Innovative construction of amine-functionalized lignin-based hydrogel for ultrafast and selective dye remediation

• Branched aminated lignin-based hydrogels (BALH) were successfully fabricated. • Hydrogel has tunable pores and surface charge depending on the lignin and PEI ratio. • The adsorption capacity for MO reached approximately 900–930 mg/g. • BALH can selectively adsorb cationic/anionic dyes. • BALH maintain high removal efficiency after 10 recycles and continuous adsorption. This study introduces a branched aminated lignin-based hydrogel (BALH) designed for the efficient removal of ionic dye pollutants from wastewater. BALH was fabricated using lignin and branched polyethylenimine with poly(ethylene glycol) diglycidyl ether as a crosslinker. BALH exhibited enhanced chemical durability and physical stability; it formed a robust three-dimensional network through polyelectrolyte complexation and chemical crosslinking. BALH demonstrated superior adsorption capacities for both cationic methylene blue and anionic methyl orange (MO) compared to traditional kraft lignin. The adsorption capacity for MO reached approximately 900–930 mg/g, following a pseudo-second-order kinetic model and the Langmuir isotherm model, indicating chemisorption and homogeneous monolayer adsorption. Thermodynamic studies revealed the spontaneous endothermic nature of the adsorption process. Remarkably, BALH maintained a high removal efficiency even after 10 adsorption and desorption cycles, and continuous adsorption experiments confirmed its practical effectiveness. Because of its ultrahigh dye-removal capacity, structural stability, recyclability, and ease of separation, BALH is a promising candidate for scalable wastewater treatment solutions. The study of lignin modification may also offer innovative systems for modifying and cross-linking lignin.