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

A new composite material (Fe 3 O 4 @GAC, Fe 3 O 4 nanoparticles loaded on a commercial granular activated carbon (GAC)) was prepared through a facile hydrothermal process at controlled Fe 2+ :Fe 3+ molar ratios in air. Fe 3 O 4 @GAC was thoroughly characterized and tested for adsorption of perfluorooctanoic acid (PFOA) in water. Fe 3 O 4 @GAC(2:1), prepared at an Fe 2+ :Fe 3+ 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 Fe 3 O 4 . GAC in the composite played an important role for PFOA adsorption. The presence of Ca 2+ ions (10 mM) at final pH 5.0–10.0 more than doubled the PFOA equilibrium uptake of PFOA by Fe 3 O 4 @GAC(2:1) due to the calcium bridging effect between PFOA and the Si-OH or Fe-OH groups in Fe 3 O 4 @GAC(2:1), and because of the Ca 2+ -modification induced formation of PFOA hemi-micelles on the surface or in the relatively large pores (2.27 nm) of Fe 3 O 4 @GAC(2:1). Fe 3 O 4 @GAC(2:1) was amenable to efficient regeneration using a mixture of NaOH solution and methanol. Fe 3 O 4 @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.