A geopolymer route to micro- and meso-porous carbon

Hexagonal and wormhole-type mesoporous geopolymers were developed by controlling the concentration of a structure directing agent (cetrimonium bromide, CTAB) with fixed ratios of Si/Al, KOH/(Si + Al), and H(2)O/(Si + Al), and their detailed porous structures were confirmed by TEM, N(2) adsorption–desorption and X-ray diffraction measurements. The as-prepared geopolymers were then used as templates to replicate porous carbons with various structures and porosities for CO(2) adsorption. To understand the correlation between the CO(2) adsorptivity and porous structures, we tuned the porosity of the geopolymer-templated carbons by modifying the structures of the geopolymers. The porous carbons obtained from the hexagonal-type porous geopolymers were found to be composed of the aggregates of carbon nanowires exhibiting large particles, while those obtained from the wormhole-like porous geopolymers were determined to be wormhole type as well, as evidenced by TEM and X-ray diffraction studies. According to the CO(2) adsorption isotherms of the porous carbons, the aggregates of carbon nanowires exhibited the highest CO(2) adsorptivity due to their highest microporosity and largest specific surface area.