One-pot in situ functionalization of cellulose in a CO₂ switchable solvent for the fluorescent detection of Fe³⁺

The development of novel methods for the selective fluorescent detection and real-time dynamic monitoring of Fe3+ remains a challenge, especially with those based on sustainable raw materials. Herein, a cellulose-based fluorescent probe was designed and fabricated via a sophisticated cascade reaction in a CO2 switchable solvent. Three consecutive reactions were carried out to realize the one-pot in situ functionalization of cellulose including dissolution of cellulose, grafting of poly(l-lactic acid) to the cellulose backbone by ring-opening polymerization of l-lactide, and grafting of a non-functional coumarin derivative to the cellulose backbone by nucleophilic substitution of methyl 6-bromomethyl coumarin-3-carboxylate and in situ functionalization of this derivative by cyclocondensation with 1,8-diazabicyclo-[5.4.0]-undec-7-ene. Excitingly, the synthesized cellulose-based fluorescent material, namely C-g-PLLA/MCD, has good thermal processing properties, which can be used to prepare a fluorescent smart tag that shows reversible "off" fluorescence response to Fe3+ with high sensitivity and selectivity, and a low limit of detection of 3.74 x 10(-6) M. The detection mechanism was revealed, which is due to the coordination interaction between Fe3+ and the carbonate bond in C-g-PLLA/MCD. The selective visual detection and real-time dynamic monitoring of Fe3+ in real water samples was demonstrated. This study provides a novel strategy for the functionalization of cellulose under mild conditions by taking advantage of the unique CO2 switchable solvent system.