Macroporous carbon materials template

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. 

The synthesis of macroporous carbon materials was first realised by Zakhidov et al. in 1998. Macroporous carbon materials with inverse opal structures, as shown in Figure 4.14, were obtained using silica opals as hard templates and phenol resin and/or propylene gas as carbon precursor. The macroporous carbons had different structures depending... 

In principle, the morphology of macroporous carbon materials is largely dependent on the degree of void infiltration of the opal template. In order to maximise the filling of the interstitial voids of the colloid crystal with carbon precursors, liquid phase carbon precursors such as phenolic resin and sucrose solution are usually used to achieve better replication.1 2 -194] variety of carbon precursors, including propylene gas, benzene and divinylbenzene can also be successfully utilised to make three-dimensional macroporous carbon materials using colloid crystals as hard templates. The... 

Figure 4.15 SEM images of macroporous carbon materials fabricated (a) by surface templating and (b) by volume templating using 250 nm silica spheres as template. The insets show carbon-colloidal silica composites. Reprinted with permission from J.S. Yu, S. Kang, S.B. Yoon and G. Chai,/. Am. Chem. Soc., 124, 9382. Copyright (2002) American Chemical Society...

The use of dual templating strategies to synthesise three-dimensional macroporous carbon materials has been explored by the groups of Zhao and of Stein. In this case, the two templates play different roles ... 

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. 

It should be noted that the t-plot analysis shows a very small amount of micropores in the sample studied, which is due to the use of the mesophase pitch as the carbon precursor. It is known that many precursors, e.g., sucrose and polyfurfuryl alcohol, infiltrate well siliceous templates but after carbonization give meso- or macroporous carbons with complementary microporosity. This is not the case for the mesophase pitch, which is used to synthesize carbon fibers that are nonporous materials. 

The colloidal-crystal-templating approach offers yet another new approach to preparing 3-D macroporous solid materials [6,17]. Spherical colloidal particles of submicrometer size can self-organize themselves into a colloidal crystal, the so-called opal [64], which can be utilized as an endotemplate to fabricate ordered macroporous carbons of two types volume-templated carbon, which is an exact inverse replica of the opal template, and surface-templated carbon, which is formed by coating the colloidal spheres. Zakhidov et al. [64] were the first to use colloidal crystals as templates to prepare highly ordered 3-D macroporous carbon of both types. As schematically illustrated in Figure 2.39, for the volume-templat-ing approach, a carbon precursor is infiltrated into interstitial spaces between colloidal spheres. Carbonization and removal of the opal template leave behind a 3-D periodic carbon structure (i.e., an inverse carbon). With this approach, macroporous carbon structures with a wide range of pore sizes have been produced. 

FIGURE 12.17 Illustration of the preparation of a bimodal mesoporous-macroporous carbon by dual-phase separation. The macropores are formed from the spinodal decomposition of glycolic solvents (a). Bicontinuous structure, framework structure, and the large macropores left by the solvent after annealing and carbonization (b). The carbon walls display large amounts of mesopores (c) templated by the triblock copolymer. (From Liang, C. D. et al., Chemistry of Materials, 21, 2115, 2009. With permission.)... 

Recently, the LbL technique has been extended from conventional nonporous substrates to macroporous substrates, such as 3DOM materials [58,59], macroporous membranes [60-63], and porous calcium carbonate microparticles [64,65], to prepare porous PE-based materials. LbL-assembly of polyelectrolytes can also be performed on the surface of MS particles preloaded with enzymes [66,67] or small molecule drugs [68], and, under appropriate solution conditions, within the pores of MS particles to generate polymer-based nanoporous spheres following removal of the silica template [69]. 

The porous skeleton of activated carbon can be used as a template on which to construct other porous materials, for example, Si02, Ti02 and AI2O3. The oxide is first dissolved in supercritical CO2 (see Section 8.13) and then the activated carbon template is coated in the supercritical fluid. The carbon template is removed by treatment with oxygen plasma or by calcination in air at 870 K, leaving a nano-porous ( nano refers to the scale of the pore size) metal oxide with a macroporous structure that mimics that of the activated carbon template. 

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... 

Monolithic carbons are easier to handle than powdered materials. Direct shaping of monolithic mesoporous carbons during their preparation is highly desirable. Mesoporous carbon monoliths may be fabricated by using mesoporous silica monoliths as template. Carbon monoliths with well-developed and accessible porosity have been produced using silica monoliths with a hierarchical structure containing macropores and meso-pores as templates and furfuryl alcohol or sucrose as a carbon precur-... 

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. 

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