An acid-resistant covalent organic polymer for detection of palladium ions in high-level liquid waste

Palladium isotopes in spent nuclear fuel serve as valuable alternative resources alongside their natural reserves. However, monitoring Pd²⁺ concentration in high-level liquid waste and subsequently isolating it during reprocessing remains challenging, particularly due to the harsh conditions involved in the process. Here, we report an acid-resistant cyano-olefin-linked covalent organic polymer (COP-TnBa) for sensitive and selective detection of Pd²⁺ ions in strong acid. Benefiting from its olefin linkage fostering the conjugation of π-electrons, COP-TnBa exhibits luminescence quenching toward Pd²⁺ ions in 1- and 4-M HNO₃ solutions with detection limits of 67 and 180 nM, respectively. Furthermore, the specific coordination between Pd²⁺ ions and bipyridine groups on COP-TnBa enables selective recognition of Pd²⁺ ions amid 18 other interfering cations in a model high-level liquid waste solution (4 M HNO₃). We further present a customized portable illuminance reading device, providing a practical solution for fast and on-site detection of Pd²⁺.