Facile fabrication of lignin crosslinked hydrogel for cationic dye adsorption and antioxidant

Lignin, renowned for its abundance of hydroxyl groups, was utilized in three dimensions to fabricate a hydrogel matrix. In this study, the optimal conditions for the preparation of a lignin-crosslinked hydrogel and its potential for dye and antioxidant removal were investigated. The hydrogel was synthesized through a cross-linking reaction, with varying amounts of cross-linking agent (poly(ethylene glycol) diglycidyl ether) added to adjust for the lignin content. Chemical structure analysis of the lignin-crosslinked hydrogel was conducted using Fourier-transform infrared spectroscopy and X-ray photoelectron spectroscopy, confirming successful hydrogel formation. Additionally, thermal analysis revealed an increase in the maximum thermal decomposition temperature with increasing cross-linker content. The lignin cross-linked hydrogel demonstrated a significantly higher swelling ability at pH 7 compared to pH 3. The dye adsorption capacity of the lignin-crosslinked hydrogel, which was evaluated using crystal violet (CV), showed a maximum adsorption capacity of 106 mg∙g-1. The CV adsorption behavior followed Freundlich isotherms and pseudo-first-order kinetics. Moreover, the lignin-crosslinked hydrogel exhibited notable antioxidant activity, which was attributed to the phenolic hydroxyl groups of lignin macromolecules. Therefore, lignin-crosslinked hydrogels prepared using cross-linking agents have promising application potential in various fields.