Activated carbon fibers for efficient VOC removal from diluted streams: the role of surface morphology

The effect of the micropore structure of activated carbon fibers (ACFs) on the adsorption of toluene at low concentration (10–80 ppmv) was studied over two types of ACFs. Both adsorbents presented similar surface chemistry but different porous structure: one ACF was ultramicroporous (d pore < 1 nm) and the other supermicroporous (d pore ~1 to 2 nm). Toluene adsorption isotherms were determined for both ACFs and were found to be consistent with Dubinin–Radushkevich (D–R) model. The toluene adsorption enthalpies calculated from temperature-programmed desorption profiles at temperatures below 330 K were close to the values obtained from D–R equations. Larger adsorption strength was found in the ultramicroporous adsorbent as compared to the supermicroporous one suggesting that the pore shape strongly influences the adsorption mechanism. The adsorbent with a lower specific surface area but narrower micropores could be more efficient at high temperatures than an adsorbent with large pore volume and wider micropores. The findings reported have a big importance for correct choice of material when designing efficient structured adsorbing bed.