Highly sensitive, selective and reversible detection of Fe³⁺ ions based on elastic cellulose nanofibrils/chitosan...

Heavy metal ions are increasingly accumulated in the natural environment due to growing water pollution, causing serious pollution to biological communities. Therefore, it is of great significance to study the qualitative and quantitative adsorption and detection of heavy metal ions in wastewater. Using cellulose nanofibrils (CNF)/chitosan (CS) composite as adsorbent framework, salicylaldehyde ethylenediamine Schiff base (SESB) as fluorescent and colorimetric probe, citric acid (CA) as crosslinking agent, and freeze-drying technology to prepare CNF/CS/CA/SESB composite sponge and membrane. After adsorbing Fe³⁺, the composites changes color from yellow-green to brownish-black under sunlight, and undergoes fluorescence quenching within 17 s under ultraviolet light, enabling highly sensitive, selective and reversible detection towards Fe³⁺. The composite sponge exhibits amphiphilicity and a underwater oil contact angle of 154°, which endows it with anti-fouling properties underwater. Its adsorption capacity is 438.68 mg·g^-1, and it has excellent underwater compressive elasticity as well as fluorescence and colorimetric reversibility, providing significant foundation for its application in water purification and collection. The composite membrane can be wide applied in information encryption and anti-counterfeiting fields. Predictably, CNF/CS/CA/SESB composites will offer theoretical reference for the assembly strategy of cellulose fluorescent probes, as well as their applications in detection and information encryption.