from an organic-organic nanocomposite. Chem. Commun. 2005 2125-2127. 

Recently, there has been an increasing interest in the synthesis of ordered mesoporous carbons, since such materials are very promising as adsorbents, catalyst supports, and electrochemical double-layer capacitors. Ordered mesoporous silicas have been shown as suitable templates to prepare periodic mesoporous carbons with various pore shapes and connectivity. The synthesis procedure involves impregnation of the mesoporous silica with an appropriate carbon precursor, carbonization of carbon source, and subsequent removal of silica using an aqueous solution of HF or NaOH. ... 

Ryoo et al. reported the first ordered mesoporous carbon, CMK-1, using cubic MCM-48 as template and sucrose as carbon source. CMK-1 exhibited a highly ordered cubic structure, as confirmed by transmission electron microscopy (TEM). However, x-ray powder diffraction patterns indicated that CMK-1 underwent a structural transformation upon the silica removal due to the two disconnected porous systems separated by the silica wall. ... 

ORDERED MESOPOROUS CARBONS WITH NEW OPPORTUNITIES FOR ADSORPTION STUDIES... 

The methods developed for the synthesis of ordered mesoporous carbons are simple and cost-efricient, and the pore size can be tailored. The synthesis process can be scaled up for production in bulk quantities. Recent works on the synthesis of mesoporous silicas brought about much improvement in the cost-efficient and custom-tailored synthesis of the templates [18]. The discovery of new mesoporous silicas is also expected to provide additional promising templates for the synthesis of new mesoporous carbons. The resulting high-surface-area materials with uniform pores promise to be suitable as... 

The information on SBA-15 pore structure can be obtained indirectly from the synthesis of mesoporous carbon by using SBA-15 as template. When SBA-15 silicas prepared at above 80 °C are used as template, ordered mesoporous carbon rods (CMK-3) and pipes (CMK-5) with 2-D hexagonal symmetry were synthesized successfully. The... 

Ordered mesoporous silica seems to be an ideal hard template, which can be used as a mold for other mesostructures with various compositions, such as ordered mesoporous carbon and metal oxides. Mesoporous silicas with various different structures are available, and silica is relatively easily dissolved in HF or NaOH. Alternatively, mesoporous carbons with a solid skeleton structure are also suitable choices as hard templates due to their excellent structural stability on thermal or hydrothermal and chemical treatment. A pronounced advantage of carbon is the fact that it is much easier to remove than silica by simple combustion. The nanocasting synthesis of mesoporous carbon by using mesoporous silica as template will be discussed in detail in the section on mesoporous carbon. In many cases, silica is unsuitable for synthesizing framework compositions other than carbon, since the leaching of the silica typically affects the material which is filled into the silica pore system. 

Zeolites were already employed as templates in the synthesis of microporous carbon with ordered structures.[247] The discovery of ordered mesoporous silica materials opened new opportunities in the synthesis of periodic carbon structures using the templating approach. By employing mesoporous silica structures as hard templates, ordered mesoporous carbon replicas have been synthesized from a nanocasting strategy. The synthesis is quite tedious and involves two main steps (i) Preparation and calcination of the silica mesophase, and (ii) filling the silica pore system by a carbon precursor, followed by the carbonization and selective removal of the silica framework. 

Ordered mesoporous carbon can also be synthesized by a catalytic CVD method.[251] The ordered carbons possess bimodal pores the pores arise from the replica frameworks of the template and the pores correspond to carbon nanotubes formed in the channels of the template. 

J.Y. Kim, S.B. Yoon, and J.S. Yu, Template Synthesis of a New Mesostructured Silica from Highly Ordered Mesoporous Carbon Molecular Sieves. Chem. Mater., 2003,15,1932-1934. 

M. Kruk, M. Jaroniec, R. Ryoo, and S.H. Joo, Characterization of Ordered Mesoporous Carbons Synthesized using MCM-48 Silicas as Templates. J. Phys. Chem. B, 2000, 104, 7960-7968. 

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