An ultrastable luminescent covalent organic polymer for selective Pd²⁺ detection in strong acid

Abstract The low natural abundance of palladium (10 ppb) in the Earth's crust highlights its considerable potential as a valuable resource, especially given that spent nuclear fuel contains approximately 1–2 kg of Pd per ton. However, the detection and separation of Pd 2+ from high‐level liquid waste (HLLW) present significant challenges due to high acidity (2–5 M HNO 3 ) and intense radiation conditions inherent in spent fuel reprocessing. We present a cyano‐olefin‐linked covalent organic polymer (COP‐TnPp) that exhibits remarkable stability in strong acidic environments and resilience to radiation. Thanks to its olefin linkage, which facilitates π‐electron conjugation, COP‐TnPp exhibits strong luminescence, whose intensity remains stable across a range of 1–5 M nitric acid solutions. Pd 2+ ions can effectively quench the fluorescence of COP‐TnPp in 1 and 5 M HNO 3 solutions with detection limits of 0.37 and 0.63 μM, respectively. Additionally, COP‐TnPp demonstrates exceptional selectivity for Pd 2+ ions, even amidst 22 other interfering ions in a simulated HLLW solution (5 M HNO 3 ), with the detection limit remaining at 0.697 μM. This work not only marks an advancement in the development of materials for detecting Pd 2+ in extreme acidic conditions but also offers new insights into the detection of other radionuclides under similarly challenging environments.