Lignin-based porous cross-linked fluorescent membrane: An efficient method for 4-nitrophenol recognition and separation

People are placing growing emphasis on sustainable development and environmental protection. Lignin, being the second most abundant biological polymer, holds significant potential for diverse applications. This study modifies and uses lignin as starting material for further applications. The esterification reactions are employed to destroy its hydroxyl groups, making it oil-soluble. Diels-Alder (DA) reactions are used to prepare lignin-based macro-monomers for RAFT polymerization. Meanwhile, this material reacted with the synthesized amine-containing thiolipid compounds with 4-bromo-1,8-naphthalenedicarboxylic anhydride. Then, 1-(2-pyridyl) piperazine replaced the -Br of the naphthalimide to prepare small molecules functioning as both a fluorescence probe and a RAFT reagent. Subsequently, lignin and glycidyl methacrylate (GMA) were incorporated into the polymer via RAFT polymerization. By utilizing polyethylene glycol (PEG) as a binder, the hydroxyl and epoxy groups underwent ring-opening reactions, leading to a lignin-based porous cross-linked network fluorescent film. The fluorescent film exhibits high sensitivity, and specific recognition toward 4-Nitrophenol (4-NP), with a detection limit as low as 0.28 μM. Notably, this research indicates that the film's adsorption capacity for 4-NP reaches 112.4 μg/cm 2 , demonstrating excellent separation performance. The application scope of lignin was enlarged, and it could find more actual usage in the future.