Adsorption Performance and Mechanism on the Removal of Multiple Heavy Metals by a Hydrochar‐Incorporated Composite Hydrogel

ABSTRACT Heavy metal pollution in water bodies is one of the major issues that affect human health and sustainable development. In this study, a silk fibroin/polyethyleneimine composite hydrogel incorporated with hydrochar is synthesized for the removal of Cr(VI), Cd(II), Pb(II), and Mn(II) from wastewater. The hydrogel composite exhibits a porous structure, enhanced thermal stability, and richer functional groups according to SEM, TGA, and FTIR characterization. Adsorption behavior follows the pseudo‐second‐order kinetics and the Langmuir model, with the maximum adsorption capacities of 176.65, 108.17, 131.61, and 52.06 mg/g for Cr(VI), Cd(II), Pb(II), and Mn(II), respectively. The adsorption of heavy metal ions involves electrostatic attraction, ion exchange, and complexation, with an additional reduction mechanism involved in Cr(VI) removal. Cr(VI) adsorption exhibits minimal interference from coexisting ions and maintains good adsorption performance in simulated wastewater. The hydrogel composite retains over 50% Cr(VI) removal efficiency after five cycles, demonstrating excellent reusability. These results indicate that the hydrogel composite is a promising adsorbent for removing heavy metals from wastewater.