Recycling ⁹⁹Tc From Nuclear Wastewater by Coupling Photocatalysis and In Situ Ion-Exchange on Bifunctional K-SnS/TiO₂...

The sustainable management of radionuclides in nuclear wastewater, typically like ⁹⁹TcO₄ ^- resulting from ²³⁸U fission, is limited by their high mobility, long half-lives and redox sensitivity. Herein, we developed a photocatalysis-ion-exchange coupling strategy for closed-loop removal and recycling of radioactive metal in nuclear wastewater based on a novel bifunctional K-SnS/TiO₂ heterojunction. The photocatalytic reduction with in situ ion-exchange converted mobile ⁹⁹TcO₄ ^- into immobilized ⁹⁹Tc³⁺. HCOOH-assisted photocatalysis by generating ·CO₂ ^- radicals on TiO₂, thus driving rapid ⁹⁹TcO₄ ^- reduction. Simultaneously, layered K-SnS captured ⁹⁹Tc³⁺ via in situ ion-exchange with the K⁺ in the framework, thereby forming stable coordination environments that inhibited the re-oxidation of ⁹⁹Tc³⁺ to soluble ⁹⁹TcO₄ ^-. Finally, the ⁹⁹Tc³⁺ could be recycled by reverse ion-exchange in concentrated KCl solution. This coupled electron-ion transfer established a dynamic interfacial mechanism that linked redox transformation with structural confinement. The system achieves efficient ⁹⁹Tc removal across diverse aqueous chemistries, including high ionic strength conditions, and enables complete recovery through reverse ion-exchange. Our results provide a generalizable route for integrating the transformation, immobilization, and recovery of redox-active contaminants, thereby advancing sustainable nuclear wastewater management.