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.