Polyethylenimine modified biochar adsorbent for hexavalent chromium removal from the aqueous solution

•A PEI modified biochar with abundant amino groups was prepared for Cr removal.•The adsorption performance of biochar for Cr removal has been significantly improved.•The maximum adsorption capacity of PEI-alkali-biochar for Cr is about 435.7 mg/g.•Adsorption–desorption studies reveal the modified biochar has a good stability.•PEI modified biochar has a good potential as a suitable material for Cr(VI) removal.

A chemical modified biochar with abundant amino groups for heavy metal removal was prepared using polyethylenimine (PEI) as a modification reagent, and used as an adsorbent for the removal of Cr(VI) from aqueous solution. The biochars before and after modification were characterized by Fourier transformed infrared spectroscopy, X-ray photoelectron spectroscopy etc. The adsorption of Cr(VI) by the modified biochar was obeyed pseudo-second-order kinetic model and Langmuir adsorption isotherm model. Its maximum adsorption capacity was 435.7 mg/g, which was much higher than that of pristine biochar (23.09 mg/g). Results also indicated that the removal of Cr(VI) by the PEI modified biochar depended on solution pH, and a low pH value was favorable for the Cr(VI) removal. The results herein revealed that the PEI modified biochar had a good potential as a suitable material for sorption and detoxification of Cr(VI) from aqueous solution.