Boosting the adsorption performance of ethanol on surface chemistry modified activated carbon fiber

As a potential adsorption material, it is still a challenge for activated carbon fiber (ACF) in efficient adsorption of ethanol due to its nonpolar surface, which is mainly emitted from the grain drying industry. This study prepared surface polarity-modified ACF using the heteroatom doping method. The modified ACF possessed a richer array of strongly polar oxygen/nitrogen-containing functional groups (primarily phenolic hydroxyl and lactone groups), a larger specific surface area, and a more developed micropore structure. The adsorption capacities of ethanol for O-ACF and N-ACF were 4.110 mmol/g and 1.698 mmol/g, respectively, which were 11.3 times and 4.7 times those of unmodified ACF. This was a significant improvement over our previous work (0.363 mmol/g). The improvement of adsorption capacity for the N-ACF was mainly due to the higher specific surface area, greater number of micropores (more adsorption sites) and abundant existence of defects, whereas, for O-ACF, the improvement mainly relied on the abundant presence of oxygen-containing functional groups on the surface. However, water had a negative effect on the adsorption of ethanol for the modified ACF due to competitive adsorption and the disappearance of capillary condensation. It was further revealed that the adsorption process of ethanol and water was quite different. It obeyed the linear driving force (LDF) model for ethanol adsorption, however, the intraparticle diffusion (IPD) model for water adsorption.