Novel Co₃O₄@TiO₂@CdS@Au double-shelled nanocage for high-efficient photocatalysis removal of U(VI): Roles of spatial charges separation and photothermal effect

Effective spatial separation and utilization of photogenerated charges are critical for photocatalysis process. Herein, novel Co₃O₄ @TiO₂ @CdS@Au double-shelled nanocage (CTCA) with spatially separated redox centers was synthesized by loading Co₃O₄ and Au NP cocatalysts on the inner and outer surfaces of Z-scheme heterojunction (TiO₂ @CdS). The reduction rate constant of U(VI) by CTCA reached 0.218 min^-1 under simulated sunlight irradiation, which was 6.6, 3.2 and 36.3 times than that of monolayer CTCA (0.033 min^-1), CTC (0.068 min^-1) and CT (0.006 min^-1). The full-spectrum light-assisted photothermal catalytic performance can enable CTCA to remove 98.8% of U(VI) and degrade nearly 90% of five organic pollutants simultaneously. Detailed characterizations and theory calculations revealed that the photogenerated holes and electrons in CTCA flow inward and outward. More importantly, Co₃O₄ acts as a "nano heater" to generate the photothermal effect for further enhancing the charge transfer and accelerating the surface reaction kinetics. Meanwhile, the photogenerated electrons and superoxide radicals play a dominant role in reducing the adsorbed U(VI) to insoluble (UO₂)O₂·2H₂O(s). This work provides valuable input toward a novel double-shelled hollow nanocage reactor with excellent photothermal catalysis ability for efficient recovery U(VI) from uranium mine wastewater to address environmental contamination issues.