Synergistic effects of oxygen vacancies and heterostructures for visible-light-driven photoreduction of uranium

Photocatalytic technology can reduce easily soluble U(VI) to insoluble U(IV) particles to realize the separation of uranium. However, the complex composition in seawater or the organic matter in uranium-containing wastewater severely restricts the separation of U(VI). Herein, a C3N4-CeO2-x heterojunction with abundant oxygen vacancies was constructed for the photoreduction of U(VI) in organic radioactive wastewater under visible light. Kinetic characterization and density functional theory (DFT) imply that the photoelectrons were transferred from g-C3N4 to CeO2-x through the built-in electric field generated by the heterostructure and were trapped by shallow traps generated by surface vacancies to achieve spatial separation. The tremendously enhanced separation rates and lifetime (∼125 %) of photoinduced carriers grant the exceptionally improved photocatalytic activity for U(VI) reduction (up to a 39-fold increase over the bulk g-C3N4). The as-prepared C3N4-CeO2-x exhibits good resilience to a variety of competing ions and over a wide range of pH values, thus it maintains excellent performance in uranium-spiked seawater and the organics (RhB) contained water. X-ray absorption fine structure (XAFS) analysis reveals that the reduction and inner-sphere surface complexation contributed to uranium immobilization. This work provides a new strategy for the separation of uranium from organic radioactive wastewater.