Ordered mesoporous carbon materials

Z. Peng/Joumal of Materials Ordered mesoporous carbon-CNT -46 1.2 80 BM CDI 0.63... 

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],... 

Despite the advantages offered by CNTs and CNFs, there are still many obstacles (cost, synthesis methods) to overcome to allow large-scale production. Another type of catalyst support material is mesoporous carbon that provides high surface area and conductivity [100, 141]. It can be classified into ordered (OMC) and disordered (DOMC) mesoporous carbon [100], OMCs have been extensively used as catalyst support materials for fuel cells [140,142-146], The large surface area and 3D connected monodis-persed mesospheres facilitate diffusion of the reactants, making them very attractive materials as catalyst supports [100]. 

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. 

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. 

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. 

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. ... 

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... 

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. 

We will not discuss here models for pores in carbons, as this topic is treated in Chapter 5, and elsewhere in specialist [15] or general reviews [106, 107]. For similar reasons, we will not discuss porosity control [44, 108] in detail. However, porous carbons prepared by the template technique, especially the ordered ones, deserve special attention. Ordered mesoporous carbons have been known to scientists since 1989 when two Korean groups independendy reported their synthesis using mesoporous silicas as templates [109, 110]. Further achievements have been described in more recent reports [111, 112]. One might have expected that the nanotexture of these materials would merely reflect the nature of the precursor used, namely phenol-formaldehyde [109] or sucrose [110] in the two first ordered mesoporous carbon syntheses (as is well known, these two precursors would have yielded randomly oriented, isotropic carbon had they been pyrolyzed/activated under more conventional conditions). However, the mesopore walls in some ordered mesoporous carbons exhibited a graphite-like, polyaromatic character [113, 114], as described in Chapter 18. This information was obtained by nitrogen adsorption at low relative pressures, as in classical... 

Kim, T.-W., Park, I.S., and Ryoo, R. (2003). A synthetic route to ordered mesoporous carbon materials with graphitic pore walls. Angew. Chem., 42, 4375-9. 

Ordered mesoporous carbons (OMCs) are new carbon materials that were developed over the last ten years. Their mesopores have a defined width with a very narrow pore size distribution. This sets them aside from older nanoporous carbons, such as activated carbons or activated carbon fibers. The last two classes of carbons are produced from various carbon-containing materials by carbonization followed by partial oxidation (activation). To a certain degree, the pore structure of these materials can be controlled by the carbonization and activation conditions. However, it is not possible to produce purely mesoporous activated carbons or activated carbon fibers. Furthermore, these materials generally exhibit a broad pore size distribution [1, 2]. 

Lately, a fascinating strategy has been successfully developed for the preparation of ordered mesoporous carbons. The synthesis procedure of these advanced carbons consists in the infiltration of an organic precursor into the pores of silica or aluminosilicate templates, followed by the subsequent pyrolysis of the precursor and dissolution of the template framework by HF [9—12]. In another process, carbon is directly introduced in the template by a CVD method [86]. The method gives a highly ordered and interconnected network of meso- and micropores [87], where the size of carbon mesopores is defined by the walls thickness of the pristine silica matrix. Such materials are very suitable for better understanding the relationships between the porous characteristics and the supercapacitors performance [88, 89]. 

Ordered mesoporous carbons (OMC) of various structures, designated as CMK-1 5, have been synthesized by carbonization of sucrose, furfuryl alcohol or other carbon sources inside silica or aluminosilicate mesopores that are interconnected into three-dimensional networks such as in MCM-48, SBA-1 and SBA-15. The mesoporous carbon molecular sieves, obtained after template removal, show TEM images and patterns characteristic of the ordered arrangement of uniform mesopores. The OMC, which are opening up a new area of the nanoporous materials, exhibit high BET specific surface areas, excellent thermal stability in inert atmospheres and strong resistance to attack by acids and bases. 

Fig. 37. XRD patems for CMK-nG-type ordered mesoporous carbons and other materials in the low-and wide-angle regions. Reprinted with jtermission from Ref. [123]. Cojytight 2003 John Wil and Sens.

Ordered Mesoporous Carbons The first ordered mesoporous carbons were synthesized by hard templating methods (141). The use of porous inorganic silica templates allowed the preparation of series of ordered mesoporous carbon materials, designated as CMK-x materials (carbon molecular sieves Korean Advanced Institute of Science and Technology). The hrst one, CMK-1, was prepared using MCM-48 as a template and sucrose as the carbon source impregnated in the... 

Lang, J. W., X. B. Yan, W. W. Liu, R. T. Wang, and Q. J. Xue. 2012. Influence of nitric acid modification of ordered mesoporous carbon materials on their capacitive performances in different aqueous electrolytes. Journal of Power Sources 204 220-229. Wang, D. W., F. Li, L. C. Yin et al. 2012. Nitrogen-doped carbon monolith for alkaline supercapacitors and understanding nitrogen-induced redox transitions. Chemistry -A European Journal 18 5345-5351. 

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