Modulating Anion Nanotraps via Halogenation for High-Efficiency TcO/ReO Removal under Wide-Ranging pH Conditions.

Efficient and sustainable methods for TcO removal from acidic nuclear waste streams, contaminated water, and highly alkaline tank wastes are highly sought after. Herein, we demonstrate that ionic covalent organic polymers (iCOPs) possessing imidazolium-N nanotraps allow the selective adsorption of TcO under wide-ranging pH conditions. In particular, we show that the binding affinity of the cationic nanotraps toward TcO can be modulated by tuning the local environment around the nanotraps through a halogenation strategy, thereby enabling universal pH TcO removal. A parent iCOP-1 possessing imidazolium-N nanotraps showed fast kinetics (reaching adsorption equilibrium in 1 min), a high adsorption capacity (up to 1434.1 ± 24.6 mg/g), and exceptional selectivity for TcO and ReO (nonradioactive analogue of TcO) removal in contaminated water. By introducing F groups near the imidazolium-N nanotrap sites (iCOP-2), a ReO removal efficiency over 58% was achieved in 60 min in 3 M HNO solution. Further, introduction of larger Br groups near the imidazolium-N binding sites (iCOP-3) imparted a pronounced steric effect, resulting in exceptional adsorption performance for TcO under super alkaline conditions and from low-activity waste streams at US legacy Hanford nuclear sites. The halogenation strategy reported herein guides the task-specific design of functional adsorbents for TcO removal and other applications.