Ethylenediamine-functionalized MnFe2O4 @ferrihydrite as a magnetic adsorbent for removal of Cr(VI): Adsorption and mechanism studies

Chromium-contaminated water can seriously harm the health of human being. In this work, a novel magnetic manganese ferrite@ferrihydrite nanocomposites (MnFe2O4 @Fh-EDA) was successfully synthesized utilizing ethylenediamine (EDA) via co-precipitation method and applied in Cr(VI) removal. Batch adsorption tests demonstrated that MnFe2O4 @Fh-EDA (qmax = 51.36 mg/g) could maintain stable removal efficiency (≥ 85.6%) at the pH of 2.0–9.0 and exhibit higher adsorption capacity than that of MnFe2O4 and ferrihydrite. Results revealed that EDA enhanced the adsorption capacity as well as acid resistance of ferrihydrite because the protonation of -NH2 consumed hydrogen ions during adsorption. The magnetic saturation of MnFe2O4 @Fh-EDA (24.82 emu/g) ensured that it could be easily separated and regenerated after reaction. It was also found that electrostatic attraction, ions exchange and redox reactions all contributed to Cr(VI) elimination. In brief, MnFe2O4 @Fh-EDA would be a promising adsorbent as it not only displayed great adsorption capacity but also maintained outstanding magnetic separation capability. Therefore, this work would offer references and inspiration to design the new MnFe2O4-based materials for further applications in heavy metal removal from wastewater.