Fabrication of CoNC@CdS type-II heterojunctions: High-efficiency photoelectrocatalytic reduction of U(VI) via spatial separation of charge carriers

Constructed a type-II CoNC@CdS heterojunction for PEC reduction of U(VI). • PEC reaction rate was 12.8 times that of photocatalysis alone. • Built-in electric field and bias synergistically promoted charge separation. • Soluble U(VI) was efficiently converted to insoluble UO 2 precipitate. Photoelectrocatalytic (PEC) reduction of U(VI) is an effective strategy for treating uranium contamination in water. Herein, a CoNC@CdS type-II heterojunction electrode was designed for the efficient reduction of U(VI) via a PEC process. Under optimized conditions, the fabricated electrode delivers an outstanding U(VI) removal efficiency of 97.8%, accompanied by a pseudo-first-order kinetic rate constant of 0.0349 min −1 . The PEC reaction rate of CoNC@CdS is 20.1 and 12.8 times higher than that of single electrocatalysis and photocatalysis systems, respectively. Stability evaluation reveals that even after six successive cyclic tests, the U(VI) removal efficiency remains above 80%, demonstrating robust cycling durability. Mechanism characterizations elucidate that CoNC improves electrode conductivity and light absorption capability, while layered CdS shortens charge migration distance and restrains carrier recombination. The built-in electric field of type-II heterojunction combined with external bias drives spatial separation and directional transport of photogenerated charge carriers, thereby efficiently converting soluble U(VI) into insoluble UO 2 precipitates. This work provides a promising strategy for uranium recovery and remediation in complex aqueous matrices.