Selective and recyclable tandem sensing of PO₄^3- and Al³⁺ by a water-stable terbium-based metal-organic framework

Herein, a luminescent water-stable terbium-based metal-organic framework (MOF) {[Tb(Cmdcp)(H₂O)₃]₂(NO₃)₂·5H₂O}_n (1, H₃CmdcpBr = N-carboxymethyl-(3,5-dicarboxyl)pyridinium bromide) has been synthesized and used for the recyclable sensing of PO₄^3- and Al³⁺ in tandem. MOF 1 acts as a fluorescent sensor for PO₄^3- by the luminescence "turn-off" mechanism with high selectivity over other anions, such as F^-, Cl^-, Br^-, I^-, NO₃^-, H₂PO₄^-, HSO₄^-, HCO₃^-, HSO₃^-, SO₄^2-, CO₃^2- and HPO₄^2-. The formed PO₄^3-@1 complex further acts as the Al³⁺ sensor with the luminescence "turn-on" mechanism, also with high selectivity over diverse inorganic cations of Fe²⁺, Mn²⁺, Co²⁺, Ni²⁺, Hg²⁺, Na⁺, K⁺, Li⁺, Ag⁺, Mg²⁺, Ca²⁺, Cd²⁺, Pb²⁺, Cu²⁺, and Zn²⁺. The detection process for both PO₄^3- and Al³⁺ can be directly observed with naked eyes under the UV light at 365 nm. The detection limits for PO₄^3- and Al³⁺ are 1.1 μM and 6.6 μM, respectively. Such a sensing cycle is further transferable to urine and serum samples with a satisfactory near-quantitative recovery, highlighting its good potential in biologically relevant applications.