Aromatic compound adsorption from aqueous solution on activated carbons: Effects of adsorbate polarity and surface functional groups

The effect of acidic functional groups on an activated carbon surface on the adsorption of benzene, phenol and nitrobenzene was examined. Adsorption experiments for these aromatics in aqueous solution were conducted using two types of activated carbon with large and small amounts of surface functional groups, DAOx and DAOxOG, respectively, to obtain the adsorption isotherms. Adsorption kinetics of nitrobenzene and phenol were also examined. The results showed that the adsorption amounts of these adsorbates were higher for DAOxOG than those for DAOx. However, the adsorbed amount of nitrobenzene on DAOx gradually increased as concentration increased, and the maximum adsorption capacity was close to that of DAOxOG. The different adsorption rates on DAOx were also observed between nitrobenzene and phenol. Two types of silica, MSU-2 and HMS, were also prepared to investigate the adsorption affinity of nitrobenzene and phenol for a hydrophilic surface. The amount of nitrobenzene adsorbed on each silica was higher than that of phenol. This indicated that nitrobenzene adsorbed more favourably on a hydrophilic surface than phenol. These results suggested that the difference in adsorptive behaviour of adsorbates on the adsorbents was due to the different adsorption mechanism of adsorbates, caused by the different polar characteristics of each substituent group.