Simultaneous reduction and adsorption of Cr (VI) on a novel magnetic nitrogen-rich nanocomposite in acidic solutions

Here, a novel magnetic nitrogen-rich biochar (MNRB), synthesized by attaching Fe 3 O 4 @SiO 2 -NH 2 particles with core-shell structure on crab shell derived/nitrogen-rich biochar (NRB), was used as absorbent and reductant to remove hexavalent chromium in aqueous systems. Characteristics of the material demonstrated that the MNRB was rich in nitrogen-containing functional groups and that the Fe 3 O 4 @SiO 2 -NH 2 magnetic particles with a diameter of approximately 150 nm were successfully added on the MNRB surface by strong ether linking (C-O-C). The maximum removal capacity of MNRB was 152.9 mg·g −1 , which was considerably higher than most reported magnetic biochar. Study of the removal mechanisms revealed that the Cr(VI) removal by MNRB involved three steps: (1) adsorption of Cr(VI) anions by protonated functional groups; (2) reduction of Cr(VI) anions to Cr(III) cations by electron-donor groups; and (3) chelation of Cr(III) cations by amine groups. The easy regeneration, satisfactory reusability, and remarkable performance in batch tests reflected the high potential of MNRB for treating Cr(VI)-contaminated water.