Highly selective adsorption of Pb(II) and Cd(II) by carboxymethyl chitosan-modified distiller's grains hydrogel

To address the heavy metal water pollution caused by industrial wastewater discharge, a novel hydrogel adsorbent was prepared using organic matter derived from distiller's grains (DGS), a by-product of the brewing industry, as the main raw material and carboxymethyl chitosan (CMCS) as the modifier. Characterization results revealed that CMCS converted the adsorbent into a three-dimensional macroporous structure while enhancing its highly selective adsorption performance for Pb(II) and Cd(II), with adsorption capacities reaching as high as 825.3 mg·g^-1 and 644.3 mg·g^-1, respectively, and removal efficiencies up to 99.4% and 95.2% within 10 min. The adsorption process fitted well with the pseudo-second-order adsorption kinetic model (R² > 0.996) and the Langmuir isotherm model, indicating that the adsorption was dominated by chemical adsorption. Mechanistic analysis revealed that the hydrogel formed complexation and coordination with Pb(II) and Cd(II) via the lone pair electrons of O and N atoms, and combined with hydrogen bonding and electrostatic attraction to achieve synergistic adsorption. Furthermore, adsorption experiments on industrial wastewater using this adsorbent demonstrated that it maintained excellent adsorption performance even after six adsorption-desorption cycles, and achieved a degradation rate of 51.3% after 28 days. The synthesis of this highly efficient adsorbent not only realizes the functional modification and high-value utilization of DGS but also provides a green solution for wastewater remediation, exhibiting great application potential.