Adsorption and desorption behavior of benzene and toluene on porous carbon monoliths

Highly porous carbon monoliths with good mechanical strength were prepared by the sol-gel polymerization of phenolic resin in oxidized polyacrylonitrile fiber felts, ambient drying, carbonization at 800℃ for 2 h and CO₂ activation at 950℃ for 1 to 3 h. Their microstructure and pore structure were investigated by SEM, TEM and N₂ adsorption. Their adsorption/desorption performance for benzene and toluene was measured by the gravimetric method. It is found that the carbon monoliths have a typical fiber-reinforced aerogel structure and the sample activated for 3 h (ACM-3) has a well-developed microporous structure with a BET surface area of 1 872 m²/g and pore volume of 0.97 cm³/g. ACM-3 shows high adsorption capacities of 117 and 287 mg/g for 50 ppm benzene and toluene, respectively, and the fastest adsorption/desorption kinetics. The Langmuir, Freundlich and DR isotherm models are used to fit the experimental adsorption data and the DR model shows the highest correlation coefficient. Moreover, ACM-3 has an excellent cyclic stability. The as-prepared carbon monoliths are promising adsorbents for the adsorption of volatile organic compounds in indoor air purification.