A synergistic ligand complexation-electrocatalysis strategy for efficient uranyl extraction from nuclear wastewater

The safe and energy-efficient treatment of uranium-containing nuclear wastewater, particularly under acidic and fluoride-rich conditions, remains a major challenge for nuclear waste management. Conventional extraction methods suffer from significant energy barriers, as they require the destabilization of stable [UO₂F_n]^2-n (n = 0, 1, 2, 3, 4) complexes prior to uranyl binding, resulting in poor extraction efficiency. Herein, we apply a synergistic ligand complexation and electrocatalytic reduction strategy using Ti-doped polyoxometalate-functionalized UiO-66-NH₂ (Ti-PMA/UiO66-NH₂) for the electrochemical extraction of uranyl from even acidic fluoride-rich wastewater. The incorporation of Ti⁴⁺ into the UiO-66-NH₂ framework creates structural defects that enhance charge separation and promote electron transport, leading to improved catalytic activity. Mechanistic studies revealed that surface oxo groups act as key active sites for uranyl capture via ligand complexation, while the Mo(V)/Mo(VI) redox couple facilitates efficient electrocatalytic reduction of uranyl to insoluble UO₂ under N₂ atmosphere or to U₃O₈ in atmospheric conditions, directly enabling uranium recovery. The resulting electrocatalysts exhibited exceptional performance, achieving 96.92 % uranyl removal from real nuclear wastewater with a high extraction capacity of 6610 mg g^-1 at an applied potential of -0.8 V, even at F^- concentrations up to 5 g L^-1. The direct uranium recovery enabled by this process offers a robust and energy-efficient pathway for uranyl removal and resource recovery from nuclear effluents, contributing to safer and more sustainable nuclear wastewater treatment and nuclear fuel cycle.