Carbon tunnels formed in carbon/carbon composite cryogels

A carbon/carbon (C/C) composite cryogel was prepared by putting almost the maximum content of cotton fibers in vials and then filling them with resorcinol–formaldehyde (RF) sols, followed by solvent exchange with t-butanol, freeze drying and pyrolysis under inert atmosphere. The mesopore structure of C/C composite cryogels was observed by a scanning electron microscope (SEM) and their porous structures were characterized by nitrogen adsorption and mercury porosimetry. The SEM images confirm that the C/C composite cryogels, being heterogeneous carbon materials, possess ordinary carbon cryogels and carbon tunnels. Here, the tunnels are comprised of (i) carbon fibers, (ii) spaces between carbon fibers and nanoporous carbon spheres, (iii) nanoporous carbon spheres with surrounding nanocages, and (iv) dense ring structures. The formation model of carbon tunnels is also proposed. The porous properties of cryogels could be changed by the cotton fiber addition and the synthesis conditions. The results support that the synthesis condition of RF sol determines the porous properties of C/C composite cryogels.

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► Carbon tunnels and nanoporous carbon spheres are formed in C/C composites.
► MesPSD curves of C/C composites become slightly broad with large mesopore radius.
► The porosity of C/C composites depends on catalyst and water used in the RF sol.