Dialysis-induced self-assembly of carboxylated lignin nanoparticles for UV-shielding and cationic pollutant removal

The increasing demand for petroleum-derived polymers and concerns regarding climate change and plastic pollution have intensified interest in sustainable bio-based materials. Here, we report a green strategy for fabricating lignin nanoparticles (LNPs) using renewable kraft lignin (KL). Carboxylated lignin (CL) was synthesized via nucleophilic substitution, introducing ionizable carboxyl groups onto the lignin backbone. KL and CL were then converted into nanoparticles via solvent-exchange dialysis, where intermolecular interactions, changes in solvent polarity, and electrostatic repulsion drove self-assembly. When incorporated into cosmetic lotions, the LNPs imparted efficient ultraviolet (UV) shielding, particularly in the UV-A-UV-B region. Owing to their dense arrangement of carboxyl groups and aromatic structures, the CL nanoparticles (CLNPs) also exhibited pH-responsive adsorption and strong selectivity toward cationic pollutants. The maximum adsorption capacity for methylene blue was calculated to be 570.56 mg/g using the Langmuir model, underscoring the promise of CLNPs as multifunctional, sustainable nanomaterials for UV protection and water decontamination.