Amino-functionalized montmorillonite/lignin hybrid hydrogel for efficient Pb(II) capture through synergistic ion exchange and coordination

Lead (Pb) contamination in wastewater poses a persistent environmental challenge. Developing effective, sustainable adsorbents from renewable resources is a key goal of cleaner production. Herein, a bio‑based organic–inorganic composite hydrogel (I‑Hydrogel) was constructed using amino‑functionalized montmorillonite nanosheets (AMMT) combined with lignin (a renewable aromatic polymer), poly(vinyl alcohol) (PVA), and polyethyleneimine (PEI). In this design, AMMT provided inorganic adsorption-active sites, while the PVA/PEI network served as a three-dimensional scaffold to immobilize lignin and AMMT, generating a hierarchically porous framework enriched with nitrogen- and oxygen-containing functionalities. The optimized hydrogel exhibited a maximum Pb(II) adsorption capacity of 190.22 mg/g. The adsorption process was better described by the pseudo-second-order kinetic and Langmuir isotherm models and was thermodynamically favorable and endothermic within the investigated temperature range. Spectroscopic analyses indicated that Pb(II) uptake originated from a synergistic mechanism involving cation exchange at clay-associated sites and coordination interactions with amino, imine, hydroxyl, and other oxygen-containing groups in the hybrid network. This work demonstrates an effective strategy for integrating functional clay nanosheets with renewable bio‑based components into recoverable adsorbent platforms, offering a sustainable materials design approach that aligns with cleaner production principles for heavy‑metal removal from aqueous systems.