Tailor-Made Multiple Interpenetrated Metal-Organic Framework for Selective Detection and Adsorption of ReO₄

Rationally designed new materials for the selective detection and adsorption of ⁹⁹Tc, a problematic element in nuclear waste, are important and challenging in environmental monitoring. Here, we utilize an interpenetration approach to develop a cationic fluorescent metal-organic framework (NCU-2), which was constructed by a flexible tridentate nitrogen-containing ligand and Ag⁺ metal ions. The NCU-2 is a scarce case of 14-fold interpenetrated with excellent chemical stability even under 0.5 M HNO₃, which is helpful for the detection and removal of ReO₄^-/TcO₄^- from nuclear waste. Excitingly, the fluorescence signal of NCU-2 was obviously quenched in the presence of ReO₄^- (a nonradioactive surrogate of TcO₄^-) due to the robust interaction between ReO₄^- and the host for the formation of a non-fluorescent complex. Furthermore, the NCU-2 exhibits a high selectivity sensing of ReO₄^- in the presence of excess competitive ions. The superior response of NCU-2 toward ReO₄^- is ascribed to the high-fold structure and the luxuriant unsaturated Ag metal sites on the wall of 1D pore channels, which can enhance the framework positive charge and accelerate the transport of guest molecules to strengthen the interaction between them. Notably, NCU-2 successfully quantified trace levels of ReO₄^- in simulated Hanford waste with a broad linear range (0.2-200 μM) and a low detection limit of 66.7 nM. Moreover, NCU-2 also shows a high adsorption capacity to ReO₄^- (541 mg/g) and rapid sorption kinetics, making it extremely attractive for waste monitoring and emergency remediation.