Functional Carbon Capsules Supporting Ruthenium Nanoclusters for Efficient Electrocatalytic (99)TcO(4) (−)/ReO(4) (−) Removal from Acidic and Alkaline Nuclear Wastes

The selective removal of the β‐emitting pertechnetate ion ((99)TcO(4) (−)) from nuclear waste streams is technically challenging. Herein, a practical approach is proposed for the selective removal of (99)TcO(4) (−) (or its surrogate ReO(4) (−)) under extreme conditions of high acidity, alkalinity, ionic strength, and radiation field. Hollow porous N‐doped carbon capsules loaded with ruthenium clusters (Ru@HNCC) are first prepared, then modified with a cationic polymeric network (R) containing imidazolium‐N(+) units (Ru@HNCC‐R) for selective (99)TcO(4) (−) and ReO(4) (−) binding. The Ru@HNCC‐R capsules offer high binding affinities for (99)TcO(4) (−)/ReO(4) (−) under wide‐ranging conditions. An electrochemical redox process then transforms adsorbed ReO(4) (−) to bulk ReO(3), delivering record‐high removal capacities, fast kinetics, and excellent long‐term durability for removing ReO(4) (−) (as a proxy for (99)TcO(4) (−)) in a 3 m HNO(3), simulated nuclear waste‐Hanford melter recycle stream and an alkaline high‐level waste stream (HLW) at the U.S. Savannah River Site (SRS). In situ Raman and X‐ray absorption spectroscopy (XAS) analyses showed that adsorbed Re(VII) is electrocatalytically reduced on Ru sites to a Re(IV)O(2) intermediate, which can then be re‐oxidized to insoluble Re(VI)O(3) for facile collection. This approach overcomes many of the challenges associated with the selective separation and removal of (99)TcO(4) (−)/ReO(4) (−) under extreme conditions, offering new vistas for nuclear waste management and environmental remediation.