Magnetic few-layer graphene nanocomposites for the highly efficient removal of benzo(a)pyrene from water

Abstract

Regarding the importance of water pollution by persistent organic pollutants and the need for innovative processes to extract them efficiently, we designed magnetic few-layer graphene-based composite nanomaterials (CNs) for high removal from water of a particularly toxic polycyclic aromatic hydrocarbon (PAH): benzo(a)pyrene (BaP). The CNs were prepared in a one-step polyol solvothermal synthesis process by introducing few-layer graphene coated with tannic acid in the reaction medium of iron oxide nanostructures. The synthesis was reproducible and allowed obtaining a large amount of magnetic CNs, which can be easily and quickly magnetically removed from aqueous medium. BaP adsorption on CNs was studied for an initial BaP aqueous concentration of 1–5000 μg L⁻¹. A very low amount of CNs (5 mg L⁻¹) was sufficient and effective to have a very high and fast BaP adsorption in comparison with previous studies reporting an adsorbent amount of 5–1000 mg L⁻¹. Removal efficiencies of 99.95 ± 0.01% in water with 1% ethanol as co-solvent were reached in minutes. The presence of iron oxide was observed to not affect the adsorption capacity of CNs. The volume percentage of ethanol in the water media influenced the removal efficiency of BaP by the CNs. With 50 vol% ethanol necessary to obtain an adsorption isotherm, the adsorption follows Langmuir's law with a maximum adsorption capacity q_max = 69.45 ± 5.20 mg g⁻¹ and a Langmuir isotherm constant K_L = 1.92 ± 0.54 L mg⁻¹. These CNs, compared with other BaP and PAH adsorbents, are clearly very promising for BaP removal from polluted media.