Ordered mesoporous carbon template

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. ... 

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. ... 

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. 

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... 

KimJ.Y., Yoon, S.B., and Yu,J.S. (2003). Template synthesis ofa new mesostruc-tured silica from highly ordered mesoporous carbon molecular sieves. Chem. Mater., 15, 1932-4. 

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 carbon molecular sieves by templated synthesis the structural varieties... 

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. 

As mentioned in Section 5.1, the templating method has been especially successfid in the mesopore area. This has been so especially since, in 1999, two Korean groups independently reported the syntesis of ordered mesoporous carbons using mesoporous silicas as templates [106,107]. Their achievements have been described by themselves in excellent recent accounts [92,93], and therefore only an outline of their most significant results will be presented here. 

Fig. 32 shows a scheme of the symthetic strategy followed for the preparation of an ordered mesoporous carbon denoted as SNU-1 [107]. Aluminum was implanted onto an MCM-48 silica template in order to generate strong acidic sites for the polymerization of phenol and formaldehyde. Then phenol was incorporated under a reduced pressure. The... 

A major difference between the two first synthes of ordered mesoporous carbons using MCM-48 mesoporous silica as template [106,107] was in the nature of the precursor. Thus, Hyeon and coworkers used phenol-fomialdehyde whereas Ryoo and coworkers used sucrose, which was impregnated twice in the presence of sulphuric acid. Carbonization and removal of the silica template led the latter team to obtain the so-called CMK-1 carbon [113], whose periodic ordered structure was ascertained by XRD and by TEM [Fig. 34a)]. CMK-1 has a high BET surface area (1200-1800 m g" ) and uniform mesopores about 3 nm in diameter. 

CMK-2 [114] is an ordered mesoporous carbon obtained from sucrose as a source of carbon and SBA-1 silica as template [Fig. 34b)]. Electron diffraction showed that this carbon is composed of c s iirtercoimected with two different types of pores (meso- and micropores). CMK-3 [115] is an ordered mesoporous carbon that was synthesized using SBA-15 mesoporous silica as template and sucrose as carbon source. The structure of CMK-3 was the faithful replica of the mesoporous silica template, as revealed by XRD and TEM. This carbon had a hi BET surface area (1500 n g % and a pore size around 4.5 nm. The systematic control of pore wall thickness of hexagonal mesoporous silica templates (by varying the ratio of surfactants CwTAB and CmEOg, Fig. 35) afforded a close control of the... 

A flaw of the templafmg method is that the structure of available templates limits the range of achievable mesopores to 2-6 nm in the case of ordered mesoporous carbons and >50 nm in the case of colloidal crystals [124]. As a contribution to overt me this limitation, Li... 

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... 

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