Self-Indicative Uranium Adsorbents: Salphen-Conjugated Microporous Polymers for Nanomolar Fluorescence Detection and High-Efficiency Capture

Porous organic polymer-based high-uranium-capture adsorbents that allow step-by-step tracking of the uranium adsorption/desorption process via visible color changes are ideal for real-world applications, yet remain a challenge to achieve to date. Herein, we report a salphenbased conjugated microporous polymer (Sal-CMP) that exhibits nanomolar fluorescence turnoff properties, revealing the initiation of the uranium adsorption, visual colorimetric changes at saturated uranium adsorption (yellow to black), and desorption (black to yellow). Sal-CMP exhibits strong quenching of its yellow emission at 578 nm in the presence of UO2 2+ due to static complex formation via coordination. Sal-CMP showed a high Stern-Volmer constant, KSV = 9.88 × 10 6 M⁻¹, and an ultralow detection limit of 7.65 nM due to the strong affinity of UO2 2+ to salphen core of the CMP. Beyond sensing, Sal-CMP demonstrates rapid, high uranium uptake capacity up to 0.35 g g⁻¹ h⁻¹, a high distribution coefficient, Kd = 1.48 × 10 5 mL g⁻¹, and removal efficiencies up to 68% at 10 ppm UO2 2+. Notably, the o-hydroxy imine-linked CMP (Im-CMP) does not exhibit such visible color changes upon uranyl adsorption. However, the uptake capacities of Im-CMP are relatively higher (0.40 g g⁻¹ h⁻¹) due to a higher binding energy of UO2 2+ @Im-CMP (−71.94 kcal mol −1) compared to UO2 2+ @Sal-CMP (−67.10 kcal mol −1). Both CMPs showed remarkable recyclability and good uranium adsorption performance. The study provides a unique porous polymer that acts as a self-indicative uranium adsorbent, exhibiting a sensitive response, uranium-capture characteristics, along with visible color changes during the uranium adsorption/desorption process.