Figure 22. X-ray diffractograms of (a) MCM-48 (template), (b) MCM-48 after completing carbonization within pores, and (c) carbon obtained by removing silica wall after carbonization. Reprinted with permission from , R. Ryoo et al., J. Phys. Chem. B 103, 7743 (1999). © 1999, American Chemical Society.
Alkaline metal amalgam or alkali metal can defluorinate poly(tetrafluoroethylene) (PTFE) to produce carbynelike structure (sp-carbon allotrope) and finely dispersed metal fluoride crystallites in the polymer matrix. Washing out the metal fluoride from the matrix promoted a transformation from sp-hybridization to sp2-hybridization by a cross-linking reaction between the adjacent carbyne chains [85, 86]. Shiraishi et al. found that heat treatments after the reaction between PTFE and alkali metals can alter the pore size distribution of the resultant carbons, (i.e., higher heat treatment temperature above 623 K caused a formation of meso-pores) [87, 88]. This was attributed to the crystalline growth of the alkali halides that are anticipated to be templates for pore formation.
Fenelonov et al. reported a unique example of the template method . They used carbon black as a template and deposited pyrocarbon from C1-C4 gases at 1123-1223 K. Templates were removed by steam gasification. In this process, at first the most defected parts of pyrocarbon were gasified. When the formed pore reached the carbon black, a preferential gasification started as shown in Figure 24. A distinct feature of this carbon was high resistance to attrition and mechanical crushing. They anticipate that this carbon can be applicable to catalyst supports.
Although the obtained pore was classified as macropores, Zakhilov et al. prepared spatially ordered porous carbon material by using opal as template . Figure 25 shows the micrographs of the obtained carbon material.
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