Polymer Ligand-Sensitized Lanthanide Metal-Organic Frameworks for an On-Site Analysis of a Radionuclide

Herein, a new strategy to increase the sensitivity of a lanthanide metal-organic framework (Ln-MOF) to UO₂²⁺ was proposed by using polymeric ligands. By utilizing [Tb(1,3,5-benzenetrisbenzoate)]n (Tb-TBT) MOF as the host, preloaded 2-vinyl terephthalic acid (VTP) was polymerized in situ, which produced a novel fluorescent composite denoted as PVTP⊂Tb-TBT. Benefiting from the coordination of PVTP to the Tb nodes, the polymeric chains performed both as molecular scaffolds that improved the water stability of the framework and as additional antennae that sensitized the photoluminescence of the Tb nodes. More importantly, the detection sensitivity and selectivity of PVTP⊂Tb-TBT to UO₂²⁺ were much improved compared to those of Tb-TBT. Detailed characterizations indicated that the incorporation of PVTP efficiently enriched UO₂²⁺ in the probe, which promoted the energy dissipation to UO₂²⁺. Besides, UO₂²⁺ was also supposed to release PVTP from PVTP⊂Tb-TBT and, thus, exposed the open metal sites to water molecules, which interrupted the sensitization effect of PVTP and induced a nonradiative energy dissipation. A limit of detection (LOD) as low as 0.75 nm was recorded by suspending the PVTP⊂Tb-TBT probe in a water sample, far below the limit in drinking water set by the United States Environmental Protection Agency (130 nm). Furthermore, a remotely controlled sampling and an on-site analysis of real water samples were realized by facilely loading PVTP⊂Tb-TBT on thin films (TFs). The LOD for UO₂²⁺ was 2.5 nm by using the TFs. This study reports a new strategy for boosting the sensitivity and selectivity of Ln-MOF to monitor UO₂²⁺ and expands the application of the strategy to an on-site analysis.