Ultrasonic spray pyrolysis assembly of a TiO2–WO3–Pt multi-heterojunction microsphere photocatalyst using highly crystalline WO3 nanosheets: less is better

Multi-heterojunctions are more promising than single-heterojunctions in photocatalysis due to the availability of more interfaces between each component. However, photocatalytic activity is highly dependent on the contact mode of individual components. In this work, we assemble TiO2–WO3–Pt multi-heterojunction microspheres using ultrasonic spray pyrolysis and focus on their contact mode governed photocatalytic activity. The results reveal that using highly crystalline WO3 nanosheets as building blocks could particularly enhance the photocatalytic activity of a TiO2/WO3 system toward the degradation of gaseous acetaldehyde and isopropyl alcohol. Furthermore, loading Pt nanoparticles onto WO3 nanosheets could facilitate a more prominent enhancement of activity than that of TiO2/Pt, benefiting from the two-electron reduction of oxygen at the interface of WO3/Pt. Meanwhile, the high crystallinity of WO3 nanosheets allows for a loading amount of Pt as low as 0.04 wt% in the TiO2–WO3–Pt system, which reduces the catalyst cost in comparison with that of the conventional amount of 1 wt%.