Exceptional Stability of a 3D Cationic Covalent Organic Polymer for ReO ₄ ^– / ⁹⁹ TcO ₄ ^– Remediation in Acidic and High-Radiation Nuclear Wastewater

The development of adsorbents that combine high efficiency, selectivity, and long-term stability under extreme conditions remains a critical challenge for the practical remediation of radioactive ⁹⁹TcO₄^- in nuclear wastewater. Herein, we report a three-dimensional porous cationic covalent organic polymer (3D-PiCOP) fabricated via a postsynthetic modification strategy. Benzene-rich framework with permanently charged -⁺N- si. This material features a stable betes, which not only delivers a high ReO₄^- uptake capacity of 390.376 mg/g and rapid equilibrium within 5 min but also exhibits exceptional stability after exposure to harsh environments, retaining over 198.956 mg/g capacity after being separately treated with 800 kGy γ-irradiation and 12 M HNO₃. Moreover, 3D-PiCOP maintains >50% capture efficiency in multianion systems and can be reused over 8 cycles, achieving 91.7% capture in simulated high-salinity Hanford wastewater. Mechanistic studies reveal that the high performance arises from an electrostatic-attraction-driven ion-exchange process, as supported by spectroscopic and Density Functional Theory (DFT) analyses. This work highlights a stable and scalable material design that effectively addresses the durability bottleneck in treating challenging radioactive effluents.