A novel magnetic biochar prepared by K2FeO4-promoted oxidative pyrolysis of pomelo peel for adsorption of hexavalent chromium

[Display omitted] •A highly adsorptive magnetic biochar was prepared using K2FeO4 in one-step.•Oxygen containing groups were simultaneously introduced with single phase ɤ-Fe2O3.•In situ generation of oxygen containing groups benefited to capturing ɤ-Fe2O3.•Both ɤ-Fe2O3 and biochar matrix contributed to adsorption of Cr(VI).•The magnetic biochar exhibited 209.64 mg/g maximum adsorption capability. Magnetic biochar was usually prepared using ferrous and ferric compounds as precursor of magnetic medium. Ferrate, which could be an internal oxidative modifier, was less explored for preparing magnetic biochar. Here, a magnetic biochar was prepared through K2FeO4-promoted pyrolysis of pomelo peel for adsorption of hexavalent chromium. Oxygen-containing groups and single phase ɤ-Fe2O3 were simultaneously introduced into biochar matrix at 300 °C. The magnetic biochar exhibited 209.64 mg/g maximum adsorption capability at 45 °C, outperformed the best magnetic biochar with 142.86 mg/g maximum adsorption capability at 40 °C in the literature. Moreover, a good magnetism was obtained, facilitating separation of the magnetic biochar from aqueous solution by a magnet. The removal of hexavalent chromium was contributed to the hybrid adsorption of ɤ-Fe2O3 and biochar matrix by reduction, electrostatic interaction and complexation. This method was attractive, required neither extra modifiers nor multiple operations for preparation of highly adsorptive magnetic biochar.