Abstract
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.