Ultrafast and efficient removal of aqueous Cr(VI) using iron oxide nanoparticles supported on Bermuda grass-based activated carbon

Abstract In this study, iron oxide nanoparticles supported on Bermuda grass-based activated carbon (Fe3O4/AC) was prepared, characterized and utilized to remove aqueous Cr(VI). By examining the crystal structure of loaded nanoparticles, the iron oxide nanoparticles contained FeO, Fe0 and Fe3O4. Among them, the Fe3O4 was proved to have the greatest influence on Cr(VI) removal. Kinetic and isotherm models revealed that the above-synthesized materials had ultrafast removal rate (3.08 mg/g/min) and excellent adsorption capacity (430.7 mg/g) for aqueous Cr(VI). Moreover, reusability of Fe3O4/AC was assessed and the results indicated that after third cycles, the absorbent maintained a 2.03-times higher adsorption capacity when using NaOH solution regeneration compared to HCl. A further increase of adsorption capacity was observed under ultraviolet conditions, which might be due to the oxidation of part Fe3O4 to γ-Fe2O3. The Cr(VI) removal mechanisms involved the reduction of Cr(VI) into Cr(III), electrostatic attraction, co-precipitation, ligand exchange and chelation.