Enhanced adsorption of perfluorooctanoic acid (PFOA) from water by granular activated carbon supported magnetite nanoparticles

A new composite material (Fe3O4@GAC, Fe3O4 nanoparticles loaded on a commercial granular activated carbon (GAC)) was prepared through a facile hydrothermal process at controlled Fe2+:Fe3+ molar ratios in air. Fe3O4@GAC was thoroughly characterized and tested for adsorption of perfluorooctanoic acid (PFOA) in water. Fe3O4@GAC(2:1), prepared at an Fe2+:Fe3+ molar ratio of 2:1, showed the best PFOA removal and offered 28.8% higher adsorption capacity than the parent GAC at final pH 4.0. The enhanced adsorption of PFOA was attributed to concurrent hydrophobic, electrostatic and complexation interactions between PFOA, GAC and Fe3O4. GAC in the composite played an important role for PFOA adsorption. The presence of Ca2+ ions (10 mM) at final pH 5.0-10.0 more than doubled the PFOA equilibrium uptake of PFOA by Fe3O4@GAC(2:1) due to the calcium bridging effect between PFOA and the Si-OH or Fe-OH groups in Fe3O4@GAC(2:1), and because of the Ca2+-modification induced formation of PFOA hemi-micelles on the surface or in the relatively large pores (2.27 nm) of Fe3O4@GAC(2:1). Fe3O4@GAC(2:1) was amenable to efficient regeneration using a mixture of NaOH solution and methanol. Fe3O4@GAC holds the potential to be used as a simple and low-cost adsorbent for enhanced adsorption of PFOA, especially in waters of high hardness and alkalinity.