Magnetic Biochar Composites Modified with Branched Polyethyleneimine for Highly Efficient Cr(VI) Removal from Water

Abstract In this study, a set of branched polyethyleneimine (BPEI) modified magnetic biochar composites (BPEI500‐MBC, BPEI1800‐MBC and BPEI20000‐MBC) were successfully prepared for capturing Cr(VI) from water solution. The results of the adsorption experiment showed that the adsorption capacity obeyed the sequence of BPEI500‐MBC<BPEI1800‐MBC<BPEI20000‐MBC. The theoretical maximum adsorption capacity of BPEI20000‐MBC calculated by Langmuir model reached 202.71 mg g −1 at 298 K. The adsorption kinetics followed the pseudo‐second‐order kinetics and the intra‐particle diffusion models, and the adsorption isotherm was fitted with the Freundlich adsorption isotherm model. Furthermore, the adsorption thermodynamics calculations proved that the adsorption was a spontaneous endothermic process. The electrostatic attraction between Cr(VI) and the protonated imidazole N + of BPEI‐MBC played a key role in Cr(VI) adsorption process, accompanied by complexation and partly Cr(VI) was reduced to Cr(III). The adsorption capacity of BPEI20000‐MBC was still remained above 86.87 % after five adsorption‐desorption cycles. Hence, BPEI20000‐MBC is predicted to be an effective adsorbent for removing Cr(VI) and other heavy metal ions from water solution.