Changes in Adsorption Behavior of Perfluorooctanoic Acid and Perfluorohexanesulfonic Acid Through Chemically-Facilitated Surface Modification of Granular Activated Carbon

Activated carbon is a versatile sorbent and effective contaminant removal media due to its complex porous structure and high surface area. The main purpose of this research is to increase the uptake of perfluoroalkyl and polyfluoroalkyl substances (PFAS) through modifications of granular activated carbon (GAC) by chemical treatment. To increase the adsorption of perfluorooctanoic acid (PFOA) and perfluorohexanesulfonic acid (PFHxS) onto GAC, the surface characteristics of two types of GAC from Calgon Carbon Corporation (charcoal-based Filtrasorb-F400 and coconut-based OLC 12 x 30-CBC) were chemically modified. Two GAC were treated with acid (hydrochloric acid [HCl]), base (sodium hydroxide [NaOH]), heat activated persulfate (PS), and hydrogen peroxide catalyzed with iron (H2O2/Fe). The extent of adsorption after 2-, 5-, and 10-day reaction time and the changes in carbon surface physical and chemical characteristics of treated GAC were compared with untreated GAC. Several characterization techniques, including Brunauer-Emmett-Teller surface area, pH of point zero charge, scanning electron microscopy with elemental analysis, and Fourier transform infrared spectroscopy, were used to analyze treated and untreated GAC. The extent of adsorption of both PFHxS and PFOA increased (7-8% in F400 and 6-9% in CBC) with HCl treatment likely due to increase in positive charge density, had no significant change with NaOH treatment, and decreased with PS (22-25% in F400 and 27-35% in CBC) and H2O2/Fe (4-8% in F400 and 12-13% in CBC) treatment. All the treated GAC had lower BET surface area compared to untreated GAC which is the main physical property deemed responsible for decreased adsorption. It was found that surface oxygen functional groups increased with treatments and decreased the hydrophobicity of the GAC surface, which resulted in lower PFAS adsorption.