Preparation and characterization of swelling porous carbon beads

Porous carbon beads have been prepared by two replica methods, Ester and CVD methods. The Ester method consists of esterification of silica gel beads with alcohol or phenol, pyrolysis of the esterified silica gel, and dissolution of the silica gel with HF solution, yielding porous carbon beads with specific surface area ranging 1100-2000 m(2) g(-1). On the other hand the CVD method consists of pyrolysis of benzene vapor on silica gel beads and dissolution of the silica gel with HF solution, yielding porous carbon whose specific surface area is 640 m(2) g(-1). Porous carbon beads made from 4-phenyl-1,2-dihydroxybenzene by the Ester method showed enormously large expansion on adsorbing benzene (their apparent volumes doubled) and contracted to the original size on desorption. These dimensional changes were reproducible, and expansion and contraction completed in a few tens of seconds. The extent of dimensional changes was influenced by the kinds of adsorbates and decreased in the following order: toluene>xylene, benzene>chloroform>carbon tetrachloride>1-butanol> 1-propanol, octane>heptane>cyclohexane, ethanol, hexane>pentane>methanol>water. On the contrary the porous carbon made by the CVD method did not show any dimensional change. A mechanism for the dimensional change of the porous carbon beads was proposed based on strain energy of carbon films, capillary force at menisci in the pores, and interfacial energy of carbon films. (C) 1997 Elsevier Science Ltd.