The modification of pore size in activated carbon fibers by chemical vapor deposition and its effects on molecular sieve selectivity Original Research Article

Pore size control of a series of activated carbon fibers was attempted by chemical vapor deposition (CVD) of benzene to clarify the influence of the pore distribution on the development of molecular sieving ability. Weight increase by CVD was found to saturate at a certain level respective to the fiber, reflecting their surface areas. However, when saturation was obtained, the molecular sieving selectivity between CO2 and CH4 was induced only in the smaller surface area fibers, whereas the fibers with larger surface areas lost the adsorption activity for both gases. Straight micropores developed from the surface can be controlled in their slit size, by carbon deposition selectively onto their wall, if benzene molecules can get into the pore. In contrast, the size of micropores developed on the walls of mesopores in the fibers with large surface area are difficult to control since the carbon deposition continues until the whole wall of the mesopore is covered by the deposited carbon, which plugs the micropores.