Synergistic effects of carbon coating and Bi-bridge in S-scheme C@CuO/Bi/Bi₂MoO₆ nanocomposites for enhanced photoreduction of Cr(VI)

The S-scheme mechanism in photocatalysis offers a promising approach to significantly enhance photoreductive activity. Here, using Bi dots as electronic media, and by changing the amount of added C@CuO on the surface of flower-shaped Bi₂MoO₆, a diverse range of CBM-x heterojunctions, were synthesized using a multi-step approach that incorporated solvothermal preparation and calcination methods. CBM-10 exhibited excellent photocatalytic activity: 96.9 % of Cr(VI) removal in 30 min, which was 38.0-fold better than CuO, 4.2-fold higher than pristine Bi₂MoO₆. Furthermore, even after five cycles of use, CBM-10 showed outstanding stability. Experiments to capture the active species revealed that electrons play a crucial role in the photocatalytic reduction of Cr(VI). In these heterojunctions, carbon doping leads to the formation of coatings on the semiconductor materials to promote the migration and separation of photogenerated carriers. The presence of carbon coating is beneficial to improve the stability of CBM-10. Bi dots grown on Bi₂MoO₆ nanosheets can act as electron transport channels in C@CuO/Bi/Bi₂MoO₆, accelerate photoinduced carrier separation. The internal electric field, and the existence of “S-scheme” charge transfer mechanism was verified by the combination of atomic force microscope and synchronous illumination X-ray photoelectron spectroscopy. This process significantly mitigates the recombination of photo-induced carriers, enhancing the overall photoreduction efficacy. This study presents a novel method for developing S-scheme heterojunction to enhance the effectiveness of Cr(VI) decontamination, paves a promising route to heavy metal removal by mild photo-reductive system, and provides new insights into the design of photocatalysts with enhanced redox capabilities.