Control of mesoporosity of carbon gels prepared by sol–gel polycondensation and freeze drying

Carbon cryogels were prepared by pyrolyzing resorcinol–formaldehyde (RF) cryogels, which were synthesized via the sol–gel polycondensation of resorcinol with formaldehyde in a slightly basic aqueous solution followed by freeze drying. Various RF cryogels were synthesized by changing the amount of reactant, catalyst and water used in the sol–gel polycondensation. The porous properties of RF cryogels were evaluated by nitrogen adsorption method and scanning electron microscopy (SEM). The mesoporosity of RF cryogels was related to the ratio of catalyst to water (C/W). Although the mesopores of RF cryogels were reduced in size to some extent by pyrolysis, the mesoporosity of carbon cryogels was also related to C/W. For the carbon cryogels synthesized under the condition of C/W⩽70 mol/m3, the peak radius of the mesopore size distribution, the BET surface area and the mesopore volume were decreased with the increase in C/W. On the other hand, for the carbon cryogels synthesized under the condition of C/W>70 mol/m3, it was difficult to prepare mesoporous carbon.