Modulating Anion Nanotraps via Halogenation for High-Efficiency 99 TcO 4 - /ReO 4 - Removal under Wide-Ranging pH Conditions.

Efficient and sustainable methods for 99 TcO 4 - 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 99 TcO 4 - under wide-ranging pH conditions. In particular, we show that the binding affinity of the cationic nanotraps toward 99 TcO 4 - can be modulated by tuning the local environment around the nanotraps through a halogenation strategy, thereby enabling universal pH 99 TcO 4 - 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 99 TcO 4 - and ReO 4 - (nonradioactive analogue of 99 TcO 4 - ) removal in contaminated water. By introducing F groups near the imidazolium-N + nanotrap sites (iCOP-2), a ReO 4 - removal efficiency over 58% was achieved in 60 min in 3 M HNO 3 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 99 TcO 4 - 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 99 TcO 4 - removal and other applications.