Ionic liquid modified covalent organic frameworks for efficient detection and adsorption of ReO4–/TcO4–

The tanglesome environments of high radiation and strong acid or alkali lead to the currently reported materials used to detect ReO4− (surrogate for 99TcO4− with nonradioactive) far from meeting the requirements of practical applications. Here, we report the ionic liquids modified covalent organic frameworks (ionic COFs) were applied to detect and adsorb ReO4− for the first time. Ionic COFs are obtained by grafting ionic liquids on the channel walls of COFs. Not only the ionic liquids enhance the fluorescence performance of COFs by expanding the conjugated structure, but bring high-efficiency fluorescence response to ReO4− through introducing specific recognition sites with the detection limit as low as 1.04 μM. Benefiting from the intramolecular charge transfer conducted by hydrogen bond and clear hydrophobic framework, ionic COFs shows ultrafast fluorescence response (2 s) and excellent selectivity to ReO4−, which is quite suitable for on-site and real-time monitoring of ReO4−. Meanwhile, abundant ionic liquids and regular pore channels provide ionic COFs with admirable adsorption kinetics (within 3 min) and superior adsorption capacity (439 mg/g). In other words, the strong-bond ionic COFs overcome the weak stability of other fluorescence sensors of ReO4− and propose a new strategy for ReO4− detection, which offer huge potential to detect and remove 99TcO4−/ReO4− under realistic conditions.