Boosted photocatalytic removal of NO using direct Z-scheme UiO-66-NH₂/Bi₂MoO₆ nanoflowers heterojunction: mechanism insight and humidity effect

In practical applications, relative humidity in the air is a key factor affecting the photocatalytic removal of NO, which is often overlooked in previous studies. Here, we developed a direct Z-scheme UiO-66-NH₂/Bi₂MoO₆ heterojunction with a nanoflower-like structure to systematically investigate the effect of relative humidity on photocatalytic removal of NO. The optimized heterojunction for the removal efficiency of NO was 71.6% at 1.07 mg·m⁻³ NO concentration (relative humidity = 10%), and the generation of NO₂ was only 1.1%. Interestingly, with the increase in relative humidity, it showed a higher inhibition effect on NO₂, while the removal of NO decreased slightly (8%), which might be attributed to the affinity effect of NO₂ with water molecules and the competitive adsorption of H₂O and NO on the surface of the heterojunction photocatalysts. Furthermore, the reaction pathways of NO removal at the developed heterojunctions were revealed by in situ DRIFTS analysis. This work provides a novel vision for the development of direct Z-scheme heterojunction photocatalysts to effectively remove NO and inhibit the formation of toxic intermediate NO₂ under different humidities.