Microwave-assisted synthesis of polyethyleneimine and carbon disulfide co-modified magnetic lignosulfonate for efficient Pb(II) and Cr(VI) removal: Preparation, performance, and mechanisms

Herein, polyethyleneimine (PEI) and carbon disulfide (CS₂) co-grafted magnetic lignosulfonate (LS) with magnetism (PEI/CS₂@MLS_MW) was synthesized through microwave-assisted synthesis technology and was employed for treating the water contaminated with Pb(II)/Cr(VI). Characterization results proved the modification substances were successfully loaded onto adsorbent, and the introduction of formaldehyde (HCHO) further enhanced PEI binding on PEI/CS₂@MLS_MW via Mannich reaction. Furthermore, PEI/CS₂@MLS_MW exhibited excellent removal capability on Pb(II) and Cr(VI), which maximally achieved 206.81 and 456.80 mg/g. Meanwhile, the uptake process of pollutants by PEI/CS₂@MLS_MW was endothermic and retained excellent uptake capacity with the interference of multiple ions coexisting. In addition, oxygen-containing functional groups on the PEI/CS₂@MLS_MW could remove Pb(II) through chelation, and protonated amino functional groups might uptake Cr(VI) via reduction. Meanwhile, nitrogen-containing functional groups, protonated amino functional groups, and iron species on the PEI/CS₂@MLS_MW participated in the adsorption process of Pb(II) and Cr(VI) via complexation, electrostatic attraction, and precipitation, respectively. Moreover, PEI/CS₂@MLS_MW could maintain an adsorption efficiency of over 70 % for Pb(II) and Cr(VI) after three cycles of regeneration experiments using different eluents. Summarily, this work proposed a novel composite material which could effectively remove Pb(II)/Cr(VI) from water, providing new ideas to treat heavy metal polluted water.