A Cd(II) post-modified hydrogen-bonded organic framework toward sensitive uranyl ion detection via turn-off fluorescence

Given the environmental and potential health hazards associated with uranyl ion (UO 2 2+ ), developing fast, cost-effective, and sensitive detection methods is of significant importance. In this study, we report a novel fluorescent sensor for the selective detection of UO 2 2+ based on a cadmium-post-modified hydrogen-bonded organic framework (HOF), H 4 -CDI-Cd. The post-synthetic metal modification enhances the π-conjugation of the framework, reduces its energy gap, and creates specific binding sites for UO 2 2+ . The probe exhibits a fast, selective response toward UO 2 2+ via a photoinduced electron transfer (PET) mechanism, achieving a low detection limit of 19.54 nM and a linear range from 75 nM to 1 μM. DFT calculations reveal that Cd 2+ coordination redistributes charge, which not only lowers the electrostatic repulsion for UO 2 2+ migration into the channels but also provides low-energy vacant orbitals (5s/5p) for secondary coordination with UO 2 2+ , thereby enhancing selective binding. The method was successfully applied to determine UO 2 2+ in real water samples (lake water and mining wastewater), with quantitative spike recoveries between 99.61% and 102.61%. This work demonstrates a feasible post-modification strategy to engineer responsive HOFs for the selective detection of UO 2 2+ in the environmental water.