A β-keto-enamine covalent organic framework fluorescent switch for selective and sensitive UO22+ detection

Abstract

Nuclear accidents, uranium mining, and nuclear weapons production pose significant health and environmental concerns, and as a consequence there is ongoing interest in techniques for rapid and selective detection of the uranyl ion (UO₂²⁺). In this study, a β-keto-enamine-linked covalent organic framework (COF) fluorescent probe was synthesized by a simple one-step condensation reaction using 1,3,5-triformylphoroglucinol (Tp) and 3,3'-dihydroxybenzidine (Db). Tp-Db exhibited a UO₂²⁺ detection limit of 99.34 nM and a 10 s reaction time, making it suitable for rapid detection in diverse environmental samples including river water, nuclear wastewater, food, and urine. Experimental analyses and density-functional theory (DFT) calculations reveal that UO₂²⁺ preferentially coordinates with the carbonyl group in Tp-Db through intramolecular charge transfer and electrostatic interactions, and the presence of the hydroxyl assistant group further improves the binding affinity. This study elucidates the interaction mechanism of different functional groups (carbonyl, hydroxyl, and imine) with UO₂²⁺ within the channels of the keto-enamine-linked COF, providing a promising rational basis for the development of an advanced UO₂²⁺ sensing platform.