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 Pd²⁺ from high-level liquid waste (HLLW) present significant challenges due to high acidity (2–5 M HNO₃) 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. Pd²⁺ ions can effectively quench the fluorescence of COP-TnPp in 1 and 5 M HNO₃ solutions with detection limits of 0.37 and 0.63 μM, respectively. Additionally, COP-TnPp demonstrates exceptional selectivity for Pd²⁺ ions, even amidst 22 other interfering ions in a simulated HLLW solution (5 M HNO₃), with the detection limit remaining at 0.697 μM. This work not only marks an advancement in the development of materials for detecting Pd²⁺ in extreme acidic conditions but also offers new insights into the detection of other radionuclides under similarly challenging environments.