Preparation and Adsorption Properties of Lignin‐Based Hydrogels

ABSTRACT Organic dyes in industrial wastewater pose significant environmental and health risks. In this study, four lignin‐based hydrogels—Mg–Al–H, Al–H, Mg–Fe–H, and Fe–H—were synthesized by incorporating sodium lignosulfonate with metal ions to develop an eco‐friendly adsorbent for dye removal. Four types of lignin‐based hydrogels were systematically characterized using a particle size analyzer, Fourier‐transform infrared spectroscopy (FT‐IR), and scanning electron microscopy (SEM). Incorporation of magnesium and iron ions enhanced the porous structure, forming honeycomb‐like surfaces with abundant active sites. Among them, Mg–Fe–H showed the highest removal efficiency for methylene blue (MB), achieving 94.87% under optimal conditions (1 g/L dosage, 360 min, 298K, pH 10). Adsorption followed a pseudo‐second‐order kinetic model (R 2 = 0.974) and the Langmuir isotherm (R 2 = 0.971), indicating chemisorption and monolayer adsorption. The excellent adsorption performance was attributed to pore adsorption, electrostatic attraction, hydrogen bonding, and π–π interactions. These results demonstrate the potential of metal ion–modified lignin hydrogels for efficient and sustainable dye removal from wastewater.