Constructing fast charge transfer channels by multi-active sites on Bi₂MoO₆ photocatalyst enhance NO deep purification and inhibit NO₂ generation

Photocatalytic purification of nitrogen oxides (NO_x) is considered an important technology for environmental protection and green sustainable development. However, photocatalytic oxidation removal of NO can easily lead to formation of toxic by-product NO₂ due to the low charge separation efficiency and insufficient generation of reactive oxygen species (ROS), and the control of NO₂ is still a difficult problem to be solved. Herein, Bi₂MoO₆ (BMO) catalyst with the synergic effect of N-ion, Bi and oxygen vacancies (BBMO-N) was successfully prepared by hydrothermal and room temperature reduction. The BBMO-N (70.8 %) showed an 8.9-times increase in NO purification activity under visible light than that of BMO (8.0 %). In addition, by the product selectivity analysis, BBMO-N converted NO into toxic by-product (NO₂) only 0.7 %, much smaller than the NO₂ generation of BMO (47.3 %). Therefore, BBMO-N greatly promoted the photocatalytic deep oxidation of NO into nitrate. Experimental observation and density functional theory (DFT) results showed that the synergistic effect of multi-active sites significantly enhanced the photoelectric performance. The Bi metals transferred electrons to oxygen vacancies (OVs) and further transferred electrons to the N-ion on surface, thus providing fast charge transport channels (Bi → OVs → N) and greatly improving the photogenerated carrier separation efficiency. Additionally, the multi-active sites can enhance the adsorption and activation of reactants, accelerate the H₂O/O₂ to ROS process, reduce the energy barrier of NO removal, and promote the deep oxidation of NO-NO₃⁻. This study has important guiding significance for the photocatalyst design of multi-active sites and NO deep oxidation.