Modulating Anion Nanotraps via Halogenation for High-Efficiency 99TcO4 -/ReO4 - Removal under Wide-Ranging pH Conditions

A halogenation strategy is reported toregulate the (TcO4)-Tc-99 (-) removalperformance ofcationic polymers under wide-ranging pH conditions. Efficientand sustainable methods for (TcO4)-Tc-99 (-) removal from acidic nuclear waste streams, contaminatedwater, and highly alkaline tank wastes are highly sought after. Herein,we demonstrate that ionic covalent organic polymers (iCOPs) possessingimidazolium-N+ nanotraps allow the selective adsorptionof (TcO4)-Tc-99 (-) under wide-rangingpH conditions. In particular, we show that the binding affinity ofthe cationic nanotraps toward (TcO4)-Tc-99 (-) can be modulated by tuning the local environment around the nanotrapsthrough a halogenation strategy, thereby enabling universal pH (TcO4)-Tc-99 (-) removal. A parent iCOP-1possessing imidazolium-N+ nanotraps showed fast kinetics(reaching adsorption equilibrium in 1 min), a high adsorption capacity(up to 1434.1 & PLUSMN; 24.6 mg/g), and exceptional selectivity for (TcO4)-Tc-99 (-) and ReO4 (-) (nonradioactive analogue of (TcO4)-Tc-99 (-)) removal in contaminated water. By introducingF groups near the imidazolium-N+ nanotrap sites (iCOP-2),a ReO4 (-) removal efficiency over 58% wasachieved in 60 min in 3 M HNO3 solution. Further, introductionof larger Br groups near the imidazolium-N+ binding sites(iCOP-3) imparted a pronounced steric effect, resulting in exceptionaladsorption performance for (TcO4)-Tc-99 (-) under super alkaline conditions and from low-activity waste streamsat US legacy Hanford nuclear sites. The halogenation strategy reportedherein guides the task-specific design of functional adsorbents for (TcO4)-Tc-99 (-) removal and other applications.

Automated summary

A halogenation strategy was reported to enhance the removal performance of cationic polymers for (TcO4)-Tc-99 (-) under various pH conditions. Through the introduction of halogen groups, the adsorption capacity and selectivity of the polymers were improved. This strategy allows for the efficient removal of (TcO4)-Tc-99 (-) from different waste streams and provides guidance for the design of functional adsorbents.