Modification of polystyrene-based activated carbon spheres to improve adsorption of dibenzothiophene

Polystyrene-based activated carbon spheres (PACS) were modified with either air, HNO3, (NH4)2S2O8, H2O2 or H2 to improve their adsorption properties of dibenzothiophene (DBT). The texture and surface chemistry of PACS were characterized by N2 adsorption, scanning electron microscopy (SEM), temperature-programmed desorption (TPD), X-ray photoelectron spectroscopy (XPS), acid-base titration and elemental analysis. The results showed that HNO3 and (NH4)2S2O8 treatments introduced large amount of acidic groups such as carboxylic, lactones and anhydride groups, while air and H2O2 had relatively mild effects and introduced a small quantity of phenol, carbonyl and ether groups. In the HNO3 treatment, the acidic groups might be fixed on the internal and external surface of PACS, which may act as active sites of adsorption, resulting in increase of the adsorption amount by 45%. Whereas H2O2 and (NH4)2S2O8 treatments might fix more oxygen-containing groups on the external surface, which may hinder DBT molecule enter into micropores, leading to rather lower adsorption capacity with the extent of oxidation. So, the concentration, distribution and types of the acidic functional groups are responsible for the removal of DBT.