Efficient removal of Cr(VI) by magnetically separable CoFe2O4/activated carbon composite

• Ferromagnetic mediums were anchored into AC, resulting in good magnetic response.
• The Cr(VI) adsorption of CoFe2O4/AC was more effective than the initial AC.
• CoFe2O4/AC could be separated and retrieved easily by an outer magnet after Cr(VI) adsorption.
• The pH, temperature and initial Cr (VI) concentration affected Cr(VI) adsorption.
• The adsorptive behavior for Cr (VI) of CoFe2O4/AC conformed to the Freundlich model.

Owing to the unique microporous structure and high specific surface area, activated carbon (AC) could act as a good carrier for functional materials. In this paper, CoFe2O4/AC composite was prepared by a facile hydrothermal method for the adsorption of Cr(VI) in wastewater. The results indicated that CoFe2O4 nanoparticles embedded in the AC pores decreased the carbon surface area. However, The Cr(VI) adsorption capacity of CoFe2O4/AC was more effective than the initial AC. The magnetic properties of CoFe2O4/AC indicated it could be separated and retrieved easily by an outer magnet after Cr(VI) adsorption. The effects of solution pH, temperature and initial Cr (VI) concentration on the Cr(VI) adsorption of AC and CoFe2O4/AC were investigated. The Cr(VI) adsorption was pH dependent and found to be maximum at pH = 2.0. It was effective Cr(VI) adsorption with increasing temperatures. The standard free energy (ΔG), enthalpy change (ΔH) and entropy change (ΔS) were evaluated. The kinetic parameters of Langmuir and Freundlich isothermal equation were analyzed, and the Freundlich kinetic model was feasible to describe the Cr(VI) adsorption process in CoFe2O4/AC composite. According to these results, it was efficient removal of Cr(VI) with CoFe2O4/AC composite and magnetically separable easily by an outer magnet after Cr(VI) adsorption.